Hydraulic drive systems are designed to run machinery with the use of a working fluid to deliver usable power. After the hydraulic fluid is pressurized, it is run to a device to convert that energy into a usable form to perform work. Hydraulic pump motors come in two wide flavors, rotary and linear. Rotary models run cyclical machinery and linear cylinders deliver a mechanical power stroke. Utilizing the energy stored in the work fluid with maximum efficiency is the job of design and process engineers. By examining the different models, we can pinpoint applications for each design style.
Rotary Hydraulic Pump Motors
These motors are used to generate torque and rotation. This type often resembles the pumps that are utilized upstream in a drive system, only in reverse. Where the initial pump ran a cyclical process to produce pressure, the pressure in the motor pushes a cyclical process.
Gear motors can run any machine that utilizes gear action to run a process. The high pressure fluid runs over a gear, turning it, then into a drain outlet. A second gear is turned by the first while not having to actually contact the working liquid. This motor type is very simple and effective.
Vane motors run by having a pair of offset, concentric cylinders. They operate by filling an empty space with the high pressure fluid that causes the outer cylinder to go off balance and rotate. This drives the central cylinder, expels the spent fluid, and allows fresh pressurized liquid to enter the chamber. Like gear motors above, they are low maintenance models best suited for high RPM applications.
Axial plunger motors are the most common type. Cylinders are pressurized in a cycle to create an alternating plunger motion that is regulated with a gearbox to a set RPM. This model is very adaptable and sees use in many different applications.
For very low RPM requirements and a high initial torque, a radial piston motor is used. This arrangement has a set of pistons arranged in a ring around a central chamber where the working fluid drives the cylinders in turn.
Linear Hydraulic Pump Motors
To deliver mechanical force in a linear stroke, a hydraulic cylinder is used. The working fluid acts on a piston to provide a controlled power stroke. These are often seen in large mechanical systems, such as construction vehicles, rather than in process equipment like pumps or conveyor systems. The science behind this setup allows a pressurized fluid to act on a large surface area, thereby amplifying the force originally generated by the hydraulic pump. The cylinder barrel is separated into two parts, the piston and the head. Pressurized fluid only runs through the piston, where work is transferred to the head via a rod.
Hydraulic pump motors showcase the versatility of the entire drive system. The same working fluid can be used to generate force in a line or as a rotation in either high or low RPMs, and with enough force or torque to move heavy equipment. The wide variety of uses is complemented by the many different motor types, allowing a design engineer to tailor fit a system to a particular job.
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