I have a compressor that I am fixing, lightly, whose pressure switch
has a rubber membrane that rotted due to 50 years age, and leaks air.
This is a 80 gallon Quincy single stag 7.5 HP 35 CFM machine that s
about the same vintage as my own two stage Quincy.
This is a 1mm or so thick membrane. Instead of buying a new pressure
switch, I would just like to buy a sheet of proper rubber at McMaster
and cut a replacement membrane.
I have a bunch of soft rubber sheets, and neoprene rubber sheets, but
I am afraid that they will bulge from pressure (up to 100 PSI).
I would love to use them if possible, but if not, tell me what rubber
sheets to buy. McMaster item number would be great.
At work we have some pressure switches that activate at low pressure, maybe
less than 1PSI, and have high pressure of over 400PSI in cycle. (safety
switches to prevent presses from opening while pressurized) They have a
thin rubber membrane as you describe and a thin piece of stainless steel.
The stainless steel sheet (Maybe 1/4mm thick) keeps the rubber from bulging
out of shape with over 400 PSI on the line. Maybe if you could fit it you
could use thin SS with your rubber, rubber for the seal and SS for strength.
Without knowing the Durometer hardness and whether the original
diaphram has reinforcing fibers, it's going to be a cut and try. A
pressure switch is like $20 from the local hardware, so, for me at
least, it's not worth messing around with it. Only if the switch was
the last of its type would it be worth it. Or if it were a multi-
hundred dollar component.
Hey, I have a slightly related problem. I need a
soft, pliable material to rebuild a fuel pump I
made for my tractor. It needs to tolerate
exposure to gasoline, the main problem I have. I
bought some gasoline diaphragm material from
McMaster, I think, and it lasted for literally 10
minutes! I had been using some miscellaneous
rubber sheet material and it would last for up to
2 years, but has finally gotten crumbly.
So, now I need some new "stuff" to make another
diaphragm. The stuff they used to have in
carburetor accelerator pumps would be ideal, it
was thin and quite flexible, and obviously
withstood gas and flexing for years. Anybody know
where to get such stuff? I need about a 2" square
of the stuff.
Jon, I suppose you already know that neoprene is needed for gasoline
contact, unless the new fuel formulas attack it, otherwise, I don't know of
any newer product that replaces neoprene.
For a diaphram, the best product will most likely be a fabric reinforced
sheet, to withstand all the flexing and some pressure.
There are a lot more products made of neoprene these days, including hip
waders and rugged severe weather garmets.
I think searching for a fabric reinforced neoprene will yield more durable
products, although some old car restoration vendors may have the correct
materials for rebuilding old fuel pumps.
I bought some stuff from McMaster-Carr, it was supposed to be reinforced
neoprene. It was really stiff with the reinforcing, and then the stuff
just disintegrated between the weave in a very short time. I suppose
the stuff could have been mismarked, and not what I ordered.
Yeah, that's what I need. Maybe I should see if I can find J. C. Whitney!
It sounds like the failure may have been fatigue. You might need a preformed
or 3D shape with pleated rings molded into the material for a certain amount
Most times I've seen diaphrams that were intended to respond to a
reciprocating stroke (some applications with a spring on one side), they
have had the rings molded into the material.