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What Hump?
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I was hooking up all of our pneumatic props tonight and I ran into an issue:

On one of my props, with a four-bar lifter mechanism, I'm using speed control mufflers, from Fright Props, on both exhaust ports.

On the B exhaust port, the one that exhausts the air on the prop's way back down...it will occasionally continue to leak air after the cylinder has fully retracted. If I loosen up the speed control muffler to let more air pass, it will stop.

I don't think it's a problem with the muffler, I think it might be that, with the airflow attenuated on that exhaust port, there's not enough airflow for the port to close completely. But I'm no expert, yet.

Has anyone experienced this?

How do I correct the issue?

I hope I've explained it clearly enough to understand.
 

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it might be your air cylinder allowing air past the piston gasket. I would try adding a couple of drops of air tool oil to your cylinder.
 

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BAD INFLUENCE
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What is the pressure you are operating the cylinder ? It may be a little bit on the low side and not fully shifting the spool in the solenoid. Try increasing the air pressure a bit.
 

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If the prop has enough weight to retract on it's own, you could just plug the unused output port of the solenoid and adjust the speed control muffler accordingly.
 

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The potential problem with increasing the PSI is that it will affect the "up" stroke of your lifter unless you have separate regulators on the lines.
 

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That's what the speed control mufflers are for.
I guess it depends on the prop. For a prop that you want to "pop" into full extension quickly, I don't use a speed control. I adjust the regulator for the proper working pressure. If he's already at 70 PSI, that's pretty high.
 
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