I kmow this has been raised previously, http://www.thaivisa.com/forum/topic/691360-pump-differences/, however the basic question was not answered as the discussion became more about Buriram Province supplier.

I am about to buy a tank and pump for our new build. It is two story, upstairs shower at about 6 meters above ground level. The tank will be above ground.

In general, two types of pump are available:-

1. What are described on the box as Automatic Water pumps, which are tall and cylindrical in shape.(right front in the picture)

2. What are described on the box as Constant Pressure pumps, which are squat and rectangular in shape. (left front in the picture)

My question is, what is the difference between theses two models and which one is the better one to use in my domestic installation.

(I can determine the wattage of the pump and the volume of the tank myself)

They are designed for different purpose - the pressure tank was designed for wells to draw water up into pressurized container - which in turn supplies the pressure to force water to taps so pump only replaces water in tank to keep pressure above a low/high setting range - output pressure will vary. The other type is designed to increase already available pressure (such as from above ground tanks or public water supply) and provides full pressure when taps are opened and will normally run most of the time during usage, and with little pressure change, but there may be a slight delay when tap opened. Some of newer models, such as Grundfos. are highbreads designed to increase pressure but using small holding tank to do this so will cycle on/off but are almost silent in operation and have only small pressure variation.

Suspect more important is noise level - which you can not judge in shop. Check with other users for quiet model if live in urban area. Grundfos brand is my choice for nose reasons.

Thank you for your prompt replies.

Arjen...from how I interpret your describe, both pumps will supply water at a constant pressure, within preset limits (even a constant pressure pump must have upper and lower pressure limits). The constant pressure pump cannot, as I understand it. vary its pumping speed unless it has an inverter power supply.

lopburi3...you do describe the different purposes of the two pumps, however, which pump is the "pressure tank" pump and which is "the other type". of the two I show. (cylindrical tall pump and squat rectangular pump)...please

Which one is normally used in the domestic situation with a ground level tank fed from the city mains?

Sorry - that cylindrical shape is a cover over a holding tank and pump. Becomes more obvious when removed.

Neither type of pump actually delivers constant pressure.

Mitsu sell a more expensive type of inverter pump (IMCH series) that uses the sales pitch "Eliminate water pressure fluctuation problem in an ordinary automatic pump".

So the label right there on the plastic cover of the square pumps that says "constant pressure" should actually read "not constant pressure".

That said either square or round type would work in your application. I wouldn't go for the inverter pumps as they are expensive and the pressure variations are not a big deal in most applications.

It's sort of like the Hitachi pump, in Homepro and elsewhere, that says right there on the pump "stainless steel tank".

It is not actually a stainless steel tank.

It is a stainless steel cover over a plastic tank. Look underneath the pump to verify this.

Have never heard of any using a plastic tank (these are pressure tanks) - but they often have plastic bladder inside to separate water and air. Perhaps you see the holding plastic mount rather than the tank itself?

Go take a look at one.

When you look at the underside of the tank it is quite clear from the design that it is a pressure vessel made from plastic.

Is this the model you are talking about?

http://www.hitachi-th.com/hitachi_new/products/productdetail.php?ModelID=9078&store=wpspec_e&ProductID=11&storename=ProductNameEn〈=

The tank, made of thick stainless steel, is durable, clean, safe and rust-free.

I have a 2 story place with a pump with no tank, it's great, now 7 tears old..........Think it is 250Watt.....

Thank you all for your help and discussion.

I went to HomePro and bought a tank and pump from them on their advice(?)

The pump is an Hitachi WM-P350GX which they have on special offer at 6,300Bt; cheaper than the 300 model (it's the squat rectangular "constant pressure" type). It maybe over spec. but will certainly do the job

Time will tell...

Is this the model you are talking about?

http://www.hitachi-th.com/hitachi_new/products/productdetail.php?ModelID=9078&store=wpspec_e&ProductID=11&storename=ProductNameEn〈=

The tank, made of thick stainless steel, is durable, clean, safe and rust-free.

Yes. That is the one.

Thank you all for your help and discussion.

I went to HomePro and bought a tank and pump from them on their advice(?)

The pump is an Hitachi WM-P350GX which they have on special offer at 6,300Bt; cheaper than the 300 model (it's the squat rectangular "constant pressure" type). It maybe over spec. but will certainly do the job

Time will tell...

What size tank did you buy in the end??