New Hydraulic Pump Failing? 4 Hidden System Issues To Check First

Here is the English translation of the technical article:

"Failure to Build Pressure or Deliver Oil" with New Hydraulic Pumps: Often "False Faults" in the System

The phenomenon of a "new hydraulic pump failing to build pressure or deliver oil" is not uncommon during hydraulic system commissioning. When encountering this situation, many users' first reaction is often: "Is the pump broken?" or "Is this pump defective?" In reality, this "failure" is frequently *not* due to a quality issue with the pump itself, but rather stems from several common yet easily overlooked "false faults" occurring during system installation or commissioning.

As hydraulic engineers, we must possess the ability to systematically troubleshoot from the system perspective. The following four key points are essential elements that every practitioner **must** check first when facing a new pump that won't build pressure:

1. Is the Pump Rotation Direction Correct?

This seems basic, but it's actually one of the most commonly overlooked root causes.

The vast majority of hydraulic pumps have specific rotation direction requirements (clockwise or counter-clockwise). If the motor phase sequence is wired incorrectly during installation, it will cause the pump to rotate backwards, preventing it from effectively drawing in oil.

Reverse rotation not only fails to build pressure but may also cause internal damage to the pump. Therefore, **before starting a new pump, always verify that the motor rotation direction matches the arrow on the pump housing.** Only proceed with testing after confirming it's correct.

2. Are There Air Leaks or Blockages in the Suction Line?

Hydraulic pumps dread "failing to suck oil," but they fear "sucking in air" even more.

In practice, suction line problems are also a common cause of pumps failing to build pressure. Common issues include:

Loose suction hose connections creating tiny gaps that draw in air;

Poorly sealed piping, leading to leaks under vacuum;

Clogged or contaminated suction strainers/screens, restricting oil flow;

Suction lines with undersized diameter or excessive length, increasing suction resistance.

These problems cause the pump to "cavitate" or "run dry," filling the pump cavity with air bubbles. This prevents pressure build-up and can also lead to cavitation damage and wear.

3. Is the Oil Viscosity and Temperature Suitable?

The viscosity and temperature of the hydraulic oil directly affect the pump's suction efficiency and initial operating condition. Especially during cold starts in winter, if oil with excessively high viscosity is used, the fluid thickens in low temperatures. This drastically increases the pump's suction resistance, potentially preventing the pump from creating sufficient vacuum. The system will exhibit symptoms of no oil delivery and no pressure rise.

It is recommended to use standard low-temperature hydraulic oil and implement a pre-heating procedure in cold environments to bring the oil temperature into the suitable range before starting the system.

4. Is the Pressure Control Set Correctly?

After installing a new pump, if the system's relief valve or pressure regulating valve is not set correctly, it can create the illusion of oil flow without pressure.

For instance:

If the relief valve setting is too low, oil will be dumped directly back to the tank as soon as the pump delivers it. The pressure gauge will read zero, and the system will naturally fail to build pressure.

Therefore, during initial commissioning, check:

Whether the relief valve is correctly set to the required working pressure;

Whether any unintended internal leakage paths are open within the system, causing oil to bypass the load.

Summary: What Appears to be a "Pump Problem" is Often System Oversight

In summary, a new hydraulic pump failing to build pressure or deliver oil is not necessarily a problem with the product itself. More commonly, it is one of these 4 "false faults":

1.  Incorrect pump rotation direction;

2.  Air leaks or blockages in the suction line;

3.  Unsuitable oil viscosity or temperature;

4.  Improper system pressure control settings.

Before concluding it's an equipment failure, it is crucial to methodically check these four aspects. This prevents misdiagnosis leading to unnecessary returns, repairs, or even system damage.