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C. Brake Selector Valve 23GG
(Ref. Fig. 007)
The brake selector valve 23GG is a solenoid operated valve (installed on the Green PTU manifold 1113GM (Ref 29-11-00)) that isolates the Green hydraulic supply from the normal brake system.
The brake selector valve has:
-a body with holes drilled in it to connect a bore and three ports
-two plugs, attached by three bolts which close the bore of the body
-
a valve held on its seat by a spring
-
a piston
-
a solenoid with a plug type electrical adaptor.
(Ref. Fig. 008)
The solenoid is electrically operated which controls a plunger which has a ball. The ball and plunger control a valve and piston in the valve body that controls the flow of hydraulic fluid through the valve body to the three ports.
The three ports are identified as:
-
the supply port (A)
-
the return port (B)
-
the service port (C).
With the solenoid de-energized and hydraulic pressure available in the supply port the ball of the solenoid is held on its seat by the spring and the core of the solenoid valve. The pressure in chamber (a) and the effect of the spring holds the valve on its seat.
When the solenoid valve is energised the hydraulic pressure applied to port A (the supply) pushes away the ball which is held against its upper seat. The pressurized fluid flows to chamber (b). The pressure in chamber (b) increases and pushes the piston. When the pressure in chamber (b) becomes more than the pressure in chamber (a) the piston pushes the valve and compresses the spring.
The pressure in chamber (b) holds the piston on its seat and closes port B (the return). Port A (the supply) is then connected to port C (the service).
When the electrical power is removed from the solenoid valve:
-the core of the solenoid valve moves because of the effect of the spring and the core pushes the ball on its lower seat.
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Brake Selector Valve 23GG
Figure 007
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Normal Brake Selector Valve - Schematic
Figure 008
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-
the pressure in chamber (a) increases and pushes the valve against the seat.
-
the pressure in chamber (b) decreases and the valve pushes back the piston. The pressure at port C (the service) then fully pushes back the positon against the plug (mechanical stop).
-
the pressure in chamber (a) and the effect of the spring hold the valve on its seat, which closes port A (the supply). Port C (the service) is then connected to port B (the return).
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D. High Pressure (HP) Filter
(Ref. Fig. 009)
The HP filter is installed near the manifold (1113GM) (Ref 29-11-00). The filter head is machined to make an inlet port, an outlet port and a port for a filter bowl. The filter bowl contains a filter element. An indicator unit is installed in the head. The unit includes a red indicator piston which shows when the filter element is blocked. The piston has a transparent cap on it for protection.
The filter bowl is a cylinder closed at one end. The open end has internal threads which engage threads in the head. A square boss at the closed end of the bowl is used to remove the bowl to get access to the filter.
Hydraulic fluid at system pressure goes through the inlet port and into the filter bowl. It goes through the filter element, and through the outlet port. When the pressure at the inlet port is 6 bar (87 psi) more than the outlet port, the indicator piston comes out. It keeps this position to show that the filter element is blocked and it must be manually pushed in after the element has been replaced.
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High Pressure Filter
Figure 009
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E. Pressure Transducer Normal Braking Supply 96GG
(Ref. Fig. 010)
The pressure transducer is located in the hydraulic compartment The pressure transducer measures the hydraulic pressure in the related brake service line. It contains an electronic bridge-type circuit which is installed on a number of circuit boards. Hydraulic pressure sent to the transducer causes a change in the electrical resistance of the brigde circuit.This changes the electrical input voltage to give an output voltage in proportion to the hydraulic pressure. The integrated-logic transducer supplies a DC voltage between 1 and 5V for a pressure signal between 0 and 200 bars.The zero has been shifted to enable BITE testing.
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