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PostPosted: Wed Jan 25, 2017 12:50 pm 
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Joined: Tue Jun 03, 2008 5:46 pm
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Location: Canada
Had the P17 out and tinkering with it a little bit. Decided to measure the force required to close the lever with the bathroom scale...using this to calculate the approximate valve chamber pressure.

Was a little surprised to see the bathroom scale top out at 25 lbs. This equates out to ~132 psi...which isn't much. Will check it with a chrony later, but wondering if anyone else who has a stock piston P17 would mind doing the same test and reporting the results??

If you've got a modified piston and don't mind doing the test, that data is welcome too. Just let me know you've a modified piston. :wink:

TIA,

Al


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PostPosted: Wed Jan 25, 2017 8:44 pm 
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Location: SW Ontario
Al, I'm no physics major, but I don't think the force measured for closing the lever translates directly to pressure in the compression chamber due to vectors of force and leverage (mechanical advantage) on the cocking arm. Or are you doing the calculations that would account for that. To get a direct correlation you would have to compress the piston straight down on the bathroom scale which means you would likely have to really lean into it. Maybe I'm way off here . . . ?


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PostPosted: Wed Jan 25, 2017 8:56 pm 
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Haven't been a physics major in some 30 years myself. :lol: It's class 2 lever with no linkage...it should be pretty straight forward...but I've been wrong before. :lol:

Suppose I could tear it down and replicate the test without the lever...... :rolleyes:

Al


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PostPosted: Wed Jan 25, 2017 9:00 pm 
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Joined: Sat Nov 26, 2011 9:35 am
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Location: Eastern Ontario
Hi Al,

If you are trying to calculate the pressure just divide the volume of the cylinder by the
volume of the pressure chamber. (Cylinder volume - Swept volume)
Use this value and multiply by your local atmospheric pressure (14.7 should be close enough).

Hope this helps.
Grunt


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PostPosted: Fri Jan 27, 2017 11:49 am 
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Gippeto wrote:
wondering if anyone else who has a stock piston P17 would mind doing the same test and reporting the results??

Just tried to see what mine sits at using your method with a bathroom scale - and well, no bathroom scale needed: cocking the P17 presented almost no pressure at all to close it. Suppose not having used it in months may be the reason. Looks like a case of dry seals. If you can tell me where to add pellgun to I'd like to try that to see if it seals properly (don't think I've ever lubed this thing). Then will try measuring it with the scale once (hopefully) things are back to normal.

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PostPosted: Fri Jan 27, 2017 4:23 pm 
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Would normally pull the piston out and use a little white lithium based grease.

Putting some oil on the piston itself when at full "draw" and then working it in should accomplish something.

Al


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