Flow control valves

In hydraulic and pneumatic systems flow control valves are necessary to vary the speed of actuator. Flow control valves are placed in between Actuator and Direction Control (DC) Valve

1. Aldel Education Trust’s ST. JOHN COLLEGE OF ENGINEERING AND MANAGEMENT, PALGHAR (ST. JOHN POLYTECHNIC) D EPARTMENT OF MECHANICAL ENGINEERING S UB: INDUSTRIAL HYDRAULICS AND PNEUMATICS T OPIC: FLOW CONTROL VALVES PREPARED BY:- Prof. Pranit Mehata Lecturer, SJCEM 7972064172

2. FLOW CONTROL VALVE F low rate Q and linear velocity is related by the formula, V=Q/A R pm of motor is related by the formula n=Q/V The velocity and rpm are directly proportional to the flow rate. Hence by changing flow rate (Q) we can vary the speed of actuator or motor. This function is performed by Flow Control Valves. Flow is controlled either by throttling or diverting it

3. TYPES OF FLOW CONTROL VALVES

4. SYMBOLS OF FCV

5. PRESSURE COMPENSATED FCV In any hydraulic circuit there are slight variations in pressure of oil. When pressure changes the rate of flow changes but many circuits require constant flow regardless of input or output pressure variations in the circuit then the pressure compensated FCV is used. Symbol of Pressure Compensated FCV Fig. Pressure Compensated Flow Control Valve

6. PRESSURE & TEMPERATURE COMPENSATED FCV To control the rate of flow of oil, we use flow control valve (FCV). By opening the FCV valve, the area of flow is increased, and thereby increasing the rate of flow and vice versa. But the rate of flow also depends upon pressure and temperature of oil. Hence any change in rate of flow of oil needs to be compensated which happens due to change in pressure and temperature in order to maintain constant required rate of flow. Fig. Pressure and Temperature Compensated FCV Fig. Symbol of Pressure and Temperature Compensated FCV

7. NON- COMPENSATED FCV Non compensated flow control valve that controls the flow by throttling or restricting. Needle valve is non-compensated valve. These are used system pressure is relatively constant and motoring speeds are not too critical. The operating principle behind these valves is that flow through an orifice remains constant if the pressure drop across it remains the same. Sometimes needle valves comes with an integral check valve for controlling the flow in only one direction. The check valve permits easy flow in opposite direction without any restrictions. Fig. Symbol of Non-Compensated FCV

8. CHECK VALVES The valve which allows flow of oil in only one direction and do not allow reverse flow of oil is called as check valve. As there is no return of flow hence it is also called as Non-Return Valve (NRV). For example, foot valve of centrifugal pumps. There are two types of check valve 1. Simple check valve 2. Pilot operated check valve

9. SIMPLE CHECK VALVES When pressurized oil comes in through port A, it will lift the cone by overcoming the spring force and flow will start from A to B. When flow from A stops spring will expand and cone will block the flow. There will be no flow from port B to port A. Fig. Simple Check Valve Fig. Symbol of NRV

10. PILOT OPERATED CHECK VALVES When pilot signal of pressurized oil is used to control movement of poppet in the check valve, it is called as pilot operated check valve. In normal position there is no flow from(A) to (B) because the movable valve poppet has blocked the flow. When pilot signal is given through port (C). Now the flow from (A) to (B) will start. As and when we cut-off the pilot signal the flow from (A) and (B) will continue .