Early Warnings of Hydraulic System Troubles:

  • Slow Operation
  • Increased Noise
  • Elevated Temperature

Slow Operation

Longer cycle times are often the first indication that there is something wrong with a hydraulic system. Decreased speed of hydraulic actuators (such as cylinders) points to decreased flow through the system.

Decreased flow can be caused by either external or internal leaks. External leakage can often be spotted very easily. Look for leaking/busted hydraulic hose, hydraulic fluid around connectors or under components.

See the related blogs on preventive maintenance of hydraulic hoses and knowing when to replace a hydraulic hose. Another related blog, “What is Causing Your Hydraulic System to Leak” has a free download of our Port End Assembly Guide, which can educate your maintenance personnel on preventing connector leaks in the first place.   

Internal leaks (such as high-pressure fluid passing around the cylinder piston, or incorrectly set relief valve pressure) are more challenging to identify. One way to identify an internal leak is by detecting elevated temperature of a failing component. A leak generates heat. Higher temperature results in decreased viscosity of the hydraulic fluid. Decreased viscosity of the fluid further increases leakage, leading to additional increases in temperature… You get the picture of how the situation escalates.

An infrared thermometer can be a useful tool to help identify components with internal leakage.

In some cases, temperature measurement is not conclusive. If an internal leak cannot be detected by locating a component generating abnormal heat, use a hydraulic flow meter.

Increased Noise

Knocking, loud whining, or screeching often indicates aeration or cavitation. Aeration means air inclusion in the hydraulic fluid, cavitation is the presence of vaporized hydraulic fluid in the system.


Banging or knocking noises can indicate that air is included in the hydraulic fluid. Other symptoms of air inclusion are foaming of the fluid, and erratic actuator movements.

Air in the system accelerates breakdown of the hydraulic fluid and decreases hydraulic fluid’s lubricating properties. Both conditions lead to increased wear of the system’s components, through increased friction, overheating, and burning of seals.

Air usually enters the system through the pump intake. Check the fluid level and a condition of the suction hose. If the hose is old or shows any warning signs, replace it. See related blogs on knowing when to replace a hydraulic hose, scheduled hydraulic hose replacement, and preventive maintenance of hydraulic hoses for more information on the subject.

Another way for air to enter the system is along the pump’s shaft. Check the pump’s shaft seal and replace it if it is leaking.


A loud whining or screaching noise can be indicative of cavitation.

Cavitation results in the erosion of metal components. The resulting metal debris in the system accelerates the wear of components located down the stream. In some cases, cavitation can lead to mechanical failure of different components.

Cavitation results from demand for hydraulic fluid not being met. Typically (but not exclusively), this happens at the pump. The insufficient flow causes the absolute pressure in the affected part of the circuit to fall below the vapor pressure of the hydraulic fluid, which in turns causes formation of vapor cavities within the fluid. When the vapor cavities are compressed, they implode and produce a knocking noise.

Elevated Temperature

Excessive temperature of hydraulic fluid (generally above 180°F), reduces its working life and damages seals in the system. In addition, viscosity of hydraulic fluid decreases with increasing temperature, which in turn results in inadequate lubrication and increased wear of the system's components.

Temperature alarms should be utilized to prevent damage caused by excessive hydraulic fluid temperatures.

There are two general causes for increased hydraulic fluid temperature: either a component produces more heat than it should, or the heat dissipation capacity of the system is reduced/inadequate.

Sources of Excessive Heat in Hydraulic Systems

  • Internal leaks
  • Aeration
  • Cavitation

Refer to the sections above to learn more about internal leaks, aeration and cavitation.

Causes of Inadequate Heat Dissipation

  • Low reservoir level
  • Obstructions to air flow around the hydraulic fluid reservoir
  • Incorrectly sized heat exchanger
  • Obstructions in hydraulic fluid and/or cooling fluid flow through the heat exchanger
  • Low viscosity of hydraulic fluid
  • Elevated ambient temperature

Regularly check the hydraulic oil level and viscosity. Check the heat exchanger for any obstructions in both coolant lines and hydraulic fluid lines. Make sure that the heat exchanger has adequate space around it.

Hydraulic System Diagnostic Tools

To properly analyze and/or troubleshoot your hydraulic system, you will need some tools. At minimum, you need to be able to measure pressure, temperature, and flow at different parts of your circuit.  The more complex your hydraulic system, the more sophisticated meters you will need to get the job done.

Parker SensoControl family of diagnostic meters offers four different diagnostic solutions to address the needs of maintenance personnel, based on the complexity of their hydraulic circuits.

Parker SensoControl Diagnostic Meters

SensoConrol Service Junior

SensoControl Serviceman

SensoControl Service Master Easy

SensoControl Service Master Plus

Pressure Sensing YES YES YES YES
Flow Sensing     YES*   YES* YES
Temperature Sensing     YES* YES YES
Rotational Speed Sensing     YES*   YES* YES
Auxiliary Sensing       YES* YES
Pressure Differential   YES YES YES
Automatic Sensor Recognition   YES YES YES
Auto Power Off YES YES YES YES
Battery Monitoring YES YES YES YES
PC Compatible (Win 7)      YES*     YES*  YES
Battery Type AA (2) Ni-MH Ni-MH LI Ion
Min/Max Memory YES YES YES YES
Self Contained Memory     YES YES
Online Data Transfer   YES YES YES
Text Dislplay Lines 2 2 8 48
Inputs 1 2 4 26
Max Data Points in Memory     1 million 1 billion
Number LCD Display YES YES YES YES
Basic Hydraulic Calculations     YES YES
USB Interface     YES YES
CAN Sensors       YES
Graphic Color Display       YES
Additional Storage Media        YES

* Additional accessories are required to perform this function


Posted by Marek Bobik

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