By Josh Cosford, Contributing Editor
Hydraulic systems are the workhorses of many industries, powering everything from heavy machinery to manufacturing equipment. The lifeblood of these machines is hydraulic oil, which transmits power, dissipates heat, carries away contamination and lubricates components. However, just like any other fluid-based system, hydraulic systems are susceptible to unique issues, including the presence of air in the oil. How can you tell if your hydraulic oil has air in it? Let’s explore the signs and symptoms that can help you identify this common problem.
A hydraulic system with air in its oil may experience erratic or reduced performance. When air is present in the hydraulic fluid, it compresses under pressure, decreasing the system’s efficiency as energy is wasted compressing gas rather than transmitting force. This can manifest as slower actuator movement or a decrease in force, but also with chattering as actuators build and release air pressure, behaving much like severe static friction.
Listen carefully to your hydraulic system — typically, it hums with the precision of a well-tuned engine (although sometimes the whine of hydraulics sounds like a bad water pump pulley). However, air in the hydraulic oil can create distinct and unsettling noises, such as knocking, grinding, or excessive whining. These sounds often indicate that air is causing turbulence within the fluid, leading to inefficiencies and potential damage to system components.
Hydraulic systems should be leak-free, and any external leakage is a cause for concern. Puddles forming beneath the suction line are a clear sign that air is getting sucked into the oil. During normal operation, any cracks in the suction hose or loose hose clamp connections will allow the pump’s vacuum to draw air, resulting in cavitation-like aeration. However, the failure results in a leak once the power unit shuts down. Be careful not to discard the potential of this disaster when only viewing the non-leaking hose during operation.
Because hydraulic oil is responsible for carrying heat away from your precious pumps, valves and actuators, any temperature fluctuations can be a telltale sign of air in the hydraulic oil. Oil is 8-10 times better at conducting heat compared to air, so the presence of air bubbles can disrupt the heat transfer properties of the hydraulic fluid, causing the system to overheat. Frequent overheating episodes should prompt an inspection of the hydraulic system to identify and address any issues related to air in the oil. Look inside the filler cap or observe the level gauge for slightly opaque or shimmering oil, which should be golden and clear instead.
Monitoring energy consumption is crucial for maintaining the efficiency of hydraulic systems, and any high-level hydraulic system provides operators with power consumption readings (in amps or watts). If you notice a sudden spike in energy usage, the culprit would be power-sapping air bubbles reducing the bulk modulus of your hydraulic oil. Because energy is wasted compressing air, less is available to transmit force, so the pump may work harder to deliver the required flow.
Spotting the signs of air in your hydraulic oil is essential for maintaining the reliability and efficiency of your hydraulic system. Regular monitoring, prompt maintenance, and adherence to manufacturer guidelines are crucial to addressing this unfortunately common problem. If you suspect air in your hydraulic oil but are unsure how to proceed, simply take a clear test sample with a suction pump that can pull from an active stream near the return pipe of the reservoir. You can then compare the appearance of the oil to your store of new hydraulic oil.