In a condition-based maintenance environment, the decision to change out a hydraulic pump or motor is usually based on remaining bearing life or deteriorating efficiency, whichever occurs first.
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Despite recent advances in predictive maintenance technologies, the maintenance professional’s ability to determine the remaining bearing life of a pump or motor, with a high degree of accuracy, remains elusive.
Deteriorating efficiency on the other hand is easy to detect, because it typically shows itself through increased cycle times. In other words, the machine slows down. When this occurs, quantification of the efficiency loss isn’t always necessary. If the machine slows to the point where its cycle time is unacceptably slow, the pump or motor is replaced. End of story.
In certain situations, however, it can be helpful, even necessary, to quantify the pump or motor’s actual efficiency and compare it to the component’s native efficiency. For this, an understanding of hydraulic pump and motor efficiency ratings is essential.
There are three categories of efficiency used to describe hydraulic pumps (and motors): volumetric efficiency, mechanical/hydraulic efficiency and overall efficiency.
Volumetric efficiency is determined by dividing the actual flow delivered by a pump at a given pressure by its theoretical flow. Theoretical flow is calculated by multiplying the pump’s displacement per revolution by its driven speed. So if the pump has a displacement of 100 cc/rev and is being driven at 1000 RPM, its theoretical flow is 100 liters/minute.
Actual flow has to be measured using a flow meter. If when tested, the above pump had an actual flow of 90 liters/minute at 207 bar (3000 PSI), we can say the pump has a volumetric efficiency of 90% at 207 bar (90 / 100 x 100 = 90%).
Its volumetric efficiency used most in the field to determine the condition of a hydraulic pump - based on its increase in internal leakage through wear or damage. But without reference to theoretical flow, the actual flow measured by the flow meter would be meaningless.
A pump’s mechanical/hydraulic efficiency is determined by dividing the theoretical torque required to drive it by the actual torque required to drive it. A mechanical/hydraulic efficiency of 100 percent would mean if the pump was delivering flow at zero pressure, no force or torque would be required to drive it. Intuitively, we know this is not possible, due to mechanical and fluid friction.
Table 1. The typical overall efficiencies of hydraulic pumps, as shown above, are simply the product of volumetric and mechanical/hydraulic efficiency. Source: Bosch Rexroth
Like theoretical flow, theoretical drive torque can be calculated. For the above pump, in SI units: 100 cc/rev x 207 bar / 20 x p = 329 Newton meters. But like actual flow, actual drive torque must be measured and this requires the use of a dynamometer. Not something we can - or need - to do in the field. For the purposes of this example though, assume the actual drive torque was 360 Nm. Mechanical efficiency would be 91% (329 / 360 x 100 = 91%).
Overall efficiency is simply the product of volumetric and mechanical/hydraulic efficiency. Continuing with the above example, the overall efficiency of the pump is 0.9 x 0.91 x 100 = 82%. Typical overall efficiencies for different types of hydraulic pumps are shown in the Table 1.
System designers use the pump manufacturers’ volumetric efficiency value to calculate the actual flow a pump of a given displacement, operating at a particular pressure, will deliver.
As already mentioned, volumetric efficiency is used in the field to assess the condition of a pump, based on the increase in internal leakage due to wear or damage.
When calculating volumetric efficiency based on actual flow testing, it’s important to be aware that the various leakage paths within the pump are usually constant. This means if pump flow is tested at less than full displacement (or maximum RPM) this will skew the calculated efficiency - unless leakage is treated as a constant and a necessary adjustment made.
For example, consider a variable displacement pump with a maximum flow rate of 100 liters/minute. If it was flow tested at full displacement and the measured flow rate was 90 liters/minute, the calculated volumetric efficiency would be 90 percent (90/100 x 100). But if the same pump was flow tested at the same pressure and oil temperature but at half displacement (50 L/min), the leakage losses would still be 10 liters/minute, and so the calculated volumetric efficiency would be 80 percent (40/50 x 100).
The second calculation is not actually wrong, but it requires qualification: this pump is 80 percent efficient at half displacement. Because the leakage losses of 10 liters/minute are nearly constant, the same pump tested under the same conditions will be 90 percent efficient at 100 percent displacement (100 L/min) - and 0 percent efficient at 10 percent displacement (10 L/min).
To help understand why pump leakage at a given pressure and temperature is virtually constant, think of the various leakage paths as fixed orifices. The rate of flow through an orifice is dependant on the diameter (and shape) of the orifice, the pressure drop across it and fluid viscosity. This means that if these variables remain constant, the rate of internal leakage remains constant, independent of the pump's displacement or shaft speed.
Overall efficiency is used to calculate the drive power required by a pump at a given flow and pressure. For example, using the overall efficiencies from the table above, let us calculate the required drive power for an external gear pump and a bent axis piston pump at a flow of 90 liters/minute at 207 bar:
External gear pump: 90 x 207 / 600 x 0.85 = 36.5 kW
Bent axis piston pump: 90 x 207 / 600 x 0.92 = 33.75 kW
As you’d expect, the more efficient pump requires less drive power for the same output flow and pressure. With a little more math, we can quickly calculate the heat load of each pump:
Drive power for a (non-existent) 100% efficient pump would be: 90 x 207 / 600 x 1 = 31.05 kW
So at this flow and pressure, the heat load or power lost to heat of each pump is:
External gear pump: 36.5 – 31.05 = 5.5 kW
Bent axis piston pump: 33.75 – 31.05 = 2.7 kW
No surprise that a system with gear pumps and motors requires a bigger heat exchanger than an equivalent (all other things equal) system comprising piston pumps and motors.
Read more on hydraulic system best practices:
The Benefits of Maximum Efficiency Hydraulic Fluids
Carrying Out Effective Repairs to Hydraulic Cylinders
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Hydraulic Filter Location Pros and Cons
How to Define and Achieve Hydraulic Fluid Cleanliness
Hydraulic motors can be used for a variety of purposes, from powering tools and equipment in construction or manufacturing to moving objects on a manufacturing line. However, which type of hydraulic motor is the most efficient for a given task?
In this article, we’ll take a look at three different types of hydraulic motors and see which is best suited for a particular application. We’ll also discuss some factors to consider when choosing a motor, such as horsepower and speed. By the end of this article, you should have a better understanding of which type of hydraulic motor is right for your needs.
There are many types of hydraulic motors, but the most efficient ones use a rotary vane pump. They are able to move a lot of water very quickly, which makes them perfect for applications like irrigation or hauling heavy objects.
There are many types of hydraulic motors, but the most efficient type is a rotary vane motor. This type of motor uses a series of vanes to turn the rotor, which in turn produces mechanical power.
There are many types of hydraulic motors available on the market, but which one is the most efficient? In this blog post, we will discuss the advantages and disadvantages of different types of hydraulic motors to help you make a better decision when choosing one.
Advantages of electric powered hydraulic motors:
1. They are environmentally friendly – electric powered hydraulic motors are the most sustainable type of motor because they do not produce any emissions.
2. They are quiet – electric powered hydraulic motors are the least noisy type of motor, which makes them ideal for use in sensitive areas such as medical facilities.
3. They are versatile – electric powered hydraulic motors can be used in a variety of applications including agriculture, construction, manufacturing, and mining.
4. They are reliable – electric powered hydraulic motors have a high reliability rate, which makes them ideal for use in critical applications.
5. They are affordable – compared to other types of hydraulic motors, electric powered hydraulic motors are relatively inexpensive, making them an affordable option for businesses and consumers.
Disadvantages of electric powered hydraulic motors:
1. They require maintenance – like any other type of engine, electric powered hydraulic motors require regular maintenance to
There are many types of hydraulic motors available on the market, and each one has its own set of benefits and drawbacks. It’s important to choose the right type for your application so you can get the most out of your machine. Here are some factors to consider when choosing a hydraulic motor:
-Power: The power rating of a motor is important because it determines how much force it can generate. Higher-power motors are typically used for applications that need a lot of power, like construction or farming.
-Speed: Most machines use slow motors to reduce noise and vibration. However, fast motors can be used in some applications, like chemical processing. Speed also affects how long the motor will last before it needs to be replaced.
-Nominal voltage: Most motors use between 12 and 18 volts, but some models use as high as 36 volts. Make sure you pick a model that fits your electrical system.
-Weight: Some heavy motors are necessary for certain applications, like mining or heavy equipment manufacturing. But other applications, like printing or agricultural work, can be done with lighter machines. Keep this in mind when choosing a motor.
For many applications, a gear-driven hydraulic motor is the most efficient type of motor. Gear-driven motors use gears to turn a shaft, which causes the motor to generate more power as it operates. They are typically used in applications that require high torque and low speed, such as agricultural machinery and heavy equipment.
However, there are other types of hydraulic motors that can be more efficient for specific applications. A direct-drive hydraulic motor uses no gears and simply uses the pressure from the hydraulic fluid to turn the shaft. This type of motor is less common, but can be more efficient because it doesn’t waste energy in the gears. It’s also less likely to jam due to dirt or debris build up on the gears.
If you’re not sure which type of hydraulic motor is best for your application, contact a specialist like Power Schaeffer to figure out which option is best for your needs.
There is no single answer to this question as the efficiency of a hydraulic motor will vary depending on a variety of factors, including the type of hydraulic motor and the application it is used in. However, some general tips can be helpful when looking to improve the efficiency of a hydraulic motor.
One way to improve the efficiency of a hydraulic motor is to ensure that it is properly lubricated. This can help reduce friction and allow the engine to work more efficiently. Additionally, using a proper filter can also help optimize performance. Finally, making sure that the system is properly maintained can also help keep the engine running more efficiently.
When looking to buy an efficient hydraulic motor, it is important to consider the type of motor and its efficiency. There are three main types of hydraulic motors: direct-drive, planetary, and asynchronous.
Direct-drive motors are the most efficient and typically use a gearbox to transfer power from the engine to the shaft. This type of motor is good for high-speed applications where efficiency is key, like farming or construction.
Planetary motors use a set of gears similar to a car’s transmission. They are good for lower-speed applications where torque is more important than speed, like manufacturing or water pumps.
Asynchronous motors use an electronic controller to manage power delivery and are less efficient than direct-drive and planetary motors. They are good for applications where speed is not as important as torque, like industrial cleaning machines.
When choosing a hydraulic motor for your project, it is important to consider the type of work you will be doing and the efficiency of the motor you choose. Some of the most common types of hydraulic motors are those that use piston displacement pumps, screw propellers, axial flow pumps, and vane pump systems. Each type has its own advantages and disadvantages when it comes to efficiency, so it is important to research which one would be best suited for your specific application.
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