It seems our friend, thermosyphon stall has come to visit me. He only comes once every few days, and most often after the machine as been idle for more than a few hours. Classic symptoms of vapor lock: When engaging the brew switch, little water will come out, and when it does, it is not hot. The water temperature measured by Scace is around 180°F. The portafilter handle and group is noticeably cooler than normal.

In Martin's post:
Thermosyphon stall on Vibiemme?
he mentions the troubleshooting step of holding the OPV tube vertically to look for a rise. This might indicate a leaking OPV. Mine shows such a symptom. I have shot video of the rise and it is here (3.4MB MP4, penny shown for scale):
https://dl.dropboxusercontent.com/u/257 ... rnTube.mp4
So my question is:
1. is ANY amount of rise in the tube normal through heat expansion, etc. or should the level be steady? Is the rise shown abnormal?

I will give the OPV a descaling through backflush of descaler to see if that helps.

For the convenience of those following this thread, I've excerpted the start and end of your video. It clearly shows the OPV is allowing water to escape.

This should only occur during water expansion and then stop (i.e., cold water is introduced into the heat exchanger and expands as it heats); some water may also escape during an extraction. No water should escape once the heat exchanger temperature has stabilized after a recent introduction of cold water. In other words, if the over-pressure valve on your machine is continuously allowing water to escape, then the rubber seat is shot, there's crud/scale preventing the OPV from closing, or the spring is tired. If the OPV allows water too much water to escape, a steam bubble will form and then the thermosyphon will stall.

START:


ONE MINUTE LATER:

HB wrote:For the convenience of those following this thread, I've excerpted the start and end of your video.

Thanks Dan. I should have thought of that.

During the descale, I let the OPV soak for a couple 1 hour periods. I recorded the rate of escape. It seems a little inconsistent...

Over 1 hour, 25ml escaped. Here are some time segments:
10 minutes: 9.4ml
22 minutes: 14.3ml
45 minutes: 21.5ml

It appears with an overall average of .42ml/min, it is faster at the beginning, but as this graph shows, it's pretty constant also.

You have convincingly proven the OPV is not working as expected.

Dana -

I do hope you have separated the OPV "excess" from the deaeration valve. Another "acid test" would be to simply do an extended flush and see if there is any output from the OPV relief port. During that test, there should be NO FLOW whatsoever from the OPV but about 1 ounce in 30 seconds from the deaeration valve, IIRC.

A pic of your existing OPV might help as there APPEARS to be, from some pics I have, two different OPV's. One is the smaller Isomac lots of us are familiar with and the other looks like a typical, easily adjusted, Quickmill adapted to the Isomac by means of a 1/8" tee.

erics wrote:I do hope you have separated the OPV "excess" from the deaeration valve. Another "acid test" would be to simply do an extended flush and see if there is any output from the OPV relief port. During that test, there should be NO FLOW whatsoever from the OPV but about 1 ounce in 30 seconds from the deaeration valve, IIRC.

Eric - Thanks for your reply. I did not separate the OPV output from the deaeration valve. I do get output during a flush, and it is about double what you suggest - 2 oz in 30 seconds, and 4 oz in one minute. This OPV is very very bad it appears.

A pic of your existing OPV might help as there APPEARS to be from some pics I have two different OPV's. One is the smaller Isomac lots of us are familiar with and the other looks like a typical, easily adjusted, Quickmill adapted to the Isomac by means of a 1/8" tee.

Yes - I have the original Isomac OPV. Photo follows. Do you have experience with both types? When I buy a replacement, any reason to go with one over the other? It looks like the QM OPV sold by Chris Coffee is easier to adjust - the Isomac required two pairs of pliers and was kind of a pain.

Oops. I posted too soon. After separating the "deaeration valve" hose, the entire flow during the flush is coming from there, not the OPV. What does that mean? I am now confused.

Here's a photo of the whole circuit:

I am now confused.

I am also. I believe that the flow from your deaeration valve is too high but I fail to see the relationship between that and a thermosyphon stall.

Yes, the larger OPV is easier to adjust but that "Isomac standard" smaller one has certainly served well for years. Hopefully, new valve inserts are available.

OK. It looks like there are 2 independent problems:
1. The deaeration/air release valve is letting water pass during the flush (and during pulls I guess)
2. The OPV valve is leaking, releasing pressure from the HX. I verified this by letting the machine heat up to pressure so that the level in the drain hose was rising, then crimping the OPV relief hose only with needlenose pliers. That stopped the rise.

Regarding the parts for the OPV, Stefano used to sell a rebuild kit with spring, o-ring, and ball, but he said he can no longer get the right spring for it, so stopped selling it. I may just go ahead and buy both replacement valves. I could try cleaning out the OPV valve. Not sure if the release valve can be serviced.

Not sure if the release valve can be serviced.

Unfortunately, there are no parts available. It is designed to be open during a flush and close at 6-8 bar according to the drawing.

If, for some reason , you decide to disassemble and clean the deaeration valve, do so in an area where you can find small parts if they drop.