ROD 8N8185 - Caterpillar

Oil Bypassed to Main Control Valve
Oil from the small pump enters the charging valve through port (17) and flows through orifices (15) and (14) into chamber (23) to contact pilot valve (13). The restriction to flow at orifice (15) causes spool (19) to unload excess pump flow through holes (26) into port (25) to the main control valve. Holes (26) are staggered to provide a gradual shift of flow as the spool moves against spring (22).Charging the Accumulator
Oil flowing through orifice (15) passes through radial holes (26) and flows to charging valve spool (7). When the accumulator oil pressure drops to cut-in pressure, springs (8) overcome the combined forces of the detents and reaction piston (11) and the charging valve spool (7) moves to the cut-in position. The oil unseats check valve (5) and flows to the accumulator through port (6). Oil also flows into passage (1) and contacts reaction piston (11).When cut-out pressure is reached, oil pressure acting on reaction piston (11), moves charging valve spool (7) against springs (8). Spring (2) force against retainer (3) holds balls (4) in the detent on the charging valve spool. Movement of the spool to the CUT-OUT position blocks flow to the accumulator and directs pump flow through passage (16) to the main control valve through port (25).Shims (9) adjust the spring force on charging valve spool (7). Adding shims raises the cut-out pressure.
CHARGING VALVE (CUT-OUT POSITION)
2-Spring. 3-Retainer. 4-Balls (nine). 7-Charging valve. 8-Springs. 9-Shims. 11-Reaction piston. 16-Passage. 25-Outlet port to steering control valve.
CHARGING VALVE (RELIEF VALVE OPEN)
7-Charging valve spool. 11-Reaction piston. 12-Passage. 13-Pilot valve. 14-Orifice. 18-Spacer and shims. 19-Flow control valve spool. 20-Spring. 21-Drain line to hydraulic tank. 22-Spring. 23-Chamber. 25-Oil line to steering control valve. 26-Radial holes.Pilot valve (13) prevents continued pressurizing of the accumulator if the cut-out action fails to shift the charging valve spool. The pilot valve opens and dumps oil in chamber (23) into drain line (21). This lowers the pressure in chamber (23) allowing flow control valve spool (19) to move against spring (22). Pump flow bypasses to the main control valve through holes (26) and port (25).Spacer and shims (18) adjust the force of spring (20) on pilot valve (13). Adding shims increases pilot valve opening pressure.Shims (10) increase the force on retainer (3) and balls (8). The pressure range between cut-out and cut-in is adjusted by adding or removing shims.Passage (12) and drain line (21) allow oil leakage past reaction piston (11) and charging valve spool (7) to return to tank.Accumulator
ACCUMULATOR OPERATION
1-Nitrogen valve. 2-Accumulator. 3-Nitrogen gas chamber. 4-Piston. 5-Pressure oil chamber. 6-Port to brake control valve.The accumulator contains a floating sealed piston (4). Chamber (3) above the piston is charged with dry nitrogen gas through nitrogen valve (1). As the accumulator receives oil through port (6), piston (4) is forced up, compressing the nitrogen gas. When a predetermined pressure is reached, the oil supply is cut off. When either brake pedal is depressed, the stored-up pressure oil in chamber (5) flows out port