哈威(HAWE)德国液压阀样本--

Piloted pressure valves type DV, DVE, DF and pilot valves type PV and PG

Pressure pmax= 420 bar Flow Qmax= 120 lpm

1.

General The main purpose of pressure valves is to rule the pressure in hydraulic systems (acc. to DIN ISO 1219-1). ' Pressure limiting valves serve to protect hydraulic systems from unpermissible peak pressures (safety valves) or to limit the max. permissible working pressure. They close the inlet to the outlet and only give way if the set pressure is achieved. This pressure setting is maintained rather constant, independent from the flow, due to the generous internal diameters. ' Pressure sequence valves maintain a constant pressure difference, rather independent from the flow quantity, between inlet and outlet. ' Feed valves block the flow until the set pressure is achieved and then when this figure is exceeded they do open and allow the flow to pass with very little back pressure. Pressure valves type DV, DVE or DF are hydraulically piloted. They consist of a main and a pilot valve. The main valve has a spool; sliding rather frictionless in a bushing and is pressure compensated via the throttle<. It is forced in closed idle position via a spring= blocking inlet P to the outlet R(A). The spring cavity (control cavity)> is blocked to the outlet duct A by means of valve cone? at the piloting valve. The spring@ rules the response pressure of the valve. As soon as this pressure is reached oil starts to flow: Inlet P→ throttle<→ valve cone?→ outlet A (control oil flow). The pressure within the control cavity> is higher due to the back pressure generated at throttle< which adds to the inlet pressure. This hydraulic force pushes the piston in direction of the spring until the spring force and the back pressure occurring ahead of the throttle are balanced again. The oil flow leaving port R(A) is depressurized to the set value by the throttling section B whose cross section area is ruled by the foresaid forces. This flow is only slightly reduced by the required control oil. The back pressure of the two pressure ranges (up to 100 and up to 420 bar) available is only 2 or 5 bar, due to the low pre-load of the spring. Valve type DV may be a pressure limiting, a pressure sequence or a feed valve only depending on whether the control oil flow is fed to R(A) or to X(L) (see above and schematic drawing at sect. 2.3). The valve can be arbitrarily operated, e.g. idle pump circulation, various pressure steps, etc. when additional valves are connected to the control cavity, see also sect. 5.1).

Main valve Idle position (top) Piloting pressure limiting valve 6 5 3 1 1 2 3 4 5 2

2.3 Valve piston and bushing (mated) Throttle Valve spring Control cavity Valve cone (piloting valve) Adjustment spring (piloting valve) Drain duct (piloting valve) Throttle section for pump delivery P→ R(A)

(a)

Inlet

6 7 8

8

Working position (bottom) 7 4

Outlet

(a) Screen filter, protecting the throttle section from coarse contaminations t

hat may occur

HAWE HYDRAULIK GMBH& CO. KG STREITFELDSTR. 25 81673 MÜNCHEN© 1967 by HAWE Hydraulik

D 4350 Pressure valves type DV.. February 2000-01