How many sets of seals have been replaced and are still leaking oil? The real culprit may not be the seal, but the pressure inside the shell!
In the maintenance process of hydraulic equipment, we often encounter a headache like situation: hydraulic motors or pumps frequently leak oil, and even if multiple sets of new seals are replaced, the problem still occurs repeatedly. The first reaction of many maintenance personnel is often that the quality of the seals is not up to standard, so they change brands, materials, or even suppliers, but the results still go against their wishes.
In fact, frequent oil leakage is not always the responsibility of the seal itself in practical applications. The real hidden problem is often the high Case Drain Pressure.
1, Why does shell back pressure cause oil leakage?
During the operation of hydraulic components such as hydraulic motors, pumps, and valves, there is inevitably a certain amount of internal oil leakage. To prevent oil leakage from accumulating inside the casing, manufacturers usually design specialized drain ports to allow the leaked oil to flow smoothly back to the fuel tank through the drain pipe.
However, when the oil leakage system encounters the following problems, it can cause an abnormal increase in pressure inside the casing:
Blockage of oil drain pipe: The oil drain path is not smooth, and the oil is not discharged in a timely manner;
Small pipe diameter design: obstructed oil reflux, resulting in reduced flow rate and increased pressure;
High back pressure in the oil return system: especially when multiple components share a main oil return line, the pressure is prone to superposition;
Directly connecting the drain port to the main return oil pipeline: the main return oil pressure is transmitted to the shell, causing a "back pressure transmission" effect;
Too many or too long bends in the pipeline: The resistance to oil flow increases, exacerbating pressure accumulation.
When the pressure inside the shell continues to accumulate, it will cause two serious consequences:
Sealed compression extrusion
Excessive pressure inside the shell beyond the design value will squeeze the sealing ring out of the original groove, causing permanent deformation or even tearing, resulting in the failure of the sealing performance.
Damage of lubricating oil film and early damage of components
Abnormal internal pressure can also damage the oil film lubrication that should exist between bearings and sliding parts, causing direct contact between metal surfaces, resulting in dry friction and early wear or even locking