Control flow

Control flow in a hydraulic system is achieve by flow control valve. These valves are used to keep a set flow constant regardless of pressure variations.

Furthermore the basic function of the valve is to reduce the volume of oil supplied in different places in a hydraulic circuit.  The valve contains a flow passage or a port whose flow area can be varied more exactly regulate the flow of oil by increasing or decreasing the throughput of a valve.

An important application of this valve in hydraulic systems is: controlling the flow rate to cylinders and motors to adjust their speeds. Any flow decrease it means a speed decrease at the actuator.

Also builds added resistance to the circuit, increasing pressure, resulting in a partial bypassing of fluid over the relief valve or a de-stroking pressure of a compensated pump. This one reduces flow downstream of the valve.

For more information about transmission of pressure in a confined body overview my TrainingCloud concept – What is a hydraulic system?

Classification of flow control valve

Flow control valve they may also be classified as: throttling or needle valve and pressure compensated.

The simple control flow valve is the throttling valve. Its serves to regulate the oil supply as required to operate different devices, or better said the device connected downstream of them will be supplied with the right amount of the oil.  Sometimes throttle is variable in a hydraulic system, as they allow adjustment of the orifice and give a degree of flexibility.

control flow throttle valve
Flow control valve with fixed and adjustable throttle

Pressure compensated valve

A pressure compensated throttle has a fixed throughput, irrespective of pressure. Now, let’s examine its functionality in greater detail. The pressure compensated will allow the same volume of oil to pass no matter of the upstream and downstream pressure. This valve comprise a automatic throttle adjustment a regulating gate with spring set at required pressure and automatically adjust to changes in pressure. Therefore, when a hydraulic system utilizes a pressure-compensated valve, the actuator speed (r.p.m) is constant, irrespective of its load.

control flow valve pressure compensated
Pressure compensated valve
To Summarize
  • Flow control valve contains a flow passage or a port whose flow area can be varied;
  • Controlling the flow rate to cylinders and motors adjusting their speeds;
  • The simple control flow valve is the throttling valve;
  • Pressure compensated throttle has a fixed throughput, irrespective of pressure..

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I'm the technical person behind the website My website is my portfolio where a share most of my experiences and know-how gain so far in electro-hydraulic systems.

1 Comment
  1. As maker of this website I would like to share my thoughts about this subject.

    What do you think is a difference between throttle valve and pressure compensated?

    Pressure difference across a throttle valve is not constant – the quantity of oil throughput of the throttle is not the same, depends of the load. If heavy load is lifted by a winch the pressure would be higher which means the pressure difference would then be smaller. So, less oil will pass the through the throttle. In the systems with changing loads the passage flow of the throttle will vary continuously which affects the speed of the hydraulic motor.
    Usually when design a hydraulic lifting installation requirement is for the oil across the throttle valve is to be kept constant. That’s why a pressure compensated flow control valve is preferred to be used, in other words the rpm of the motor has to be constant irrespective of its load.

    All the best!

    Don’t hesitate to share

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