Hydraulic Systems - Study Notes

Hydraulic Systems - Study Notes

• Hydraulic Fluid Pressure:

  • Atmospheric Pressure: Pushes hydraulic fluid towards the pump inlet.
  • Head Pressure: Pressure at the bottom of a standing liquid.
  • Pressure Transmission: Force applied to a confined liquid is transmitted equally and undiminished throughout the containing vessel.

• Force Calculation:

  • Force (F) = Pressure (P) x Area (A): Used to determine piston force.
  • Example: 30 psi applied to a 5-inch squared piston results in 150 pounds force (667.23 Newtons).

• Flow Rate:

  • Definition: Volume of fluid moving through a system per unit time.
  • Measurement: Flow gauges, or pump speeds.
  • Effect of Hose Diameter: Decreased hose diameter increases fluid velocity.
  • Pump Output: Determines the rate of flow.

• Fluid Velocity: Rate of speed past a given point at a given time.

• Pascal's Law: Force applied to a confined fluid is transmitted equally and undiminished in all directions.

• Relief Valves:

  • Direct Acting Relief Valve: Operates directly via spring force, opens immediately when pressure exceeds the spring setting.
  • Pilot Operated Relief Valve: Uses a small pilot valve to control a larger valve, opens immediately when pressure exceeds the spring setting.

• Pump Types and Function:

  • Fixed Displacement Pumps: Produce a constant flow rate.
  • Variable Displacement Pumps: Used in closed-center systems, and adjustable flow.
  • Open Center Systems: Pumps produce continuous flow
  • Closed Centre Systems: Pumps produce flow when needed.
  • Purpose: To pump hydraulic fluid and create flow in a system.

• Reservoir Considerations:

  • Return Line Submergence: Prevents aeration of the fluid.
  • Pressurized Reservoirs: Aid in supplying the pump with fluid.
  • Inlet Port Location: Reservoir supply port is 1 inch from the bottom to prevent sediment entry into the pump.

• Cylinder Force and Speed:

  • Force: Increased with larger bore of cylinder with a diameter piston.
  • Stroke and Speed: Slower movement is seen with larger cylinders, increased fluid demand.

• Hydraulic Fluid Function: Transmits power within the system.

• Troubleshooting Piston Seals:

• Valve Types:

  • Directional Control Valves: Open center and close center.
  • Pressure Relief Valve: Protects the hydraulic system from overpressure.
  • Pressure Reducing Valve: Supplies one circuit with lower pressure than system pressure.
  • Flow Control Valve: Restricts fluid flow.
  • Bypass Valve: Protects cooler in oil-water heat exchange systems.

• Cylinder Types:

  • Single Acting: One-way operation
  • Double Acting: Force for both extension/retraction (balanced/unbalanced)

• Actuators: Convert fluid power to mechanical power.

• Filters: Spin and Cartridge filters.

• Hydraulic Motors: Convert hydraulic flow and pressure into mechanical rotational force.

• Seals:

  • Static Seals: Non-moving parts
  • Dynamic Seals: Moving parts (Radial lip seals, o-rings).
  • Exclusion Seals: Prevent entry of contaminants.

• Accumulator Considerations: Gas charged accumulators: nitrogen is the common gas used; release both hydraulic and accumulated pressure before removing

• Hydraulic Oil Considerations:

  • Viscosity: Measures its resistance to fluid flow.
  • Contamination: Milky oil indicates water contamination.
  • Oil Oxidation: Starts above 125°C (250°F).
  • Drainage: Drain oil at operating temperature.

• General Maintenance:

  • Storage: Keep components covered/maintained with appropriate caps
  • **Routing:**Hoses should be free of kinks or tight bends.
  • Preparing for Service: Lock out, lower attachments, shut down engine, and cycle controls involved.

• Troubleshooting:

  • Smaller-Diameter Hoses: Increased velocity and temperature.
  • Variable Displacement Pumps: Flow rate is adjusted via swashplate angle.
  • Flow Rate and Pump Output: Constant for fixed displacement pumps. Dependent on the swashplate angle for variable displacement pump.

• Component Interactions:

  • Pressure: Result of resistance to flow.
  • Manifold Blocks and Cartridge Valver: Advantage for more simplified system control.

• Hydraulic Machine Preparation for Service:

  • Lock out protocol, safety precautions must be put in place before any fluid removal or component removal or reconnection.

• Hydraulic Fluids:

  • Purpose: Transmits power in a hydraulic system.

• Hydraulic Pumps:

  • Types: Fixed displacement and variable displacement classified based on flow capabilities.
  • Rating Criteria: Flow rate, pressure, displacement.