What is the function of this valve? Is there a way to test it? Mine is fairly heavily corroded and is now soaking in JoGlo, but wondering if there's a way to test it, wondering what it does, and wondering how it effects the functioning of the machine?

Thanks!

It's the expansion valve. The T1 is a heat exchanger type of machine. The heat exchanger is sumberged in the boiler.


The boiling water and steam outside the heat exchanger causes the water inside the heat exchanger to heat up to above boiling point. When the machine is sitting idle, the check valve at the H-X inlet prevents expansion back toward the pump, the closed brew valve prevents expansion out through the head... Without an expansion valve the H-X would burst. That's why you punch a hole in a can before cooking it on a campfire.
You could test it by raising your pump pressure higher than 13 bar and adjusting the expansion valve to begin relieving at that pressure.
Then adjust your pump back down to something reasonable.

Thanks for the reply. I did remove this valve, take it apart and clean it when I replaced the cracked drain box. I notice that when I'm pulling shots, I get a fairly steady flow of water coming out the drain pipe--I assume this to be because of the expansion valve? How do you adjust these? There is an adjustment nut, I just don't know which way to turn it. Also, I do not have the newer double gauges that show both the boiler pressure and the group head pressure--though I do have a home made brew pressure gauge. I'm assuming that there should not be a flow of water coming out of the expansion valve while I'm pulling shots, correct?

Thanks!

If the brew pressure gauge is reading cold water (from the diagram above, it looks like this is the case), then the way to set it is to first tighten until no water comes out with your pump set to 9 bar and then adjust your pump to 12 bar or so and set the expansion valve to weep when the pump runs. Then lower the pump pressure back to 9 bar and you should be set.

If you have a brew pressure gauge reading the pressure in the HX circuit, then you can set the expansion valve without messing with the pump pressure by running some water through the group and then adjusting the valve such that after you shut the water flow off, the pressure approaches, but does not exceed 12 bar on the gauge.

The job of the expansion valve is to let some water out when the cold water that the pump injects into the HX is heated up and expands, hence the name. If you have "hot" gauge, you can see the cracking pressure of the EV in real time. If you have a "cold" gauge, you have to use the pump to set the EV.

Cheers!

- Jake

While under normal brewing parameter, no you should not have a streaming out of it,
it will start to releise while the heating cycle is still active and reaches the set parameter
it should be adjusted to open at 12bar to prevent the Heating Exchange circuit to explode,
if you have restriction in the grouphead normal water patch then the water will find the path of less resistance which could be your expansion valve.

Ok, so I was finally able to gt my homemade portafilter group head pressure testing gizmo to seal properly against the grouphead gasket. My first test showed 120PSI (8.21 bar) and by adjusting the pressure screw on the Procon pump it's now reading 160 PSI (11bar). the expansion valve starts to release a steady stream of water at about 90PSI. So, either the grouphead is clogged as per Stefano, or, I need to adjust the valve. Attached is a pic of the valve from Stefano's website (Stefano, I hope this is ok, if not, please let me know and i will remove the image ASAP).




As pictured above, the two brass "adjusting nut surfaces" are shown tightened together. Is this setting (which is how it is set on my machine currently) for maximum or minimum pressure? In other words, with the two adjusting nuts set tight to each other, will the expansion valve release water flow at the lowest pressure level (i.e. 8 bar) or, is this the highest (i.e. 13 bar release) setting? and if this is the lowest setting, then creating space between the adjusting nuts will raise the pressure level so that the valve opens at 12bar?

Many thanks!

Screwing the ends together, shortening the valve, will be compressing the spring and raising the pressure needed to open the expansion valve.
So yes, tighten the ends together until it just barely leaks at 12 bar, then anjust your pump back down to 9.2-10Bar or wherever you like it, and the expansion valve will only drip due to expansion because the pump is limiting it's output to a lower pressure.

Thanks so much John! In checking the expansion valve, it was already set with the two adjustment nuts close together, which I understand from you post above means it was set for the maximum pressure and it was still leaking like a sieve.

I was finally able to find the time to take apart the grouphead and check for any obstructions. I had done this when I first bought the machine, but I had since descaled and wondered if maybe the gicleur or shower dispersal plate had gotten clogged with sediment. It was free and clear, and after testing again with my home made portafilter pressure tester, it would seem that the expansion valve is bad. So, ordered a new one from Stefano's Espressocare, and I'm hoping that will solve the problem!

Also, take the existing expansion valve out, unscrew it all the way and examine it. If you can see why it leaks you may be able to clean and fix it.
It's simply a blockage in a tube held in place by a spring. The tighter the spring presses it, the higher the pressure has to be to unseat the blockage and get past it. If something is in there holding the blockage open, the water can leak past it. Have a look.

Well, the new expansion valve was the ticket, yay! Upon removing the old one I did not find any blockage, but, I remember when I first got the machine and removed it to clean it that I felt the spring was pretty worn, as was the rubber/brass cap on top of the spring that seats against the valve body to make a good seal.

So, while it is a bit tedious to adjust the valve, it's opening/weeping at about 13 bar and not leaking at drop at 9 bar, so I think I'm good to go!

Many thanks everyone for helping me get this sorted out