While it’s not usually possible to see inside a hydraulic pump and motor assembly and observe the wear taking place, there is one surefire clue that makes it possible to know if these important components are on their way out. Declining efficiency is a sign of leakage and/or increased internal friction, which is why keeping an eye on the efficiency of your pumps is a good way to monitor the health of your equipment. In this article, we’ll explore two aspects of hydraulic pump and motor efficiency and what they can tell you about what’s going on inside. Allowing you to repair and replace worn units in time to avoid costly failures.
The Two Aspects of Hydraulic Pump & Motor Efficiency.
Every new pump or motor has a specified ‘theoretical’ flow and torque rating. These are the numbers the unit should be able to achieve in a perfect world. However, the real world is never perfect and in reality, things like friction will mean that your actual performance will always be somewhere below the ideal theoretical number.
In addition, over the lifespan of the unit, various components such as bearings, pump elements, fluid, and other internals begin to deteriorate and as this happens, the pump gradually becomes less efficient. This deterioration can be measured in relation to the specified performance of the pump. This is useful to understand because it’s a clear indication of pump wear and gives us a valuable clue to alert us to repair or replace these units before its too late.
We can measure this loss of efficiency by looking at two aspects of efficiency, which are hydro-mechanical efficiency and volumetric efficiency. Each of these tells us something about the condition of the pump/motor and whether it is likely to fail in the near future.
Volumetric Efficiency (Flow)
In layman’s terms, Volumetric Efficiency refers to the amount of fluid a pump delivers and it is usually measured in litres per minute. In ideal conditions, a positive-displacement pump should deliver the same amount of liquid for each rotating cycle. As the unit wears, fluid slippage slowly increases and the amount of liquid delivered per cycle decreases. Thus, a decrease in volumetric efficiency indicates losses due to leakage or bypass. The decline in volumetric efficiency is accompanied by an increase in the cycle time of actuators such as hydraulic cylinders as the flow has been slowed. If the degradation is allowed to continue, the hydraulic system may become completely inoperable, requiring the repair or replacement of the worn pumps and motors to get up and running again.
Hydro-Mechanical efficiency (Friction)
The second category to look at is hydro-mechanical efficiency, which indicates the amount of fluid and mechanical friction within the system. To determine a motor’s hydro-mechanical efficiency, look at the actual torque output compared to the unit’s rated torque output. If a motor’s real-world output is 20% below its theoretical torque rating, then the motor can be said to be 80% efficient. A reduction in actual torque is, therefore, a sign that bearings and other mechanical internals are becoming worn and generating more friction.
The benefit of keeping an eye on efficiency.
Hydraulic pump and motor efficiency can have a significant effect on your hydraulic system. Inefficient components draw more power and drive up the running costs of your operation, so always a good idea to be aware of how your equipment is performing. However, declining efficiency is also an important way to monitor the health of your hydraulic pumps and motors. Warning signs such as slowing hydraulic actuators and loss of torque are a symptom of decreasing efficiency that - if left unchecked - will eventually lead to failure of hydraulic equipment. These components will eventually need to be repaired or replaced, but in the long term it's more cost-effective to do so before they fail or start to inflate operating expenses.