Anyone recommend a lubricant for 1.5" Sch 40 PVC pipe joints ?

I am trying to help a Middle School Science class with a project. It
involves launching a ball through a PVC tube using a 2 liter soda
bottle as air source. A weight is dropped on the bottle.

We need to be able to quickly and easily swap bottles from one shot to
the next. The bottles are glued to a PVC cap fitting with a hole
drilled for the bottle neck. From one test shot to the next the caps
can be easy or hard to remove.

We have tried Vaseline, and silicone spray. They seemed to make the
cap fit tighter on the pipe! We have also filed down the pipe end a
little, but don't want to make it too loose either.

You might try "Wire Pulling Lubricant". It is made for pulling electrical
cables through conduit. It can be messy, but it's really slippery stuff
that is ideal for plastic to plastic lubrication.

You can usually find a bottle in the electrical section at Lowes or Home
Depot for $10-15 or so.

Otherwise, I would probably try some kind of wax, or even bar soap.

You might also try putting a garden hose washer inside the bottle cap to
prevent it from fully tightening down in the threads.

Anthony Watson
www.mountainsoftware.com
www.watsondiy.com