VD4S030 pages
SEAT VALVES
nnnnFEATURES
nnnn|VELJAN|
nnnnVeljan Seat Valves are body type mounting series VD4S
nnnnand cartridge units series VCAR. The complete range of
nnnncartridges - body mounted VD4S and manifold mounted
nnnnVCAR are sized from 3/8" to 1 1 /2" permit flows from
nnnn1 80 Ipm to 600 Ipm and pressures up to 350 bar
nnnnThe interface porting on the subplate body versions follow
nnnnCETOP, ISO and DIN standards and is dimensionally
nnnnidentical with the VELJAN VR4 series of pressure
nnnncontrols. Hence VD4S and VR4 valves can be
nnnnconveniently used in combined circuitry
nnnnThe modular design is used in all valve sizes and the valves
nnnnare used for a variety of functions :
nnnn- As a leak - proof directional control
nnnn- As a pressure control for the adjustment
nnnnor limitation of the pressure
nnnn- As a check valve to obtain unidirectional flow
nnnn- As a throttle valve to control and limit the
nnnnrate of flow
nnnnA variety of standard combinations of internal components
nnnnare available along with additional options to suit speda
nnnncircuitry. These options are :
nnnn- Poppet stroke limiter :
nnnnto control maximum flow rate,
nnnn-Vent valve sandwiched :
nnnnto electrically control poppet operation,
nnnn-Seatarea changes :
nnnnto vary operational characteristics,
nnnn-Shuttle va Ives :
nnnnTo take pilotoil from Port Aand Port B.
nnnnAdvantages of VCAR cartridge valves are that when
nnnnintegrated with specially designed manifold blocks they
nnnnoffer space and cost savings in comparison with
nnnnconventional piped circuit construction. A manifold design
nnnnusing cartridges is more sophisticated than utilising VD4S
nnnnunits and greater attention is required in the assembly of
nnnnthe cartridges into the manifolds.
nnnnFast response and rapid frequency of operation even at
nnnnthe highest flow is achieved due to poppet design and
nnnnprecise ratio between its mass and stroke. The cast
nnnnpassages within the VD4S valve body when used with
nnnncorrectly designed manifolds ensure circuits in which
nnnnpressure drop and oil turbulence is minimal.
nnnnVeljan seat valves and cartridges function to direct flow
nnnnfrom port A to port B or vice - versa and their operation is
nnnndependent upon the effective pressure area and spring
nnnnforce on the poppet. The cracking pressure is proportiona
nnnnto the ratio of control area to seat or ring area. Pilot
nnnnpressure at port X acting on the control area closes the seat
nnnnvalve, thus forces generated by cylinders or hydraulic
nnnnmotors can be decelerated to zero by controlling the
nnnndifferential pressure.
nnnnAcceleration or deceleration of fluid which the seat valve is
nnnncontrolling will take place whilst the valve is opening or
nnnnclosing and the time normally necessary to overcome
nnnnoverlap in conventional spool valves is eliminated. In
nnnnaddition to this improved response time, the action also
nnnnensures that the seat valve functions without introducing
nnnnsystem pressure peaks or shocks and therefore machine
nnnncycle times may be reduced without detriment. Various seat
nnnnvalve combinations are manufactured to suit a wide variety
nnnnof specialized industrial applications.
nnnnCracking pressure depends on the area ratio of individua
nnnncombination of spool and sleeve.
nnnnPilot pressure px
nnnnoperates on area A x
nnnntogether with spring
nnnnforce pF
nnnnPilot pressure pE
nnnnoperates on ring
nnnnarea A B
nnnnSystem pressure pA
nnnnoperates on seat
nnnnarea A A
nnnnExample : With a ratio of 95% seat area to 5% ring area and a
nnnnspring pressure^ 2.2 barthen the following cracking pressures
nnnnapply.
nnnnDirection 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 |
It is obvious that with flow direction B to A and a control (pilot
nnnnpressure) at X of more than 15 bar, pressure in excess of
nnnnmaximum valve rating would be exceeded before the valve
nnnnwould open. Under static conditions the valve would stil
nnnnremain leakproof even at substantially higher pressure.
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