Hydraulic Clamping Fundamentals

LINE SIZING It is recommended that the flow through the lines be in the Laminar region. To keep flow in the laminar region requires a Reynolds number of 2000 or less. Flows in 2000 to 4000 range are transitional, and above 4000 are turbulent. Transitional and turbulent flows generate higher back pressures and may interfere with sequence valve, PRV and PLV function, therefore should be avoided when ever possible.

microns in size; a human hair about 70, and talcum powder is about 10. The most common filtration recommendation for hydraulic clamping system is 10 - 25 microns, which will filter such things as grit, fines, and sludge. However, to stop contaminants such as chips from traveling in a system, a micron rating of up to 180 (0.0070”) has proven adequate. Screen (mesh) is a coarse strainer element that stops larger contaminants from moving down stream, but typically may not retain them. Screens are rated by U.S. Sieve No. instead of microns. While these two ratings are not the same, they can be compared as to the size of contaminates they will collect. For example, (from the “Lightning Reference Handbook, 8 th Edition © Copyright 1990 published by Berendsen Fluid Power, Tulsa, Ok) a screen with a Sieve number of 50 has an approximate micron equivalent of 297 (0.0117” particulate); Sieve 140 is approximately 105 micron (0.0041” particulate); and Sieve 325 in approximately 44 micron (0.0017” particulate). While a screen with a Sieve No. of 100 (0.0059” particulate) should adequately stop chips and debris from traveling in your system; the screen should not be considered a replacement for a primary filter element. FLOW REQUIREMENT: Determine the time in seconds (T) allows for clamping. (Verify that this in the operating ranges of the devices) Pick the devices required for fixturing application. Determine displacement in cubic inches for each device. (Including volume of oil in the accumulator and flex hose if applicable). Add the displacement for the devices together (Dt).

d μ 3162 Where: Nr = Reynolds number Q = Flow rate, GPM Q N r × × =

μ =Viscosity in Centistokes, 132 for ISO 32 Hyd. fluid. d = Inside diameter of line in inches.

Velocity is the next consideration. For double acting only systems, this can be as high as 33 FT/Sec. For systems containing single acting actuators, this should be limited to 10 FT/Sec.

= 320833 .





Where:A= cross sectional area = .785 2 d × V=Velocity in Ft/Sec.

CIRCUIT DESIGN Before the hydraulic circuit can be designed, the following things must be defined: The type and number of each type of hydraulic actuator to be used on fixture. The oil capacity of each actuator. (In cubic inches)

= D GPM t (231CIM = 1 GPM = 3.85 CIS) T

231 60


To determine required flow:


Hydraulic Clamping Fundamentals Aug 09 Rev - D

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