Why does a hydraulic pump lose pressure?

Hydraulic pumps are key components in many industrial machines and systems, converting mechanical energy into hydraulic energy. Their primary function is to generate pressure that powers the hydraulic system. A loss of pressure in a hydraulic pump can lead to serious operational problems.

The main causes of pressure loss in hydraulic pumps

A loss of pressure in a hydraulic pump can be caused by a variety of factors, ranging from contamination to mechanical damage.

Contaminants in hydraulic
oil This is one of the main causes of hydraulic pump failure.

• Types of contaminants: Solid particles and water are the most common contaminants. Water can cause corrosion of pump components and negatively affect oil viscosity, resulting in pump failure and temperature control issues.
• Consequences: Contaminants force the pump to work harder and can lead to seal damage. They can also cause excessive wear on components, reduced performance, and failure. Contaminants can block openings in valves, such as the relief valve, leading to a loss of pressure in the system.

Damaged seals
: Over time, high pressure in the hydraulic pump damages the seals, leading to leaks.

• Internal leaks: Oil flows uncontrollably between pump sections, impairing the pump’s efficiency and forcing it to work harder. This is a common cause of low volumetric efficiency and insufficient flow, resulting in low pressure.
• External leaks: Visible oil loss, which can lead to more serious problems in the hydraulic system.
  Worn seals are a common cause of pressure loss.

Excessive pressure and overload
Every pump has its limits. Operating at pressures higher than those recommended by the manufacturer or under overload conditions increases the likelihood of failure. Prolonged operation under increased pressure negatively affects the service life of components and can lead to mechanical damage. This may be caused by improper adjustment of relief valves by the user, valve sticking, or blockage due to frozen water in the oil at low temperatures.

Air in the system (cavitation/aeration)
Excess air in the hydraulic oil or in the pump itself impairs its efficiency.

• Causes: A drop in oil pressure can lead to the formation of air bubbles. Air can enter the system through leaks in the suction line or when the oil level is too low and the end of the return line is above the oil surface. A suction line with too small a diameter can also cause air to be drawn in.
• Consequences: The pump may be unable to maintain adequate pressure. Large air bubbles can compromise the durability of hydraulic hoses. An air-locked pump makes unusual noises and vibrates. It is recommended to use HM- and HV-grade oils to minimize the risk of air lock.

Mechanical wear of pump
components: Prolonged use leads to wear on the pump’s internal components, resulting in increased internal leakage and reduced volumetric efficiency. As a result, the pump’s output flow is insufficient and the system pressure is low. Damage to the pump impeller is also a cause of pressure loss.

Improper installation or configuration
Installation errors, such as failing to account for potential axial or radial forces, can lead to failure. Using the pump for purposes other than its intended use—for example, selecting a replacement with an inappropriate nominal operating pressure or displacement—can also cause problems. If the speed of the motor driving the pump is too low, it can result in insufficient flow and low pressure.

Problems with hydraulic oil

• Low oil level: If there is no oil or the oil level in the reservoir is too low, the pump cannot operate properly or generate pressure.
• Oil suction hose too thin: This can cause excessive suction resistance, resulting in insufficient flow and low pressure.

Blockages in the hydraulic
system: When the oil suction filter becomes clogged with contaminants, it creates excessive suction resistance for the pump, leading to insufficient flow and low pressure in the system. Similarly, a blocked relief valve or a valve spool stuck in the open position can cause hydraulic oil to return directly to the reservoir, eliminating pressure in the system.

High system
temperature The optimal operating temperature for a hydraulic system is typically 50–60°C. Consistently exceeding this range or a continuous rise in temperature indicates problems that may affect pressure. Overheating is a common issue that affects pump performance.