Hydraulic Clamping Fundamentals

displacement is so small, and the differential pressure changes so rapidly. While the methodology for calculating flow through an orifice can be tedious, it is well documented in various technical manuals, and will not be elaborated on here. However, because of the nature of clamping systems, to obtain the desired results for an individual system, it is usually preferable to establish orifice sizing by testing in your specific system. An orifice restricts flow in both directions and therefore could possibly inhibit their return performance of single acting devices, due to an increase in back pressure. The orifice is prone to plugging from system contamination. Additional filtration maybe required to proved acceptable performance. Pressure drop is highly dependent on fluid viscosity, which will greatly influence orifice performance. FILTRATION Proper filtration is extremely important to the integrity of a hydraulic system. Contamination can lead to premature device failure, catastrophic device failure, intermittent system problems, degradation of seals, and poor overall system performance. Contamination is not limited to foreign materials such as chips but also from ingress of coolants and water into the system. Water/coolants in the hydraulic system can lead to corrosion, reduced lubrication film thickness, and accelerated metal surface fatigue. Filter is a device whose primary function is the retention of insoluble contaminants in a fluid, by some type of porous medium. A filter’s rating is typically given in microns, which an indication of the size of contamination it will collect. A micron is defined as thirty-nine millionths (.000039) of an inch. For reference, an average grain of table salt is about 100

decoupler and just slightly opening the handle on a pallet decoupler allowing the hydraulic oil to return to the pump’s reservoir). The gage in the system will loose pressure very slowly, until the accumulator pre-charge has been reached, at which point the gage reading will fall to zero almost instantaneously. To achieve reliable performance from an accumulator, the pre-charge of the gas on an accumulator should be in the range of 20% to 75% of maximum hydraulic pressure. The following formula will estimate the oil volume for an accumulator with the Nitrogen stabilized. ( ) ( ) ( ) ( ) 2 1 1 2 1 P v V P V ∗ − = Where: 2 v =Hyd. fluid volume. 1 P = Accumulator pre-charge (PSI) 2 P =Max. hyd. system pres (PSI) 1 V =Accumulator volume. (For VektorFlo®, accumulator 10-1016-XX the oil capacity 1 V is 3.4 cubic inches and for 10- 1014-XX it is 1.2 cubic inches.) ORIFICES An orifice is a device in the hydraulic line with a small hole through it, which restricts the flow of fluid based on the differential pressure (inlet pressure minus the outlet pressure) across the orifice. The larger the differential pressure, the more fluid will pass through the orifice. Due to the compact nature of many hydraulic work-holding actuators, the fluid capacity is relatively small. Because of this small capacity, it is relatively easy to drive these actuators with excessive speed. One way to address this is through the implementation of an orifice. In most work holding devises, the flow through an orifice is often considered constant because the

Hydraulic Clamping Fundamentals Aug 09 Rev - D

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