Hydraulic Flow Control Valves

A flow control valve is a device used for adjusting or manipulating the flow rate of a liquid or a gas in a pipeline. The valve contains a flow passage or a port whose flow area can be varied. The role of a flow control valve in a hydraulic circuit is very important and its very location is critical to optimum system performance.

The basic function of a flow control valve is to reduce the rate of flow in its leg of a hydraulic circuit. One of the most important applications of flow control valves in hydraulic systems is in controlling the flow rate to cylinders and motors to regulate their speeds. Any reduction in flow will in turn, result in a speed reduction at the actuator. There are many different designs of valves used for controlling flow. Many of these designs have been developed to meet specific needs.

Some factors, which should be considered during the design stage of a flow control valve are:

• The maximum and minimum flow rates and the fluid density, which affect the size of the valve
• The corrosive property of the fluid, which determines the material of construction of the valve
• The pressure drop required across the valve
• The allowable leakage limit across the valve in its closed position
• The maximum amount of noise from the valve that can be tolerated
• The means of connecting the valve to the process i.e. screwed, flanged or butt welded.

Flow control valves are classified as:

Fixed or non-adjustable flow control valves represented symbolically as in Figures 6.28(aHd).

fixed flow control valve

Adjustable flow control valves represented in hydraulic circuits as

adjustable flow control valve

Additionally they may also be classified as:

and pressure-compensated flow control valves represented as:

pressure compensated flow control valve

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