Sirai Pressurestat Membrane / Diaphragm Rebuild

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
nguye569

#1: Post by nguye569 »

Does anyone rebuild the Sirai membranes as a preventative measure or do you only wait until something is wrong with the pressurestat? I'm rebuilding a 90's machine that hasn't been used in years and wondering if I should do this while I have things apart.

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civ

#2: Post by civ »

Hello:
nguye569 wrote: Does anyone rebuild the Sirai membranes ...
A Sirai pressurestat is industrial duty equipment and made to last.
They are practically indestructible but quite noisy and a repair kit is what is usually done when the diaphgram stretches, which it inevitably does with time and use. This affects the deadband, which for an espresso machine can be critical but not so much for a 5.0 hp compressor.

Unfortunately, the price the repair kits go for is many times usually high in relation to what a new unit costs.
But not always so it pays to shop around, not necessarily in espresso repair oufits, you can also get them at industrial supply stores.

So, depending on the price, a repair kit is probably worth it.

See this post.

Cheers,

CIV

nguye569

#3: Post by nguye569 »

The machine i'm restoring has been having lots of inconsistencies with brew temps and I can hear it clicking on and off very often. I think some of the instability is in part due to an old pressure stat membrane.

The new pressurestat will cost $60+ while I can get a membrane for under $20 from espressoparts.com (30% discount right now). For less than $20, I think its worth a shot, especially since this machine is atleast 20 years ago.

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civ

#4: Post by civ »

Hello:
nguye569 wrote: ... inconsistencies with brew temps ...
... can hear it clicking on and off very often.
... instability is in part due to an old ...
Hmm ...
No.
Not necessarily.
Clicking on and off very often is not a sign of instability.

A pstat will turn on and off according to how its set points are adjusted.
A wide deadband does not require a very precise mechanism or membrane.
eg: on at 1.0 bar and off at 1.5 bar pressure
In this case, the on and off will be spaced out in time.

And unless the pstat membrane is totally shot, it will work perfectly well as it is a wide (0.5bar) deadband.

Now, a narrow deadband would require a more precise mechanism or membrane.
eg: on at 1.0 bar and off at 1.1 bar pressure
In this case, the on and off will very close in time as it is a narrow (0.1bar) deadband.

Obviously, you can only get a precise deadband with a membrane that it in good shape.
ie: in the case of a Sirai, it is elastic and not rigid or out of shape.

Now ...
What are the inconsistencies with brew temps you refer to?
You have not said what machine you have and it could well be that you are simply not used to it.

Try this:
Turn on the machine.
Let it come to operating temperature - say at least 1 hour idling.

Once you're at that point in time, make a note of the presssure on the dial.
Then do two or three consecutive flushes and make a note of the pressure when the Sirai clicks on and then when it clicks off.

Now, sit close to/in front of the machine and record the time between ons and offs and their corresponding pressure readings for at least 15'.
That will give us some hard data to evaluate.
nguye569 wrote: ... a membrane for under $20 from espressoparts.com ...
Shop around, I've seen Sirais for less than $50, but less than $20 for a repair kit is seems OK.
The rest of the thing will last years.

But I have the impression that you don't need it.

Cheers,

CIV

nguye569

#5: Post by nguye569 »

Thanks for the thorough responses!

I'm working on a 90's Salvatore Famosa, one without a boiler gauge. I've rigged up a steam wand pressure gauge to help me as I try to restore it.

The issue I've noticed is there are times where the water temp at the grouphead and boiler pressure seem fine after warm up (~190F water temp), and there are times after warm-up where the the water temp is lower and boiler pressure is low (~160-170F water temp). I've noticed this on a few occasions in the past week. In all times I am noticing the pressurestat does go on and off as it's supposed to, so I just think there could possibly be something wrong with the membrane setting off at different times.

Of course there could be something else wrong with my machine as well, but for now, I'll still replace the membrane.