Pressure control valves

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1. HYDRAULIC PRESSURE CONTROL VALVE PRESENTED BY :- Vikram Golchha ( A -65 ) Shubham Sankhala (A -42) keshav Patil (A -31) GUIDE :- S.P. Mankani Sir

2. Contents Introduction Classification of Pressure control valve Pressure relief valve Direct acting relief valve Pilot operated relief valve Sequence control valve Conclusion Reference

3. INTRODUCTION Pressure development via restriction. control and check of the developing pressure thus pressure relief valve is used. manipulation of pressure and flow of oil in different circuits.

4. Terms related to Pressure Valves Cracking Pressure :- The pressure at which the valve just begins to bypass the pressurized fluid to reservoir is called Cracking-Pressure. At this pressure the force developed by fluid at ball or poppet (which ever is used) just over-come the compressive force of spring retaining ball or poppet on valve seat.

5. b . Full-Flow Pressure :- As fluid start by-passing through the valve, the poppet gets lifted from it seat. This lifting of poppet cause compression of spring. As spring get compressed its force on poppet increases. Hence to further compress spring and allow more passage to fluid for free flows require more pressure. Hence for full-flow of fluid through relief valve is at much high pressure than cracking pressure. The pressure at which full-flow of pump by-passes to reservoir is called “Full-Flow Pressure”.

6. Types of Pressure Control Valves There are six types of pressure-control valves are: 1 . Pressure Relief valves 2 . Unloading valves 3 . Sequence valves 4 . Pressure-reducing valves 5 . Counter-balance valves 6. Safety value

7. Pressure Relief Valve (PRV) A closed valve is to limit the pressure in to prescribed maximum by diverting some or all output of pump to tank. The pressure can rise in a hydraulic system if: T he flow rate from the pump is larger than the flow rate through the actuator T he volume of a closed system is reduced. T he hydraulic resistance of the system rises . The pressure relief value are normally closed.

8. construction It consists of a valve body, poppet, spring and adjusting screw Poppet held on valve seat by spring compression, which is adjusted by screw.

9. WORKING

10. Pilot Operated Relief Valve: - In case of direct acting relief valve the pressurized fluid Is stop by spring loaded poppet against by-passing to the reservoir While in case of pilot operated relief valve a balanced piston or spool block the passage of pressurized fluid against bypassing to reservoir. Excess pressure cause unbalances of the piston, because of which it slides to one side allowing pressurized fluid to by-pass to the reservoir.

11. WORKING As pressure increase the poppets of direct acting relief valve get lifted and pressurized fluid by passing to reservoir. This causes a flow of fluid across the orifice, when fluid flow through small orifice, their pressure drops due to throttling so there is less pressure than pump side. Hence this difference in pressure cause an unbalance force on piston and it slides to low-pressure side. This side shifting of piston open path to pressurized fluid of pump to bypass to reservoir.

12. As pressure decreases, poppet of direct acting relief valve again sits on valve seat and blocking the small amount of fluid by-passing to reservoir. Which cause increase of pressure on this side of piston or spool, as when there is no flow across orifice there is no pressure drop, and pressure get equalized on both side of piston This forces back piston to its original position where it blocks the path of fluid of system to bypass to reservoir.

13. WORKING OF PILOT OPERATED PRESSURE RELIEF VALUE

14. Advantages Smaller package on larger pipe size More option for control Seals more tightly as system pressure approaches but doesn’t reach the set pressure. Control pilot can be mounted remotely It can be used in engines

15. DISADVANTAGE More complex ,resulting in various fail –open failure modes more expensive at smaller size Small parts in pilot values are sensitive to contaminants particles

16. SEQUENCE VALVE The function of sequence valve is to provide flow to a second consumer in the case when the pressure level at a particular consumer has reached a threshold valve. As the name implies it is used for sequencing the operation one after another.

17. Operation :- It is nothing but a pilot operated relief valve, in which the drain is connected to second consumer. The drain is directed to the main drain. In normal position the sequence valve is closed. When the operation of consumer one is completed and when pressure start building, and when reaches set value of piliot relief valve, fluid flows through spools to drain. As the fluid flows through spool, the orifice causes the pressure difference between spring side and spool side. The pressure difference result in differential force with lift the spool causing it to uncover the part B and thus supplying fluid to another consumer B. Thus achieving the sequencing operation.

18. Such application is mostly for in “Tooling and Automation” where several operation are sequenced in pre determined manner. A check valve is connected in parallel with sequence valve so that both cylinder will retract simultaneously ( no sequencing is desired in retracting). Applications

19. Counter balance valve Control the vertical cylinder to not allow it to fall freely. Also known as back pressure valves.

20. APPLICATIONS Mainly Used in FORKLIFTS when heavy loads are to be brought down Also used in loaders and JCB’S for easy load pickup and lowering of loads . Hydrolic machines

21. Pressure Reducing Valve Open pressure control valves Used to maintain reduced pressure in the required portion. done by increasing the area where the oil could release the pressure.

22. APPLICATIONS Air Compressors Used in inlet of flow of load in pressure reactors. Aircrafts and Aerospoace Cooking water pressure reduction. Oxifuel welding and cutting. Propane/ lpg gas – industrial. transportation and storing. Mining industries

23. Safety values All the pressure relief values are kind of safety values. Safety values are values that acts as a fail safe in a thermal hydraulic plant. Safety value came to existence as the early steam boilers ware prone to explosion.

24. Questions…….??