1. Flow Control Valves & Pressure Relief valves
Hydraulics Module 4

2. Objectives Explain the functions of flow control valves.
Distinguish between the different types of flow control valves
Identify the symbols of different flow control valves
Explain the function of Pressure relief valve.
Identify the symbol of a Pressure relief valve.
Simulate a hydraulic circuit that controls the speed of a double acting cylinder by using a two way flow control valve.
Explain the operation of the hydraulic circuit that controls the speed of a double acting cylinder by using a two way flow control valve
Assemble the hydraulic circuit that controls the speed of a double acting cylinder by using a two way flow control valve

3. Flow Control Valves
The flow control valve is used to control the speed of a cylinder or a motor by controlling the amount of fluid flow rate passing through it.
The flow rate is the volume of fluid that moves through the system in a given period of time. Flow rates determine the speed at which the output device (e.g., a cylinder) will operate.
The flow velocity of a fluid is the distance the fluid travels in a given period of time which is the extension speed of the cylinder.
V = __Q__
Flowrate (m3/s)
Velocity (m/s) A
Area (m2)

4. Flow Control Valves The One Way Flow Control Valve
The Two Way Flow Control Valve

5. The One Way Flow Control Valve
The one way flow control valve is used to control the flow rate in the hydraulic circuit only in one direction (throttling part: from A to B), and allows a free flow in the opposite direction (from B to A).
Throttling is achieved by adjusting the valve screw.
Adjusting Throttle Screw
ISO Symbol

6. The Two Way Flow Control Valve
The two way control valve provides a constant flow rate in the case of variable loads.
This valve has two ports (A) and (P) and adjusting throttle screw.
Adjusting Throttle Screw
ISO Symbol

7. Pressure Releif Valves
These valves are used to control and regulate the pressure in the hydraulic system.

8. Pressure Relief Valves
Pressure relief valve is used mainly as safety valve.
It prevents the maximum permissible pressure in the hydraulic system from being exceeded.
If the maximum pressure is reached at the valve inlet, the valve outlet is opened and the oil will flow out to the tank.
The valve remains open until the built-in spring closes it after reaching the preset pressure in accordance with the spring characteristic.
ISO Symbol
Input Pressure
Tank Port

9. Practical Tasks 1 & 2

10. Practical Task 1:
Controlling the speed of a double acting cylinder using a two way flow control valve

11. Practical Task 2:
A special machine is used to emboss graphic symbols on metal foil. The foil is fed through the embossing machine. The advanced motion of the stamp must be capable of being varied in accordance with the fed speed. The return motion must always be executed as a rapid traverse. A One way flow control valve is used to control the speed of the stamp, while a pressure relief valve is used to prevent the weight of the stamp from pulling the piston rod out of the cylinder. A 4/2 way valve is used to switch between advance and return motion

12. Solution:

13. Don’t Forget your H.W.