valve retention ?

[hpmr2400]

hey guys if i switch out that little wimpy screw on a 22xx for a stronger 8-32 schs and get it to fit snug , would 1600 psi be way to much , or should i just drill tube for two more holes

[Ribbonstone]

Little more info would help.  Why are you retaining the valve?

Am all for the idea of valve retention when using either a bulk fill valve and end cap or when using a HiPac unit.

Of the two, the bulk fill valve actually needs more retention than the HiPac.  Bulk fill pressurizes the outside diameter of the valve.  HiPac would pressurize just the inside of the valve. 

Lets call the bulk fill valve .72” in diameter.  So the square inches works out to  about  .43 square inches, so 1600psi would push back with about 650 pounds of force.   Inside of the valve might be something like .39-.40, area works out to about .125 square inches,  so the backwards force would be something closer to 200 pounds of force.

You can use one larger screw in place of the issue screw in a HiPac conversion with some drilling/tapping, but conversions that pressurize the air tube really need the two add on tube screws for valve retention.

Occurred to me….the issue valve in the Crosman 22XX guns doesn’t seal to the air tube at all, so it’s not suitable for bulk filling (air or co2).  It works by jamming the neck of a 12gr. against a seal on the end of the valve, so only the inside of the valve is pressurized.  You could drill the air tube to look like swiss cheese and it would still work as intended with a 12gr

[AmBraCol]

Occurred to me….the issue valve in the Crosman 22XX guns doesn’t seal to the air tube at all, so it’s not suitable for bulk filling (air or co2).  It works by jamming the neck of a 12gr. against a seal on the end of the valve, so only the inside of the valve is pressurized.  You could drill the air tube to look like swiss cheese and it would still work as intended with a 12gr

The Discovery valve should fit the tube just fine, shouldn't it?  And it already comes drilled and tapped, just need to drill the tube to match.

[Ribbonstone]

From what I've read, it should be a go. Believe the Discovery fill cap will fit as well.

[rsterne]

A single 8-32 Holo-Krome screw (the strongest available) with the head taking the load into the tube wall.... operating at 1600 psi.... would have less than a 2:1 safety margin in shear.... and in a mild steel tube the bearing load would be very close to the yield point.... Therefore I would not recommend it.... Since you need to seal the valve into the tube anyway, I would recommend a Disco valve, with three holes in the tube wall.... If you use three 8-32 Holo-Krome screws, drilling the two side holes 0.265" to fit the heads (the lower hole in a 22XX tube is already the right size).... you would have enough strength in the valve installation for 3000 psi.... ie you would never have to give it a second thought....

Incidently, Ribbonstone, the end force on a HiPac installation is only the pressure times the area at the seal, which is about 1/4" diameter.... with an area of about 0.05 sq.in.... That means at 1600 psi the force is only about 80 lbs.... While it is true that there is a rearward force on the inside of the valve of about 200 lbs, there is a corresponding forward force on the front of the valve that is the same area as the rear, less the seal area.... However, you do have to add the end force created by tightening in the HiPac, which even finger tight is considerable....

Bob

[Ribbonstone]

Still not seeing why pressure just acts on the area of the seal, but you well could be right.  Figured the pressure worked on whatever the inside diameter of the valve, partly on the valve stem and partly on the free area around the valve stem seal.

Reguardless, are right about the inclined plane (screw thread) offering a great deal of force to the screw if over tightened.

[rsterne]

Think of the inside of the valve like a balloon.... the pressure acts in all directions and the balloon doesn't move across the room if the neck is tied shut.... If you untie the neck, the force is the pressure times the area of the neck.... In the case of a 22XX valve on CO2 (or with a HiPac pressed against it), the neck is the point where the seal is between the CO2 cartridge and the valve.... The force as a result of that area where they meet is backward on the valve and forward on the cartridge....

If we assume the inside of the valve is a cylinder, there is a force backwards on the back end equal to the pressure times the area.... There is also a force forwards on the front end equal to the pressure times the area, but the front area is the same as the back MINUS the area of the seal between the valve and cartridge.... Therefore the net force backwards on the valve is the pressure times the area of the seal.... If the valve is 1/2" ID and the seal is 1/4" at the point where the seal occurs.... we have:

Force on back = PI x 0.25^2 x pressure = 3.14 x 0.0625 x 1600 = 314 lbs
Force on front = PI x (0.25^2 - 0.125^2) x pressure = 3.14 x (0.0625 - 0.0156) x 1600 = 3.14 x 0.0469 x 1600 = 236 lbs
Net force towards the rear = 314 - 236 = 78 lbs.... and there is a corresponding force forward on the cartridge....

The forward 78 lb. force is taken into the tube by the threaded plug at the front.... and the rearward 78 lb. force is taken into the tube by the single 6-40 screw in the bottom of the valve....

Bob