Accumulator Charging Valve
(1) Pump inlet port.
(2) Tank port and adjustment screw for cut-in pressure
and cut-out pressure. (3) Plug.
(4) Accumulator port for the front brakes.
(5) Flow through port to the hydraulic oil filter.
(6) Port for the oil pressure switch for the service brakes.
(7) Accumulator port for the rear brakes.
(8) Pressure relief valve and standby function.
(9) Adjustment screw cover. (10)Priority spool. (11) standby pressure spring.
(1) Inlet from the brake pump. (2)
Outlet to the hydraulic oil tank. (4)
Accumulator port for the front
brakes. (5) Flow to hydraulic oil
filter. (6) Port for the brake oil
pressure switch. (7) Accumulator
port for the rear brakes. (8) Pressure
relief valve. (10) Priority spool. (11)
standby pressure spring. (12)
Charge rate orifice. (13) Check
valve. (14) Cut-in, cut-out spool.
(15) Inverse shuttle valve.
valve controls the flow of oil from the
pump to the brake circuits. The hydraulic oil is diverted, based on the pressure
of the brake circuits. The standby pressure spring (11) will also maintain a
standby pressure in order to supply pressure for the implement system and the
steering pilot system.
When the engine is started, the accumulator charging valve receives the flow of
oil from the pilot/brake pump at the inlet port (1). Pressure relief valve (8) will
cause the pump flow to return to the hydraulic tank if the oil pressure in the
brake system exceeds 16550 ± 690 kPa (2400 ± 100 psi).
Priority spool (10) regulates the flow of oil through inverse shuttle valve (15)
to the brake accumulators. Until the oil pressure reaches cut-out, the priority
spool directs the oil to inverse shuttle valve (15) through charge rate orifice
(12) and check valve (13). The charge rate orifice allows the accumulators to
fill at a controlled rate. The check valve will maintain the pressure in the brake
circuit by preventing the pressurized oil in the accumulators from flowing back
through the priority valve. During charging, inverse shuttle valve (15) allows
flow to both accumulators. After reaching cut-out, the inverse shuttle valve
allows only the lower accumulator pressure to act on the cut-in, cut-out spool
and at the pressure switch port.
Cut-in, cut-out spool (14) controls the cut-in pressure and the cut-out pressure
for the accumulator charging valve. When the cut-out pressure is reached, the
cut-in, cut-out spool shifts and blocks the pilot pressure for the priority spool
(10). Priority spool pilot pressure is drained to the hydraulic tank allowing the
priority spool to shift to the left. This reduces the restriction to flow to the
hydraulic tank. The standby pressure spring (11) keeps the priority spool from
fully shifting to the left. This maintains the standby pressure in the pump line
which provides pressure in order to operate the implement pilot system. Since
this pressure is now lower than the accumulator pressure, this causes check
valve (13) to close.
Each time the brakes are applied, oil from the accumulators is used and the
accumulator pressure decreases. When either of the accumulator pressures drop
below cut-in, the cut-in, cut-out spool (14) shifts to the left. The cut-in, cut-out
spool will then feed pilot pressure to priority spool (10). The pilot pressure will
cause the priority spool to shift to the right. When this occurs, the priority spool
will divert pump flow to the brake accumulators through inverse shuttle valve
(15).
Adjustment screw (9) will allow the cut-in pressure setting and the cut-out
pressure setting to be changed. The drain hose that is connected to the tank port
(2) must be disconnected in order to gain access to adjustment screw (9).
Pressure switch port (6) connects to the brake oil pressure switch. The brake oil
pressure switch sends a signal to the Caterpillar monitoring system when the
brake oil pressure is below 8960 ± 537 kPa (1300 ± 75 psi).
