Hydraulic Pressure versus Hydraulic Flow

In the practical realm of maintaining and repairing hydraulic systems, the most common approach is to replace certain parts, believing that changing a specific component will rectify a particular issue. While this method is important and often effective, it does not truly constitute troubleshooting but rather a straightforward parts replacement that may not address the root cause of the problem. Subsequently, the outcome might be that the machine is repaired, and everyone is content, or the system reaches a point where professional assistance is required. Unfortunately, during this process, multiple parts may have already been replaced, which could have been avoided had troubleshooting been the initial line of defense.

The reason behind this inclination to resort to parts replacement rather than troubleshooting lies in the failure to grasp the distinction between pressure and flow in hydraulic systems. The fundamental role of the pump is to transfer fluid from one location to another. However, a common misconception is associating low pressure with a faulty pump, disregarding the fact that the pump governs the flow rate. Pressure, in reality, is a consequence of resistance to flow. For instance, fixed-displacement pumps are commonly used in industrial systems, where the amount of fluid delivered corresponds to each rotation of the pump driven by a primary mover like an electric motor or an engine in mobile equipment. The pump facilitates the movement of oil from the reservoir into the system, and the actuator's speed is directly linked to the flow rate. Unfortunately, instances have been observed where pumps were replaced merely due to low system pressure.

The truth is that a pressure issue in a hydraulic system is rarely caused by the pump itself. It is more often attributable to another faulty component in the system. Therefore, replacing the pump should be considered as a last resort when troubleshooting pressure problems. Another common misconception is assuming that the pump outputs a fixed pressure, like 1,500 psi, based on the belief that pressure originates solely from the pump. However, the pressure gauge does not indicate the pump's pressure output but rather the resistance that the system is currently overcoming. A profound understanding of this concept is vital for becoming an adept troubleshooter in hydraulic systems.