The drysump pump for my meth monster project is in pieces, and I am getting my head around how it works. It has a spring-loaded relief valve to set oil pressure, similar to a standard grey motor oil pump. The relieve valve piston has a stop on the end of it (a thin steel rod). The stop bears up against a bolt, and sets the piston position when it is closed. The bolt is a plain 5/16-18UNC bolt, sealed into the pump casing with a fibre washer.
- drysump fitting 3.jpg (28.36 KiB) Viewed 102 times
The tip of the bolt is in the exact right place to measure the pump discharge pressure. By making the bolt hollow, I can let the discharge pressure out of the casing, and fit a pressure gauge. There are two reasons that I can't just replace the bolt with a gauge nipple:
a) the UNC threads on the casing are not common, so fittings are hard to find (if it had of been UNF instead of UNC then a -2AN ORB fitting might have worked).
b) the bolt needs to provide the stop for the piston, which a fitting won't do (most are way too short, and too big a bore).
I got cute and machined up a standard 5/16-18UNC bolt. It can work, but it is ugly (least of my problems) and only big enough to get a 1/16NPT thread into... and even then the thread is shallow.
- drysump fitting 4.jpg (54.07 KiB) Viewed 102 times
- drysump fitting 2.jpg (23.96 KiB) Viewed 102 times
What I really need is something like a 5/16-18UNC bolt, but with a much bigger (round) head, and tapped to 1/4NPT... something like this (not to scale):
- drysump fitting 1.jpg (85.93 KiB) Viewed 102 times
Mr Hobbs, my tech drawing teacher, is probably grimacing seeing that drawing. Prefer ally, but could be stainless, or steel.
Harv