Pumps and Valves in Food Processing (July 2021) PDF

Manufacturing and Processing Technology in Food  Introduction to processing equipment ▪ The transport of a fluid (especially liquid) in a transport system is directly related to the liquid properties, in particular, viscosity and density. These...

Manufacturing and Processing Technology in Food  Introduction to processing equipment ▪ The transport of a fluid (especially liquid) in a transport system is directly related to the liquid properties, in particular, viscosity and density. These properties will influence the power required for liquid transport as well as the flow characteristics within the pipeline. ▪ A typical liquid transport system consists of four components: ▪ Vessels ▪ Pipelines ▪ Pump ▪ Valves  Introduction to processing equipment ▪ Pumps: ▪ Where gravity cannot be used to move liquid product or product components, some type of mechanical energy is required to overcome forces opposing transport. ▪ Two of the most popular types of pumps in the food industry are: ❖Centrifugal ❖Positive Displacement Pumps  Learning Outcomes – Pumps ▪ The trainee will be able to ▪ Name the different types of pumps and valves in common use ▪ Explain how and where each might be used ▪ Describe the operation of the different pumps and valves ▪ Describe the operational problems associated with each ▪ Be aware of the safety features associated with them © TU Dublin  Pumps Typical viscosities encountered in food processing ▪ Food and Drinks Temperature, oC Viscosity, cP (F&D) industry Water 120 0.23 Water 20 1 has a wide range Alcohol 20 1.5 of applications, Milk Sodium hydroxide solution 20 20 2.0 20 ranging from Olive oil 20 84 water to pastry, Sugar solution 20 120 all with different Butter cream Yoghurt 20 20 550 900 properties, e.g. Caster oil 20 1,000 Orange juice concentrate 20 1,900 viscosities Honey 45 2,020 Chocolate 40 2,600 Powdered milk solution 20 4,300 Process cheese 80 6,500 Mustard 20 11,200 Leicithin 20 16,000 Biscuit mixture 20 28,000 Processed cheese 20 30,000 Toffee 40 87,000 Mincemeat 30 100,000 Processed meat 5 100,000  Pumps ▪ Unlikely that one pump type will be effective and efficient for all processes in all applications. ▪ Cold water is used in many processes as a basic ingredient. ▪ Hot water is essential for CIP/SIP processes. It is one of the worst liquids to pump as it have no lubricating qualities. ▪ The two most popular types of pumps are centrifugal and positive displacement (deliver fixed quantity with each stroke/cycle). There are variations of each type , but the operating principles are the same.  Pumps – Common types 1. Centrifugal pumps 2. Positive displacement pumps ▪ Rotary pumps ❖Lobe ❖Gear ❖Peristaltic ▪ Reciprocating pumps ❖Piston ❖Diaphragm  Introduction to processing equipment Pumps http://www.liquid-dynamics.com/animations/images/Anim-selection-4-pumps-at-LDI_2.jpg © TU Dublin  Pumps Introduction Introduction to pumps and Pump Terminology The operation of Centrifugal Pumps The operation of Rotary Pumps The operation of Reciprocating Pumps The main uses of each type of pump The safety features associated with the pumps The common operational problems that might arise  Pumps Introduction ▪ The type of pump used is governed by the physical and chemical properties of the material that is to be transferred, will the pump type damage sensitive products (shear rate)?, or will the pump simply be capable of pumping our product (viscosity)? ▪ Some foods are extremely shear sensitive ❖ eggs, custard, chocolate mousse, yoghurt, marmalade ▪ Others Viscosity is a function of shear rate ❖ Mayonnaise becomes less viscous as shear rate increases ❖ Starch becomes more viscous ▪ The type of pump is also governed by process conditions, e.g. how quickly do we need our feed? What volume of feed do we need to deliver, at what pressure do we need our feed? © TU Dublin  Terminology Description of pump properties: ▪ Priming - Certain pumps must be primed before use. This means that the pump chamber must be filled with the liquid to be pumped before pumping can begin. This procedure of replacing air with liquid in the pump chamber is called priming. Certain types of pumps will not work unless the priming operation is carried out correctly. ▪ Pulsed Flow - This is where the flow of liquid from a pump is not continuous but instead it stops and starts at regular intervals. ▪ Vapour Bubbles - These are produced by certain liquids pumped at low pressures. Liquids that are pumped under high pressure are less likely to produce vapour bubbles. Vapour bubbles which burst inside pumps can cause serious pump damage. This phenomenon is termed cavitation. © TU Dublin  Pumps Terminology ▪ Differential Pressure -The driving force for flow is pressure difference. This pressure difference across a pump is called differential pressure. ▪ Throttling - The term throttling means to slowly close the valve on the discharge of a pump to decrease flow. ▪ Dead-Heading - The term deadheading means to operate a pump with the discharge valve fully closed, i.e: ▪ Deadheading a pump can reduce the life of the pump or cause line ruptures depending on pump type. © TU Dublin  Centrifugal Pumps - Introduction ▪ Centrifugal pumps are widely used in food industry. ▪ They use centrifugal or rotational force, rather than mechanical force, to deliver fluids. ▪ Centrifugal pumps are capable of pumping large volumes of liquids quickly for example. Work best with “watery” liquids. They can also be used with liquids containing suspended solids. Although they should not be used where the suspended solids are sensitive and could break down i.e a gentle action is required. High Shear rate. © TU Dublin  Centrifugal Pumps - Operation ▪ The centrifugal pump is powered by an electric motor which drives an impeller within the static chamber casing (stator). The impeller has a series of curved blades. ▪ As the liquid is drawn in, it is thrown outwards towards the outlet. This occurs because of the centrifugal force generated by the rapidly rotating impeller. ▪ As liquid leaves, the pressure differential created is responsible for drawing more liquid through the inlet and the process is repeated to give a continuous flow. © TU Dublin Centrifugal Pumps - Operation © TU Dublin  Centrifugal Pumps - Operation Example of the operation of a centrifugal type pump http://www.plant-maintenance.com/articles/centrifugalpumps.pdf © TU Dublin  Centrifugal Pumps - Characteristics ▪ Priming - Centrifugal pumps must be primed with liquid before they can operate. If they are not, the rotor blades will just cut through air and will be unable to draw in or expel any liquid. ▪ Once primed and pumping, the inlet valve must be left open to prevent air from being drawn in and preventing the pump from working. ▪ Flow - High flow rates can be achieved with centrifugal pumps. The flow rate can be controlled by adjusting the outlet valve. ▪ Viscous Liquids - Cannot be pumped efficiently with this type of pump because the pump is unable to “throw” the liquids sufficiently towards the outlet. Rule –of-thumb: only use when viscosity of liquid is less than 300 cP. © TU Dublin  Centrifugal Pumps - Characteristics ▪ Cavitation - the damage caused when vapour bubbles burst inside equipment. ▪ Centrifugal pumps do not produce high pressures during their operation. ▪ The influence of low pressure on a liquid is that it can reduce the liquid’s boiling point. ▪ If the liquid in the centrifugal pump approaches its boiling point, vapour bubbles will form and cavitation will result. ▪ This type of pump should never be used with a liquid that will reach a temperature at or near its boiling point at any stage during the pumping process or else vapour bubbles can be produced resulting in cavitation. ▪ Signs that cavitation is occurring in a pump are 1. A distinctive popping or cracking sound 2. Excessive pump vibrations 3. Reduced pump output © TU Dublin Cavitation © TU Dublin  Cavitation Cavitation damage valve plate for an axial piston hydraulic pump Cavitating propeller model in a water tunnel experiment. High speed jet of fluid impact on a fixed surface. http://en.wikipedia.org/wiki/Cavitation © TU Dublin  Centrifugal Pumps - Summary ▪ The operation of centrifugal pumps ▪ The main uses of the pump ▪ The safety features associated with the pumps and the common operational problems that might arise © TU Dublin  Positive Displacement Pumps Rotary Pumps - Introduction ▪ The rotary pump is used extensively in the food industry. ▪ Rotary pumps draw in a certain quantity of liquid and then expel it. However, with rotary pumps this is not achieved with pistons but with semi-interlocking rotors. ▪ Rotary pumps can be used effectively to pump viscous fluids because they do not contain narrow inlet and outlet valves. ▪ Low shear rate ▪ There are a number of different types of rotary pumps, for example the gear pump, mono pump, peristaltic. © TU Dublin  Rotary Pumps - Gear Pumps Rotary Gear Pump - Operation ▪ The rotary pump consists of a liquid inlet, a liquid outlet and a stationary casing that houses two gear wheels. ▪ The gear wheels are known as rotors because they can rotate and the casing is known as the stator because it remains stationary. ▪ When the pump is switched on, the two rotors rotate and their teeth partially interlock. The liquid enters the pump through the liquid inlet. As the liquid reaches the rotors, pockets of liquid are caught between the “teeth” of the rotors and the pump casing. The liquid is forced around towards the liquid outlet where it is expelled. ▪ This creates a space for more liquid to be drawn in from the inlet. © TU Dublin  Rotary Pumps - Gear Pumps ▪ Example of operation of the Rotary Gear Pump ▪ Other types of rotary pumps are peristaltic, screw, and mono pumps. © TU Dublin  Rotary Gear Pumps - Characteristics ▪ Priming - These pumps are self priming ▪ Flow - A continuous smooth flow is produced. Higher flow rates can be achieved than with reciprocating pumps because of the high rotor speeds. ▪ Cavitation - This type of pump experiences very few problems with cavitation because the pump is maintained at a high pressure during normal usage. ▪ Unsuitable Liquids - Generally rotary pumps are not effective at pumping slurries. The solid particles become trapped between the moving parts or rotation mechanism causing damage. They should not be used with liquids with no lubricating properties. No lubrication leads to increased wear and tear of the gears, thus reducing the pump’s efficiency. ▪ Pressure - Rotary Gear pumps generate large pressures which can make them useful in membrane filtration systems. Rotary pump – Lobe pump © TU Dublin  Rotary Pumps - Lobe Pump Stator © TU Dublin  Rotary lobe pumps How rotary lobe pumps work http://www.megator.com/lobe_pumps.htm © TU Dublin  Rotary lobe pumps Various rotor forms are available, including bi-wing (shown here) and multi-lobe options http://www.vikingpump.com/en/products/RotaryLobe/lobeAnimation.html © TU Dublin  Rotary Pumps - Peristaltic Pumps ▪ A peristaltic pump operates by placing a length of silicon rubber or other elastic tubing between a series of rotating rollers. As the rollers rotate, they flatten the tube against the track at the points of contact. The “flat” regions move the fluid by positive displacement. ▪ Peristaltic pumps are particularly where all forms of contact must be avoided. The flow from these pumps is continuous and can be precisely controlled. Peristaltic pumps are self priming The lowest shear rate © TU Dublin  Peristaltic pump ▪ Peristaltic pumps are typically used to pump clean/sterile or aggressive fluids, because cross contamination cannot occur. ▪ Some common applications include ▪ pumping IV fluids through an infusion device, ▪ aggressive chemicals, ▪ high solids slurries © TU Dublin  Peristaltic Pump – How It Works! ▪ A peristaltic pump, or roller pump, is a type of positive displacement pump used for pumping a variety of fluids. ▪ A rotor with a number of "rollers", "shoes" or "wipers" attached to the external circumference compresses the flexible tube. ▪ As the rotor turns, the part of tube under compression closes (or "occludes") thus forcing the fluid to be pumped to move through the tube. ▪ Additionally, as the tube opens to its natural state after the passing of the cam ("restitution" or "resilience") fluid flow is induced to the pump. ▪ This process is called peristalsis and is also used in many biological systems such as the gastrointestinal tract. © TU Dublin Rotary Pumps - Peristaltic Pumps © TU Dublin  Peristaltic pump Perstaltic pump animation http://en.wikipedia.org/wiki/Peristaltic_pump © TU Dublin  Peristaltic pump ▪ Advantages ▪ Because the only part of the pump in contact with the fluid being pumped is the interior of the tube, it is easy to sterilize and clean the inside surfaces of the pump. ▪ Since there are no moving parts in contact with the fluid, peristaltic pumps are inexpensive to manufacture ▪ Their lack of valves and seals makes them comparatively inexpensive to maintain, and the use of a hose or tube makes for a relatively low-cost maintenance item compared to other pump types. ▪ Peristaltic pumps also minimize shear forces experienced by the fluid, which may help to keep colloids and slurry fluids from separating. © TU Dublin  Rotary Pumps- Summary ▪ The operation of Rotary Lobe Pumps ▪ The operation of Peristaltic Pumps ▪ The main uses of each type of pump ▪ The safety features associated with the pumps and the common operational problems that might arise © TU Dublin  Reciprocating Pumps ▪ Reciprocating pumps are generally used pumps where high pressures are required. They are designed to handle clean, watery liquids, viscous liquids, and products that include very abrasive solids. ▪ There are two main types of reciprocating pumps: ▪ The piston pump ▪ The diaphragm pump © TU Dublin  Reciprocating Pumps - Piston Pump ▪ The piston pump is a small, often portable pump that can deliver particle-free liquids at high pressure. The piston pump works on a similar principle to a bicycle pump with liquid drawn in and expelled using a mechanical piston. When the piston is drawn out (the suction stroke), the inlet valve opens and liquid is pulled into the chamber. When the chamber is full, the piston direction changes. The inlet valve closes and the outlet valve opens. This allows the piston to force the liquid out of the pump (delivery stroke) into the outlet pipe. The cycle is then repeated - a suction stroke followed by the delivery stroke. © TU Dublin Reciprocating Pumps - Piston Pump © TU Dublin  Reciprocating Pumps - Piston Pump ▪ The out-in motion of the piston means that liquid only leaves the pump on the delivery stroke of the piston and this results in a pulsed flow. ▪ Pulsing can be undesirable for some types of liquids and vessels. This is a parameter that must be carefully considered for each application. ▪ A more even flow can be obtained if two reciprocating pumps work together, one on its suction stroke when the other is on its delivery stroke; or use double acting reciprocating pumps. © TU Dublin  Reciprocating Pump – How It Works http://www.tulippumps.com/Site_DE/Media/dbld18fr.gif Reciprocating Pumps - Diaphragm Pump ▪ The diaphragm pump operates on the same principle as the piston pump except that the fluid does not come into contact with the piston. The piston is protected by a flexible diaphragm that is sealed to the sides of the pump chamber. These pumps are very frequently used for pumping liquids in the pharma industry. ▪ This means that diaphragm pumps can be used to pump liquids that contain suspended particles (slurries). There is less chance of pump corrosion and contamination of products, and lubricants from the piston are never in contact with the liquid being pumped. The diaphragm can be chosen such that it is compatible with the fluid. ▪ Fluid is drawn into the pump chamber on the suction stroke of the piston. This causes the diaphragm to flex. The liquid is then expelled on the delivery stroke by pushing the piston back and flexing the diaphragm outwards. © TU Dublin  Reciprocating Pumps: Single-Acting Diaphragm Pumps ▪ Fluid is drawn into the pump chamber on the suction stroke of the piston. This causes the diaphragm to flex. The liquid is then expelled on the delivery stroke by pushing the piston back and flexing the diaphragm outwards. ▪ The cycle is then repeated - a suction stroke followed by the delivery stroke. ▪ The out-in motion of the piston means that liquid only leaves the pump on the delivery stroke of the piston and this results in a pulsed flow. ▪ Pulsing can be undesirable for some types of liquids and vessels. This is a parameter that must be carefully considered for each application. © TU Dublin Reciprocating Pumps - Diaphragm Pump © TU Dublin  Reciprocating Pumps: Single-Acting Diaphragm Pumps © TU Dublin  Reciprocating Pumps: Double-Acting Diaphragm Pumps ▪ One way of reducing or eliminating pulsing is to use a double-action diaphragm pump. ▪ This pump acts on the same principle as before. ▪ However, instead of having one inlet and one outlet valve, the pump has two of each i.e. two chambers. ▪ On the inward stroke of the piston one inlet valve is open and liquid is drawn in. ▪ At the same time one of the outlet valves is also open, allowing the contents to be expelled. ▪ On the outward stroke, the opposite valves open and the process is repeated. ▪ This gives a continuous, non-pulsed flow © TU Dublin  Reciprocating Pump – How It Works http://www.tulippumps.com/Site_DE/Media/dbld18fr.gif  Reciprocating Pumps: Characteristics ▪ Safety - It is essential when operating reciprocating pumps that valves on the piping leading into and out of the pump are open. If, for example, an outlet pipe has been closed off, the pump will keep trying to expel the liquid into the outlet pipe (Deadheading the pump). This will create a pressure increase that can cause the pipe or the pump to rupture. Some pumps will automatically shut off if the pressure becomes too high, safety relief valves are often included on reciprocating pumps. ▪ Priming - These pumps are self priming, as they automatically fill the chamber on the suction stroke. Sometimes it takes several cycles to completely prime. ▪ Flow Rate - The flow rate is lower with these types of pump than it is with others but they can be used to deliver set volumes of liquids very accurately. Therefore they are often used for the addition of chemicals e.g. in CIP systems. © ITT Dublin Reciprocating Pumps - Characteristics ▪ Cavitation - Can occur in reciprocating pumps but less likely than with Centrifugal pumps. In a diaphragm pump, cavitation damage would usually be restricted to the diaphragm itself in comparison to the numerous expensive components in other pump types. ▪ Portability - Diaphragm pumps can be operated with only compressed air as a utility. This makes them more portable than pumps which run on electrical power. ▪ Diaphragm or Piston Pump - Diaphragm pumps are more frequently used than piston pumps for pumping liquids in the pharmaceutical industry. This is because the moving parts are protected by the diaphragm reducing corrosion. They can be used for conveying liquids gently. © TU Dublin  Reciprocating Pumps - Characteristics ▪ Maintenance - All pumps need to be maintained properly. A split diaphragm or a damaged pump will have implications for both the product and the pump. Therefore, regular preventative maintenance must be carried out on all pumps. ▪ Viscous Liquids - Reciprocating pumps are not suitable for viscous liquids because they have great difficulty in passing through narrow inlet and outlet valves. © TU Dublin  Reciprocating Pumps - Summary ▪ The operation of single acting and double acting diaphragm pumps ▪ The main uses of each type of pump ▪ The safety features associated with the pumps and the common operational problems that might arise © TU Dublin  Static Electricity ▪ The transfer of fluids and materials along pipelines and through pumps results in the generation of static electricity. Large voltages can build-up in the pipeline, in the pump or within the fluid being pumped. This is very dangerous and could cause a fire or explosion, especially when flammable or explosive materials are being transferred. ▪ One method of preventing such dangerous incidents from occurring and minimizing the build-up of static electricity is to earth the pump or pipeline. Earthing the pump prevents static electricity from building up to a dangerous level by allowing the electricity to drain away through the copper conducting cable. For certain materials the pump is made explosion proof. © TU Dublin  Operator Awareness An operator observing any unusual signs from a working pump must report it immediately to their supervisor. This could include: a) Excessive heat generation b) Smoke c) Leaks d) Vibration or e) Knocking noises. Operational procedures for pumps must always be followed by the operator. Different types of pumps are specified for different operations for a good reason. Only use the type of pump that was specified for a particular operation © TU Dublin  Pumps - Summary The operation of Centrifugal Pumps The operation of Rotary Pumps ▪ Gear pumps, peristaltic pumps The operation of Reciprocating pumps ▪ Piston Pumps ▪ Diaphragm pumps and Double diaphragm pumps Characteristics and main uses of each type of pump The safety features associated with the pumps and the common operational problems that might arise © TU Dublin