The early Industrial Revolution saw the introduction of numerous innovations, one of the most consequential being the various motors. While the earliest prototypes used magnetic force to create rotational force, industrialist William Armstrong used a water-powered motor to move what was then the world’s largest swing bridge that spanned the United Kingdom’s River Tyne.
While Armstrong’s contemporaries sniffed over his design, hydraulic engines have proliferated and are employed in many industrial uses today. In this guide, we will provide you with information regarding the components of hydraulic motors, the most popular configurations you’ll encounter, how to determine what kind of motor you should purchase, and common hydraulic motor end uses.
Components of Hydraulic Motors
All hydraulic motors use some kind of pressurized fluid (often oil) to create rotational force, although the exact hardware employed will differ from motor to motor. (See the following section for more information.) However, there are a number of common components that virtually all hydraulic motors contain. These are primarily concerned with the hydraulic system itself rather than the motor.
The first element of a hydraulic motor is the reservoir, a container of some kind that holds the fluid which creates hydraulic force. Reservoirs can be either vented or pressurized. Hoses and/or pipes will help deliver the fluid to the appropriate places, while seals discourage leaking.
Other than the reservoir, a pump is the most important part of a hydraulic system. Pumps impart energy to fluid, which can then be used to generate rotational force, and in hydraulic motors, they are powered in some way. Valves direct the flow of the liquid. Accumulators, which include pistons, springs, bladders, and weights, all diffuse shocks. Filters help remove contaminants that could damage or destroy the hydraulic system.
All of these elements are important, but none of them are actually the parts of a motor. That would be the actuators, which turn flow into mechanical energy. We’ll discuss them more down below.
Popular Types of Hydraulic Motors
At their most basic, hydraulic motors use a hydraulic system to force mechanical components to rotate. However, the components themselves and the ways in which they move differ significantly from pump type to pump type. They break down into three main types: vane motors, gear motors, and piston motors.
- Gear motors are probably the easiest type to conceptualize. They contain a pair of interlocked gears, one of which is attached to a rotating shaft. When high-pressure fluid gets pushed into the housing containing the gears, it causes the linked gears to move, generating rotational force. This type of motor is particularly susceptible to wear, and while this is a downside, it also means that gear motors don’t tend to fail in dramatically dangerous ways.
- Gerotor motors are somewhat similar to gear motors. A stator with a certain number of teeth encapsulates a rotor with one fewer tooth, and when fluid flows into the assembly, it forces it to turn. Gerotors excel at generating high starting torque, operating smoothly even at low speeds, and continuing to function even in harsh environments.
- Vane motors direct the flow of fluid into a housing that contains a rotor. That rotor’s end has an arrangement of vanes on it that catch the fluid. The housing is fabricated in such a way that the rotor can only turn in one direction. Additionally, well-designed vane motors must maintain a strong seal so that fluid doesn’t slip past without turning the rotor, but they must also ensure that the vane doesn’t actually touch the housing, which can lead to wear and fatigue. Vane motors come in two primary configurations, namely radial and rolling.
- Piston motors employ pistons that either push inward or outward in order to generate force. Though this sounds relatively simple, piston motors come in many different kinds of designs, all with different benefits and drawbacks.
How to Properly Size a Hydraulic Motor
Sizing a hydraulic motor requires you to know several things about the motor itself and your end use application. Elements you should have knowledge on include:
- Required speed (revolutions per minute)
- Motor power (horsepower)
- Pressure differential (defined as supply pressure minus return pressure)
- Motor displacement (how much fluid the motor needs in order to completely turn the output shaft one time)
- Mechanical efficiency (calculated as a percentage)
- Volumetric efficiency (calculated as a percentage)
With these elements you should be able to calculate the required torque and the motor displacement. Determining how to do so is beyond the scope of this guide, but you can read more about how to perform proper calculations in order to size a hydraulic motor in the industry periodical Power & Motion. However, it’s worth remembering one rule of thumb the article notes, namely that “lower operating pressures result in lower overall efficiencies because of fixed internal rotating losses that are characteristic of any fluid motor.”
What to Look for When Buying a Hydraulic Motor
There are a number of common elements you’ll want to consider when buying a hydraulic motor, which include:
- Size: Make sure to factor in both the weight and physical footprint of the pump prior to purchase.
- Speed: Motor speeds are listed in a range of revolutions per minute (RPMs).
- Viscosity Range: Some motors, such as gear motors, can handle fluids at a range of viscosities, meaning they may continue to operate well at different temperatures. Sometimes this may be noted as operating temperature.
- Operating Pressure: This metric shows the pounds per square inch (PSI) that the motor is designed to operate at and that the hydraulic system must supply.
- Displacement Per Revolution: This metric describes how much fluid gets moved with every revolution of the motor.
- Voltage: How much power is required to successfully operate the pump supplying the hydraulic system
- Fluid Flow: How much fluid moves through the motor over a predetermined period
Applications and Industries
Hydraulic motors have numerous real-world applications. Some of these include:
- Agricultural equipment
- Diesel generators
- Tool and die machines
- Milling and sawing machinery
- Winches
- Band and reciprocating saws
- Wind turbines
- Conveyor and feeder drives
- Cooling fans
- Injection molding machines
- Boring augers
- Snow plow salt spreaders
- Machinery used in mining
- Cranes and excavators
- Textile manufacturing
- Cold steel forming
- Industrial presses
- Clamping hydraulics
- Military and commercial vehicles
- Trommels and kilns
Accessories
Hydraulic motors typically don’t require additional accessories. Instead of purchasing add-ons, most owners of hydraulic motors seek out spare parts, such as:
- Bearings
- General sealing kits
- Motor sealing kits
- Pump mounts
- Adapters
- Quick connectors
- Pump drive hubs
- Gear pumps
- Hose splicers
Keep in mind, many of these spare parts and accessories may be branded for a particular model or type of hydraulic pump.
Tips for Finding and Buying a Hydraulic Motor
When it comes time to purchase a hydraulic motor, you don’t want to buy it from just anywhere. Make sure to buy from a reputable source — one with a tried-and-true history like Surplus Record. Once you’ve determined exactly what kind of hydraulic motor you’d like, you can easily search our listing to find out what’s available.
In addition to our classified listings, we have connections with multiple dealers who specialize in all kinds of different equipment. You can find dealers in your area or by name who specialize in a variety of different kinds of hydraulic motors.
