Hydraulic pumps are designed to have small internal leakage to lubricate the inner-workings of the pump. When a pump is running, a small “but steady” amount of oil is actually intentionally leaked inside the pump in order to have the necessary lubrication it needs in order to do its work. A port called the “case drain” is where this leakage is released from, and can be used to understand health of the pump.
Why Pumps Fail
Over time the inner-workings of these pumps do deteriorate due to the simple fact of friction of the oil and any contaminants within the hydraulic oil, which causes the pump to lose efficiency and eventually fail. But signs of this happen well before the pump is in critical condition.
Proof Of Case Drain Monitoring
Since the inner-workings are losing their tight tolerances and they are becoming larger, more oil can be leaked through the inside of the pump. In turn there will be a greater flow of oil coming out of the case drain. This is why the case drain can be used to understand the health of the pump and begin to predict failures.
Every manufacturer of piston pumps has a stated maximum amount of flow GPM oil coming out of the pumps case drain. Once the GPM reaches 85% of this max flow, the pump by industry standards is declared inefficient and should be replaced and sent out for repair in order to avoid any unexpected downtime due to pump failure.