What are System Tests for Piston Pumps?
The pump serves as the central component in nearly all hydraulic systems and is typically the first element examined when troubleshooting any operational issues. Although the pump may not always be the root cause of problems, focusing on it during initial troubleshooting can help identify specific issues and lead to effective solutions. This article primarily discusses troubleshooting pressure-compensated, variable-displacement piston pumps, but the principles can be applied to other types of variable-displacement pumps as well.
One critical consideration when troubleshooting a circuit with pressure-compensated pumps is the compensator setting. The pressure compensator is responsible for monitoring downstream pressure and adjusting the pump's internal configuration to maintain a preset pressure. Common issues in circuits with pressure-compensated pumps involve improper compensator cut-off pressure settings in relation to the system relief valve's spring setting. To ensure proper functioning, the relief valve must always be set higher, typically by 100 to 150 psi, than the compensator. This allows part or all of the pump output to flow over the relief valve when the system pressure reaches the relief valve's setting. However, it's essential to be aware that this may cause a rise in fluid temperature due to energy loss resulting from the pressure drop over the relief valve. Care should be taken to prevent excessive case pressure development from a partially obstructed case drain line, as it can lead to erratic and damaging behavior of the compensator.
An invaluable tool for troubleshooting is a pressure gauge installed downstream from the pump. By checking if the pump shaft is rotating correctly and determining whether there is insufficient system pressure due to an "open system" condition, such as no resistance to fluid flow (e.g., open directional control valve) or an improperly set relief valve, one can diagnose potential issues. Additionally, blocked inlet connections to the pump or faulty downstream components can impair fluid flow and system pressure buildup.
In cases where the above troubleshooting measures do not resolve the problem, it becomes necessary to examine the internal condition of the pump. A quick and easy check involves using the sense of touch to determine if the pump case drain line is hotter than the pump outlet line. If this is the case, shutting down the pump and replacing the solid piped pump case drain line with a hose can be useful. By holding the hose over a bucket and restarting the pump, one can gauge the extent of internal leakage. If a substantial amount of oil runs through the hose, it indicates that the pump rotating group is significantly worn or damaged.
In conclusion, understanding the intricacies of pressure-compensated, variable-displacement piston pumps and employing the appropriate troubleshooting techniques can help pinpoint and address issues effectively, ensuring the smooth functioning of hydraulic systems. Regular maintenance and thorough checks are essential to identify and rectify potential problems before they escalate and cause significant damage to the equipment.
