VD4S060 pages

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SEAT VALVES

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VELJAN

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FEATURES

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Veljan Seat Valves are body type mounting series VD4S

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and cartridge units series VCAR. The complete range of

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cartridges - body mounted VD4S and manifold mounted

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VCAR are sized from 3/8" to 1 1 /2" permit flows from

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1 80 Ipm to 600 Ipm and pressures up to 350 bar.

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The interface porting on the subplate body versions follow

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CETOP, ISO and DIN standards and is dimensionally

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identical with the VELJAN VR4 series of pressure

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controls. Hence VD4S and VR4 valves can be

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conveniently used in combined circuitry.

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The modular design is used in all valve sizes and the valves

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are used fora variety of functions :

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- As a leak - proof directional control

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- As a pressure control for the adjustment

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or limitation of the pressure

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- As a check valve to obtain unidirectional flow

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- As a throttle valve to control and limit the

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rate of flow

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A variety of standard combinations of internal components

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are available along with additional options to suit speda

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circuitry. These options are :

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- Poppet stroke limiter :

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to control maximum flow rate,

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-Vent valve sandwiched :

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to electrically control poppet operation,

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-Seatarea changes :

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to vary operational characteristics,

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-Shuttlevalves :

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To take pilot oil from PortAand PortB.

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Advantages of VCAR cartridge valves are that when

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integrated with specially designed manifold blocks they

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offer space and cost savings in comparison with

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conventional piped circuit construction. A manifold design

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using cartridges is more sophisticated than utilising VD4S

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units and greater attention is required in the assembly of

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the cartridges into the manifolds.

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Fast response and rapid frequency of operation even at

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the highest flow is achieved due to poppet design and

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precise ratio between its mass and stroke. The cast

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passages within the VD4S valve body when used with

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correctly designed manifolds ensure circuits in which

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pressure drop and oil turbulence is minimal.

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Veljan seat valves and cartridges function to direct flow

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from port A to port B or vice - versa and their operation is

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dependent upon the effective pressure area and spring

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force on the poppet. The cracking pressure is proportiona

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to the ratio of control area to seat or ring area. Pilot

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pressure at portX acting on the control area closes the seat

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valve, thus forces generated by cylinders or hydraulic

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motors can be decelerated to zero by controlling the

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differential pressure.

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Acceleration or deceleration of fluid which the seat valve is

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controlling will take place whilst the valve is opening or

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closing and the time normally necessary to overcome

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overlap in conventional spool valves is eliminated. In

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addition to this improved response time, the action also

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ensures that the seat valve functions without introducing

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system pressure peaks or shocks and therefore machine

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cycle times may be reduced without detriment. Various seat

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valve combinations are manufactured to suit a wide variety

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of specialized industrial applications.

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Cracking pressure depends on the area ratio of individua

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combination of spool and sleeve.

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Example : With a ratio of 95% seat area to 5% ring area anda

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spring pressure = 2.2 bar then the following cracking pressures

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apply.

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Direction of flow		Supposed pilot pressure Px (bar)
		0	9	15	30	100	250	330
PA	A- B	2.2	1 1.7	18.0	34	108	265	350
PB	B -A	42	222	342	>350 646	>350 2052	>350 5035	>350 6650

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It is obvious that with flow direction B to A and a control (pilot

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pressure) at X of more than 15 bar, pressure in excess of

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maximum valve rating would be exceeded before the valve

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would open. Under static conditions the valve would still

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remain leakproof even at substantially higher pressure.

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