Basic Hydraulics Module 1 PDF

BASIC HYDRAULICS MODULE 1 MINE MAINTENANCE SERVICES M.S.T.C  MINE MAINTENANCE SERVICES (PVT.) LTD....

BASIC HYDRAULICS MODULE 1 MINE MAINTENANCE SERVICES M.S.T.C  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Table of Contents 1. Safety in Hydraulics......................................................................................................................... 6 1.1 Importance of safety in Hydraulics............................................................................................... 6 1.2 Safety measures...................................................................................................................... 6 2. Introduction.................................................................................................................................... 7 2.1 What is Hydraulics?....................................................................................................................... 7 3. Basic hydraulic symbols....................................................................................................................... 9 4. Basic hydraulic system................................................................................................................... 10 4.1 Categories in a hydraulic system................................................................................................. 11 4.2 Types of hydraulic systems.......................................................................................................... 12 5. Hydraulic Fluid............................................................................................................................... 13 5.1 Task of hydraulic fluid.................................................................................................................. 14 5.2 Basic properties of pressure fluids.............................................................................................. 14 5.3 What to consider when choosing hydraulic fluid for your application -:.................................... 14 5.4 Storage of oil......................................................................................................................... 15 5.5 Chemical properties of Hydraulic Oil.................................................................................... 15 5.6 Types of hydraulic oils................................................................................................................. 17 5.7 Why not use water as a pressurized fluid?................................................................................. 18 6. Hydraulic Tank............................................................................................................................... 20 6.1 Functions of a tank...................................................................................................................... 20 6.2 Characteristics of a Tank.............................................................................................................. 20 7. Filtration........................................................................................................................................ 23 7.1 Ways in which contamination can occur-:.................................................................................. 23 7.2 Common types of contaminants................................................................................................. 23 7.3 Grading of oil contaminants........................................................................................................ 23 7.4 Parameters of a filter.................................................................................................................. 24 7.5 Types of Filters............................................................................................................................ 25 7.6 Types of wear in a hydraulic system............................................................................................ 28 3  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 8. Pump............................................................................................................................................. 29 8.1 Types of pumps........................................................................................................................... 29 8.2 Modes of displacement............................................................................................................... 30 8.3 Types of flow............................................................................................................................... 31 8.4 Factors that can destroy a pump................................................................................................. 31 8.4.1. Aeration............................................................................................................................... 31 8.4.2. Cavitation............................................................................................................................ 32 8.4.3 Overpressure........................................................................................................................ 33 8.4.4. Water saturation........................................................................................................... 33 8.5 Criteria for choosing a pump....................................................................................................... 35 8.4 How to calculate flow.................................................................................................................. 35 9. Prime mover.................................................................................................................................. 36 9.1 Power rating of a drive unit......................................................................................................... 36 10. Hydraulic Lines.............................................................................................................................. 37 10.1 Types of hydraulic lines............................................................................................................. 37 10.2 Considerations when selecting a hydraulic line to use............................................................. 37 10.3 Construction of a hose.............................................................................................................. 38 11. Accumulators................................................................................................................................ 40 12. Pressure control valves................................................................................................................. 43 12.1 Pressure relief Valves................................................................................................................ 43 12.1.1 Purpose of a Pressure Relief Valve..................................................................................... 43 12.2 Types of Pressure relief valves.................................................................................................. 44 12.2.1 Directly controlled PRV...................................................................................................... 44 12.2.2 Pilot operated PRV............................................................................................................. 45 13. Directional Control Valve.............................................................................................................. 46 13.1 Construction.............................................................................................................................. 46 13.2 Description of DCVs................................................................................................................... 46 13.3 Components of Directional Control Valves............................................................................... 47 14. Flow control Valve......................................................................................................................... 49 14.1 Types of flow control devices.................................................................................................... 49 15. Actuators....................................................................................................................................... 50 15.1 Types of cylinders...................................................................................................................... 50 4  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 15.2 Area ratio in Differential Cylinders............................................................................................ 51 16 Hydraulic Motors.............................................................................................................................. 52 Types of Hydraulic Motors:............................................................................................................... 52 Applications of Hydraulic Motors:................................................................................................. 53 Advantages of Hydraulic Motors:.................................................................................................. 53 16. Pascal’s Law................................................................................................................................... 54 17. Maintenance of Hydraulic Systems............................................................................................... 55 17.1 Hydraulic system maintenance tips.......................................................................................... 55 5  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 1. Safety in Hydraulics 1.1 Importance of safety in Hydraulics  Hydraulics operates at high pressures which can cause significant risks if not handled properly.  Common injuries and health risks include-:  Flying Debris  Dermatitis from handling hydraulic fluid  Cancer risk from direct contact of hydraulic fluid  Burns  Fluid injection  Crushing  Proper training, awareness and safety measures are essential to ensure safe operation and maintenance of hydraulic systems. 1.2 Safety measures  Always wear appropriate PPE e.g goggles, gloves, flame resistance worksuits, ear plugs, safety shoes e.t.c  Use appropriate lifting techniques when working on hydraulic systems since they are generally heavy (Maximum hand lifting weight is 25kg, Above 25kg use mechanical methods e.g crane or seek assistance. Failure to follow this might result in back injuries.  Never service hydraulic system whilst engine is running unless necessary e.g when bleeding system. Failure to follow this might result in crushing because of mechanical rotating parts.  Proper house keeping and oil disposal e.g use of drip trays, plugs, use of spill kits. Failure to observe proper house keeping will result in slips and trips.  Proper training and awareness  Inspection of equipment before use  Follow warning signs and instructions  Use of barrier cream when handling hydraulic oil  Avoid fire hazards e.g open flames, loose electrical connections Golden 5 finger rule when working on a hydraulic system-: 1. Disconnect Power supply 2. Secure against Resupply by locking out and tagging* 3. Depressurize system 4. Check that the system is depressurized 5. Prevent danger from neighbouring systems 6  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] BEFORE CARRYING OUT ANY WORK ALWAYS DO A RISK ASSESSMENT!!! 2. Introduction All machines require some type of power source and a way of transmitting this power to the point of operation. The three methods of transmitting power are:  Mechanical  Electrical  Fluid In this course we are going to deal with the third type of power transmission which is the Fluid Power in conjunction with both mechanical and electrical. 2.1 What is Hydraulics? It is the transmission of force and movement by the use of a pressurized fluid. Advantages of Hydraulics-:  Variable speed  Direction of operation can be reversible i.e clockwise movement can be changed to anticlockwise movement  Precise control e.g brakes  Simple overload protection e.g can be stalled  Force multiplication  Low maintenance cost  High power output  Reliable and durable  Relative consistent power transmission  Ease of transmission over long distances  Controlled stopping Disadvantages of Hydraulics-:  High acquisition costs  High degree of cleanliness required  Increased requirements for environmental protection  Fire hazard since hydraulic oil can be flammable  Transmission losses e.g leakages, friction over long distances, cavitation  Complex pipe and hose line system  Equipment is generally heavy 7  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected]  Complexity in troubleshooting Applications of hydraulics  Aviation e.g actuation of wings, aircraft doors, cargo lifts and landing gear  Agriculture e.g Tractors, Combine Harvesters, Sprayers, Planters  Automotive e.g Braking system, Steering System  Construction equipment e.g excavators, cranes, bulldozers and loaders  Mining equipment e.g LHDs, Drill rigs, Bolters  Manufacturing and Industrial Machinery e.g Hydraulic presses, Injection moulding machines, CNC machines  Marine and offshore application e.g Shift steering, Deck machinery 8  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 3. Basic hydraulic symbols Hydraulic symbols are a standard designed to provide a clear representation of how each hydraulic component functions in a hydraulic system. They are used to come up with a hydraulic schematic. A hydraulic schematic is a road map or representation of a hydraulic system, and to a technician skilled in reading and interpreting them, it is a valuable aid in identifying possible causes of a problem. Examples of hydraulic symbols are given below-: 9  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] For more symbols refer to Appendix A 4. Basic hydraulic system A basic hydraulics system comprises of the following components -:  Reservoir / Tank  Pump  Filter  Valves  Hydraulic lines  Prime mover  Actuators 10  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 4.1 Categories in a hydraulic system 1. Control Devices Valves control the direction, pressure, and flow of the hydraulic fluid from the pump to the actuator/cylinder. 2. Output Devices The hydraulic power is converted to mechanical power inside the output device. The output device can be either a cylinder which produces linear motion or a motor which produces rotary motion. 11  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 3. Fluid The fluid is the medium used in hydraulic systems to transmit power. The fluid is typically oil, and it is stored in a tank or reservoir. 4. Conductors The conductors are the pipes or hoses needed to transmit the hydraulic oil between the hydraulic components. 4.2 Types of hydraulic systems 1. Open Loop System It is a hydraulic system where fluid flows from the reservoir to the pump, then to the actuator and back to reservoir. Characteristics-:  Simple and easy to maintain  Less prone to contamination  Fluid flows in one direction  No feedback required 2. Closed Loop System It is a system where hydraulic oil is recycled between the pump and the actuator e.g motor. Characteristics-:  Usually used for high pressure applications e.g Automotive and aerospace industries  Fast response time  Precise position of actuators 12  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected]  Reduced fluid consumption (which means less fluid required)  Can operated in either direction  More heat generated hence it often needs heat exchangers 5. Hydraulic Fluid Hydraulic fluid is the life blood of a hydraulic system. Why use oil in hydraulics over other fluids?  Compressibility Hydraulic fluid is almost incompressible. Fluid react to pressure forces with a small change in volume.  Shear Fluids do not resist shear forces statically, but only dynamically that is when they are in motion. 13  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 5.1 Task of hydraulic fluid  Lubrication- for moving components to reduce wearing out  Cooling- it increases system reliability as it reduces strain of overheating  Transmission of Force-the movement of the fluid allows force to be transmitted to the hydraulic actuators  Dampening noise  Shock absorbing  Motion control  Corrosion prevention 5.2 Basic properties of pressure fluids The properties of hydraulic fluids are weighted differently depending on the tasks they have to perform. These include:  Certain toughness (viscosity, ideally 36 cSt or 36mm/s)  Load capacity / shear strength (according to Brugger, 35-50N/mm)  Low compressibility (force is transmitted immediately)  No increase in volume  Good lubricity  High ageing resistance  Good air and water separation properties  High specific heat (thermal conductivity)  Neutral chemical behaviour  No harmful effects on health  High flash point (lower risk of ignition)  Low pour point (temperature at which no movement of liquid is visible for 10 seconds)  High flash point 5.3 What to consider when choosing hydraulic fluid for your application -:  Viscosity  Working temperature  Maximum temperature  Area of application e.g biodegradable for food processing facility  Compatibility  Miscibility 14  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] DO NOT MIX OILS!!! USE THE SAME OIL BRAND AND VISCOSITY GRADE THAT IS BEING USED IN THE SYSTEM. 5.4 Storage of oil Storage of hydraulic fluid is crucial to its use. So as to reduce health and environemental hazards the following precautions are to be taken.  Store in a cool dry place  Make sure the cap is tightly closed  Keep away from fire or ignition  Make sure drums are well labelled to avoid mixing 5.5 Chemical properties of Hydraulic Oil Ageing stability Hydraulic fluids must not change their properties over time. So called redox reactions can take place in organic fluids, causing molecular chains to breakdown. This can lead to the formation of corrosive or toxic derivatives, the lubricity can change or sludge, coatings can form due to polymer formation. This can be prevented by use of oxidation inhibitors. Hydrolytic stability 15  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Similar to oxygen, water can act in the presence of metal abrasion. To avoid hydrolysis, it must be ensured that water cannot penetrate the hydraulic system (hydrolysis is the splitting of a chemical compound by a reaction with water) Media compatibility This term means that the pressure fluid does not attack other system components. This particularly concerns paints, coatings, seals and plastic components. The compatibility of the pressure fluid with all components in contact with the media must be ensured. Complex tests are carried out during the validation phase of products for this purpose. Fire behaviour Many pressure fluids are flammable. The fire behaviour is characterised by the flash point and the ignition temperature. Toxicity and biodegradability Many pressure fluids contain toxic carcinogenic or mutagenic components. Biodegradable oils also contain highly toxic antifouling agents. The manufacturers' safety data sheets provide information on the health and environmental hazards of handling pressure fluids. Low temperature behaviour Oils are mixtures of substances and therefore have no definite melting point. At low temperatures, long-chain molecules (paraffins) form a close order. With inexpensive oils, this results in the formation of precipitates that can clog filters and valves. At even lower temperatures, the oil stagnates and no longer flows by itself. Therefore, so-called VI improvers are added to the base oil. Foaming behaviour Hydraulic fluids come into intensive contact with air in many applications. The air is foamed and small and large air bubbles form. These air bubbles rise in the tank and form foam on the surface. This foam can even escape from the filling opening, the tanks air filter, and causes considerable disturbance in the system. Therefore certain oils and cooling lubricants are added with defoaming agents. 16  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Viscosity It is the measure of a fluid’s resistance to flow. The thicker the oil the higher the viscosity, the thinner the oil the lower the viscosity. Factors affecting viscosity-:  Temperature  Pressure  Composition of the fluid  Shear rate (rate at which a fluid deforms so viscosity can decrease or increase) Compatibility It refers to the ability of two or more oils to coexist and function together without adverse effects on performance, stability or equipment. Miscibility It refers to the ability of two or more oils to blend together without separating, settling, or forming undesirable compounds. 5.6 Types of hydraulic oils Name Synthetic Oil Mineral Based Oil Biodegradable oils Fire resistant oils 17  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Description Is a type of oil that is Mostly commonly used hydraulic fluids designed to breakdown type of lubricant chemically formulated from made from refined petroleum oils with quickly and safely in the designed to minimize individual molecules to added additives to enhance their environment making them the risk of fire and provide superior performance performance ideal for use in ignition in high and protection in various environmentally sensitive temperature application. areas applications. Examples Polyester (POE), Hydrocracked -Water- based e.g Oil (HCO) water glycol, water polymer -Synthetic e.g phosphate ester, polyester -Halogenated e.g chlorinated, fluorinated -Hydrocarbon e.g high flash point mineral oil Applications Automotive engines, Automotive e.g construction agriculture, transmissions machinery, forklifts and factory pharmaceuticals, machinery. food processing Characteristics -High viscosity index -Good lubrication properties -Environmentally friendly -High flash point -Maintains consistency across -Wide temperature range (But can -Can have lower oxidative -High fire point temperatures degrade at high temperatures) stability and higher -Low volatility -High thermal stability, Resists -Easy to find and relatively inexpensive moisture absorption -High thermal stability breakdown from heat -Non-flammable or -Low volatility minimizing self-extinguishing evaporation and oil consumption -Improved lubricity, reducing friction and wear -Enhanced cleanliness, resisting contamination and sludge formation 5.7 Why not use water as a pressurized fluid? Water as a pressure fluid has a number of advantages: 18  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected]  It is non-flammable, non-toxic and not harmful to the environment  It is not very compressible  It is inexpensive and readily available  Water has a high heat capacity  It is well compatible with most plastics and elastomers However, as a pressure fluid in power transmission applications, it has three critical disadvantages:  Water does not lubricate  Water supports corrosion  The operating temperature range is limited to +4°C to about 60°C. Water already darkens at low temperatures. This is why clear water with small additives to prevent corrosion is mainly used in heat engineering systems as a heat transfer fluid. High-pressure water applications include water jet cutting systems, high-pressure cleaners and descaling systems. Another field of application for so-called clear water hydraulics is the food industry or other special hydraulic applications in which contamination must be avoided at all costs in the event of external leakage. Owing to the high initial costs and the limited operating temperature range, however, clear water hydraulics remain limited to market niches. 19  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 6. Hydraulic Tank 6.1 Functions of a tank Storage of hydraulic fluid It holds and supplies a specific amount of fluid that ensures a constant supply of fluid for the pump to circulate through the system. Cooling The tank’s volume and walls allow heat to be dissipated to the atmosphere. The cooling capacity depends mainly on the tank size and thus the volume of oil. The longer the medium can remain in the tank the more the heat can be radiated. Separation of air and contaminants The tank provides a space for air bubbles, moisture and contaminants to separate from the hydraulic oil. Fluid level control The hydraulic tank helps maintain an appropriate fluid level in the system by ensuring that there is enough fluid to meet the system’s requirements Maintaining fluid pressure It can also work as a reservoir of low pressure helping to stabilize the pressure of the fluid on the suction as it enters the pump. By providing a low pressure supply of fluid the tank helps to ensure that the pump operates efficiently without having to draw from high pressure areas which can cause strain or cavitation. Ventilation They are usually vented to allow air to enter and exit as the fluid level rises and falls. 6.2 Characteristics of a Tank 20  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Breather Types of breathers-: Open to atmosphere- maintains the fluid level to avoid cavitation. It has a filter to ensure that air is filtered when going in and out of the tank Pressurized breathers – maintains pressure in the tank (to a specified pressure) to force feed the suction of the pump. It also has a filter to ensure that air is filtered when going in and out of the tank Baffle plates To give the oil in the tank a specific oil flow path in order to achieve a prescribed dwell time. These plates mostly prevent hot oil that is returned from the pump from being sucked back in directly. The dwell time in the tank is also used to calm the oil i.e air can escape and dirt particles can settle at the bottom of the tank. 21  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Suction and Return line The suction and the return line should be on opposite sides of the baffle plate. The suction line should be immersed deeper in the medium than the return line. Suction strainer It is used to filter large particles from the oil that is being sucked by the pump from the tank protecting the pump against catastrophic failure. Thermometer It monitors the temperature of the oil in the tank. Sight Glass It gives a visual sight of the oil level in the tank. Clean-out plate/ Inspection cover Gives access to the inside of the tank for inspection and cleaning Level sensor It gives additional monitoring of the oil level in the tank. Drain Plug Allows for the periodic draining of free water, oil or debris from the tank. Drain plugs can also be magnetic to trap metallic debris. 22  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 7. Filtration Filters are part of the oil treatment elements and reduce the number and size of oil contaminants. Contaminants can enter the hydraulic system in a variety of ways. A distinction is made between contamination that occurs during assembly and contamination that occurs during operation. 7.1 Ways in which contamination can occur-:  Installation impurities i.e cutting or grinding dust, sealing material, chips or similar can be avoided by taking a certain amount of care during installation.  Contamination during operation is to a certain extent part of the normal life cycle of a hydraulic system.  Ageing residues usually caused by high oil temperatures can have a negative effect on the properties of the hydraulic fluid i.e they impair the friction properties and reduce the lubricity and thus increase wear.  Improper topping up of the fluid level can already lead to a deterioration of the oil quality. According to DIN 51524, fresh oil from the drum for conventional hydraulic systems is already considered dirty when filled. 7.2 Common types of contaminants  Metals Can enter system in various ways which include wearing of moving parts, left over filling from drilling and worn-out hoses.  Polymers O-rings and seals can break down and become contaminants  Rust Rust corrosion can occur in a system when humid air drawn through breather condenses into water.  Fibers Fibers may come from wood, cardboard, paper used to package new valves N.B New oil from the drum for conventional hydraulic systems is already considered dirty when filled according 7.3 Grading of oil contaminants Purity Class  Is the measure or level of contamination in a substance by particles of different sizes.  Usually given in 3 numbers e.g 18/16/13 or 20/18/15 23  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Where -:  1st number represents number of particles that are greater than 4 microns in size  2nd number represents number of particles that are greater than 6 microns in size  3rd number represents number of particles that are greater than 14 microns in size 7.4 Parameters of a filter  Working pressure A filter is usually given with a maximum pressure rating that it can handle.  Microns measurement Represent the smallest particle size that the filter element can filter  Oil Flow Given as the maximum permissible flow to flow through the filter element.  Beta rating The ratio of the number of particles upstream of the filter versus the number of particles downstream of a specific size. The Beta rating given means that for every 75 particles of 10 microns or larger entering the filter on 1 particle will remain Reasons for having a filter in a hydraulic system: 1. Contaminant Removal: Suction filters are designed to remove contaminants such as dirt, metal particles, and other debris from the hydraulic fluid before it enters the system components. This helps prevent damage to pumps, valves, and other sensitive components. 2. Preventing System Damage: Contaminants in the hydraulic fluid can cause wear and tear on system components, leading to reduced efficiency, increased maintenance costs, and potential system failures. Suction filters help prevent such damage by capturing contaminants before they can cause harm. 3. Maintaining Fluid Quality: By capturing contaminants at the inlet, suction filters help maintain the cleanliness and quality of the hydraulic fluid, which is crucial for the proper functioning and longevity of the hydraulic system. 4. 24  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Advantages of having a filter in a hydraulic system: 1. Extended Component Life: By removing contaminants from the hydraulic fluid, suction filters help extend the life of system components such as pumps, valves, and cylinders. This leads to reduced maintenance costs and downtime. 2. Improved System Performance: A clean hydraulic system operates more efficiently and effectively. Suction filters help ensure that the hydraulic fluid remains clean and free from contaminants, which in turn enhances the overall performance of the system. 3. Reduced Maintenance Costs: Regularly replacing or cleaning of filters is a cost-effective way to prevent damage to expensive hydraulic system components. By investing in suction filters, you can reduce maintenance costs associated with system repairs and replacements. 4. Enhanced Reliability: A hydraulic system equipped with a suction filter is more reliable and less prone to unexpected failures caused by contamination. This increased reliability is crucial for applications where system downtime is costly or dangerous. 7.5 Types of Filters Suction Filter Characteristics of suction filters:  Location: Suction filters are typically located at the inlet of hydraulic pumps or other components to filter the fluid before it enters the system. They are positioned in the low- pressure side of the hydraulic circuit.  Mesh Size: Suction filters come with mesh screens or filter elements that are designed to capture contaminants such as dirt, debris, and particles of various sizes. The mesh size of the filter determines the size of particles that can be filtered out.  Low Pressure Drop: Suction filters are designed to have a low pressure drop to ensure that the pump or other components do not experience excessive back pressure. This helps maintain the efficiency and performance of the hydraulic system.  Ease of Maintenance: Suction filters are typically designed for easy maintenance and replacement. They are often easily accessible for cleaning or changing the filter element, allowing for quick servicing without major system downtime.  Compatibility: Suction filters are available in various sizes and configurations to suit different hydraulic systems. They can be selected based on flow rates, pressure ratings, and compatibility with specific hydraulic fluids.  Materials: Suction filters are commonly constructed from materials such as stainless steel, aluminium, or other corrosion-resistant materials to ensure durability and longevity in harsh operating environments. 25  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected]  Protection: Suction filters protect hydraulic system components such as pumps, valves, and cylinders from damage caused by contaminants in the fluid. By filtering out particles and debris, they help extend the life of these components.  Prevent Cavitation: Suction filters play a crucial role in preventing cavitation, a phenomenon where vapor bubbles form in the hydraulic fluid due to low pressure, leading to damage to system components. By maintaining clean fluid, suction filters help prevent cavitation.  Cost-Effective: Suction filters are a cost-effective solution for maintaining the cleanliness of hydraulic fluid and protecting system components. Regularly replacing or cleaning suction filters can help prevent costly repairs and downtime. Return Filter  Location: Return filters are typically placed in the return line of a hydraulic system, between the components and the reservoir. They filter the fluid as it returns to the reservoir, capturing contaminants before the fluid is recirculated through the system.  Efficiency: Return filters are designed to efficiently capture contaminants such as dirt, debris, and particles that may have accumulated in the system during operation. They help maintain the cleanliness of the hydraulic fluid to protect system components.  Filter Media: Return filters utilize various types of filter media, such as cellulose, synthetic fibers, or metal mesh, to trap contaminants of different sizes. The filter media's efficiency rating determines the size of particles that can be captured.  Pressure Rating: Return filters are designed to withstand the pressure levels present in the return line of the hydraulic system. They should be selected based on the system's operating pressure to ensure proper filtration performance.  Bypass Valve: Some return filters are equipped with a bypass valve that allows fluid to bypass the filter element if the pressure drop across the filter becomes too high. This feature ensures continuous fluid flow in case of a clogged filter.  Maintenance: Return filters are designed for easy maintenance, with features such as quick- change filter elements or filter cartridges that can be easily replaced. Regular maintenance of return filters is essential to ensure optimal filtration performance.  Compatibility: Return filters come in various sizes, flow capacities, and configurations to accommodate different hydraulic systems. They can be selected based on the flow rate, viscosity of the hydraulic fluid, and system requirements.  Heat Dissipation: Return filters also aid in dissipating heat generated during system operation. By filtering the fluid before it returns to the reservoir, they help remove heat and maintain the optimal operating temperature of the system.  Extended Component Life: By capturing contaminants and maintaining clean hydraulic fluid, return filters help extend the life of system components such as pumps, valves, and actuators. This leads to reduced maintenance costs and improved system reliability. 26  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] High Pressure filter  Location: Installed in the pressure line of the hydraulic system ahead of the device which are sensitive to dirt e.g proportional valves.  Pressure Rating: High-pressure filters are specifically designed to withstand and operate effectively at high pressure levels commonly found in hydraulic systems. They are rated to handle pressures well above standard operating pressures.  High Filtration Efficiency: High-pressure filters are engineered to provide high filtration efficiency, effectively capturing contaminants such as dirt, debris, metal particles, and other impurities present in the hydraulic fluid. They often use fine filter media to achieve this level of filtration.  Filter Media: These filters are equipped with specialized filter media that can trap and retain contaminants of various sizes, ensuring that the hydraulic fluid remains clean and free from particles that could damage system components.  Construction: High-pressure filters are constructed using robust materials such as stainless steel, aluminium, or other durable alloys that can withstand the high-pressure conditions in hydraulic systems. This ensures the longevity and reliability of the filter.  Pressure Drop: High-pressure filters are designed to maintain a low pressure drop across the filter element to prevent excessive back pressure in the system. This helps maintain system efficiency and performance.  Compatibility: High-pressure filters are available in various sizes, configurations, and connection types to suit different hydraulic systems. They can be selected based on flow rates, pressure ratings, and compatibility with specific hydraulic fluids.  Bypass Valve: Some high-pressure filters come equipped with a bypass valve that allows fluid to bypass the filter element if the pressure drop becomes too high. This feature ensures continuous fluid flow in case of a clogged filter.  Maintenance: High-pressure filters are designed for ease of maintenance, with features such as quick-change filter elements or cartridges that can be easily replaced. Regular maintenance is essential to ensure optimal filtration performance.  Protection: High-pressure filters play a crucial role in protecting sensitive hydraulic system components such as pumps, valves, and actuators from damage caused by contaminants. They help extend the life of these components and improve system reliability. Bypass Filter  Parallel Filtration System: A bypass filter operates in parallel to the main filtration system in a hydraulic or lubrication system. It diverts a small portion of the fluid flow through a separate filter circuit for additional filtration.  Continuous Filtration: Bypass filters continuously filter a small portion of the fluid flow, typically at a slower rate compared to the main filtration system. This continuous filtration helps maintain the cleanliness of the fluid over time. 27  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected]  Fine Filtration: Bypass filters are designed to capture very fine particles that may not be effectively removed by the primary filtration system. They often use high-efficiency filter media to trap contaminants down to a specific micron size.  Compact Size: Bypass filters are typically compact in size and can be easily integrated into existing hydraulic or lubrication systems without requiring significant modifications.  Customizable Filtration Levels: Bypass filters can be customized to provide specific levels of filtration based on the requirements of the system. They can be tailored to target certain types or sizes of contaminants for optimal system protection. 7.6 Types of wear in a hydraulic system Hydraulic systems are subject to different types of wear. These include-: Abrasion It is caused by dirt particles that are located between reciprocating surfaces and thus remove material in this area. It can usually also be seen on the outside of the piston rods of a cylinder. Erosion It is caused by high flow velocities and the possible presence of dirt particles. Edges of control slides, for example, are literally broken out. Wear of this kind has a particularly negative effect on valves that have a zero cut, i.e. when the control edges of the piston and the ring groove coincide with great precision. Not only does the leakage rate increase enormously, but also the control quality of the valves decreases massively. In addition, it should be mentioned that the detached material break- outs are now distributed in the downstream system where they can cause further damage. Adhesion It is a kind of cold welding of two surfaces. It usually occurs at too high oil temperatures, i.e. when the viscosity of the oil decreases significantly and the lubricating film breaks off. Significantly too high loads (surface pressures) can also be the cause of adhesion damage. Fatigue Material or surface fatigue leads to minor cracking in the material, which in turn can cause coarser break-outs. 28  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 8. Pump What is the purpose of a pump? It creates flow. How does a pump create flow? By increasing the volume (creating vacuum) and decreasing the volume (pumping effect) (displacement and centrifugal pumps) So how is pressure created? It is created when flow meets resistance. 8.1 Types of pumps Positive displacement pump It is a pump that always displaces the same amount of fluid regardless of the system resistance. Non-positive displacement pump It is a pump which has an output flow rate that changes in response to resistance on the outlet. 29  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 8.2 Modes of displacement Fixed displacement As the name suggest, it does not have a control to change its displacement hence it will always displace the same amount of fluid per revolution. However, if you want to change the flow rate, the only way to do so is to change the RPM of the prime mover. Examples of fixed displacement pumps are gear pumps, vane pumps and piston pumps (with fixed swash plates) Variable displacement These can change displacement while continuing to turn at the same RPM. Examples of variable displacement pumps are piston pumps, unbalanced vane pumps 30  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 8.3 Types of flow Laminar Flow Also known as streamline flow. It is the smooth orderly movement of a fluid in which the fluid particles flow almost parallel to each other. Turbulent Flow Refers to the flow of a fluid in an irregular pattern, while the overall flow is in one direction. 8.4 Factors that can destroy a pump 8.4.1. Aeration Aeration occurs when outside air enters the hydraulic system usually through the suction line of the pump. 31  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Causes of aeration are-:  Air leak in the suction line  Fluid level too low  Leaking system o-ring( when they lose their air- tight characteristics)  Pump shaft leakage  Turbulence or sloshing in the reservoir  Releasing of air suspended within the fluid 8.4.2. Cavitation It is the formation and collapse of air cavities in a liquid. A pump that is cavitating will create a reduced flow until it destroys itself. Causes of cavitation are-:  Oil viscosity too high  Clogged suction filter  Too high RPM on drive unit  Poor plumbing  Flow restrictions Results of cavitation  Excessive heat  Violent implosions  Noise and vibration  Overheating  Reduced system efficiency The greatest damage caused by cavitation results from the excessive heat generated as the vapour bubbles collapse under the pressure at the pump outlet or discharge side. Recognising cavitation  Sound produced by the pump (whining sound, a rattling sound just like marble in a can)  Physical evidence  Damage (inspection of the filter) 32  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Preventing cavitation  Pump should be as close to the reservoir as possible with no 90-degree fittings or unnecessary bends and connections.  Reservoir should have an appropriate breather  Shutoff valve should be fully open with no restrictions (when system is installed with one)  To ensure laminar flow, the length of supply hose should be at least 10 times the size of its diameter.  Regular maintenance of the hydraulic system  Increase suction pressure (by pressuring the tank)  Use fluid with the correct viscosity for your climate and application 8.4.3 Overpressure Since a positive displacement pump will always try to displace an almost constant flow no matter the resistance. So, when faced with great resistance it will result in strain on the pump and it will eventually break thus durability is reduced. Causes of overpressure  Excessive pump pressure due to incorrect pump setting, pressure set too high, pump too large for the system and pump faulty or malfunction.  Restriction in the system (debris in the system, kinked hoses )  Incorrect system sizing  Incorrect pressure relieving (pressure relief valve too small to handle the pressure)  Rapid changes in load (pressure spikes)  Case drains should not be plumbed with high pressure lines or high volume return lines (pumps with case drains) Prevention of overpressure  Correct sizing of pumps, system and type of pump.  Use of the correct pressure relief valve with the correct opening behaviour  Use of the appropriate shock-load valves  Ensure the use of appropriate bending diameters whilst plumbing and use of correct hoses. ( spiral braiding) 8.4.4. Water saturation Water saturation refers to the presence of water within the hydraulic fluid. Water contamination is often measured in parts per million (PPM), which indicates the concentration of water in the hydraulic fluid. Causes of Water Saturation in Hydraulic Systems: 33  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected]  Ingress from External Sources: Water can enter hydraulic systems through various external sources, such as condensation, leaks in seals or gaskets, exposure to humid environments, or direct contact with water during maintenance or operation.  Seal Degradation: Over time, seals and gaskets in hydraulic systems can degrade or develop wear, creating pathways for water to enter the system. This is particularly common in older systems or systems with inadequate maintenance.  Inadequate Breather Filters: Breather filters are designed to prevent contaminants, including moisture, from entering the hydraulic system as the fluid expands and contracts with temperature changes. If breather filters are clogged or ineffective, moisture can enter the system.  Improper Fluid Handling: During maintenance or fluid replacement procedures, if proper precautions are not taken to ensure the cleanliness and dryness of the replacement fluid, water contamination can occur.  Operating Environment: Operating in humid or wet environments can increase the likelihood of water contamination in hydraulic systems. Machinery exposed to outdoor conditions or environments with high humidity levels are particularly susceptible.  Incomplete System Sealing: Hydraulic systems rely on proper sealing to prevent contaminants, including water, from entering the system. Incomplete sealing due to damaged components or improper installation can lead to water saturation.  Lack of Monitoring and Maintenance: Regular monitoring of hydraulic fluid condition and maintenance practices, such as fluid sampling and analysis, can help identify and mitigate water contamination issues before they cause significant damage to the system. Recognizing water saturation in a hydraulic system  Cloudy Appearance: If the hydraulic fluid appears cloudy or milky, it could indicate water contamination.  Separation: Water is denser than hydraulic fluid, so if you see a clear separation of water at the bottom of the tank, it suggests water contamination.  Foaming: Excessive foaming or bubbling of the hydraulic fluid can also be a sign of water contamination. Effects of water saturation  Reduced lubrication efficiency  Corrosion of components  Degradation of system performance 34  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 8.5 Criteria for choosing a pump A pump for your hydraulic system is chosen upon considering the following -:  Operation Required Variable or fixed displacement flow required  Space Limitation Space available to fit the hydraulic pump  Pulsation How a pump responds to fluctuations in pressure in a system  Working pressure The working pressure rating for the hydraulic system  Nominal Size The amount of flow a pump can produce  Flow Amount flow required by the system  Cost How much you are willing to spend on a pump  Availability of spares  Certification and compliance  Efficiency and energy consumption 8.4 How to calculate flow 𝑁𝐺 ∗ 𝑛 𝑞𝑣 = 1000 Where-:  qV is the flow (usually in l/min or cubic decimeter )  NG is the nominal size (usually given in cc cubic centimetre)  n is the Revolutions per minute (RPM) 35  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 9. Prime mover It is used to drive the pump. Name Electric Motor Diesel Engine Description it is an electromechanical It is an internal combustion converter that translates electrical engine that converts chemical energy into mechanical energy energy into (fuel) mechanical energy. Advantages  High efficiency (+-90%)  Energy source can be  Maximum torque over stored and transported the entire speed range relatively easily  No emissions (exhaust  The speed is easy to vary gases and noise) directly  An internal combustion at the engine engine can deliver power  Simple construction, low autonomously over a maintenance cost long period of time, the energy supplier can easily be carried along Disadvantages  Electricity must always  Maximum power only in be available as a source a narrow speed range of energy, storage  Poor efficiency (+-30%) batteries are limited in with a diesel engine terms of capacity  Complicated  Weight of the batteries construction  A high amount of waste heat is produced  Emissions directly on site 9.1 Power rating of a drive unit 𝒑 ∗ 𝒒𝒗 𝑷= 𝟔𝟎𝟎 ∗ 𝒏𝒆𝒇𝒇 Where-: P is the power rating (Given in kW) qv is the flow rate (Given in litres per minute) neff is the efficiency (Given as a %) 36  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 10. Hydraulic Lines They provide a means of transport for the hydraulic fluid from the reservoir to the pump then to the actuators. 10.1 Types of hydraulic lines Steel pipes N.B Steel pipes should generally be preferred to hose assemblies (less chances of bursting) thus they are preferred where they are in close proximity to the operator. Hose assemblies A hydraulic line basically consists of a hydraulic hose and 2 fittings that are pressed(crimped) onto the ends of the hose so that they cannot be detached. All components of the line must be matched to each other and to the respective requirements. This is the only way to ensure that a hydraulic hose line works safely and reliably. 10.2 Considerations when selecting a hydraulic line to use  Size  Temperature i.e. Operating temperature of the hydraulic system  Application (suction, pressure line, tank line, rotating parts e.g centre articulation )  Material i.e. type of oil flowing through the hose  Pressure i.e. working pressure  Environmental influencers (Extremely cold or extremely hot, Corrosive environment) 37  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 10.3 Construction of a hose Inside the hose is the tube. This is the material layer that comes into direct contact with hydraulic fluids. The tube transports the medium inside the hose, if it fails the medium will leak from the inside to the outside. A defect like this is often visible in the form of a bulge on the outer layer. In the middle is the pressure carrier (2). This can be one or more layers of steel plastic or textile fabric which enclose the tube. If there are several pressure carriers the individual layers are separated from each other by insulating layers (3). This prevents friction between the pressure carrier layers. The pressure carriers determines the pressure behaviour and partly the bending behaviour of the hose. The outer layer (4) is also called the cover. It has the task of protecting the inserts against all external influences such as moisture, aggressive media, chemicals, heat, radiation, ozone or abrasion. They can come as 1 wire 2 wire or 3 wire 4 wire. There are various designs of hoses for hydraulic applications which differ according to the pressure requirement and nominal diameter. Storage of Hydraulic hoses  Store in a cool, dry place: Keep hoses away from direct sunlight, rain, heaters, and electrical equipment.  Store in their original container: Keep hoses in a relaxed state, free from tension, compression, or other deformation. 38  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected]  Don't stack hoses too high: If you must coil hoses, store them horizontally and avoid piling.  Use a first-in, first-out system: Keep track of when you store hoses so you can use them in that order.  Visually inspect and test hoses before use: Look for signs of wear, such as wetness, leaks, cracks, or loss of flexibility.  Eliminate electric or magnetic fields: High-tension cables or high frequency generators can cause currents in metal couplings, which can heat them N.B BSI recommends between 3 to 8 years and SAE recommends a max of 10years, while both agree on “infinite” shelf life of thermoplastic hoses. 39  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] 11. Accumulators Fluids are practically incompressible and cannot therefore store pressure energy. The compressibility of a gas is utilised in hydraulic accumulators for storing fluids. Accumulators are based on this principle, using nitrogen as the compressible medium. An accumulator consists of a fluid section and a gas section with a gas-tight separation element. (bladder, piston and diaphragm) The fluid around the separation element is connected to the hydraulic circuit so that the accumulator draws in fluid when the pressure increases and the gas is compressed. When the pressure drops, the compressed gas expands and forces the stored fluid into the circuit. Accumulators can be used in a wide variety of applications, some of which are listed below:  Energy storage  Emergency operation  Force equilibrium  Leakage compensation  Volume compensation  Shock absorption  Vehicle suspension  Pulsation damping  Hydraulic dampers Types of accumulators 1. Bladder type: Separates gas from oil by a rubber bladder. 2. Diaphragm type: Sometimes used as a small accumulator. 3. Piston type: Shaped in the form of a cylinder without a rod. 4. Spring type: Often used to prevent pulsations. 5. Weight loaded type: Designed for large-scale machinery and consisting of a cylinder and a plummet. 40  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe Tel. 051-2823 / 2824 0712 615 419 [email protected] Cautions on Usage of Accumulators  Accumulators should be vertically positioned so that their oil ports face down.  Pre-charge pressure should be approximately 85 to 90 percent of the minimum working pressure, and should not be less than 25 percent of the maximum working pressure.  Inert nitrogen gas (N2) should be used, while oxygen is strictly prohibited. Safety considerations for hydraulic accumulators are crucial to prevent accidents and ensure the proper functioning of hydraulic systems. Here are some important safety tips and considerations when working with hydraulic accumulators: 1. Proper Installation: Ensure that the accumulator is installed correctly according to the manufacturer's instructions. This includes proper mounting, connection, and positioning within the hydraulic system. 2. Regular Inspection: Periodically inspect the accumulator for any signs of wear, damage, or leaks. Check the condition of seals, diaphragms, bladders, and other components for any deterioration. 3. Pressure Relief Devices: Hydraulic accumulators should be equipped with pressure relief devices to prevent over pressurization. These devices help to release excess pressure and protect the accumulator and the entire hydraulic system from damage. 41  MINE MAINTENANCE SERVICES (PVT.) LTD. C/o Mining Skills Training Centre P.O. Box 324 Zvishavane, Zimbabwe