1377 check valve

1377 check valve

Joined: February 23rd, 2010, 10:28 pm

December 14th, 2011, 2:27 pm #1

Could someone explain to me the mechanics of the check valve in the 1377 (and other similar Crosman guns)? Is it simply the pressure of the pump stroke overcoming the spring force and blowing air through the inlet, pushing a "seat" open to fill the valve cavity?

Thanks,
Chris S.
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Joined: November 28th, 2002, 6:26 pm

December 14th, 2011, 3:10 pm #2

...two things about the pressure required to open the checkvalve.

1. It's often surprisingly large - 100psi to 200psi.
2. It's permanently subtracted from the pressure developed by the pump before air begins to flow into the valve accumulation volume.

In other words, in order to accumulate air at Xpsi, the pump must generate something like X + 200psi, which adds to the effort of pumping and decreases pump volumetric efficiency.

http://www.network54.com/Forum/275684/m ... heck+valve.

This is why mod's that reduce excess checkvalve closing force (as posted above) are useful in improving both ease of pumping and power.

Steve
Last edited by pneuguy on December 14th, 2011, 3:11 pm, edited 1 time in total.
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Joined: March 1st, 2002, 12:22 am

December 14th, 2011, 4:02 pm #3


Oh man, how did I miss that all this time.....

And thats true of all pumpers using a check valve setup, I suppose..... oh man.....

hmmmmm, so now th eissue is how to get the 1377 valve to allow an ICV setup......

lost, yikes. Now I'm depressed......

 


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Joined: November 28th, 2002, 6:26 pm

December 14th, 2011, 4:09 pm #4

...at the inlet per-se, but the pressure differential across the valve. Consequently, the pressure at the pump piston must always be that much higher than the pressure accumulated in the valve volume.

And because, to save a few pennies, Crosman uses the same spring to close both valves, that pressure differential is a biggy - usually subtracting more than one whole pump stroke worth of PSI, headspace loss, and pumping effort.

Steve
Last edited by pneuguy on December 14th, 2011, 4:10 pm, edited 1 time in total.
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Joined: March 1st, 2002, 12:22 am

December 14th, 2011, 4:15 pm #5


for flattop valves an piston, and the ICV.

1 full pump, like from 10.... yikes thats 10% loss just to crack the valve.

oy.... the 1377 valve doenst have the shelf like the 39x valve do to hang the ICV hardware on. Soooo... drill out the valve the create the shelf from the valve body,or drop a small it of tube in.......

And I'm going to suppose that the size and shape of the check valve itself has little bearing on the opening forces required.....


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Last edited by dan_house on December 14th, 2011, 4:21 pm, edited 1 time in total.
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Joined: February 23rd, 2010, 10:28 pm

December 14th, 2011, 4:51 pm #6

...two things about the pressure required to open the checkvalve.

1. It's often surprisingly large - 100psi to 200psi.
2. It's permanently subtracted from the pressure developed by the pump before air begins to flow into the valve accumulation volume.

In other words, in order to accumulate air at Xpsi, the pump must generate something like X + 200psi, which adds to the effort of pumping and decreases pump volumetric efficiency.

http://www.network54.com/Forum/275684/m ... heck+valve.

This is why mod's that reduce excess checkvalve closing force (as posted above) are useful in improving both ease of pumping and power.

Steve
Thanks Steve. Good to know my engineering degree hasn't gone to waste. I didn't want to disassemble my 1377 to prove my theory. But I really appreciate the link. Looks like I'm going to disassemble anyways!
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Joined: March 1st, 2002, 12:22 am

December 14th, 2011, 5:07 pm #7

if ya come up with any

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Joined: February 23rd, 2010, 10:28 pm

December 14th, 2011, 7:24 pm #8

I'm presently studying the flow with a CFD software. If anyone has a spare valve to send me (at this point I'm not wanting to take apart mine) to take dimensions off of or has said dimensions for each of the components I will tweak my model and re-run the analyses.

Without re-designing the valve with two separate springs to reduce the stroke force I don't believe that changing the existing style of the valve cone is going to do much of anything. But if I come up with anything I will post.

Chris S.
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Joined: June 13th, 2008, 2:52 am

December 14th, 2011, 7:39 pm #9

Typical engineer, not wanting to get his hands dirty :P It shouldnt take more than a few minutes to take apart your gun/valve and get measurements. You can make a washer type device to seperate the two springs that sits between the valve halfs. Personally, I just use a cut down stock spring with only a mm or so of preload so that it is loose in the valve untill about a turn and a half before you get the valve closed. Minimal force for the check valve to overcome but more than enough to resist the hammer when shot. Has desiarable effects for the air metering capabilities of the valve as well (good for ACP)

PS I only kid about getting your hands dirty, im a very soon to be engineer myself. I just see a lot of my peers who get too caught up in math and dont spend enough time doing real world testing. I wouldnt be busting out NX to do analysis for these valves its about as simple as they get. You will see for yourself when you open one

-Mike

Edit: Forgot to mention that once there is any pressure in the valve a significant ammount of the force required to open the check valve is from the air in the valve. The area of the face on the valve interior is larger than that on the pump side, so the pump must have very little head space so that it can develope much more pressure than that inside the valve to get most of the pump volume into it
Last edited by 2289hunter on December 14th, 2011, 7:46 pm, edited 1 time in total.
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Joined: September 23rd, 2002, 6:16 pm

December 14th, 2011, 8:45 pm #10

Typical engineer, not wanting to get his hands dirty :P It shouldnt take more than a few minutes to take apart your gun/valve and get measurements. You can make a washer type device to seperate the two springs that sits between the valve halfs. Personally, I just use a cut down stock spring with only a mm or so of preload so that it is loose in the valve untill about a turn and a half before you get the valve closed.


Minimal force for the check valve to overcome but more than enough to resist the hammer when shot.

comment: " what pray tell do you mean by this?" the check valve doesn't overcome anything and the hammer could care less about resistance from the weakened valve spring.


Has desiarable effects for the air metering capabilities of the valve as well (good for ACP)

PS I only kid about getting your hands dirty, im a very soon to be engineer myself. I just see a lot of my peers who get too caught up in math and dont spend enough time doing real world testing. I wouldnt be busting out NX to do analysis for these valves its about as simple as they get. You will see for yourself when you open one

-Mike

Edit: Forgot to mention that once there is any pressure in the valve a significant ammount of the force required to open the check valve is from the air in the valve. The area of the face on the valve interior is larger than that on the pump side, so the pump must have very little head space so that it can develope much more pressure than that inside the valve to get most of the pump volume into it

comment: I don't know where to begin on this last paragraph.

The check valve opens ONLY due to adequate differential pressure across it.
The area on the inside is bigger than on te outside? say what?
The pump must only develop more than the final valve pressure plus check valve cracking pressure
If the pump can do that and have a volume of air at that pressure to add to the valve volume then vlave pressure will increase.

Walter....

Engineers.....


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