Someone mentioned that option while discussing the setup of the consumer espresso lab at the SCAA conference. I'm a teenie bit concerned that priming the line / running dry might damage the pump, even if it ran only for a few moments. Admittedly, I tend to be overcautious and doubly-so when it involves expensive equipment that doesn't belong to me. Being curious, I asked a friendly lurker who installs and repairs commercial equipment for a more complete answer:
Not all machines activate the pump when filling. Those that do work very well with this simple system as the Procon pump is designed to do just that, pump. Machines that simply fill by water pressure will need the help of a bottle pump or standard Shurflo. This is another way of suppling the machine that makes perfect sense. The incoming pressure should be 22 PSI max and most line water pressure is significantly higher, so the pump could theoretically allow the solenoids to operate at a calmer pressure. The most important factor I've found in the success of this procedure is the addition of rubber o-rings at each water connection joint. If the machine gets air bound it could be a pain but I get very few calls because of it. If it runs out of water the exchanger will not flow but it will take quite a long time before all of the water will evaporate from the boiler. Hopefully the machine has a high limit thermostat though some do not. Again, this is a great way to make commercial machines portable for catering parties, nice and quiet and large enough to mean business.
A check valve is little more than a fitting with a ball inside that prevents water from flowing back. Despite the reassurances above, the idea of running a rotary dry doesn't appeal to me (the sound surely wasn't nice when I did by mistake), so if it were my machine, I'd supply positive pressure. If that wasn't possible, priming the line under pressure should be enough precaution, even for paranoids like me. :-)
Dan, Your lurker friend suggests max 22 psi for a flo-jet system. Do you know if this is true for plumbed in vibe pumps too? I have mine set at 30, as I thought I saw that setting recommended here somewhere, but I want to be on the safe side....
Yes, same answer. Being Mr. Cautious, I have mine set at 14 PSI. OTOH, some routinely ignore this advice and run directly off line pressure. Some machines won't complain, others will drip from the grouphead solenoid. I can't think of an advantage of running it higher than the minimum, especially for vibe pumps, which are (technically) spec'd at zero positive pressure.
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