Runaway Pump (Cavitation)

If your pump is experiencing cavitation, the first step is to turn it off using the pump shut-off knob. Depending on your pump model, this may involve twisting the knob to the “off” position, pushing in a push-pull style knob, or turning a red knob to the right.

Once the pump is turned off, check to ensure that grease isn’t flowing somewhere unexpected. Verify that all hoses are connected properly, no fittings are missing, and no valves are open. If you confirm that grease is not being dispensed and the pump is still cycling, it is likely cavitation. Cavitation occurs when the pump intake shaft, which should be filled with grease, is instead filled with air. This causes the pump to cycle rapidly without moving any material.

There are several potential causes of cavitation. One common cause is air in the material container. When changing containers, refer to the pail change instructions in your operator’s manual or instructional video. Properly bleeding the container is essential. For larger pumps or dual-post systems, ensure that you open the appropriate valve or remove the T-handle to release air from the container. Once the air is bled, close the valves to prime grease into the center feed for the pump. After bleeding both the container and the pump using the pump bleed valve, your system should be ready to operate.

However, even after following the proper procedures, air bubbles can still remain in the material, particularly if you are using reused grease. Thick grease that has been transferred to a spare container may trap air, making it difficult to eliminate all bubbles. This trapped air can lead to cavitation at any point.

Another common scenario occurs when the pump has been running normally, but suddenly starts to cavitate. This can happen if the ram lever is left in the neutral position. In neutral, the system stops pressing down on the material, which allows an air pocket to form as the grease level drops. Always ensure that the lever is in the “down” position and that adequate pressure is applied. The required pressure depends on the thickness of the material; thicker materials require higher pressure to push the grease into the center feed.

If your lever is correctly positioned and pressure is sufficient, cavitation could be caused by air in the material or a disconnection in the downstream system. A third possibility is worn seals within the grease pump itself. The intake shaft and air motor section contain seals that, when worn, can allow the pump to cycle without effectively moving grease. In this case, the pump may appear to function but fails to transfer material properly.

These are the main causes of cavitation or a runaway pump. If you need further assistance diagnosing the issue, feel free to contact us. If you suspect a worn motor or need replacement parts such as a rebuild kit, we’re happy to help.