A local vendor here had a demo unit of a plumb-in double boiler machine with a E61 brew group for sale, but something about the set up of the machine in the show room bothered me.. (I'm not sure if it has a Rotary or Vibration pump, lets assume my question could be for either one.) I noticed that the store fed it off of a standard 19 Litre water cooler bottle without a pump between the machine and the bottle.
I realize that not having a separate water pump like a Flo-Jet would prevent pre-infusion from happening, but would feeding it from a bottle directly adversely damage the pump inside the machine when brewing? Since the bottle was on the floor in the showroom, wouldn’t it siphon water from the boilers? (Especially during pre-infusion)
It all depends upon the pump. Most all rotary pumps are a differential pressure style pump. They have a maximum differential that that can maintain for their rated life cycle. Most in this industry have a differential rating of about 130-170psi. They do not really state this but if you call them they have it on file. The rating is for the difference in pressure between the inlet and outlet. The inlet can also be negative (sucking water up a tube) or positive (like a water supply). If the pump is one the ground (not in the machine) then it usually has zero pressure at the inlet and is rated for this at normal extraction pressures. If the pump is in the machine then it usually has to suck water up to the machine. Also just as a side note, most all manufactures use bottled water to supply water to their machines at trade shows.
I personally know of many shops that use water reservoirs for their espresso machines. Even David Shomer does this. Most do it to avoid the pressure fluctuations of the mains water supply. Some even have auto fills on their reservoirs to maintain the water level.
If it is a Vibrating pump then it really depends upon the difference in height from the water reservoir to the pump. About half of the home espresso machines out there have the pump located on top of the water reservoir so they have to suck water up.
In the pressure ratings for an espresso machine, the pumps do not care if there is a water supply or a reservoir, or have to suck water up a distance. They are rated for differential pressures; if you exceed this you just do not get as much pressure at the outlet.
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