1.36 HYDRAULICS Inlet section (PVSP) (36) LS (1) Load sensing (to steering valve) CF Steering valve B1 Main brake B2 Trailer brake (optional) B3 Pressure test point (67) LS Load sensing T Return to tank P Pressure A BAC valve spring (37) LS shuttle valve (41) Priority valve (42) Steering priority valve (compensator) (43) Filter (44) Brake accumulator charge (BAC) (68) Test point Function The inlet section (PVSP) provides oil to: (a) The brake circuit through the BAC valve (44) , this gives a charge of between 138-159 bar (2000-2300 psi) and operates in preference to all other services. Brake charge pressure can be tested at test point B3 (68) .
(b) The steering circuit with oil on demand by the steering priority valve (42) . The oil arriving at P is delivered to the BAC valve and onto the accumulators, the resistance to charging the accumulator causes the pressure to rise at P which, as it is connected to the LS line via the BAC valve, signals to the pump. The pump responds by delivering oil at the required pressure. The system charges at 138 bar and stops charging at 159 bar. At the upper limit 159 bar, the oil pressure at P overcomes the force of the BAC valve spring (A) and closes the connection between P and LS; the pump therefore goes to standby.
When the pressure in P falls below 138 bar, the spring force opens the valve and the system recharges. At the same time, pump pressure is supplied to the steering unit via the CF port. If the steering is not being used, the pump at standby pressure overcomes the spring force in the priority valve (41) and supplies oil to the other consumers. When the steering wheel is moved, the resistance to oil from the steering cylinders builds in the CF line. This is also sensed by the LS line, which, as it is linked to the steering priority valve (42) . makes sure steering is given priority as well as signalling the pressure requirement to the pump.