Hello:

I need to replace the (deformed) teflon membrane in a Sirai pressurestat. The other membrane with the plunger seems to be in good shape as well as the set of contacts used. I will nevertheless shift to the next set of contacts, just in case.

Unfortunately the Sirai service kit like the one pictured below is not available locally and the alternative of having it shipped in is prohibitive.



As an alternative, I can purchase 0.25 / 0.50 mm. Teflon stock and have as many 55 mm. membranes as I need cut with a plotter for a very reasonable price.

Do any of the forum members know what the spec (thickness) for the membrane is?

Thanks in advance,

CIV

Hello:

civ wrote:Do any of the forum members know what the spec (thickness) for the membrane is?

Went ahead and put in an order for 0.25, 0.50 plain and 0.375 fibre reinforced Teflon stock.

I then took out the the Sirai, disassembled it and measured the membrane: in case anyone else needs this information in the future, please take note:

It's 0.20 mm. thick and 55 mm. in diametre. (at least in this older unit, with metal cover)

I then cut a new membrane from the 0.25 mm stock, reassembled and reinstalled the unit.
It's now clacking away happily on a 0.15 bar deadband. (~0.875 - ~1.025)
I don't think that can be improved on, IIRC, that's the design spec for this Sirai.

The instrument used to cut a 55mm. membrane from Teflon was a Olfa Compass Circle Cutter.



As Teflon is by design 'very' slippery, the trick is to be very patient and work slow trying to keep the material from moving around. You have to use the small plastic centre provided with the cutter (has scibed cross-hairs and a thin rubber base) so that you don't puncure the centre of the membrane and render it useless. There's no need to press too hard (new blade is mandatory) as marking the Teflon well will suffice. Once marked, you can tear away the circle.

Although I purchased all of the three Teflon variants available locally and as the rubber membrane with the plunger and the retaining ring were in perfect condition (probably the usual scenario), the total cost was far below the cost of a full repair kit.

It's possible that, being now 0.25 and not 0.20 thick, the membrane will last longer.
Time will tell. =-)

Cheers,

CIV

Good job if it works
however shipping internationally to Argentina starts at around $10.00 for such a small item,
if your time and the piece of mind is worth that, then is a plus project.
I will personally be very concern about a modification of a such an important part on a machine.
but don't get me wrong ingenuity is always a good thing and I wish you not to regret it

Hello:

stefano65 wrote:Good job if it works

Thanks. =-)
I really appreciate your saying so.

Up to now, it is working perfectly well.
Like I said above: " ... clacking away happily on a 0.15 bar deadband."
Of course, I'll immediately post an update if I come across any problem.

And if there are no problems within six months, I'll also post an update.

stefano65 wrote:... shipping internationally to Argentina starts at around $10.00 ...

Indeed ...
But the problem does not lie in the shipping charges per se.
The problem lies within the import taxes to be paid, which is high for parts.
The shipping charges, however small, are also part of the cost (cost+shipping) on which the tax is calculated.

stefano65 wrote:... if your time and the piece of mind ...

It may seem reckless to you that I have done this and sincerely thank you for your concern.

But if after three years of high school shop training plus a degree in architecture I can't manage cut a 55 mm. circular membrane from Teflon stock with the required care and tidyness (ie: produce an almost exact copy), take apart the pressurestat to replace the old one with it and put it back together and in place, I probably should not be doing it with the one that comes with the repair kit either.

That said, my Junior D/1 is not in a commercial environment, it is part of my espresso hobby and as such, the time I put into it is not an issue for me: I thoroughly enjoy finding and solving apparently difficult problems (But rest assured, I did try to get a repair kit locally).

stefano65 wrote:I will personally be very concern about a modification of a such an important part on a machine.

Quite so ...

At first I was rather concerned about the diference in thickness of the available Teflon stock (hence my original post asking for the spec) but after much thought and consultations with a coupe of friends 'in the know' (so to speak), I finally concluded that the risk was minimum and that at worse, there would a variation in the width of the deadband, nothing more.

stefano65 wrote:... wish you not to regret it.

Me too ...
And hopefully, I won't.

Once again, thank you very much for your concern.

Cheers,

CIV

I was not been sarcastic for the records
I really appreciate the entrepreneurs,
hell I'm one of them too.

Caro Stefano: =-)

stefano65 wrote:I was not been sarcastic for the records

Of course ...
Nor did I think that was your stance or purpose.
Please do accept my apologies if my reply reflected that on my behalf.

Ciao,

Carlo Izzo Videla

We cool
you don't need to apologize
I just want to make sure my intentions were not misinterpreted,
after all English is my second language
ciao
buena suerte