HHTel wrote: ↑Fri Jan 25, 2019 11:54 am
They are claiming constant pressure regardless of flow,
That sounds very much like connecting a pump to the main supply which is illegal. With a storage tank, flow doesn't really come into it and there are a multitude of good pumps on the market. I have a Mitsubishi which serves my two story house and six garden taps. I can run half a dozen sprinklers and still have a shower.
This pump has lasted me for 13 years with only a new pressure switch required at one point.
Not sure just what you are getting at there? The output flow of a pump has nothing to do with where it gets its supply. A flooded suction head, such as from a surface tank, will make the pump more "efficient" in as much as less power is used in "sucking" rather than "pushing", but the output pressure and flow is entirely due to the design of the pump.
To get "constant pressure" requires some form of monitoring a pressure set point and adjusting, or "modulating" the output pressure to maintain that set point. I suspect that they are achieving this electronically by passing some of the pumps output back to the suction side. If the demand flow increases the pressure will start to drop and the control loop will compensate for it by reducing the by-pass flow.
Yes, Mitsubishi make good pumps, I have a couple of them. If the particular pump has enough output to run several taps you may not see any drop on either pressure or flow, but I assure you it will be there. Also, some of the pumps used here do not like a flooded suction, and will eventually become completely flooded without any air cushion, which is needed to provide the system pressure. Rapid starting and stopping is the usual indication.
In one of the handouts concerning the Stiebel pumps it states that they use a rubber bladder pressurised with Nitrogen in place of air. At one time all of these types of water pressure systems used this method of maintaining the system pressure. Sometimes called a Hydrocell. (edit: or Hydrophore tank)