pinning a valve 1377

pinning a valve 1377

Joined: November 29th, 2009, 9:53 am

April 21st, 2011, 10:32 pm #1

i read a post in the tech section on pinning a valve
how important is it that the pin ia in the center of the tube?
if its a little off what can happen?
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Joined: January 29th, 2002, 1:26 pm

April 22nd, 2011, 1:12 am #2

Not needed so off center should not matter. You can increase the diameter of the grip screw that goes into the valve for more strength. Dave
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Joined: April 1st, 2009, 3:18 am

April 22nd, 2011, 1:37 am #3

i read a post in the tech section on pinning a valve
how important is it that the pin ia in the center of the tube?
if its a little off what can happen?
Yeah, it really isn't needed. With the rear flange and the grip screw, all should be fine.

One reason folks pin the valve is so the striker energy is not absorbed by valve movement forward. In the 1377 the grip frame screw takes care of that. Now, on a 2100, 2200, etc - guns that don't really have anything holding the valve from forward movement except for the transfer port bucking, securing the valve is a huge plus.

On PCP guns, securing the valve (often radially) distributes the load on to the tube evenly due to the very high volume and pressure of air being stored.

"Well, I thought it was a rabbit but it turned out to be Bear Grylls in a rabbit hide."

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Joined: June 5th, 2006, 12:49 am

April 22nd, 2011, 2:57 am #4

"don't really have anything holding the valve from forward movement except for the transfer port bucking"

Forgetting about the pump arm pivot? Most of the striker energy goes into cracking the valve.
And prior to cracking the forwards movement is resisted by the pump linkage.
The reaction force on the pivot pin in idle state is the pressure on the front side of the
check valve multiplied by piston area. This is the force the striker must overcome
to even start the valve body moving forwards.

Extra securing never hurts unless it's positioned badly. If the holes are aligned
so that the screw takes all the piston's force before the rear lip does, then you
could end up with a damaged screw that's hard to remove.
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Joined: November 29th, 2009, 9:53 am

April 22nd, 2011, 4:23 am #5

so as long as the valve is resting on the little stop when i pin it there shouldnt be a problem,right???
what is happening
i adjusted my piston according to the instructions just so the piston hits the valve.it hits just enough to keep the arm closed.after a few sessions i need to adjust the piston again because the arm keeps fallng open and fps drops
i took the aluminum valve out saw some damage to the rear of the valve where it hits the stop.
i figured if i added some retaining screws it would stop the valve from moving like on the pcps or 22xx
i was worried if i didnt get the truly centered the valve would shift somehow
and cause problems
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Joined: April 1st, 2009, 3:18 am

April 22nd, 2011, 4:47 am #6

"don't really have anything holding the valve from forward movement except for the transfer port bucking"

Forgetting about the pump arm pivot? Most of the striker energy goes into cracking the valve.
And prior to cracking the forwards movement is resisted by the pump linkage.
The reaction force on the pivot pin in idle state is the pressure on the front side of the
check valve multiplied by piston area. This is the force the striker must overcome
to even start the valve body moving forwards.

Extra securing never hurts unless it's positioned badly. If the holes are aligned
so that the screw takes all the piston's force before the rear lip does, then you
could end up with a damaged screw that's hard to remove.
...more like the entire series of items, such as (in order) the pump cup, piston rod, lever link, lever, and then the front pivot hole/pin.

I understand the math and simple physics involved fully.

A bit of realism: securing screws are pointless on the 1377, honestly. Rearward movement of the valve is halted by the tube stamping; forward movement is halted by the frame securing screw, and the series of items in front of it. In fact, the 1377 is probably one of the most secure pumpers Crosman has of current, when we speak of valve securing. Bone stock it is just fine. Also, it can be fired when the pump arm is open in a very reliable manner. Other Crosman pumpers are poor performers (2100 et al) when fired with he pump arm open. No real reason to shoot that way, but proves the point.

You are right. Extra securing never hurts but, also remember, it never helps with some units, like the 1377.

"Well, I thought it was a rabbit but it turned out to be Bear Grylls in a rabbit hide."

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Joined: April 1st, 2009, 3:18 am

April 22nd, 2011, 5:01 am #7

so as long as the valve is resting on the little stop when i pin it there shouldnt be a problem,right???
what is happening
i adjusted my piston according to the instructions just so the piston hits the valve.it hits just enough to keep the arm closed.after a few sessions i need to adjust the piston again because the arm keeps fallng open and fps drops
i took the aluminum valve out saw some damage to the rear of the valve where it hits the stop.
i figured if i added some retaining screws it would stop the valve from moving like on the pcps or 22xx
i was worried if i didnt get the truly centered the valve would shift somehow
and cause problems
...is getting dented/messed up, the forward securing hole should be getting damaged too (elongated). I have modded many a 1377 to extremes and never secured the valves. Not needed.

Now, did you inspect the rear of the valve before any modifications have been made? You should have noticed that they tend to be a little indented a bit from factory installation (very slightly there is a visible mark from the tube stamping).

Check the front securing hole too and the tube. If there is damge to the back of the valve, there should be damage to the front area.

What piston do have? Flat top adjustable? Does the piston use nuts to lock the piston in place or at least a set screw? IF noting, it is most likely unscrewing on you as you pump.

"Well, I thought it was a rabbit but it turned out to be Bear Grylls in a rabbit hide."

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Joined: June 5th, 2006, 12:49 am

April 22nd, 2011, 5:08 am #8

so as long as the valve is resting on the little stop when i pin it there shouldnt be a problem,right???
what is happening
i adjusted my piston according to the instructions just so the piston hits the valve.it hits just enough to keep the arm closed.after a few sessions i need to adjust the piston again because the arm keeps fallng open and fps drops
i took the aluminum valve out saw some damage to the rear of the valve where it hits the stop.
i figured if i added some retaining screws it would stop the valve from moving like on the pcps or 22xx
i was worried if i didnt get the truly centered the valve would shift somehow
and cause problems
I've only worked with brass valves, one pumper I hotted up over 20fpe with no extra valve
securing. The pump also held its adjustment over 1000's of strokes, but it has a spring
to keep pressure on the adjustment thread. If you don't have this, or some kind of lock
nut, it will lose its adjustment.

In fact it was the pump pivot holes that gave way in mine, stretching out slowly, so
had to drill them out and replace with a larger, stepped, solid pin. The brass valve
held up OK. Correct, if you're going to pin it, just butt it up against the lip
and match drill the hole(s).
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Joined: June 5th, 2006, 12:49 am

April 22nd, 2011, 5:21 am #9

...more like the entire series of items, such as (in order) the pump cup, piston rod, lever link, lever, and then the front pivot hole/pin.

I understand the math and simple physics involved fully.

A bit of realism: securing screws are pointless on the 1377, honestly. Rearward movement of the valve is halted by the tube stamping; forward movement is halted by the frame securing screw, and the series of items in front of it. In fact, the 1377 is probably one of the most secure pumpers Crosman has of current, when we speak of valve securing. Bone stock it is just fine. Also, it can be fired when the pump arm is open in a very reliable manner. Other Crosman pumpers are poor performers (2100 et al) when fired with he pump arm open. No real reason to shoot that way, but proves the point.

You are right. Extra securing never hurts but, also remember, it never helps with some units, like the 1377.

"Well, I thought it was a rabbit but it turned out to be Bear Grylls in a rabbit hide."

Because it's the only part that transfers reaction force from the tube.
Also take into account that the securing screw and metal transfer seal have a bit of clearance
around them, allowing movement. I wonder how much a pumper's velocity loss from firing with
the arm open is attributed to this. Sounds like a good experiment.
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Joined: September 6th, 2006, 3:27 am

April 22nd, 2011, 3:44 pm #10

I have seen the valve get pushed backward, significantly, particularly if using a high number of pump strokes.

The cure was to add set screws through the tube and into the valve to keep it in place.
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