Water Pump Cycling

[MichaelJohn]

I've read a lot on forums about water pumps but none that answer my query.

I've a Hitachi WMP-350GX and 2 story house. The pump draws from a storage tank.

Sometimes, if the demand for water is low (i.e. washing hands under a slow tap, running the water filter which can only cope with slow throughput) the pump "cycles" on for 2/3 secs, off for 2/3 secs, on for 2/3 secs, off for ......

If the demand is strong, tap on fully, shower etc then the pump runs continuously.

Is the "cycling", at low demand, normal or is there something wrong?

Any help would be much appreciated.

[CharlieH]

Mine does the same and apparently you can actually adjust how it responds inside the box next to the valve. Personally it doesnt bother me and as long as it pumps I dont mess with it.

[tig28]

Hi MichaelJohn

Unfortunately the pump behavior you describe is "normal" for most pumps. It shortens pump life considerably. For most local installations they simply "under-pump" the house and put up with low pressure.

I know of 2 solutions.

#1: You could purchase a "bladder tank" to be installed after your pump. These tanks act as the primary storage & delivery system for water to your house. Dependent on the size chosen they allow hundreds of liters to be delivered without your pump even starting.

#2: You could replace your existing pump with a Hiatachi inverter WM-PxxxGK (I use the P400GX)

This pump slows/speeds-up the electric motor according to demand which allows a tap to be only 10% on and the pump simply runs slowly. More demand -- more pump speed. No cycling.

It is about twice the price of a conventional pump -- but comes with a 5 year guarantee.

http://www.hitachi-th.com/hitachi_new/products/productdetail.php?lang=&ProductID=11&ModelID=9077&store=wpspec_e&storename=ProductNameEn

Hope this is of help.

Edited September 3, 2012 by tig28

[Rooo]

Moving to housing forum.

[MichaelJohn]

Thanks for your replies :-)

We considered the Inverter type but weren't aware of the "problem" (issue) before we bought.

Next time - which I guess will be quite soon (!) we'll buy the better one - thanks Tig28, most useful.

[tig28]

"We considered the Inverter type but weren't aware of the "problem" (issue) before we bought."

Precisely as I did!

[Langsuan Man]

If you replace your current pump then I would suggest the Grundfos line of pumps since they have the bladder as part of the pump system

http://www.grundfos.com/companies/grundfos-thailand-sales.html

[Pib]

Since the Hitachi WMP-350GX on has a small 1 liter bladder/nitrogen pressure tank there is very little water draw-down capacity from the small tank (probably around 250ml which is really meant to prevent frequent pump turn-on due to small leaks), the pump will basically turn-on whenever you draw water. It's pretty much designed to run whenever water is needed compared to pumps with larger pressure tanks which cycle less due to the larger water draw-down capacity.

[electau]

A pump system such as this would suit your requirements, similiar types are available from other manufacturers such as Grundfos. This particular type may be available in Thailand.

http://www.davey.com...re_Systems.aspx

Edited September 4, 2012 by electau