I've been rebuilding a 1981 Elektra/Faema Microcasa A Leva. The old style brass pressurestat is well made and simple in design but the diaphragm will age and need to be replaced. The original diaphragm is no longer available so I'm working on finding a suitable replacement. The original is a mesh inserted type diaphragm material approx. 1 mm-3/64" thick. Doug from Orphan Espresso sent me a few scraps of Viton and silicon of various thicknesses and Duro readings. Looking online I've also found a cloth and a nylon inserted diaphragm material that I will see about getting some small samples to try, here's an example cloth inserted diaphragm material. I'm thinking the cloth inserted may be more stable.
I'm just waiting for the base(the plating was shot and may replate in future)that I painted to dry and harden then I will finish putting the machine together and try Dougs samples in the pressurestat.

farmroast wrote:I've been rebuilding a 1981 Elektra/Faema Microcasa A Leva. The old style brass pressurestat is well made and simple in design but the diaphragm will age and need to be replaced. The original diaphragm is no longer available so I'm working on finding a suitable replacement. The original is a mesh inserted type diaphragm material approx. 1 mm-3/64" thick. ... [/i]

An interesting project.

Maybe you can make a contact with an espresso-enthusiast here:

http://www.contitech.de/pages/produkte/...en_en.html

http://www.fabricreinforceddiaphragms.c...diacom.htm

I've also tried a couple of type (also from the most helpful Doug) but I was unable to find a suitable one that didn't drift with time.

See my pressure stat rebuild and skip the ones I've already tried.

What worried me was that mine drifted to having a higher pressure than what I initially set by a large amount. Perhaps the rubber stiffened under the heat of daily use for a couple of months.

Mark

Mark
So you found the 1/16" viton was too stiff after a period of time? My diaphragm was 26.5mm where yours was 30mm so there was more than one design. What year is yours?

Mine was a 1988 model.

The stuff that hardened up was the soft 40D stuff. It did seem to work at first.

Mark

Contact a water well supply or pump supply company, they will have a wide selection of pressure membranes for the head control units.

-Cecil

Of the samples Doug sent I tried the silicon 1/16" 50-Duro. I had it running for about an hour and it stayed stable at about a .1 deadband and is totally adjustable. I had it low at about .5 when I fired it up then adjusted it up to approx. .875- 1.0 Will see what happens with time.

Good that you are getting some success with the bits of rubber....when you look at that old membrane you ask the question....is it presently stiffer than when new (after all it did fail)...should it me more or less flexible, more or less stretchy, more or less hard. All a big experiment. Does a stiffer material make the deadband smaller or larger? Takes a lot of changing out pieces and parts to get at that little bit of infe. The silicone is rated to 600F so it should not change much over time in its stretch characteristics, nor should it change much at the rairly low heat that it is exposed to. Now that it is cold in our storage, the EPDM and Viton sheets are like stiff taffy at 32F but get soft right away though the silicone seems to not change over the temerature ranges that I observe. Sounds good so far.

Doug I am sure you have looked at many more p-stat membranes than I have, but looking at several of the commercial p-stat branes like the Sirai I seem to remember them being a fiber reinforced plastic more than a rubber surface. With a bonded pressure push button epoxied on to transfer the pressure from the brane to the relay shaft with less wear. How do you reduce surface wearing with the rubber membrane?

-Cecil

I agree that the rubber alone is likely not the perfect long term solution since the original is a composite memebrane. But why did the original fail? Did it become too stiff or too flexible? Where is the wearing surface? From the construction of the brass parts you have pressure exposed through an orifice on one side and a flat piston plate on the other so there seems to not a lit of frictional wear. The composite materials will be interesting to look at once we get some in hand....they seem better in theory at least.