Machinery Lubrication

Machinery Lubrication March April 2016

Machinery Lubrication magazine published by Noria Corporation

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20 | March - April 2016 | By al an Dellinger, gPM hyDraulic consulting Hydrostatic drives are used in a variety of applications throughout all types of indus- tries. They are sometimes referred to as hydrostatic transmissions. Anytime one or more hydraulic motors need to be driven at variable speeds with bi-directional cap ability, a hydrostatic drive is often used. Common applications include conveyors, log cranes, mobile equipment, centrifuges, chemi-washers and planers. Hydrostatic drives are some of the least understood systems because many of the components are located on or inside the hydrostatic pump assembly. A schematic of a typical hydrostatic drive is shown in Figure 1. The bi-direc- tional, variable displacement pump controls the direction and speed of the hydraulic motor. This type of drive is commonly called a closed-loop system. Notice how the pump's two ports are hydraulically connected to the two ports on the motor, forming the closed loop. Main Pump A piston-type pump is always used in a hydrostatic system. The pump volume can range from zero to the maximum amount. In Figure 2, the pump swashplate is in the vertical position, which means the pump output is zero gallons per minute (GPM). HYDRAULICS Hydrostatic Troubleshooting Understanding and Systems Figure 1. A typical hydrostatic drive

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