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| Illustration 1 | g00795858 |
Load Control Valve for Telescoping Cylinder | |
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| Illustration 2 | g00795854 |
Schematic of Load Control Valve for the Telescoping Cylinder (1) Housing for load control valve (2) Passage (piston side) (3) Telescoping cylinder (4) Counterbalance valve (5) Chamber (6) Valve (7) Passage (rod side) (8) Passage (pilot oil) (9) Orifice (10) Orifice (11) Check valve (relieving) (12) Passage (13) Passage (14) Spring (15) Check valve | |
Housing (1) for the load control valve is bolted to telescoping cylinder (3). Two valve cartridges are installed into the housing. One of the cartridges includes counterbalance valve (4) and check valve (15). The other cartridge includes valve (6) and check valve (11) .
The following section describes the operation of the load control valve when the boom is extended.
Oil from the bank valve flows through passage (13) in housing (1) and into the valve cartridge for check valve (15). The oil flow causes check valve (15) to open against the force of a spring. The oil passes through passage (2) and into the piston side of the telescoping cylinder. As the pressure and the volume of oil in the piston side of the telescoping cylinder increases, the piston begins to move and the telescoping cylinder is extended.
As the telescoping cylinder extends, the oil flows from the rod side of the telescoping cylinder through passage (7) to the bank valve in order to return to the hydraulic tank. When the bank valve is returned to the HOLD position, the oil flow is stopped and check valve (15) is seated by the spring. This blocks oil into the piston side of the telescoping cylinder.
The following section describes the operation of the load control valve when the boom is in the HOLD position.
Oil is blocked in the piston side of the telescoping cylinder by the valve stem in counterbalance valve (4). The valve stem is seated by the force of spring (14). The weight of the boom and the weight of the load creates pressure in the piston side of the telescoping cylinder which is transmitted through chamber (5) to the face on the valve stem. This pressure is resisted by spring (14) which is acting against the valve stem.
Under shock load, spring (14) would compress slightly. This would allow the valve stem to move in order to relieve any excess pressure from the piston side of the telescoping cylinder.
The following section describes the operation of the load control valve when the boom is retracted.
Oil from the bank valve flows directly to the rod side of the telescoping cylinder through passage (7) in housing (1). Also, oil flows into passage (8) from passage (7). Valve (6) and check valve (11) are closed. Oil flows slowly through orifice (10) into passage (12) .
The pressure that is developed in the rod side of the telescoping cylinder is transmitted to passage (8). As the pressure increases in passage (8), valve (6) opens in order to allow the oil to flow more rapidly into passage (12). The valve is pressure compensated in order to control the rate of pressure increase in passage (12). Oil continues to flow into passage (12) until the valve stem in counterbalance valve (4) opens at a controlled rate and rests against the valve stop.
Oil from the piston side of the telescoping cylinder flows through the counterbalance valve into passage (13) in order to allow the telescoping cylinder to retract. The oil is returned to the hydraulic tank via the bank valve. The pressure that acts on the valve stem will determine the retracting speed of the telescoping cylinder. The clearance at the valve seat varies in proportion to the pilot pressure. This controls the oil flow from the telescoping cylinder which controls the speed of the telescoping cylinder.
When pressure at the rod side of the telescoping cylinder is decreased, pressure is also decreased in passage (8). Pressure in passage (12) is relieved through check valve (11) and orifice (9) until the valve stem in counterbalance valve (4) is seated. Oil in the piston side of the telescoping cylinder is prevented from returning to the hydraulic tank via the bank valve and the telescoping cylinder stops retracting.