Confirmation on different types of pumps, shower etc.

[xr4x4]

Hello all,

I'm looking to find a definitive answer of the different types of pumps, shower and the like. As there's a lot of different answers out there on the web.

As I understand it there's two main/common types of pump out there..
1 positive head (most common)
2 negative head (less common and more expensive)

Now, let's say for example im talking about a twin impeller pump for a shower.

Is it correct that....

A positive head pump needs to have a certain head of water, therefore needs to installed under the main cws tank and the tap/shower outlets must be below the head of the cws.

A negative head pump is the same as above but outlets can be above the head of the cws. I.e in loft conversions for example.

Could someone please confirm, or put me straight please.

Many thanks in advance.

 

[Madrab]

Yes that's about it.

It's all to do with where the head of the shower is located.

If the showerhead is located at least 100mm below the level of the cold water tank then it's usually classed as positive head.
If the showerhead is less than 10mm or above the level of the cold water tank then it's classed as negative head.

The way to know is, if the showerhead is on the rail at the height you use it and when you turn on the water, there is a minimum amount of water coming out of the showerhead (usually around 1>2 ltrs/min) then you can use a positive head pump, anything less then a negative head pump should be used.

As to pump location, ideal is situated beside the hot water cylinder on the floor.

 

[denso13]

Useful diagrams here http://www.bellabathrooms.co.uk/blog/2011/03/shower-pumps-explained/