VR4S030 pages

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PILOT OPERATED SEQUENCE VALVE - Series VR4S

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VELJAN

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Veljan Sequence Valve Series VR4S are pilot operated controls and enable

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a hydraulic system to operate in a sequence. Fluid is allowed to pass to a

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secondary system ( Port B ) after the primary system ( Port A ) pressure

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reaches the preadjusted value set at pilot spring.

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VR4S consists of a high flow poppet type seat valve section controlled by

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the low flow, adjustable pilot section mounted on top. Pressure setting is

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altered by means of a knurled knob. For tamper proof setting , acorn nut

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with lead seal is available as option. Optional vent valve VWO

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sandwiched between the pilot section and the main body can be used for

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venting the VR4S valves. Pilot drain can be taken out externally from a pilot

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head or from a subplate.

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Exceptionally fast response is obtained due to the precise ratio between the

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main piston area and its mass. The unique design features of pilot allows for

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accurate and stable secondary pressure controls. Precise adjustment and

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quick response eliminate pressure variation and system shocks.

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Port A is connected to the primary section and port B to the

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secondary section of a hydraulic system. At low pressure,

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flow entering to Port A is blocked by the main poppet.

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Pressure at Port A passes through orifices to the pilot section

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as well as to the top of the main poppet. No flow takes

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place to this section until the pressure overcomes the spring

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setting of the pilot cone. The pilot cone is lifted from its seat

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releasing a small pilot flow through external drain and

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resulting in a pressure drop across the main poppet. The

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main poppet opens and allows only enough flow to the

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secondary system ( Port B ) maintaining the primary system

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pressure ( Port A ) at the pre-set value until the pressure at

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secondary port rises to the same value. As soon as the

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pressure is equal in both ports, the control piston in the pilot

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section closes preventing loss of oil through external drain.

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The main poppet opens fully and allows pressure at A and

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B to rise to a higher value than set. In such a situation the

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VR4S works as a gate valve allowing flow in either

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direction.

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