Pneumatic flow control valve problem

I have a flow control valve like this: http://www.grainger.com/Grainger/PARKER-Air-Flow-Control-Valve-4A789?Pid=search It controls the speed of a 2x10 cylinder and the movement of the cylinder
and mechanism is making the adjustment knob move so the cylinder gets faster and faster. It does have a set screw that will lock the adjustment knob but the operator needs to change it often and during the stroke. Is there a simple way to stiffen the knob without locking it? (Yes, I could get a new one.)
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Can you take the knob off and stick some O rings, felt washer, rubber washer or simlar on the shaft and then refit the knob? Maybe a stack of thin BeCu wave washers + flat washers?
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wrote:

You're looking for a way to stiffen your knob? (allright get my mind outa the gutter)
How about a large custom wingnut at the base. Losen wingnut, adjust, tighten wingnut. McMaster sells several or make your own.
Karl
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Tom Gardner wrote:

I'm guessing the knob has very little friction and turns easily.
You could put a stiff compression spring under the knob to add some friction. There may be a packing nut under the knob that can be tightened which will also add friction.
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Tom Gardner:

Tom, why not add a leaf spring with a rib that engages the straight knurl on the knob? That's the traditional way of keeping carburetor needle valves from creeping.
Lloyd
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Tom Gardner wrote:

Remove the knob and install a lever that the operator can just slide back and forth to adjust? Or maybe take the knob off, drill through the setscrew hole to create a second hole on the other side, then install a couple nylon setscrews that you can tighten down so it is stiffer. Or pull the knob off and see what they use to keep the valve from leaking through the stem, if it is set up like some are you can probably tighten it some there.
--
Steve W.

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Tom Gardner wrote:

Other folks have suggested ways to stop the knob from drifting, but I have to ask - If the operator has to constantly adjust the speed setting for this cylinder, could the whole mechanism use some redesign so that intervention isn't required?
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On Wed, 07 Mar 2012 02:40:18 -0500, Tom Gardner wrote:

Pid=search
If the suggestion to straight-knurl and spring-keep the knob doesn't float your boat, how about making a splined shaft and dog clutch arrangement, so the operator pulls the knob to disengage the clutch, turns it, then lets go to let it settle back onto the clutch.
It's way more work than a knurl and a spring, but it's way more positive, too.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
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wrote:

Can you live with two-speed rather than variable speed? Plumb in a parallel circuit with another adjustable valve and a quarter-turn ball valve. With the new circuit closed, adjust for low speed. With it open, adjust for high speed. Lock both adjustable valves in place. The only moving part would then be the ball valve.
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"Tom Gardner" wrote in message

1. Why not re-plumb the valve to a location that does not vibrate and possibly is more convenient to the operator?
2. check out http://www.mcmaster.com/#3408a667 Ball-Nose Spring Plunger as a replacement set screw
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A knob that is part of a threaded stem/fastener.. not enuff information.
Blue Loctite?
--
WB
.........


"Tom Gardner" < snipped-for-privacy@gmail.com> wrote in message
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wrote:

Tom, Description claims there is a setscrew to lock the knob in position.. .. Simply replace the set screw with a "friction" setscrew - one which has a spring and a brass/nylon plug in the end of it to apply tension. After it has been adjusted for the proper "tension" - only a slight change once in a while should be needed due to wear of the nylon/brass insert. Ken Sterling
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"Ken Sterling" wrote in message
wrote:

Tom, Description claims there is a setscrew to lock the knob in position.. .. Simply replace the set screw with a "friction" setscrew - one which has a spring and a brass/nylon plug in the end of it to apply tension. After it has been adjusted for the proper "tension" - only a slight change once in a while should be needed due to wear of the nylon/brass insert. Ken Sterling ________________________________
I'll try that! If there are enough threads it will be a good solution!
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