Household water pumps

[PeteC]

I consider the below good news as they make the best water heater I've found here so it's a good bet their pump will be very high quality. Cost unknown at present and that could be a stumbling block except for those looking for the Mercedes of water pumps. Pete

...."Stiebel Eltron, a Thai manufacturer of water heaters, water filters and hand-dryers, says its latest Stiebel Boost water pump has been Thailand certified by the Thai Industrial Standards Institute.".....

http://www.nationmultimedia.com/detail/ ... s/30362881

[handdrummer]

I've been using their countertop water filter for the past 4 yrs and have no complaints.

[Nereus]

Caveat Emptor:
…………………………………………………………………………………………………………………………
Yes, their water heaters are the best by far.

I have yet to find any specs on these new pumps, and they are referring to them as "booster" pumps. BUT, before you go and connect one up to any Thai installed PVC water system make ABSOLUTELY sure what pressure they put out!

Grundfos are also probably the best brand of small pumps, and the pressure they put out compared to the usual small pumps WILL blow the first shoddy connection it comes across. Usually the one buried under your nice sand wash!

[Nereus]

Found the following online. The pressure listed is comparable with most other home pumps, so should not be a problem. They are claiming constant pressure regardless of flow, so to obtain that the pump has to have a higher pressure controlled electronically on the discharge to the system.

http://www.stiebeleltronasia.com/index. ... tail&id=78

[HHTel]

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.

[Dannie Boy]

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.

I must be doing something wrong - I have a Mitsubishi pump and it will barely provide sufficient pressure to allow 2 sprinklers at the same time!!

[HHTel]

You really need to look at the pressure and head when you buy. There are numerous models. Mine is one of the 'more expensive' models as I needed the pressure and the smaller ones just wouldn't do. I have a WP 355 which has Head 17.3 m Max. Flow Rate 310 l / min.
which is more than enough.

[Nereus]

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)

[PeteC]

"constant pressure regardless of flow" is called a reciprocating pump by Hitachi and I believe Mitsu as well. When it senses a drop in pressure outward it ups the game somehow by increasing power to keep all outlets at equal pressure. How many outlets it can do this for I guess is dictated by the model and power you buy as mentioned by HHTEL. These type pumps don't have the bottom water reservoir but are more or less square boxes as you see on the Stieble site.

[Nereus]

"constant pressure regardless of flow" is called a reciprocating pump by Hitachi and I believe Mitsu as well. When it senses a drop in pressure outward it ups the game somehow by increasing power to keep all outlets at equal pressure. How many outlets it can do this for I guess is dictated by the model and power you buy as mentioned by HHTEL. These type pumps don't have the bottom water reservoir but are more or less square boxes as you see on the Stieble site.

It does not necessarily require a positive displacement pump, and I have not seen any Mitsubishi pumps that are used in house systems.
There are two ways to achieve constant pressure: one as I have posted, and the other speed control. With modern elecronics maybe Stieble are using a variable frequency speed control, similar if you like, to what is used in air conditioners.

[PeteC]

This is the Mitsu we have here. As is on the cover they call it a "constant pressure water pump". I forget what power it is and I was chased out of my pump room by a crazed squirrel nesting in there so didn't linger looking! This particular unit will keep two showers at the same time running constant and strong, but not more than that.

[Nereus]

This is the Mitsu we have here. As is on the cover they call it a "constant pressure water pump"

Yes Pete, it is constant pressure, but still has a centrifugal pump. Sometime ago I posted a diagram and description of how they work, but cannot find it just now. I think Cameljockey asked about them.

And you really should take better care of your pet squirrel, he is probably hungry.

[Nereus]

Not looked at this right through, but I think it is correct:

[HHTel]

Wow. As someone who doesn't really know what I'm talking about, I've created plenty of technical jargon. I was assuming quite simply that I understood it to be constant pressure regardless of the flow (inward). You've pointed out my ignorance. When I have multiple devices running, there is a drop in pressure I'm sure but hardly noticeable because of the pump power I guess.
Anyways, my Mitsu handles both floors and several outside taps without any noticeable drop in pressure.
Thanks for making me feel stupid!!!!...

[Nereus]

Thanks for making me feel stupid!!!!...

There is nothing stupid about finding out how things work! I have been doing this crap since I was 10 years old on a farm.

There is an interesting comment towards the end of the video where he points out that a pump(centrifugal)actually draws less energy if you throttle in the discharge. During my apprenticeship we used to repair a lot of pumps, mostly close coupled centrifugal types from the farms around where the shop was. I still remember when I was about 17 or 18 years old having an argument with my boss, whom was a very well qualified engineer, plus the rest of the tradesman in the shop, about this very fact. Ended up we set up a repaired pump, put an ammeter in the circuit and I showed them it was true.

A positive displacement pump, usually a piston pump, is an entirely different matter. Close in the discharge on one of them and stand well back, as it WILL definitely break something!