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is this safe?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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is this safe?

Unread postAuthor: Vaeevictiss » Thu Jan 12, 2012 10:34 pm

I am building a new cannon off a design ive had for a while. I got in a couple sch80 reducer bushings today as i couldnt find any 40s. The rest of the cannon is sch40 with a 2" sprinkler valve.

For the most part the sch 80 fittings fit fine, where im having a problem is on the 3" t-fitting. I have 2 3">2" reducer bushings and the slip in and out of the t pretty easily dry. Im normally used to a pretty tight fitting even when dry.

Now they dont just fall in and out, there is some resistance. I cant turn it upside down and have the fitting fall out, but it takes almost no effort to fully seat and remove it. Is this safe to use or not? Is there maybe a thicker cement i can use? possibly tapping and seating a few screws to hold it in place along with the cement?

I normally dont go higher than 100psi but sometimes will go as high as 125 in my cannons. Ive never had this issue before so i want to make sure if this is safe or not before i go gluing. Thanks for any info.
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Unread postAuthor: Gun Freak » Thu Jan 12, 2012 10:38 pm

That's pretty strange. As long as the two fittings mate well (good tolerances, no gaps or wiggle room), they should bond properly. Make sure to pay very special attention to gluing those joints. Use the proper techniques and new primer/cement.
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Unread postAuthor: Vaeevictiss » Thu Jan 12, 2012 11:36 pm

Well i looked at it a bit more. Its loose to the point it will fall out if i leave about 1/2" out of the t-fitting. If i push in that last 1/2" it still slides in easily, but actually takes a bit of force to turn the bushing inside the t-fitting. It is snug when in all the way, no gap, no wiggle. It seems as tho with cement in there it should work. Maybe its just easy because the fittings are so smooth. The sch80 fittings are almost mirror shiny unlike the 40s thats the flat finish.
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Unread postAuthor: Technician1002 » Fri Jan 13, 2012 11:28 am

The small diameter of the sched 80 bushing can be carefully cut off to shorten it into a sched 40 bushing permitting the larger diameter portion to seat properly into the schedule 40 socket on the T.

Bevel the new cut edge with sandpaper so the sharp cut edge does not scrape the glue off as it is inserted into the socket. It should now fit tight as the fitting is tapered.
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Unread postAuthor: Vaeevictiss » Fri Jan 13, 2012 3:00 pm

well the bushing still fully sits in the sch40 tee, none of it sticks out.
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Unread postAuthor: motorfixer1 » Fri Jan 13, 2012 7:38 pm

Gun Freak wrote:That's pretty strange. As long as the two fittings mate well (good tolerances, no gaps or wiggle room), they should bond properly. Make sure to pay very special attention to gluing those joints. Use the proper techniques and new primer/cement.


Seconded.

Some of the fittings I used on my piston valve launcher were of similar fit up and I have had it to 150psi a couple of times during the initial testing. The first time you pressurize it you should be in another room as always with pvc cannons!
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Unread postAuthor: Technician1002 » Fri Jan 13, 2012 7:50 pm

Vaeevictiss wrote:well the bushing still fully sits in the sch40 tee, none of it sticks out.


That is weird. The sched 80 fittings I used have a longer socket depth than sched 40 parts, so it should stick out. On my Dragon cannon, you can tell which end has a sched 40 reducer and which end has a sched 80 fitting just from the socket depth in the chamber.

The end with the deep socket is sched 80.
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