Machinery Lubrication

Machinery Lubrication July-August 2019

Machinery Lubrication magazine published by Noria Corporation

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18 | July - August 2019 | www . e speed of a hydraulic system is determined by the amount of f low delivered. Normally, fl ow controls are used to accomplish this. While many people are aware that a fl ow control or orifi ce will limit the hydraulic fl ow in a system, they may not realize that orifi ce size isn't the only variable that will aff ect the fl ow and therefore the speed of a hydraulic actuator, such as a cylinder or hydraulic motor. ere actually are three variables that aff ect fl ow: the orifi ce size, the pressure diff er- ence between the inlet and outlet of the orifi ce, and the oil temperature. Orifi ce Size e size of the orifi ce is fairly straightforward. e bigger the hole, the more fl ow will pass through it. Many fl ow controls have a variable orifi ce size, so turning the adjust- ment counterclockwise will increase fl ow, while turning it clockwise will close the valve, limiting the fl ow and slowing down the actuator. Pressure Diff erence Whenever a f low control is adjusted so that it limits fl ow, there will always be a pressure drop across the orifi ce. Any restriction of fl ow causes back pressure to build upstream of the valve. e greater the pressure drop, the more fl ow will pass through it. Figure 1 provides a good example of this. Oil Temperature You may notice some machines move more slowly at startup than they do once the oil gets up to temperature. is is to be expected, because the higher the oil tempera- ture, the lower the oil viscosity will be. icker oil cannot move as rapidly through an orifi ce as thinner oil can. Fixed Orifi ce The fixed-orifice f low control (Figure 2) may or may not be a proper component in a machine. By defi nition, it is nothing more than a hole of a specifi c size that cannot be adjusted. It may be simply a drop in Controlling the Speed of a Hydraulic System HYDRAULICS Jack Weeks | GPM Hydraulic Consulting "If speed control is important to your operation, switching to one of these flow controls may help." Figure 1. The higher the upstream pressure reading on gauge A (as compared to gauge B), the harder the fl ow is pushed through the orifi ce. A B

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