Hydraulic Motor Efficiency: Get The More Power Out of Your Hydraulic Motors

Have you been looking to get more out of your excavator? Perhaps you’re looking to increase the power and performance of your machine, while reducing fuel consumption and emissions. If so, then improving the efficiency of your hydraulic motors is a must.

Without proper knowledge, you cannot optimize the efficiency of hydraulic motors. Sufficient knowledge and understanding on hydraulic motor efficiency are key to getting the most out of your machine.

In this blog post, we’ll explore how you can measure the efficiency of hydraulic motors. We will also discuss what causes loss in efficiency? and how you can avoid such losses? Stay tuned!

Introduction to Hydraulic Motor Efficiency

The hydraulic motor in your final drive possess a specific level of effectiveness and efficiency. As you continue using your hydraulic motor this efficiency level drops.

The inevitable truth is that no matter how efficient a system might be. There will always remain some degree of inefficiency.

  • The studies have shown that the efficiency of radial piston motors is around 95 percent.
  • On the other hand, the efficiency of axial piston motors is around 90 percent.

This is true when you use highest quality equipment and follow proper maintenance measures. The above-mentioned motors are the essential components of most final drives.

Types of Hydraulic Motor Efficiencies

Efficiency is a tricky concept to define. The reason is a lot of variations, the exact meaning varies depends on the kind of system you concern. When it comes to hydraulic motors, there are three different types of efficiencies that plays major role. These are:

  • Volumetric Efficiency
  • Hydraulic/ Mechanical Efficiency
  • Overall Efficiency

1.   Volumetric Efficiency

Volumetric efficiency deals with actual flow rate that hydraulic motor carrying out and theoretical flow rate. The volumetric efficiency allow you determine wear and leakage exist in your hydraulic motor. You can make use of this formulae to calculate theoretical flow rate:

QT= Theoretical Flow Rate

VD = Displacement Volume

Nrpm= Rotational Speed

y = number of cylinders

A = piston area

S = stroke

D = Bore diameter


You can measure the actual flow rate (QA) using flow meter. All the measurements carried out in system international units. This means if the unit of displacement is cc/ rev and the unit of speed is rpm. Then you will get the results in unit of liters/ minute.

You can then calculate the volumetric efficiency using the above formulae.

2.   Mechanical Efficiency

Theoretical work done and actual work done collectively determines the mechanical efficiency of the system. These works done determined per revolution that takes place in hydraulic motor.

You can calculate theoretical work done using theoretical torque. On the other hand, you can calculate actual work done using actual torque. The reading of these torques is mostly around 90 percent in hydraulic motors.

You can determine the value of actual torque using dynamometer. But this happens rarely. The loss which results in mechanical efficiency is mainly due to excessive friction occurring between mating parts.

3.   Overall Efficiency

You can define overall efficiency as the sum of mechanical efficiency and volumetric efficiency. By multiplying both of these efficiencies (mechanical and volumetric efficiency) you will get overall efficiency. Overall efficiency determines how effective is your hydraulic motor in overall functioning.

Types of Losses Occur in Hydraulic Motor Efficiency

There are two types of losses which mainly contributes to the reduction in hydraulic motor efficiency. These are:

  • Fluid Leakage internally which is also known as volumetric loss
  • Frictional loss which is also known as mechanical loss

1.   Internal Leakage

Internal leakage is the loss of fluid in the motor. Higher internal leakage generally means more fluid out of the system. This can cause a lot of problems for a hydraulic motor system. Because it does not allow for proper lubrication and causes damage to internal parts.

Although internal leakage is beneficial when it holds up to a certain level. But crossing the certain level it becomes an issue. The sole cause behind the internal leakage of your hydraulic motor is wear and tear.

For an instance the different clearances that exist between the various components of your hydraulic motor increase over time. This is because of excessive abrasive wear which leads to internal leakage. The reason behind this wear is the usage of hydraulic fluid having contaminants. This can also be due to wear and tear occurring normally.

2.   Frictional Loss

Frictional Loss is the loss of kinetic energy of a fluid as it moves through a conducting channel. Frictional losses, are always present in all forms of mechanical devices. It occurs whenever two surfaces slide over each other. Friction losses heat up the motor and reduce its efficiency.

The frictional losses occur when there are rough surfaces present. This will lead to the less power transmission within the system. The other sources of friction in hydraulic motor is due to wear and tear of plane bearings and anti-frictional bearings.

How to Prevent These Losses?

There are various maintenance measures that you can practice to such efficiency losses in your hydraulic motors. Some of the major prevention measures are:

1.   Use Clean Hydraulic Fluid

Clean hydraulic fluid is crucial to maintaining efficiency of hydraulics. The level of dirt in the oil can significantly affect the performance and also cost of a machine.

The cleaner the oil, the smoother action it has and hence fewer instances of leakage. Well kept, clean and properly mixed fluids will reduce wear and maintenance requirements of hydraulic motors. This will also lead to a longer life of your machine.

2.   Timely Replacement of Hydraulic Filters

Timely replacement of hydraulic filters is beneficial in maintaining efficiency of hydraulic motors. Lubricants and contaminants enter the oil through leakage at the filter screen or broken seals.

The contaminants damage the internal components, reducing oil life and increasing operating costs. Timely replacement ensures that your equipment can continue to perform as expected by providing optimum oil flow and lubrication.

3.   Avoid Hydraulic Leakage

Hydraulic leakage means system failure due to blocked vents and chipped/ damaged passages. This might cause the motor oil level to fall below the level required by the control system. Timely detection of leakage can help you prevent the further decrease in motor efficiency.

Apart from the above-mentioned measures take care of excessive noises, vibrations and heating buildup in your hydraulic motors. This will help you maintain the efficiency and effectiveness of your hydraulic motors while reducing maintenance costs.

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