The problem is the age old one of being in the shower and someone else runs water, this will reduce the pressure in either hot or cold flow. Am I right in thinking that all the balanced pressure valve does is to maintain the BALANCE of the hot and cold feed to the shower head as set by the individual at that time? The reason for this apparently daft question is because I have been told that the valve maintains the pressure to the shower head regardless of other activities in the rest of the house/system. If I am correct then it seems to me that to maintain the pressure to the shower would require a separate feed from the mains pipe owned by the water company. Please put me right or confirm. Thanks