The main causes of pressure, heat, and noise/vibration in a hydraulic or fluid power system

Hydraulic and fluid power systems are the workhorses of modern industry, supplying immense force and precision for everything from construction equipment and manufacturing machinery to aircraft controls. They work by using pressurized fluid to transmit power. Like all sophisticated systems, however, they are subject to problems that show up as excessive pressure, debilitating heat, and irritating noise/vibration.

These symptoms are often interrelated and can be indicative of problems that, if left unaddressed, can result in system inefficiency, high operating costs, and eventual component failure. Understanding the root causes of these three unwanted symptoms constitutes the first step toward effective maintenance and troubleshooting.

The Root Causes of Excessive Pressure

Pressure is a basic means of power transmission in a hydraulic system. This is accomplished by the fluid flow that resists motion. While necessary, pressure that is continually too high beyond the design specifications of the system is dangerous.

The principal excessive pressure causes relate to flow blockage or faulty pressure control:

Relief Valve Malfunction: The relief valve is intended to provide protection against overpressure. If its setting is too high, if it has jammed shut, or if it fails owing to contamination or wear, the pressure in the system will rise unchecked until a hose bursts or until a pump fails.

Variable displacement pumps have a load-sensing mechanism or compensator that determines the amount of flow supplied from the pump to match any system demand. If the control mechanism fails or is not set correctly, the pump will continue to push maximum flow into the system, leading to unnecessary spikes in pressure.

Flow Blockages: Any restriction in the line downstream of the pump can cause pressure to rise significantly, including a clogged filter, a pinched or collapsed hose, or a blocked orifice in a valve or actuator.

Incorrect Sizing of Components: If the components involved, such as cylinders or motors, are too small to handle the work being done, the effort to move the load will inherently involve higher operating pressures than expected.

The Principal Producers of Destructive Heat

Of all the possible enemies of a hydraulic system, heat is probably the most insidious. For operating temperatures above recommended values, the fluid rapidly deteriorates through loss in viscosity, damage to seals, and shorter life in every component in the system.

Excessive heat is almost always a result of wasted energy—energy put into the system that is not converted into useful work but is instead lost as thermal energy:

Internal Leakage (Wastage): This is the single biggest cause of excessive heat. The internal clearances broaden as components like pumps, motors, and valves wear out. Fluid leaks across these clearances from the high-pressure side toward the low-pressure side. This flow through the restricted path generates intense friction that converts hydraulic energy directly into heat.

Operating at Relief Valve Pressure: When a system is idled, or a cylinder is held at the end of its stroke, the entire pump flow is often dumped over the main relief valve. That is essentially running a high-pressure flow through a tiny, restricted opening, which is an extremely efficient way to generate heat. The pump is doing maximum work, but zero useful output is achieved.

Inefficient Cooling: The inability of the heat exchanger (cooler) to pass heat, either internally or externally, or a faulty cooling fan, leads to a continuous rise in temperatures since the system cannot dissipate naturally produced heat.

High Viscosity/Incorrect Fluid: Using a hydraulic fluid with too high viscosity will create more internal resistance and friction when the fluid is forced through small passages and lines. As a result, operating temperatures higher than desired will be experienced.

Noise and Vibration that Causes Trouble

Noise and vibration are more than just an annoyance; they are usually the audible symptoms of severe mechanical or fluid-related problems that threaten the integrity of the pump and motor bearings.

The most common culprit is a destructive phenomenon called cavitation:

Cavitation (Noise and Damage): This refers to the formation and collapse of vapor bubbles - or, said another way, voids - in the hydraulic fluid, usually extremely rapidly and repeatedly, and almost always occurring on the pump's inlet or suction side. While the fluid is being accelerated into the pump, it will often see a reduction in pressure below the vapor pressure of the oil, which causes it to boil, forming bubbles. Once these are moved to the high-pressure discharge side of the pump, they collapse rapidly, creating a powerful shockwave that erodes metal, pitting, and creates a loud rattling or gravel-like noise.

Understanding the Unwanted Trio: Pressure, Heat, and Noise in Hydraulic Systems
Hydraulic and fluid power systems are the workhorses of modern industry, supplying immense force and precision for everything from construction equipment and manufacturing machinery to aircraft controls. They work by using pressurized fluid to transmit power. Like all sophisticated systems, however, they are subject to problems that show up as excessive pressure, debilitating heat, and irritating noise/vibration.

These symptoms are often interrelated and can be indicative of problems that, if left unaddressed, can result in system inefficiency, high operating costs, and eventual component failure. Understanding the root causes of these three unwanted symptoms constitutes the first step toward effective maintenance and troubleshooting.

The Root Causes of Excessive Pressure

Pressure is a basic means of power transmission in a hydraulic system. This is accomplished by the fluid flow that resists motion. While necessary, pressure that is continually too high beyond the design specifications of the system is dangerous.

The principal excessive pressure causes relate to flow blockage or faulty pressure control:

Relief Valve Malfunction: The relief valve is intended to provide protection against overpressure. If its setting is too high, if it has jammed shut, or if it fails owing to contamination or wear, the pressure in the system will rise unchecked until a hose bursts or until a pump fails.

Variable displacement pumps have a load-sensing mechanism or compensator that determines the amount of flow supplied from the pump to match any system demand. If the control mechanism fails or is not set correctly, the pump will continue to push maximum flow into the system, leading to unnecessary spikes in pressure.

Flow Blockages: Any restriction in the line downstream of the pump can cause pressure to rise significantly, including a clogged filter, a pinched or collapsed hose, or a blocked orifice in a valve or actuator.

Incorrect Sizing of Components: If the components involved, such as cylinders or motors, are too small to handle the work being done, the effort to move the load will inherently involve higher operating pressures than expected.

The Principal Producers of Destructive Heat

Of all the possible enemies of a hydraulic system, heat is probably the most insidious. For operating temperatures above recommended values, the fluid rapidly deteriorates through loss in viscosity, damage to seals, and shorter life in every component in the system.

Excessive heat is almost always a result of wasted energy—energy put into the system that is not converted into useful work but is instead lost as thermal energy:

Internal Leakage (Wastage): This is the single biggest cause of excessive heat. The internal clearances broaden as components like pumps, motors, and valves wear out. Fluid leaks across these clearances from the high-pressure side toward the low-pressure side. This flow through the restricted path generates intense friction that converts hydraulic energy directly into heat.

Operating at Relief Valve Pressure: When a system is idled, or a cylinder is held at the end of its stroke, the entire pump flow is often dumped over the main relief valve. That is essentially running a high-pressure flow through a tiny, restricted opening, which is an extremely efficient way to generate heat. The pump is doing maximum work but zero useful output is achieved.

Inefficient Cooling: The inability of the heat exchanger (cooler) to pass heat, either internally or externally, or a faulty cooling fan, leads to a continuous rise in temperatures since the system cannot dissipate naturally produced heat.

High Viscosity/Incorrect Fluid: Using a hydraulic fluid with too high viscosity will create more internal resistance and friction when the fluid is forced through small passages and lines. As a result, operating temperatures higher than desired will be experienced.

Noise and Vibration that Causes Trouble

Noise and vibration are more than just an annoyance; they are usually the audible symptoms of severe mechanical or fluid-related problems that threaten the integrity of the pump and motor bearings.

The most common culprit is a destructive phenomenon called cavitation:

Cavitation (Noise and Damage): This refers to the formation and collapse of vapor bubbles - or, said another way, voids - in the hydraulic fluid, usually extremely rapidly and repeatedly, and almost always occurring on the pump's inlet or suction side. While the fluid is being accelerated into the pump, it will often see a reduction in pressure below the vapor pressure of the oil, which causes it to boil, forming bubbles. Once these are moved to the high-pressure discharge side of the pump, they collapse rapidly, creating a powerful shockwave that erodes metal - pitting - and creates a loud rattling or gravel-like noise.

Causes of Cavitation:

Clogged Suction Filter: A restricted inlet filter starves the pump of fluid.

Air Leaks: A leak on the suction side pulls air into the fluid to produce a similar effect often called aeration.

High Fluid Viscosity/Low Temperature - If the oil is too thick, the pump cannot draw it in fast enough.

Mechanical Misalignment: If there is misalignment between the electric motor and hydraulic pump (from a worn coupling or from improper installation), the excessive vibration can eventually cause both units to experience bearing and shaft seal failure.

Loose Parts: Any loose mounting bolt, pipe clamp, or manifold block can magnify normal operating vibration into disturbing noise.

Worn-out pump/motor bearings: Bearings in rotating parts wear down and generate friction, heat, and a typical screeching or grinding noise.

The Path to a Healthy System

Pressure, heat, and noise/vibration form a trio of symptoms rather than diseases in themselves. Their rectification through troubleshooting requires an effort to delve into their respective causes: Pressure - Relief valve settings, check for flow restrictions and verify pressure compensators are operating properly. Heat: Check cooler, system demand, and, most importantly, look for internal leakage in pumps and cylinders, which requires specialty flow testing. Noise/Vibration: Check the pump inlet for filters and air leaks in the hoses, check that all components are properly aligned, and listen carefully to isolate worn bearings. A healthy hydraulic system is one that is quiet, cool, and efficient, delivering power with consistency as designed. The key to keeping this unwanted trio in check is through regular fluid analysis and preventative maintenance.

Clogged Suction Filter: A restricted inlet filter starves the pump of fluid.

Air Leaks: A leak on the suction side pulls air into the fluid to produce a similar effect often called aeration.

High Fluid Viscosity/Low Temperature - If the oil is too thick, the pump cannot draw it in fast enough.

Mechanical Misalignment: If there is misalignment between the electric motor and hydraulic pump (from a worn coupling or from improper installation), the excessive vibration can eventually cause both units to experience bearing and shaft seal failure.

Loose Parts: Any loose mounting bolt, pipe clamp, or manifold block can magnify normal operating vibration into disturbing noise.

Worn-out pump/motor bearings: Bearings in rotating parts wear down and generate friction, heat, and a typical screeching or grinding noise.

 The Path to a Healthy System

Pressure, heat, and noise/vibration form a trio of symptoms rather than diseases in themselves. Their rectification through troubleshooting requires an effort to delve into their respective causes: Pressure - Relief valve settings, check for flow restrictions and verify pressure compensators are operating properly. Heat: Check cooler, system demand, and, most importantly, look for internal leakage in pumps and cylinders, which requires specialty flow testing. Noise/Vibration: Check the pump inlet for filters and air leaks in the hoses, check that all components are properly aligned, and listen carefully to isolate worn bearings. A healthy hydraulic system is one that is quiet, cool, and efficient, delivering power with consistency as designed. The key to keeping this unwanted trio in check is through regular fluid analysis and preventative maintenance.