Coolant Pressure Control Solenoid Valve, Component Description - Mercedes-Benz OM 471 Introduction Into Service Manual

GF20.30>W>1001H
MODEL 963, 964 with CODE (B3H) Secondary water retarder
Location
Shown on model 963, front coolant
expansion reservoir
Y57 Coolant pressure control solenoid
valve
The coolant pressure control solenoid valve
(Y57) is located on the coolant expansion
reservoir.
Task
The coolant pressure control solenoid valve
(Y57) enables the pressure in the cooling
system to be raised or lowered.
Design
The coolant pressure control solenoid valve (Y57) consists of the
following components:
Intake valve (reservoir pressure)
f
f Exhaust valve (atmosphere)
Function
The coolant pressure control solenoid valve (Y57) is actuated by
the drive control (CPC) control unit (A3). The pressure level is
taken from a characteristic filed in the drive control (CPC) control
unit (A3). The characteristic, and therefore the pressure level,
increases along with the coolant temperature. If the pressure
drops below the stored value, the compressed air is routed out of
the consumer circuit into the expansion reservoir until the
required pressure level is reached. If the pressure increases beyond
the stored value, the pressure is released from the expansion
reservoir. When in an operating temperature condition, a
pressure of between p = 480 mbar and max. 1480 mbar is
regulated, depending on the coolant temperature level.
i Introduction of engine OM 471 and exhaust aftertreatment > 09/2011 >

Coolant pressure control solenoid valve, component description

– This printout will not be recorded by the update service. Status: 09 / 2011 –
System components
This regulation is necessary to ensure that a high pressure level is
achieved at all operating conditions. A higher pressure level is
required, in particular, when activating the secondary water
retarder.
i Coolant is taken from the cooling circuit when the secondary
water retarder is activated. This in turn results in a drop in
pressure in the cooling system.
The increased pressure serves to prevent pressure dropping below
a critical threshold. This helps to avoid any cavitation damage in
the cooling circuit, while also preventing the coolant in the
exhaust gas recirculation cooler from boiling.
i Cavitation damage is caused by blistering (hollow spaces) in
the cooling circuit. If, for example, a turbine wheel moves in such
a hollow space and impacts then with the coolant flow, extremely
high mechanical forces will be generated on the surface of the
turbine wheel. In the long term these will destroy the turbine
wheel.
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