megaflo pressure

[budvar]

Can anyone please tell me why when I open a cold tap, the pressure drops noticeably on my shower; however, when the hot tap opens, there is less of a change. If I open both the hot and cold tap in the bathroom, the hot is noticeably faster running than the cold. I have a

water softner fitted with a highflow kit but even if I bypass that, the

cold isn't as good as the hot. There is 7bar coming into the house, reduced to 3 at the megaflo and I am getting approximately 20-25 litres

per minute out of the shower. Is this normal or does something sound not right? Many thanks in advance.

[Ron Lowe]

I've observed something similar on my 250l megaflow, with the hot running faster than the cold.

I theorised that this is due to the expansion air volume in the cylinder acting as an acumulator on the hot side, as the water heats up. The check valve in the expansion core unit prevents this pressure from venting back to the cold feed. So the cold feed is regulated to 3 bar, but the hot output will be higher as a result of the thermal expansion. Also, the cold pressure will drop from standing pressure to a flowing pressure, but the hot has an accumulator to even out instantaneous pressure drops caused by running another tap.

I don't get much problem with the shower, though.

Have you plumbed the cold supply to the shower mixers from the correct place: eg a 3-bar ballanced feed from after the pressure reducing valve, but before the expansion core unit ( combined expansion relief /Check Valve )?

If you are feeding the shower cold directly off the 7-bar mains in, then it may be more prone to pressure variation than if you use the regulated 3-bar tee-off like you're meant to.