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Spazbarista

pump/opv problem???

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Got a problem with the Brewt.

 

When extracting, on hitting full pressure (9b) there is an intermittent noise (can't think of a word to describe it) that sounds like the pump sqwaking on and off. As it happens the pressure drops 0.5b. So the pressure dial wobbles 3 times a second.

 

To reiterate, on each laboured sound the pressure drops.

 

Anybody know what it is?

 

Informed responses only please, no guesses ;)

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Can you get a video of the problem?

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yep - opv valve (or expansion valve as I'd call it on a commercial machine).

it's job is to allow water in either the heat exchanger or the brew boiler (depending on the type of machine) to escape at a preset pressure: the trapped water expands as it's heated, and the excess pressure has to go somewhere!

Normally, on a commercial, I'd set the expansion valve to release pressure at 2 to 3 bars above pump pressure - so if the pump is delivering at 9 bars, the expansion valve will release any pressure in excess of about 11 or 12 bars.

If it's releasing under pump pressure, it makes a very distinctive couple of noises: what you described is one of them, and the other would be a high pitched continuous screech while the pump is running.

Sounds like you need to either adjust the valve (if possible), or strip and service it and set it correctly, or if neither of these options is possible, replace it.

It's also worth checking that your pump isn't delivering excess pressure - I suspect not, since you didn't mention tweaking or replacing it.

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