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Pressure Relief Valves

Pressure Relief Valves

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Pressure Relief Valves

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  1. Pressure Relief Valves Operation, Maintenance and Adjustments

  2. Types of Pressure Relief Valves (PRV’s) • Ball Type • Uses a ball bearing to relieve pressure at a set pressure • Has 3 ports; 1 for pressure in, 1 for pressure out, and one back to the tank • Uses a ball that opens when the pressure becomes too high

  3. Types of Pressure Relief Valves (PRV’s) • Poppet Type • Works similarly to a ball type • Uses a poppet to relive excess pressure

  4. Types of Pressure Relief Valves (PRV’s) • Pilot Operated Type • Uses a large shuttle valve to relieve main pressure • A smaller shuttle valve to activate the larger valve • The large shuttle relieves more fluid than the ball or poppet type

  5. Ball Type PRV Operation • When fluid enters the housing, it presses against the ball • When the pressure is under the set pressure, the spring pressure keeps the ball closed • When the pressure exceeds the spring pressure, it forces the ball open and lets the fluid flow to the tank

  6. Pilot Operated PRV Operation • The smaller shuttle is tied to the main pressure • The other end is spring pressure adjusted by a knob • When the spring pressure overcomes the system pressure, the shuttle stays shut

  7. Pilot Operated PRV Operation • When the system pressure overcomes the spring, the shuttle moves and allows oil to force the main valve open • This allows excess oil to flow back to the tank

  8. PRV Adjustments • When adjusting any PRV you must have full system pressure • In a working system, this is achieved by bottoming out a cylinder or stalling a hydraulic motor

  9. PRV Adjustments • When adjusting a PRV, keep in mind that it must be set to the system pressure specifications in the manual • Incorrectly set PRV’s can result in hose rupture or other component damage • A prime mover can be stalled if the pressure becomes too great

  10. Setting a PRV • Make sure to oil is at 80°F (minimum) • Connect the pressure gauge to the pressure line • Bottom a cylinder or stall a hydraulic motor • Quickly adjust the PRV by turning the screw either in (to raise pressure) or out (to lower pressure) until the pressure is within specs

  11. Setting a PRV • Most PRV’s have a lock nut on the adjusting screw to prevent movement after setting • Make sure to lock that nut tight after adjusting • Reinstall the screw cover (if equipped) • Recheck the stall pressure

  12. Setting a Pilot Operated PRV • Make sure the oil is warm, you have the pressure gauge attached, and a cylinder bottomed • Adjust the PRV pressure by turning the knob either in (to raise pressure) or out (to lower pressure) until the pressure is within specs • Make sure to tighten the lock nut and recheck the pressure

  13. Cautions • Do not hold a cylinder bottomed or a motor stalled too long as it builds heat • Do not set the pressure over the recommended pressure as component or machine damage can occur • Always set the relief pressure below the pressure that stalls the prime mover

  14. Hydraulic Bench Specs • Our hydraulic bench has a maximum pressure of 250 PSI • There is a pilot operated and ball relief valve • The pilot operated can be disassembled, but the ball cannot

  15. Go to work on Lab 5