Hydraulic Motor

A vane motor consists of a housing with an eccentric bore, in which runs a rotor with vanes in it that slide in and out. The force differential created by the unbalanced force of the pressurized fluid on the vanes causes the rotor to spin in one direction. A critical element in vane motor design is how the vane tips are machined at the contact point between vane tip and motor housing. Several types of "lip" designs are used, and the main objective is to provide a tight seal between the inside of the motor housing and the vane, and at the same time to minimize wear and metal-to-metal contact.

A gear motor (external gear) consists of two gears, the driven gear (attached to the output shaft by way of a key, etc.) and the idler gear. High pressure oil is ported into one side of the gears, where it flows around the periphery of the gears, between the gear tips and the wall housings in which it resides, to the outlet port. The gears mesh, not allowing the oil from the outlet side to flow back to the inlet side. For lubrication, the gear motor uses a small amount of oil from the pressurized side of the gears, bleeds this through the (typically) hydrodynamic bearings, and vents the same oil either to the low pressure side of the gears, or through a dedicated drain port on the motor housing, which is usually connected to a line that vents the motor's case pressure to the system's reservoir. An especially positive attribute of the gear motor is that catastrophic breakdown is less common than in most other types of hydraulic motors. This is because the gears gradually wear down the housing and/or main bushings, reducing the volumetric efficiency of the motor gradually until it is all but useless. This often happens long before wear causes the unit to seize or break down.Gear motors can be supplied as single or double-directional based on their usage, and they are preferred in either aluminum or cast iron bodies, depending on application conditions. They offer design options that can handle radial loads. Additionally, alternative configurations include pressure relief valve, anti-cavitation valve, and speed sensor to meet specific application needs.

The gerotor motor is in essence a rotor with n − 1 teeth, rotating off center in a rotor/stator with n teeth. Pressurized fluid is guided into the assembly using a (usually) axially placed plate-type distributor valve. Several different designs exist, such as the Geroller (internal or external rollers) and Nichols motors. Typically, the Gerotor motors are low-to-medium speed and medium-to-high torque.

For high quality rotating drive systems plunger motors are generally used. Whereas the speed of hydraulic pumps range from 1200 to 1800 rpm, the machinery to be driven by the motor often requires a much lower speed. This means that when an axial plunger motor (swept volume maximum 2 litres) is used, a gearbox is usually needed. For a continuously adjustable swept volume, axial piston motors are used. Like piston (reciprocating) type pumps, the most common design of the piston type of motor is the axial. This type of motor is the most commonly used in hydraulic systems. These motors are, like their pump counterparts, available in both variable and fixed displacement designs. Typical usable (within acceptable efficiency) rotational speeds range from below 50 rpm to above 14000 rpm. Efficiencies and minimum/maximum rotational speeds are highly dependent on the design of the rotating group, and many different types are in use.

The crankshaft type with a single cam and the pistons pushing inwards is basically an old design but is one which has extremely high starting torque characteristics. They are available in displacements from 40 cc/rev up to about 50 litres/rev but can sometimes be limited in power output. Crankshaft type radial piston motors are capable of running at "creep" speeds and some can run seamlessly up to 1500 rpm whilst offering virtually constant output torque characteristics. This makes them still the most versatile design. Multi-lobe cam ring types (e.g. Black Bruin, Rexroth, Hägglunds Drives, Poclain, Rotary Power or Eaton Hydre-MAC type) have a cam ring with multiple lobes and the piston rollers push outward against the cam ring.

Regularly sample your oil for undesirable contaminants such as water, as it can help prevent the need for costly repairs in the future. Contamination is one of the main reasons why the hydraulic system can leak. As a result of the leakage, the hydraulic pumps can be blocked or accelerate the wear rate. Take your oil for testing from a specific sample point to ensure consistency in measurement. Ideally, you are advised to take a sample from an active return line because testing from a stagnant source like a reservoir drain can result in inaccurate results.

A hydraulic filter indicator monitors the contamination caught by the filter. It displays the contamination level electrically, visually(using a pop-up indicator or a gauge), or both methods. Consider replacing the filter when the indicator reads that it has reached its maximum acceptable contamination holding capacity. If left unmonitored, the filter can start leaking bypass fluid (if your hydraulic system was fitted with a bypass valve), making it vulnerable to more contamination. Check that the gauge style indicator is working correctly, or check the indicator with cold oil for an early warning.

If the performance level of your hydraulic system is slowly decreasing, it could be a result of being used for a more extended period without proper maintenance. Swiftly declining performance can be a precursor for catastrophic hydraulic system failure. Closely monitor your system’s oil and temperature levels, actuator speed, and case drain flow to predict failure in one of the systems. This will help prevent expensive repairs of the failed parts in the future.

Temperature levels on your hydraulic system can adversely affect your oil’s viscosity. If your oil is above the normal working range of the system’s components, it can reduce its lifespan. For example, high viscosity can result in a temperature drop in the suction lines leading to cavitation. On the other hand, low viscosity reduces the thickness of the film’s consistency between the components, resulting in wear and tear.

Knowing how to clean hydraulic motor parts is very important if you want yours to last long. Grime and dirt are generally harmless on the exterior of your equipment. However, it puts the internal parts at risk of being contaminated. Contaminants can enter the system when the hydraulic components are disconnected for relocation or maintenance during an oil change or replacing the filter system.