Pressure Unloading Valve
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Pressure Unloading Valve, Size 4 Qmax = 30 l/min, pmax = 250 bar Two-stage, various on-off pressure differentials, with manual adjustment Series DWPB-4N… S Compact construction for cavity type AN – 3/4-16 UNF S External pilot drain S On-off differential independent of tank line pressure S Choice of 5 on-off differentials S 3 pressure ranges available S With integral pressure-relief function S Available with hand-knob S All exposed parts with zinc-nickel plating S Can be fitted in a line-mounting body Series DWPB-4N… cartridges are size 4, two stage, high performance pressure-unloading valves with an 3/4-16 UNF mounting thread. They consist of a spool-type main stage and a leak-free, ball-type pilot stage. Unloading val­ ves are used wherever a pump has to be disconnected from and re-connected to a pressure circuit. For this purpose, ei­ ther the 'Off' pressure or the 'On' pressure of the cartridge can be set. When the 'Off' pressure is set, the 'On' point will depend on the selected percentage on-off differential, or the other way round. To disconnect the pump, the cartridge re­ sponds to rising pressures at ports 4 and 1 by opening the connection from 4  3. This connection is then kept open until the selected percentage on-off differential is reached (falling pressure at port 1) and the connection 4  3 closes again (the 'On' point). Because ports 2 and 3 are run back to tank separately, the on-off differential (bar) is unaffected by any back-pressure in port 3. These unloading valves are predominantly used in accumulator-charging circuits, 2-pump systems, and circuits for fast-ad vance  feed changeover, and in such cases the cartridges also provide a pressure-relief function e.g. for protecting the pump (see the application examples). All external parts of the cartridge are zinc-nickel plated to DIN 50 979 and are thus suitable for use in the harshest operating environments. If you intend to manufacture your own cavities or are designing a linemounting installation, please refer to the section “Related data sheets”. Technical data General characteristics Description, value, unit pressure unloading cartridge valve two-stage, with manual adjustment, various on-off pressure differentials Mounting method Tightening torque nominal size 4, cavity type AN

General characteristics Description, value, unit Mounting attitude Ambient temperature range Hydraulic characteristics Description, value, unit Maximum operating pressure Maximum flow rate Nominal pressure ranges On-off differentials (on-off differential from 'Off' (unload) pressure) Flow direction Hydraulic fluid HL and HLP mineral oil to DIN 51 524; for other fluids, please contact BUCHER Hydraulic fluid temperature range Viscosity range Minimum fluid cleanliness Cleanliness class to ISO 4406 : 1999 Performance graphs measured with oil viscosity 33 mm2/s (cSt) p = f (Q) Pressure drop -...

On-off differential On-off differential 8…12 % On-off differential 13…17 % On-off differential 8…12 % On-off differential 13…17 % and 17…23 % On-off differential 8…12 % On-off differential 13…17 % 9) On-off differential 17…23 % On-off differential 27…33 % On-off differential 37…43 %

Dimensions & sectional view With adjusting screw “S” With hand-knob adjuster “H” Installation information IMPORTANT! When fitting the cartridges, use the specified tightening torque. Set the switching point by means of the adjusting screw (s1) or the hand knob. Either set the 'Off' pressure, in which case the 'On' pressure will depend on the selected per­ centage on-off differential, or the other way around. After you have set the valve, lock the ad­ justing screw with the lock nut. Backup ring ATTENTION! Only qualified personnel with mechanical skills may carry out any maintenance work....

Accumulator-charging circuit In this application, the DWPB-4N… unloading cartridge performs an automatic accumulator-charging function in re­ sponse to the pressures at ports 4 and 1. Here, the normal procedure is to use the adjusting screw to set the upper, 'Off' pressure p2, and when this pressure is reached the pump will therefore be switched over to unloaded bypass (con­ nection 4  3 open). The 'Off' pressure p2 and the on-off differential (10...40 %) determine the lower, 'On' pressure p1. When demand causes the pressure in the accumulator circuit to fall to p1, the unloading cartridge...

High-/Low-pressure circuit with two pumps IMPORTANT! We strongly recommend that unloading cartrid­ ges with an on-off differential of 30 %…40 % be used in all applications of this type. There are applications with one high-pressure pump and one low-pressure pump where the load pressure is used to automatically change the cylinder out-stroke speed from fast to slow. The DWPB-4N... unloading cartridge is used here to switch the low-pressure pump 'Off' i.e. to unloaded bypass. When the cylinder is in-stroked, the low-pressure pump is brought back on-load again, provided that the dy­ namic load...

Related data sheets The form-tool hire programme Line-mounting body, type GANA (G 3/8”) E 2014 by Bucher Hydraulics AG Frutigen, CH-3714 Frutigen All rights reserved. Data is provided for the purpose of product description only, and must not be construed as warranted characteristics in the legal sense. The information does not relieve users from the duty of conducting their own evaluations and tests. Because the products are subject to continual improvement, we reserve the right to amend the product specifications contained in this catalogue. Classification: 430.305.315.305.305.355...