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.
- Meter-in circuit
- Meter-out circuit
- Bleed off circuit
To see the above flow rate controlling methods,
please find the post “Meter-in, Meter-out and bleed off hydraulic circuit”.
We will discuss the classification of flow control valves and non pressure compensated flow control valves in our next post.
Image courtesy: Google
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