Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1171112
and normally does not need to be adjusted during the initial pump setup. In most pumps, the factory preset is approximately 200-300 pounds per square inch (psi). e most common reason to adjust a load-sensing valve is because someone unfamiliar with the pump has mistakenly attempted to set the maximum system pressure by adjusting the load-sensing valve instead of the compensator. is not only can result in unstable system pressure but in some cases can also void any warranty on the pump. A typical confi guration of a pressure-compensating pump is shown in Figure 1. A pump-loading valve is used to determine whether the system is idle or prepared to move a load. e pump-loading valve is de-energized whenever the system is idle. Pilot pressure on the left- hand side of the load-sensing valve is then released to the tank. e pilot line on the right-hand side of the load-sensing valve is connected to the pressure line at the pump outlet. System pressure shifts the load-sensing valve and directs pressure to reduce the pump stroke so that system pressure drops to the load-sensing setting of 300 psi, as illustrated in Figure 2. When a load is to be moved, the pump-loading valve is energized. is directs pilot pressure to the left side of the load-sensing valve, keeping it from shifting. System pressure shifts the compensator valve to de-stroke the pump exactly the amount necessary to limit system pressure to the compensator setting, 3,000 psi as shown in Figure 3. To make the pressure settings, always adjust the load-sensing valve fi rst. e pump should be deadheaded by closing the manual hand valve. With the pump-loading valve de-energized, pressure will build only to the current setting of the load-sensing valve. Adjust the load-sensing valve to the desired pressure. Once the load-sensing valve is set, energize the pump-loading valve. System pressure will then build to the current compensator setting. Adjust the compensator to the desired setting. Open the manual valve, and the system can be placed back into service. ere are several variations of this design. Sometimes a throttle valve will be used to determine if a load is available. e pressure drop that results when oil moves through the throttle valve signals the need for higher system pressure. Another common variation is to use the load-sensing valve in conjunction with a proportional relief valve connected in series. Standby pressure will then be determined by the sum of the load- sensing pressure and the electronically controlled setting of the proportional relief. In more complex arrangements such as this, hand valves should be installed that can be opened or closed to deadhead the load-sensing valve and also to release its pressure to the tank to enable setting the pressure. ML About the Author Jack Weeks is a hydraulic instructor and consultant for GPM Hydraulic Consulting. Since 1997 he has trained thousands of elec- tricians and mechanics in hydraulic troubleshooting methods. Jack has also taught radio-wave propagation for the U.S. Air Force and telecommunications equipment operation and repair for the Central Intelligence Agency at American embassies overseas. Vistit Us at Booth #423