TSM 363 Fluid Power Systems

1. TSM 363 Fluid Power Systems Control of Power Distribution- Valve-based Controls

2. How to Make it Functioning as Expected?

3. 1. Pressure Controls • System Pressure Control • Use of a line relief valve to limit the maximum allowable system pressure • Other Pressure Control Functions • Unloading • Pressure reduction • Load holding • Sequential control • Others

4. Inlet Pilot Outlet Line Relief Valve • Line relief valve is a pressure control valve. • A basic LR valve has a pilot pressure applied. • There are a few types of LR valves available.

5. Pressure Override Characteristics

6. Pilot Operated Relief Valves Function:protect a hydraulic system with low override characteristics. Operation:The spring loaded puppet valve opens when the pressure reaches the cracking pressure, the flow cause the back pressure drop, which leads the open of the spool valve.

7. P P P P full full flow flow full full flow flow P P P P D D D D Improved Pressure Override Characteristics

8. M R P H T M 800 psi 800 psi Application of Relief Valves 1,000 psi It is recommended that there is always at least 200 psi difference between two line release (pressure relief) valves in a line.

9. Heat Generation in Pressure Relief

10. Example Other Pressure Controls:-- Sequence Valves

11. Functionality and Operation of a typical Sequence Valves • Controls the order of operations in branch circuits • The sequence valve is normally closed. It is set to react to a system pressure less than the setting of the pressure relief valve. • Pressure increases resulting from an actuator reaching the end of its stroke open the sequence valve.

12. 2. Flow Controls • Uncompensated Flow Control • Example – metering-in/metering-out using needle valves • Compensated Flow Control • Example - • Proportional Flow Control • Often use of proportional directional control valve (discuss in direction control)

13. Metering Controls of Flow • Often us of a needle valve • Simple, but energy inefficient • Commonly used in some light load, inexpensive systems for load control.

14. Typical Metering Flow Control Approaches

15. Flow Divider –Example of Pressure-compensated Flow Control

16. Functionality and Operation of a Flow Divider Valve • Directs flow to two or more branches • Controls flow and also direction (e.g., priority control) • Common on off-road equipment to divide flow between circuits (e.g., power steering and front-end load or left and right crawler tracks)

17. 3. Direction Controls • Simple direction control • On-off type direction control • Multi-direction Control • Circuits Switching-type direction control • Proportional direction control • Direction and flow integrated control

18. P P P Pp Pp Pp QT QT PT PT PT T T T PT PT PT QP QP Qk Qk Q2 Q1 Q2 Q1 2 1 P1 P2 P2 P1 P1 P2 1 2 Simple direction Control

19. Simple direction Control

20. M M M M M P P P P P R R R R R M M M M M H H H H H T T T T T Multi-direction ControlCase 1: Hydraulic Cylinder Controls

21. M M M M M M M M M M M M Multi-direction ControlCase 2: Hydraulic System Priority Controls

22. Theoretical Base for All Valve Controls:Orifice Equation • Cd is determined experimentally • Pressure drop is proportional to flow • Valve Principles: Area is a adjusted to control pressure and flow rate • Density of petroleum-based fluids 850-950 kg/m3

23. Lecture Summary • Discussed the basic principles of different methods of using valves to control a hydraulic system: • Pressure controls • Flow controls • Directional controls • All valved-based controls follows the same control principle