Too much pressure in a Disco? Will you become a statistic?

[lloyd-ss]

Manny,
You asked a simple yes-no question but go ahead and read through this whole answer.  Your daughter will be glad you did.

If Norm did the work of installing the 10-32 screws, you are ok in that department, but  you should do a visual inspection of the gun to help ease your mind.
This visual inspection procedure can be used for the special 10-32 screws like I assume you have, and for folks who have the factory 8-32 screws, even if they never accidentally overfill their Disco.

For this first part of the inspection leave the air in the gun.  Make sure the gun isn't cocked.  Remove the action from the stock.  Remove the trigger assembly. 

There will be 3 screws located 90 degrees apart, located underneath the breech, that secure the valve into the main air tube.   Here's a good picture of the 3 special high strength low profile socket head cap screws that we are referring to as the 10-32 screws.   
SAFETY NOTE TO EVERYONE- If your gun only has the standard Crosman 8-32 Phillips head screws, never ever ever fill your Disco above the recommended 2000 psi max fill.  The 8-32 screws are the limiting mechanical factor in the fill pressure.  This picture shows the special 10-32 screws that many people use to increase the safety factor in the Disco.
Find these 3 screws and look at them very carefully in good light.



With the air still in the gun, look very carefully at the 3 screws.  You will notice that the screws will be pushed all the way to the back edge of the holes (toward the rear of the gun) because the air pressure is always  trying to push the valve out the rear of the air tube.  Look carefully at the tube where the screws are pushing on it. Look for any bulged or puckered up areas where the metal in the tube has distorted.  This picture, and the next picture show the tiniest bit of distortion in the tube from the screw bearing hard against it.  (BTW, these are test pieces that I made to do valve screw failure testing.)


Here is the same tube and you can see the distortion more clearly.  If you see this with the factory Phillips head screws, you've got serious trouble.  If you have the 10-32 screws and have been filling to 3,000 psi, you might see this distortion at ONE screw only.  The reason is because the holes in the valve and the holes in the tube aren't normally going to line up perfectly, and some movement is going to occur as the 3 screws settle in to the point that they all bear an equal portion of the load.  Again, if you see a tiny bit of distortion on only one 10-32 screw, you are ok.  If you see it on all 3 screws, bad news.
   


Here is a picture of a test piece made from a factory tube that was severely overloaded.  If you see this, again, you've got big trouble.


Here is an A513 Type 5 steel tube (commonly used)  that was overloaded even more than the previous factory tube.  All of the components have yielded and the actual failure pressure was higher than predicted because of the way ALL components are sharing the overload.


Here is the screw removed from the severely overloaded tube.  The tube and valve body, and screw were all distorted and the screw was extremely difficult to remove.  Failure can be a multistage process with the weak points changing between the various components until you get a big ka-pow.


So what do you do if you see some distortion and have some concerns?

Again, this is good for the factory screws and the 10-32 special screws.  First off, go ahead and put the trigger assy back on the gun and shoot all the air out.  Make sure the gun is totally empty.  Take the trigger back off.  Try removing the valve screw that shows the most distortion.  Once it breaks loose, how does it unscrew? Does it come out smoothly, or does it feel bent?  If it feels bent, look at the screw and the threaded hole. How bad are they?   Screws that are constantly overloaded, or that are removed and tightened often, can have a short life and it is not a bad idea to periodically replace  them.  If it seems like something is wrong, don't take a chance.  Fix the problem.  Safety has to be number one.

Lloyd

[MichaelM]

that's an excellent post Lloyd good descriptions and pics!!!

[Ribbonstone]

Come on...I can get one more use out of this screw, it ain't broke yet.

(OK...I cheated and it's a scope mount screw...but you get the idea.)

[Nomadic Pirate]

I was gonna check my daughter's disco, but can't get the stock off because the safety button is in the way, how do you get that trigger unit off ? I just can't see the way.

[UCChris]

I was gonna check my daughter's disco, but can't get the stock off because the safety button is in the way, how do you get that trigger unit off ? I just can't see the way.

Take a jewelers screwdriver and pull the small metal bar that is behind the safety. Then the safety button will slide out. Then take off the stock and remove the rear bolt and stock lug that is holding the trigger unit on. Careful to not crank down on the stock lug when tightening back up. They are notorious for stripping.

[Nomadic Pirate]

Did it.

Everything looks perfect on this gun, no metal imperfections, ....while I was there I cranked up the power adjuster to max,
....Maybe a .177 Hog hunt in the future ?

[wll2506]

Great post, I don't think I've had my Disco to 1900psi, and have only had about 10 fills, if that. Put a RVA in it and clipped the spring and played with it a bit, and she is shooting pretty good :- )

I will change the screws to a better quality 8x32, and after reading your post, may well rethink my up to 2100 psi plans.

Thanks Lloyd !

wll

[lloyd-ss]

Great! Sounds like everyone is on the safe track.

[campinman7]

Quick question about pressure ..... After your done shooting should you remove all pressure from gun?

Does that matter?

Thanks

[UCChris]

Quick question about pressure ..... After your done shooting should you remove all pressure from gun?

Does that matter?

Thanks

Leaving pressure in the gun is fine. In fact, depressurizing the gun can be harmful simply because the pressurized gun keeps particulates out of the system for the most part.

[campinman7]

Cool thanks for the info!

Lance

[wll2506]

Just fixed the valve body and installed 10x32's the hole I thought was bad was the air hole, so I drilled and tapped the correct one.

Major question ..... I can't seem to get answered !!!!!! My 3 drill holes go through into the poppet hole ... is that bad ? The 1/4" 10x32 fits tight and the poppet moves freely still.

http://s20.postimg.org/3zjlxpsal/10x32_in_Valve_smx.jpg

wll

[rsterne]

I don't think you will have a problem with the holes going through into the hole for the stem.... If it leaks, it will only do so during the shot.... Normally, you would shorten the 10-32 screws to 3/16".... I use blind holes and a bottoming tap....

Bob

[wll2506]

I don't think you will have a problem with the holes going through into the hole for the stem.... If it leaks, it will only do so during the shot.... Normally, you would shorten the 10-32 screws to 3/16".... I use blind holes and a bottoming tap....

Bob

Bob, thank you, I was worried about it blowing the screw out. I will add a touch of blue Locktite also just to make sure the air does not loosen the screw. This was my first try at this valve and I thought I measured right ?,  the starting tap may have pushed through, I should have just given it a few twist and then used a bottom tap, better yet I should have ground off the tip of the starting tap to begin with, and then gone to a bottom tap.

Thank you Bob.

[lloyd-ss]

William,
the blue Loctite is a good idea when you break thru into the valve.  You can do a few test shots before installing the action back into the stock and feel if there is excessive air coming out around the screws when the gun is fired. Like Bob said, it shouldn't be a problem.  I know a few people who, when modifying a Disco valve for high power, and drilling out the throat and installing the high strength 10-32 screws, just go ahead and drill thru into the exhaust port area rather than go to the extra trouble of not breaking thru.  They can also use a little longer screw that way, and they just plan on using the gel type blue loctite to take care of the sealing.  It works.
Lloyd

[wll2506]

William,
the blue Loctite is a good idea when you break thru into the valve.  You can do a few test shots before installing the action back into the stock and feel if there is excessive air coming out around the screws when the gun is fired. Like Bob said, it shouldn't be a problem.  I know a few people who, when modifying a Disco valve for high power, and drilling out the throat and installing the high strength 10-32 screws, just go ahead and drill thru into the exhaust port area rather than go to the extra trouble of not breaking thru.  They can also use a little longer screw that way, and they just plan on using the gel type blue loctite to take care of the sealing.  It works.
Lloyd

Great news, as one of the major problems I had was drilling and worrying about going through the poppet hole. This makes doing this job much, much easier. Since I have another Disco, this will be done for the one in the box that I have not shot yet ... yes before I air her up for the first time.

Thanks guys for all you help and testing, knowing that many airgunners including myself at times can fly by the seat of their pants sometimes, and HPA's are way to dangerous for that.

wll

[Rivers3Plinker]

I want to thank Lloyd for starting this post and the great information.
Thanks also to Bob and others for theirs.

wll - I followed a previous post from Bob on disco valve mods for more power. I opened the throat on an otherwise brand new disco valve to 15/64 and subsequently see daylight through the bottom of all three screw holes. Like you, I was initially concerned.
I will drill and tap them for 10-32 low SHCS ( steel alloy from McMaster ) and through hole them when I do. I plan to shorten the 1/4" screws if they protrude into the chamber past the opening, cleaning up the threads so they don't gall the aluminum.
Another forum member suggested some Loctite low strength formula for the screws to help with sealing. Keep in mind this area is behind the poppet and is only pressurized when you fire it. I was initially contemplating a dab of RTV on the threads but I will instead go with the Loctite 222.
I am not planning crazy pressures but exploring what I can get with more pressure before required hammer spring and cocking forces exceed my liking. The extra safety with a little extra FPS is my goal.

[wll2506]

I want to thank Lloyd for starting this post and the great information.
Thanks also to Bob and others for theirs.

wll - I followed a previous post from Bob on disco valve mods for more power. I opened the throat on an otherwise brand new disco valve to 15/64 and subsequently see daylight through the bottom of all three screw holes. Like you, I was initially concerned.
I will drill and tap them for 10-32 low SHCS ( steel alloy from McMaster ) and through hole them when I do. I plan to shorten the 1/4" screws if they protrude into the chamber past the opening, cleaning up the threads so they don't gall the aluminum.
Another forum member suggested some Loctite low strength formula for the screws to help with sealing. Keep in mind this area is behind the poppet and is only pressurized when you fire it. I was initially contemplating a dab of RTV on the threads but I will instead go with the Loctite 222.
I am not planning crazy pressures but exploring what I can get with more pressure before required hammer spring and cocking forces exceed my liking. The extra safety with a little extra FPS is my goal.

We are on the same page ;-  )

wll