thanks for the reply, i've been doing a little research on the type of auto valve i would need, and i think i made a booboo when i called it a bypass valve, because that is what i want to use it as, however, looking at the bypass valves available, and how they work, it is unlikely i will find a suitable one, because they work on a differential pressure basis, and i doubt anyone would expect a differential of 2.5 to 3 bar across the valve
.. what i actually need is a self resetting pressure relief valve
so, sorry, by bad on using the wrong phraseology
23.5 metres, could well be about right, it sounds about right
... to be honest, i've not actually worked it out
and yes, initial tests on the pump and pipework during the flushing stage, with the supply disconnected from the shower, and the flow triggered via a makeshift pipe pointed into the bath with a full bore valve to open and close the end resulted in the bath filling faster than it could drain
But, this was with the bypass closed completely, and i knew that would never be the case when the shower was fitted because of it's method of restricting the flow to allow time to heat the water (and also supply pipe size at the shower inlet) the only reason i am thinking of an auto system rather than the manual valve is that like electricity, water will take the path of least resistance, so if i have the manual bypass open too far, the pressure behind the shower unit is somewhat low and not exactly optimum, however, if i close it off too much and someone turns up the temp fairly high, with the shower set to low flow via the selectable buttons, then i would create too much back pressure at the pump !
the pump btw, is rated at 45 litres per minute, so i have to feed the excess back into it's supply line, or the storage tank would be gone before i had time to finish washing my hair