Type DAW…FS… (freely adjustable switching pressure differential)
The pressure valve type DAW is a pilot-operated pressure cut-off valve. For example, it is used in accumulator charging circuits. Here, an accumulator is filled until the accumulator charging pressure is reached. After reaching the accumulator pressure, the valve switches the flow to depressurized circulation until the pressure in the hydraulic system has fallen by the switching pressure differential. Afterwards, the charging process is started again.
The pressure cut-off valve generally consists of main housing (1), pilot control valve (2 and 3), main spool insert (4) and check valve (7).
- Switching of the pump flow from P to B to P to T.
The pump delivers via the check valve (7) into the hydraulic system (P to A). The pressure applied in channel A acts via the control line (8) on the control spool in the pilot control valve (3). Simultaneously, the pressure in channel P is applied via nozzle (5) to the spring-loaded side of the main spool (4) and via the control line (9) and at the inlet (11) of the screw-in cartridge valve (3). As soon as the top cut-off pressure set at the screw-in cartridge valve (3) by means of the adjustment spindle (12) is reached in the hydraulic system, the screw-in cartridge valve opens the connection from the spring-loaded side of the main spool (4) to the return line (10) to T internally (type DAW ...) or externally via port Y (type DAW ...Y).
Due to the nozzle (5), a pressure drop occurs at the main spool (4). It is lifted from the seat and opens connection P to T. The check valve (7) closes the connection from P to A. The actuator pressure A holds the screw-in cartridge valve (3) in open position.
- Switching of the pump flow from P to T to P to A.
If the actuator pressure A has fallen to the pressure value set at the adjustment spindle (14), the screw-in cartridge valve (3) switches to initial position and closes the connection from the spring-loaded side of the main spool (4) to the return line (10). This way, the pressure on the spring-loaded side of the main spool (4) is increased and the connection from P to T is closed by the compression spring (6). The pump again delivers via the check valve (7) into the hydraulic system from P to A.
Version "FSB07"
The nozzle of this valve is located in the control line (11) for potential switching shock damping. This way, the circulation pressure (P to T) is increased. See characteristic curves.
Notices!
- Only indirect pressure limiting function:
A pressure limiting function of the pump pressure (to the tank) is not directly provided but only indirectly via the check valve (7), control line (8) and pilot control valve (2) to channel T.
- Setting the switching pressure differential
At the factory, the valves are set at nominal pressure to a switching pressure differential of approx. 10 % to 12 %. A setting of 50 % of the nominal pressure is possible.
On delivery, the adjustment spindle (12) is screwed out and set to the minimum adjustable switching pressure.
By screwing in the adjustment spindle (12), the top switching pressure may be increased.
The switching pressure differential is adjusted via the adjustment spindle (14): Screw out to reduce, screw in to increase.
The pressure adjustments are secured via the clamping screw (13) and lock nut (15).
- Different system conditions (particularly high pump and actuator flows) may lead to higher switching pressures than indicated in the characteristic curves. Here, the valve offers the possibility of optional adjustment of the switching pressure differential to the system.
Type DA 10 -2-5X/.FS…
Type DAW… (fixed switching pressure differential 10 % or 17 %)
The function of this valve complies with the function of version "FS". At the pilot control valve, however, only the top switching pressure and not the switching pressure differential can be set.
The pilot spool surface (16) exceeds the effective ball (17) surface optionally by 10 % or 17 %.
This way, the effective force at the pilot spool (16) exceeds the effective force at the ball (17) by 10 % or 17%.
- Switching of the pump flow from P to B to P to T.
The pressure in channel P is applied via nozzles (5) and (9) to the spring-loaded side of the main spool (4) and at ball (17) in the pilot control valve (2). As soon as the cut-off pressure set at the adjustment spindle (12) is reached in the hydraulic system, the ball (17) opens against the spring (18). The hydraulic fluid now flows via nozzles (5) and (9) into the spring chamber (19) to the return line (10) to T (type DAW ...) or externally via port Y (type DAW ...Y). The main spool (4) is lifted from the seat and opens connection P to T. The check valve (7) closes the connection from P to A. Via the pilot spool (16), the actuator pressure A holds the ball in the pilot control valve (2) in open position.
- Switching of the pump flow from P to T to P to A.
If the actuator pressure A drops by the switching pressure differential range of 10 % or 17 % in comparison with the set cut-off pressure (according to characteristic curves on page 11), the spring (18) closes the ball (17) in the pilot control valve (2). This way, the pressure on the spring-loaded side of the main spool (4) is increased and the connection from P to T is closed by the compression spring (6). The pump again delivers via the check valve (7) into the hydraulic system from P to A.
Type DA 10 -1-5X/…
The function of this valve complies with the function of valve type DAW …. However, switching can be realized as required from P to T or from P to A by means of solenoid-actuated directional spool valve (20) for pressure below the set cut-off pressure.
Type DAW 20 -1-5X/…6E..K4…
Type DAWC…
Pressure cut-off valve type DAWC 30 …FS…
This valve consists of pilot control housing (2), screw-in cartridge valve (3) as pilot control element and a main spool insert (4).
Pressure cut-off valve type DAWC …10/17...
This valve consists of pilot control valve (2) and an optional main spool insert (4).
Notice for circuit design with type DAC...
- The ports required for actuator (A), pump (P) and tank (T), the required control lines (8) and (10) as well as the required check valve (7) are not included in the scope of delivery. These have to be selected according to the applicable size and the flow. Connections require sufficient cross-section and blocking has to be prevented by appropriate design and layout.
- Between actuator (A) and pump (P), a sufficiently dimensioned check valve with flow characteristics in compliance with or exceeding the characteristic curves specified on page 12 has to be applied.
