Bomag BW 156 D-3 Service Manual page 73

Multi-function valve
High pressure limitation
Pumps of series 90 are equipped with a follower valve, which activates a pressure override and a
pressure relief valve, one after the other.
When the adjusted pressure value is reached, the pressure override will return the pump very quickly
back towards neutral, thereby limiting the system pressure. The average response time is less than 90
ms.
In case of an extremely quick pressure increase the function of the high pressure relief valves is utilised
as an additional safety. In such a case the pressure override works as a pre-control unit for the control
piston of the pressure relief valve. The pressure relief valve, the pressure setting of which is higher than
the pressure level of the pressure override valve, is actuated if the pressure increase is so fast, that the
pressure override valve cannot return the pump quick enough back to neutral.
Pressure override and high pressure relief valve are arranged together in the multi-function valve inside
the pump case. This so-called multi-function valve is a further developed and improved kind of pressure
limitation.
Fig. 10 Multi-function valve, details
1 Reducing fitting
2 Hydraulic by-pass piston
3 Spring plate
4 Spring
5 High pressure relief valve
6 Valve seat
BW 156/177 D-3/PD-3
BW 178/179 D-3/PD-3
2
1
11
Service Training
3
4
9
8
10
7 Check valve
8 Pressure limitation
9 Spring
10 By-pass housing
10 By-pass sleeve
5
6
7
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