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How Do Directional Control Valves Affect Oil Flow?

Hydraulic control system and tubingA directional control valve is an essential component of a hydraulic system. It moves from a fully opened to a fully closed position very quickly, triggering rapid acceleration or deceleration of fluid.

In a hydraulic system, fluid flow can be managed with the following directional control valve types:

  • Spool Type – A spool valve consists of a cylinder inside an outer case with several ports drilled through the outer case from one side to the other side. As the spool inside the cylinder moves, it opens and closes the desired ports, depending on the system functions desired.
  • Cartridge Type – Cartridge valves are also called 2/2-way valves. They are usually compact and are used for flow, directional, check, and pressure control.
  • Pilot-Operated Check Valves – PO check valves are used to maintain pressure inside a cylinder or section of the circuit, in case of a pressure drop. When the valve is opened, the pressure is released to either open or close the cylinder.
  • Diverter Type – This type of hydraulic valve can divert fluid  flow from one line to another, depending upon the complexity of the diverter one or more lines may be diverted with each movement.

Simple directional control valves tend to be of the diverter type and are often used to control the movement of hydraulic cylinders, oil entering one port and being sent on an either/or basis via two other ports or together with a tank port to both ends of a double-acting cylinder to extend or retract it.

The more sophisticated spool types have three or sometimes four positions. Depending upon the specification of the spool, it will be neutral in the central position, and then the two service ports will either be pressurised or open to tank in the two other positions.

Control valves for hydraulic machineryThese are mainly used to control fluid flow through valve ports and cylinders but have the advantage over diverters of being easier to operate under pressure. In addition, they can be used to operate multiple cylinders and/or motors, as well as other actuators from the same block of spools.

Some manual spool valves will sometimes have a fourth position, described as a float valve. It is effectively linked to the two service ports so that the attached hydraulic cylinder will move in and out as the load dictates (e.g., on a grading blade).

A pilot-operated check valve will allow oil to move freely in one direction.  However, it will move only in the opposite direction when pilot pressure is applied to lift the check off its seat to let the blocked fluid pass through.

The cartridge-type directional control valves operate similarly to the other types.  The valve mechanism is contained within a cartridge, so it can, for example, be combined with different sorts of cartridge valves within the same block.

For further information about directional control valves or to order a directional valve, hydraulic oil pump, or any other part for your hydraulic system today, please feel free to browse our online catalogue or call White House Products, Ltd at +44 (0) 1475 742500. We are also happy to provide assistance with product selection and hydraulic troubleshooting.

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