Hydraulic Motors

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Hydraulic motors are fairly simple machines that are composed of a reservoir, a pump and rotating machinery. A type of oil is usually the pressurized fluid that creates motion by physically pushing the motor, causing the rotating components to turn very quickly, generating mechanical energy because the motor is linked to the machinery and the energy is transferred. There are three kinds of hydraulics motors: gear, vane and piston type. Each is identified by the design of the rotating component inside. Hydraulic motors are able to produce much more power than other motors of the same size and for this reason are used for larger loads than electric motors.  The main enclosure and interior components of the motor are made from metal such as steel or iron so they can withstand high pressures and operating speeds. Hydraulic motors are commonly used in machinery that requires strong pressurized actions such as aircraft for raising the wing flaps, heavy duty construction vehicles such as backhoes or crane industrial lifting or for powering automated manufacturing systems. Hydraulics motors are also used in trenchers, automobiles, construction equipment, drives for marine winches, waste management and recycling processes, wheel motors for military vehicles, self-driven cranes, excavators, forestry, agriculture, conveyor and auger systems, dredging and industrial processing.

Hydraulics is a area of science and engineering that studies the mechanical properties of liquids. Because most fluids are incompressible, a force applied to a fluid in a closed system at one point will be transmitted to another point through the fluid. Hydraulics motors take advantage of this concept and apply it to motors to generate power. Sometimes incorrectly spelled as hydrolic motors, these devices are widely used, especially when combined with reservoirs, pumps and hydraulic cylinders in a hydraulic system. Hydraulic systems are used to power many different machines, especially those used for construction applications. A hydraulic pump motor is composed of three main parts-a reservoir, a pump and a hydraulic cylinder-that work together to convert hydraulic energy into mechanical energy. Another name for this kind of motor that is widely used in hydraulic systems is a hydraulic drive motor. It is so named because the motor is driven by a small pneumatic engine that pumps oil from a reservoir through an inlet valve to an outlet valve through a series of gears, turning vanes or cylinders, depending on what specific type of hydraulic motor it is. When space constrictions are an issue, small hydraulic motors are used. Small hydraulic motors have small stroke lengths; they may be less than an inch.

There are certain modifications that hydraulic motors can have to optimize them for specific applications, conditions or usages. One common kind is the hydraulic gear motor. Fluid is pumped into the gear box at high pressures which rotates the gears, generating energy. Another type is piston type motors. Radial piston hydraulic motors have pistons mounted around a center shaft that is eccentrically balanced. Fluid causes the pistons to move outward, causing rotation. Hydraulic wheel motors are built into wheel hubs to supply the power needed to rotate the wheels and move the vehicle. A hydraulic wheel motor can operate a single wheel or multiple wheels, depending on the power of the motor and the size of the machine. Other motors focus on the rotational speed and torque. High speed hydraulic motors convert hydraulic pressure into force at elevated rotations per minute thereby generating large amounts of power. High torque hydraulic motors run at low speeds while operating with increased torque, thus earning the name low speed-high torque (LSHT) motors. Hydraulic systems require more than the motor itself. A hydraulic power unit pumps fluid from a reservoir and sends it to the motor while regulating fluid temperature. They are an integral part of machines that rely on hydraulic power for operation.

Hydraulic motors are effective because of a simple and well-understood physics concept that humans have studied for thousands of years. French scientist Pascal is generally credited with furthering the understanding of how fluid mechanics works; Pascal's Law is a famous principle that states that "pressure exerted anywhere in a confined fluid is transmitted equally in all directions throughout the fluid." Since that declaration, our understanding of how fluids behave in systems has advanced significantly. Today's hydraulic motors and cylinders perform many important operations that would require much more time, effort and fuel if done another way. Despite the apparent simplicity of hydraulic motors, engineers and manufacturers must take into account certain variables in order to build an efficient and safe device. The fluid used in the motor or system must be a good lubricant, first and foremost. It should also be chemically stable and compatible with the metals inside the motor. The pump, fluid reservoir and relief valves should be of appropriate power, capacity or strength to allow the motor to perform at optimum levels. Advances are still being made to hydraulic motors. Hybrid hydraulic automobiles are being developed as an alternative to gas/electric hybrid cars. Hybrid hydraulic vehicles are particularly efficient at reclaiming energy when braking or slowing down.

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Hydraulic Motor Types

• Axial piston hydraulic motors use pistons along one axis, as opposed to the radial piston motors, which are circular.
  
• High speed hydraulic motors operate with high rotations per minute.
• High torque hydraulic motors have low rotational speeds but produce high torque.
• Hydraulic drive motors are used in systems with cylinders, pumps, valves and other components.
• Hydraulic drum motors are an advanced and highly efficient conveyor drive system in which the motor, transmission and bearings are totally enclosed within the drum shell.
• Hydraulic gear motors have interlocking gears that rotate when acted upon by pressurized hydraulic fluid.
• Hydraulic power units are the pumps that force hydraulic fluid into the motor.
• Hydraulic pump motors are used in systems with cylinders, pumps, valves and other components.
• Hydraulic systems consist of hydraulic motors, cylinders, pumps, valves and other components and are used in equipment and machinery that require strong pressurized actions.
• Hydraulic wheel motors have very few parts. Hydraulic wheel motors can run forward or backward, depending on the direction in which the hydraulic fluid is injected.
• Hydraulics motors convert pressure from hydraulic fluid into mechanical energy.
• Hydraulic vane motors, the most popular general purpose hydraulic motor, consist of spring loaded vanes that are connected to a rotor.
• Hydrolic motors convert pressure from hydraulic fluid into mechanical energy.
• Radial piston hydraulic motors consist of multiple pistons mounted around a center shaft; they are forced outward when fluid fills the volume.
  
• Roller hydraulic motors, a type of orbital hydraulic motor, have rollers that are hydro-dynamically supported to minimize friction, ensuring maximum durability and high output at high pressure.
  
• Rotor hydraulic motors, a type of orbital hydraulic motor, are particularly suited for long working cycles at average pressure. Rotor motors are operated by lobes that are fixed and set directly on the stator.
• Small hydraulic motors have relatively small stroke lengths yet can be as powerful as other kinds of larger motors.

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Hydraulic Motor Terms

Aeration - Air in hydraulic fluid.

Accumulator - A container that stores fluid under pressure. Accumulators, the common types of which are piston, bladder and diaphragm, are used as an energy source or to absorb hydraulic shock.

Cylinder - A device that converts hydraulic energy into linear mechanical motion and force.

Displacement - The amount of fluid that passes through a pump, motor or cylinder in a period of time or during a single actuation event, such as a revolution or stroke.

Dry Friction Coefficient - The degree of friction that results from the contact between the moving surfaces of a motor shaft.

Filter - A device within a hydraulic system that is used to remove contaminants from the oil.

Fluid Power System - A system that utilizes fluid pressure to transmit and control power.

Gear - A toothed wheel used to transfer mechanical energy.

Hydraulics - The science dealing with the transmission of force through the medium of a contained fluid.

Hydraulic Tester - A device that is used to troubleshoot and check hydraulic-powered system components.

Line - A tube, pipe or hose that acts as a conductor of hydraulic fluid.

Oil - A slippery and viscous liquid that is not miscible with water. Oil is often used in hydraulic systems because it cannot be compressed.

Piston - A cylindrical piece of metal that moves up and down inside the cylinder of a hydraulic motor.

Pressure Plate - A plate on the side of a gear or vane pump or motor cartridge that is used to keep clearance and slippage to a minimum.

Pump - A mechanical device that transports liquids and gases by suction or pressure.

Resistance - In hydraulics, the condition engendered by an obstruction or restriction in the flow path.

Shaft - A device that is mechanically attached to the work load and provides rotary motion in motors.

Stroke - The movement of an element of a valve spool, cylinder rod or pump or motor displacement in a straight line that sets the limits of motion.

Throttle - A restriction to the normal flow of fluid.

Torque - The measure of the force applied to produce rotational motion, usually measured in foot-pounds.

Valve - A device that controls fluid flow rate, direction or pressure.

Vane - In a hydraulic motor, a flat surface that rotates and pushes against the fluid.

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