What is More Efficient: Hydraulic or Electric Motors?

Across various industries, you'll find both electric and hydraulic motors in use. In some cases, they may be used interchangeably, and in other cases, electric motors are selected for one application while hydraulic motors are selected for others.

Why does this happen? Is one style of motor more efficient than the other, perhaps? Or maybe it is just a matter of preference. Read further for our discussion on the pros and cons of electric vs hydraulic motors, when they are most efficient, and what applications they are most suited for.

What is a Hydraulic Motor?

Like all other types of motors, hydraulic motors are energy conversion devices. They convert the pressure and flow of a fluid into torque and rotational force. Using the theories of hydrodynamics and hydrostatics, these motor systems contain an incompressible fluid used to multiply force and move an object.

A hydraulic motor system works by a pump pushing against an incompressible fluid in the system, pushing against a piston inside a cylinder. The piston moves and the movement is converted into a rotational force. However, each hydraulic motor type works a little differently and is individual to the application.

The circumference and length of the hydraulic cylinder and piston determine the amount of force that can be produced. The force needed to produce motion can be reduced by increasing the size of the cylinder, which means that the input force can be significantly less than the output force. When it comes to power to size ratio, hydraulic motors feature the highest power density. The force it can achieve is only limited by the motor's design, construction, and materials.

Types of Hydraulic Motors

There are a few types of hydraulic motors, all with individual designs based on the hydrodynamics and hydrostatics theories.

• Axial piston motors
• Radial piston motors
• Gerotor Motor
• Vane Motor
• Gear Motor

Pros and Cons of Hydraulic Motors

Pros

• Can generate a very high output force in relation to the input force.
• Higher degree of accuracy in movement.
• Work great in harsh environments with water, dirt and other contaminants as the system is already sealed to keep the hydraulic fluids contained.
• Can stop and start easily under large loads without causing damage.
• Can complete slow and precise movement under heavy loads.
• Can generate incredibly high torque in a fraction of the size of an electric motor and without gearing.
• Smooth and store energy as fluid under pressure in the accumulators, increasing the efficiency of the system.
• Can hold a load at a standstill while consuming no power.
• Can be sized for the average load, reducing the size of the motor needed.
• Can be mounted remotely with only the accumulator, actuator, and control valves close to the application.

Cons

• Often have a higher initial purchase price.
• Messy to operate and maintain with filters, hydraulic pumps, and oils that need to be regularly checked, exchanged, or cleaned.
• Hydraulic fluid leaks pose safety and environmental hazards.
• Hydraulic systems require many components: actuators, accumulators, release valves, hydraulic fluid.
• High vibration will eventually cause fluid leaks in the system.
• Loud operating noise.
• Hydraulic fluid must be inspected, cleaned, and topped up more regularly than the maintenance that must be carried out on an electric motor.
• Lose more efficiency due to heat loss than electric motors.

Pros and Cons of Electric Motors

Pros

• Cost less than their hydraulic counterparts.
• Can achieve fast RPMs.
• High positioning accuracy with programmable speeds and stop positions.
• The addition of VFDs allows for precise control with feedback on motion and force.
• Systems can be easily scaled.
• Electric motors run more smoothly and quietly.

Cons

• Can be complicated to install and troubleshoot, often requiring an electrician or engineer.
• The windings of electric motors are sensitive to water, dust, dirt, and other contaminants.
• Heavy loads can cause the motor to stall or trip out, resulting in failure and possibly damage.
• A gearbox is needed to move a load at a slower speed, reducing the system's efficiency.
• Can't easily be used underwater as making them perfectly waterproof is very difficult (if at all possible).
• To generate high torque, the size becomes impractical.
• Must be oversized to meet the max load requirements; this will consume more power than generally needed.
• Must be mounted close to the application.

Types of Motors Better Suited to Different Environments

While hydraulic motors can complete practically the same tasks as an electric motor, hydraulic motors are better suited for heavy machinery applications. They are often more efficient when it comes to tough jobs with heavy loads.

Hydraulic Motor Applications

• Heavy-duty equipment for various industries.
  • Construction
  • Mining
  • Agriculture
• Metalworking machines.
• Vehicle braking systems.
• Applications with:
  • A lot of back-and-forth motion.
  • A large number of motion axes – a single pump can power multiple actuators, helping to reduce the weight on the system.
• In applications where one actuator moves another.
• Systems that apply constant torque and where binding or jams can occur.

Electric Motor Applications

• Continuous motion applications without many starts and stops.
• Where precision positioning is required.
• Where fine speed control and high speeds are necessary.
• Where hydraulic fluid leaks would become a hazard.
• Where the operator would like to complete maintenance on a less frequent schedule.
• Applications where there isn't space for the accumulator, actuators, coolers, and filtration components.

Summary

These pros and cons lists seem daunting and maybe a little unbalanced. But when it comes down to it, the choice between hydraulic and electric motors is mostly a personal preference, if not a selection based on an industry standard. There are applications where each type of motor will be more efficient, but that doesn't discount the fact that they are each capable of completing the task at hand.

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