Saturday, 7 May 2016

HYDRAULIC FLOW CONTROL VALVES

HYDRAULIC FLOW CONTROL VALVES

We were discussing the basics of directional control valve and its classifications as well as the working principles and types of check valves in our previous posts. Today we will focus here another type of valve used in hydraulic units i.e. flow control valve.

 
Let us first understand, what is flow control valve and why it is used in hydraulic units?
As name indicates, a flow control valve is used in hydraulic units in order to control or regulate the flow rate of fluid entering or leaving the actuator. If we see the water tap, there will be one handle and flow rate of water will vary when we will rotate or turn the handle in clockwise or anti-clockwise direction. There will not be any water flow, if valve is closed. Water tap could be considered as the best and simple example of flow control valve.

If we consider the fixed displacement pump, pump displacement will be constant throughout the operation of the pump. Let us consider one case where we have fixed displacement pump of capacity of 20 LPM. It indicates that pump will deliver the hydraulic oil with a rate of 20 liters per minute. We must note it here that speed or velocity of any hydraulic actuator will be dependent over the volume of oil entering to the actuator or leaving the actuator. Therefore if we need to vary the speed of actuator, we will have to vary the volume of oil entering to the actuator or leaving the actuator.

In simple words, we can say that speed of actuator will be directly proportional with the flow rate of hydraulic oil. We have considered above the case of fixed displacement pump, so fixed displacement pump will deliver the fixed volume of hydraulic oil per minute. So, we have one question that how we will vary the speed of actuator if we are having fixed displacement pump in our circuits. Flow control valves will be used here to secure the desired control over the speed of actuator.

Flow control valve and its hydraulic symbol

 
Flow control valves regulate the speed of actuators in hydraulic system by regulating the flow of fluid entering or leaving the actuator. Flow control valves also permit a fixed displacement pump to deliver the fluid to two or more than two branch circuits of hydraulic system with different flow rate values on the basis of requirement.

Applications of flow control valves could be seen in various areas such as in vertically loaded cylinder. Flow control valve is used here in order to regulate the speed of actuator during downward or upward movement. Applications of flow control valves could also be seen in regulating the speed of cutting tool in machining section and also in regulating the speed of hydraulic motor.

 
Flow control valve is also available with check valve. Check valve permits here the reverse flow. Such type of valve is also termed as the flow control series of flow control and check valve. There is one more form of flow control valve which is termed as flow control and overload relief valve. In such valve, there will be one integral relief valve and it will be associated with flow control valve for limiting the system pressure.

Main functions of a flow control valve in a hydraulic system

Flow control valves regulate the speed of actuators.
Flow control valves regulate the flow of pump to two or more than two branches of circuit as per requirement.

Methods of controlling the flow rate of hydraulic oil

There are three main types of controlling methods of flow rate of hydraulic oil going to actuator or leaving the actuator and these are as mentioned here.
  1. Meter-in circuit
  2. Meter-out circuit
  3. Bleed off circuit
To see the above flow rate controlling methods, please find the post “Meter-in, Meter-out and bleed off hydraulic circuit”.


Image courtesy: Google

Also read

Archivo del blog

Copyright © ENGINEERING MADE EASY | Powered by Blogger | Designed by Dapinder