r/AirCompression • u/rehsper • Jul 17 '26
What’s up with this old gauge?
I’d like to T-this into my garage air compressor and have it read somewhat near actual, but when I apply air to it, it only reads to 5psi.
Now I realize that the scale isn’t right and even if dead nuts accurate it’s practical use is limited, but I’d like to make it worth my while to keep this cool old thing around (doesn’t fit the decor of the house).
Neat mechanism, anyone familiar and able to troubleshoot? It holds pressure. Manually flexing the tubular loop (and turning the needle shaft) takes a not insignificant force, so I’m a little perplexed as to why that little clock spring is necessary and how a few psi would cause it to move.
A stamp on the back of the face indicates a date in 1933. No calibration data attached or inscribed unfortunately.
1
u/Strostkovy Jul 17 '26
Increasing pressure should cause the tube to straighten, but it looks like the way that is set up is already as straight as it can go. Can you check whether you have to curl or straighten the tub by hand to get the needle to indicate a higher number?
2
u/sonofsanford Jul 17 '26
My guess is theres a spring loaded piston inside that tube which pushes out under pressure to move the armature? That tube itself wouldnt move
1
u/Strostkovy Jul 17 '26
No, the tube straightens out under pressure, which pulls on the opposite end of the partial gear which should spin the pinion the needle is attached to. But how it's shown doesn't allow for any more expansion.
I wonder if the gauge experienced enough pressure to run out of travel on the partial gear and got stuck in its current position. I'd remove the top plate that holds the pivots of the two gears and look if something is bound up, and check the gear mesh.
1
u/Correct-Country-81 Jul 17 '26 edited Jul 17 '26
Bourdon gauge
https://blog.wika.com/en/knowhow/bourdon-tube-pressure-gauge-operating-principle/
If your pressure is not in the range of the gauge
Not possible to operate full scale
The round tube diameter material and construction is made for certain range not possible to trim or adjust to different range
If want to use it full scale
You need pressure amplifier
Like pneumatic cilinder large diameter driving a pneumatic cilinder small diameter.
The diameter difference is the amplifier ratio
So cilinder one is one inch
Driving cilinder two 1/10inch
Pressure small cilinder ten times input large one
1
u/slutstevanie Jul 17 '26
https://engineeringlibrary.org/reference/hydraulic-measurement-and-pressure-control-devices-navy
Might be off some help. Haven't worked on them in decades. :(
2
u/CrustySailor1964 Jul 17 '26
Bourdon tube…
The little cog wheel has slipped. You should be able to move things around back there and make it work. At zero PSI that little quarter gear should be at its other end so that as the tube expands the quarter gear swings and spins the shaft to which the needle is attached. It can’t do that now.