Look for a tap that says 0.2bar, or lower.

Normally any tap with 10mm flexible tails would be unsuitable.

15mm copper tails or flexible hoses, anything smaller you can forget normally.

I am trying to establish pressure bar figure more accurately
Guide line is 1 mtr column of water equates to 0.1 bar pressure
I have measured from basin tap outlet to top of water in cold storage tank,this measures 2.05 mtrs,therefore 0.25 bar pressure.
Are my assumptions correct.
If figure is correct would you install a single mixer basin tap bearing in mind tap minimium operating pressure is 0.2 bar.
Apologies for dragging this one out again

Quote:


0.25 bar would be the static pressure with the storage tank full and no water flowing. There will be some pressure losses in the pipes, bends and valves when the water is flowing so in practice the tap will "see" less than 0.25 bar. 

These days most manufacturers say high pressure is >0.5 bar and low pressure is <0.5 bar.

To be honest it's a waste of time trying to work it out very accurately. The problem is that you have 0.1-0.25 bar when a mains pressure system (eg combi boiler or mains pressure tank) would deliver perhaps 1 to 4 bar.  

As TheScruff said earlier, you need to find taps that claim to work on 0.2  bar or possibly even lower. Taps that claim to work on 0.1 bar should work better for you than those rated for 0.2 bar and above. It will help if they have copper tails rather than flexible because flexible pipe needs thicker walls that reduce the internal diameter and restrich the flow. I would also look to see if the manufacture claims the taps were specifically designed for low pressure.

The problem is that modern tap design has been driven by the availability of higher pressures. The way ceramic taps work means that the free area is never more than half the bore and frequently nearer a quarter. Nobody back in Victorian times would have designed a tap that worked like that. Their taps were the shape they were for practical reasons.. it lets more water past the washer.  

I think it's more a case that the introduction of mains pressure systems (1986?) allowed tap designers greater flexibility to design modern single hole taps.  Prior to that all(?) systems were gravity so all taps had to be suitable for low pressure.