VR4U10
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Catalog excerpts

PILOT OPERATED UNLOADING VALVE - Series VR4U Veljan Unloading Valves series VR4U are pilot operated controls and used to jnload a circuit at low pressure when pilot pressure at portX is maintained higher than that of inlet pressure at port A set by the pilot spring. A typical use of an unloader valve is to unload the low pressure side of a double pump. A Pump connected toan Accumulator circuit can also be unloaded by the VR4U valve. VR4U consists of a high flow poppet type seat valve section controlled by the low flow, adjustable pilot section mounted on top. Pressure setting is achieved by means of knurled knob. For tamper proof setting, acorn nut with lead seal is available as option. Optional ventvalve VW01 sandwiched between pilot section and main body can be used forventing the VR4U valves. Exceptionally fast response is obtained due to the precise ratio between the main piston area and its mass. One of the unique features of VR4U is that it works as a relief valve at the set pressure even in the absence of external pilot signal. nternal Drain External Drain Normally port A is connected to pump and port B to tank. At low pressure, flow entering port A is blocked by the main poppet. Pressure from port A passes to the pilot section through orifices in the main poppet and in the pilot section. No flow takes place in this portion until the pressure overcomes the spring setting of a pilot ball. The pilot ball is lifted from its seat releasing a small pilot flow to tank and resulting in a pressure drop across the main poppet. The main poppet opens and allows only enough flow from port A to port B maintaining inlet pressure at the set value of the pilot spring as in thecase of a reliefvalve. h this condition, the external pilot pressure from another part of system if applied at port X causes a small override piston to act against the ball pushing it further off its seat resulting in very low pressure drop across the main poppet as long as pilot pressure is maintained, the main poppet opens further and unloads the inlet flow at very low pressure drop. As soon as the pilot pressure drops to approximately 10% below the pilot setting, the main poppet closes with a snap action diverting the main pump flow back to the hydraulic system. Excessive restriction in the tank line or the pilot pressure signal at port X should be avoided to attain a correct function.

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PILOT OPERATED UNLOADING VALVE - Series VR4U Mounting position Port sizes (nominal] Ambient temperature Special working conditions Pilot operated Unloading Valve Poppet type Consult VELJAN Pressure control range Maximum operating pressure PortX (pilot) PortY, Yl (Pilot drain Minimum - depends on flow Internal pilot drain - 50 psi (3.5 bar) External pilot drain - 430 psi (30 bar] Fluid Temperature Range Mineral oil as per DIN 51 524/25 or other fluids on request Viscosity Range Optimum operating viscosity Seal compatibility Cleanliness recommended Code 1 (Buna N) or Code 5 (Viton) (contact...

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PILOT OPERATED UNLOADING VALVE - Series VR4U ORDERING CODE Max. Pressure of Valve Body Body Mounting - Threaded body 1 - Threaded body - VR4U03 = V2 NPTF 6 - Threaded body VR4U03 = V2" B.S.PP D - Threaded body VR4U06 = % B.S.PP Subplate mounting (Yi port - V4 NPTF with drain line code 2] SAE - 4 (7/16" - 20 UNF) with drain line code 2) ( Yi Port = W B.S.PP ; with drain line code 2) Flange body 2 - Flange body ( X,Yi port - V4" NPTF ) Seal Class Design letter Solenoid Voltage (Omit for non vent version) Electrical Vent Omit for non vent version With manual override (Solenoid de-energized :...

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PILOT OPERATED UNLOADING VALVE - Series VR4U PERFORMANCE CURVES Pressure Differential Charecteristics Typical application sytsems Double pump system, to unload nloading" (pressure settling) Accumulator system with unloading valve R4U The differential between Unloading and Onloading is typical 15%. When system pressure (for instance accumulator) drops 15% below the pilot setting, the valve closes and pump feeds the system again.

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PILOT OPERATED UNLOADING VALVE - Series VR4U Panel opening 1 ) Optional from pilot head or subplate. PortYl is only available at drain line (code 2) external from the pilot head. Note : For details of Subplate & mtg. screws please refer page 40

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PILOT OPERATED UNLOADING VALVE - Series VR4U Location hole Mounting screws are included in subplate order. For valves ordered without subplate, mounting screws must be ordered seperately.

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PILOT OPERATED UNLOADING VALVE - Series VR4U

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PILOT OPERATED UNLOADING VALVE - Series VR4U OPTIONAL CONTROL Type of control - Code 3 Type of control - Code 2 Acron nut with lead seal Hand knob 50mm dia (not for version with vent valve VVV01) B1 A1 PC Y1 B4 B3 A2 B2 Y1 Dimensions in Dimensions mm A1 5.51 140.0 A2 1.49 in 38.0 B1 mm 5.55 141.0 42.5 B2 1.67 B3 1.49 38.0 B4 ø1.96 ø50.0 Version with Vent Valve VVV01 Weight (VVV01) : 3.73 lbs (1.7 kg) Screws for additional vent valve installation. 4 x M10 X 90 long Y1 Dimensions Dimensions in 1.85 C1 mm 47.0 mm in ø10.5 ø0.41 D1 D2 D5 60.3 3.49 88.7 0.51 13.0 D11 C1 58.7 2.37 D9 Y1 2.31 D8 Z...

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