What is a Hydraulic flow control valve?

A Hydraulic flow control valve adjusts and controls the volume flow of air within a pneumatic system. They can often be used to adjust the speed of operation of an actuator. They should not be confused with pressure controllers, or regulators. Whilst there is a relationship between pressure and flow, this is not necessarily linear and using a pressure regulator to control flow can result in wasted energy and the potential for component damage.

They can also be referred to as mass flow controllers or, for certain types, needle valves.

How do flow control valves work?

Whilst there are different types of flow controller, they all work on a simple basic principle. The smaller a hole, or orifice, in a pipe, the lower the rate of flow of air at a given pressure (or more correctly differential pressure either side of the orifice). Flow controllers often have a finely machined tapered stem which matches exactly to the profile of a seat. Fully closed, results in no air flow; as the valve is progressively opened more and more air is allowed to flow until, at fully open, air will pass at the maximum rated flow of the device. Bi- directional valves will control air flow in either direction, whilst uni-directional devices control air flow in one direction only – either on the in-flow to a component, or the exhaust side. Uni-directional valves often have a check device allowing full air flow in the opposite direction to the control direction.

How do I select a flow control valve?

There are a number of factors to consider:

flow rate control – what is the minimum and maximum controllable flow rate required for a component or process; this will also relate to the port size of the unit. What precision and accuracy of flow is required and is the process cyclical?

configuration – for a uni-directional valve, is control required on the exhaust or in-flow cycle? Or, is a bi-directional valve required?

connection - is threaded or push-in most suitable? What conforms to other components in the system

control method – is manual adjustment suitable for the application, or is a remote method required?

working environment – do factors such as aggressive environments, or temperature, limit the choice of the material used in construction of the valve?

working pressure – what is the maximum operating pressure of the system or application?

Types of flow control valve?

There are a variety of types to suit the selection requirements above:

proportional flow control valve – a directly operated spool, with micro-processor driven position control, gives precise flow control. The units offer a choice of valve function (5/3; 3/2; 2/2) and a choice of control parameters (4 to 20mA; 0 to 10V; -5 to +5V). They offer high flow, up to 5000 l/min, with low pressure drop.

motorised flow control valve – here the method of flow control is often different to that outline above. Two ceramic discs, with open segments, rotate relative to each other. When the open segments align exactly, the unit will allow maximum flow; as the open segments mis-align the flow is restricted until the flow path can become completely blocked. DC synchronous or stepper motors allow accurate positioning and, hence, flow control. Position feedback can be set to 0 to 20mA or 4 to 20mA.

Typical applications for a flow control valve?

Flow control valves are often used to control the speed of pneumatic actuators. Any process reliant on a controlled flow of air, particularly for the quality of a finished product, will need to utilise a flow control valve with sufficient precision.

Do I need anything else for a flow control valve?

Piping and fittings will be required in order for the connections to be completed within the system.

Post time: Aug-02-2022
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