Hydraulic Pump Not Building Pressure? Causes and Recommended Checks
When a hydraulic system can no longer develop the required force, the hydraulic pump is often the first component to be suspected. In practice, however, insufficient pressure, slow cylinder movement or loss of performance under load can have many different causes.
The problem may originate from the pump, but it can also be related to the oil supply, valves, directional control valve, cylinders or other components within the hydraulic circuit.
For this reason, replacing the pump before identifying the actual cause may not solve the problem.
Cuprins
Does a Hydraulic Pump “Create” Pressure?
From a technical standpoint, a hydraulic pump supplies oil flow, while pressure develops when that flow encounters resistance within the circuit.
This distinction is important when diagnosing a hydraulic system.
In simplified terms, flow rate affects the speed of cylinder movement, while the force developed by the cylinder depends on the pressure within the circuit and the effective piston area.
Therefore, a cylinder that moves slowly and a cylinder that can no longer develop the required force do not necessarily indicate the same fault.
What Are the Signs of a Hydraulic System Problem?
Symptoms that may indicate improper hydraulic system operation include:
- The cylinder moves more slowly than normal
- The system can no longer develop the required force
- The indicated pressure is lower than the normal operating value
- The system operates normally when cold but loses performance as it warms up
- The pump produces unusual noise
- Cylinder movement becomes erratic or jerky
- Hydraulic oil temperature rises excessively
- Pressure fluctuates during operation
- Some system functions operate normally while others do not
A single symptom is not sufficient to identify the faulty component. Different faults can produce very similar symptoms.
1. Hydraulic Oil Level or Condition
The quantity and condition of the hydraulic fluid directly affect system operation.
A low oil level may allow air to enter the circuit, while contaminated or unsuitable hydraulic fluid can affect pumps, valves and other system components.
Possible symptoms include unusual noise, unstable operation, overheating and variations in system performance.
If the oil level repeatedly decreases, the cause of the fluid loss should be identified rather than simply topping up the reservoir.
2. Air in the Circuit or Oil Supply Problems
The pump must receive an adequate and continuous supply of hydraulic fluid.
Air in the oil or inadequate pump inlet conditions may result in noise, vibration, jerky movement, insufficient flow and reduced system performance.
Under certain conditions, cavitation may also occur. If it persists, cavitation can damage internal pump components.
Because the symptoms of aeration and cavitation can be similar, identifying the cause based solely on pump noise is not always possible.
3. Filters or Restrictions in the Circuit
A clogged filter or a restriction in the oil flow path may reduce flow or cause a pressure drop, with the effects depending on the location of the affected component within the circuit.
Depending on where the restriction occurs, symptoms may include slow actuator movement, overheating, incorrect pressure, unusual noise or delayed actuator response.
Identifying the restriction requires an assessment of the hydraulic circuit and the operating conditions under which the symptom occurs.
4. Pressure Relief Valve
The pressure relief valve protects the hydraulic system against exceeding the maximum allowable pressure.
If its operation is affected by wear, contamination or another fault, the system may fail to reach the required pressure even though the pump continues to operate.
Arbitrarily increasing the pressure setting is not a solution.
The maximum allowable pressure must remain within the rated limits of all components in the hydraulic system.
5. Hydraulic Pump Wear
As internal pump components wear, internal leakage may increase.
In some cases, the pump may appear to operate normally under little or no load, while performance decreases when the system is required to operate at higher pressures.
One possible symptom is satisfactory operation when the system is cold, followed by a gradual loss of performance as the hydraulic fluid and system warm up.
However, this behaviour does not automatically confirm that the pump is faulty.
Internal leakage may also occur in other components.
6. The Problem May Be in the Hydraulic Cylinder
If a hydraulic cylinder has internal leakage, this may contribute to a reduction in available force or an inability to maintain the required position, depending on the circuit configuration and the applied load.
Depending on the system configuration, symptoms may include reduced force, slow movement, inability to maintain position or different behaviour as the hydraulic fluid warms up.
These symptoms can be mistaken for a worn hydraulic pump.
For this reason, the pump and cylinder should not be assessed independently from the rest of the hydraulic circuit.
7. Directional Control Valves and Other Valves Can Produce Similar Symptoms
Directional control valves route hydraulic flow through the different paths of the circuit, while other valves may control or limit pressure, flow or load holding, depending on their type and configuration.
Wear, contamination or improper operation may result in internal leakage, insufficient pressure at the actuator, slow movement, inability to maintain a load or excessive system heating.
If only one function of a machine is affected while the others operate normally, this information can be important during diagnosis.
8. Hydraulic Oil Temperature Can Provide Important Clues
Hydraulic fluid temperature and viscosity are closely related.
If the system operates normally immediately after start-up but loses performance as the oil warms up, internal leakage may be present and may become more significant at higher temperatures.
Overheating can be both a cause and an effect of a hydraulic system problem.
For this reason, temperature measurement alone is not sufficient to identify the faulty component.
How Can You Tell Whether the Pump Is Actually the Problem?
This is one of the most common difficulties when diagnosing a hydraulic system.
A worn pump, a cylinder with internal leakage, a malfunctioning valve or a damaged directional control valve can produce very similar symptoms.
The system can no longer develop sufficient force
The pump may be responsible, but internal leakage may also be present elsewhere in the circuit.
The cylinder moves slowly
The cause may be insufficient flow, a restriction or a control-related problem.
The system loses performance as it warms up
Hydraulic fluid temperature and possible internal leakage should be assessed.
The pump produces unusual noise
The cause may be related to the pump inlet conditions, air in the circuit, cavitation or a mechanical fault.
For this reason, a correct diagnosis cannot be based on symptoms alone.
Why Is Checking the Pressure Gauge Alone Not Enough?
Pressure is an important parameter, but by itself it does not provide all the information required to assess the condition of a hydraulic system.
Depending on the type of fault, diagnosis may require several parameters to be considered together, including:
- pressure;
- flow rate;
- temperature;
- system behaviour under load;
- differences between cold and warm operating conditions.
The interpretation of these values depends on the system configuration and the characteristics of the components used.
For this reason, two hydraulic systems showing apparently identical symptoms may have completely different underlying causes.
When Is Specialist Diagnosis Recommended?
A technical assessment is recommended when:
- pressure no longer reaches the normal operating value;
- the system progressively loses force;
- the problem occurs only after the system warms up;
- the pump produces unusual noise;
- hydraulic oil temperature becomes excessively high;
- the cylinders can no longer maintain the load;
- the problem persists after routine checks;
- the faulty component cannot be clearly identified.
In such situations, replacing components by trial and error may result in additional costs without addressing the root cause of the problem.
The system should be assessed to determine whether the problem originates from the pump or from another part of the hydraulic circuit and, where a fault is confirmed, whether repair or replacement is technically justified.
Should the Hydraulic Pump Be Repaired or Replaced?
There is no universal answer.
The decision depends on the pump type, the nature and extent of wear, the condition of the internal components, the cause of the failure, the operating conditions and the cost of repair compared with replacement.
Identifying the cause of the damage is also important.
If a pump has been damaged by contamination, cavitation or another problem within the hydraulic circuit, installing a new pump without eliminating the underlying cause may result in the same failure occurring again.
Conclusion
When a hydraulic system can no longer develop the required pressure or force, the pump should not automatically be considered the faulty component.
The problem may originate from the hydraulic oil supply, filters, valves, directional control valve, cylinders, fluid temperature or internal leakage in different areas of the circuit.
Symptoms can provide useful indications, but accurately identifying the cause requires the hydraulic system to be assessed as a whole and several operating parameters to be considered together.
A correct diagnosis before repairing or replacing components can prevent unnecessary work and reduce the risk of the same failure occurring again.
Important: Hydraulic systems can operate at very high pressures. Components must only be removed or disconnected after the system has been properly shut down, secured and fully depressurised. Measurements, tests and adjustments carried out while the system is operating must only be performed by qualified personnel, in accordance with the manufacturer’s documentation and applicable safety procedures.
Unable to Identify the Problem with Certainty?
When the same symptoms may have several possible causes, assessing the hydraulic system as a whole can help avoid unnecessary component repair or replacement. Hidromold provides inspection, diagnostic and repair services for hydraulic equipment and systems.
