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Unread 30-03-2011, 00:23
Roboman01 Roboman01 is offline
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Re: Solution: Variable position of cylinder in compliance with <R74>

Quote:
Originally Posted by PAR_WIG1350 View Post
The requirement to hold the piston in place doesn't change as the piston moves along the cylinder, stopping it half way is the same as stopping it one third of the way out. The sum of the forces must be 0 to maintain constant motion or to stay at rest. If the regulator is set at a constant setting that balances the forces resulting from the pressure pushing against the 2 surfaces of the piston, which have different areas, then friction will quickly bring the cylinder to a stop and keep it there. The accuracy of such a system decreases with momentum.

You seem to be confusing volume or surface area of the inside of the cylinder with force exerted on the piston. The force exerted on the piston is what matters, the other two are irrelevant.
According to the schematic symbol, it would appear that the two cylinder ports are tied together, and pressure is applied. Wouldn't this cause the cylinder to creep back to a position around the midpoint? In any case, it would appear that using a center-pressure valve for this application is not generally accepted in industry, according to the Norgren Valve Guide. From page 225, section 3: "3. 3-POSITION - Inlet Open to Cylinder Ports
a) Equal pressure supplied to both sides of the piston creates an
unequal force, due to rod area differential, which causes the
cylinders to extend. Many times a regulator will be installed in
the blind end cylinder line to drop the blind end pressure and
equalize the force (we all know this would be an improper
application of a regulator). The application of full-line pressure
to this regulator during normal cylinder cycling leads to
premature regulator failures.
b) Cannot be used to support vertical loads."

It would appear that is causes unnecessary and undesirable strain on the components.
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