If the pump is running steady and not cycling on and off while you are using water, there is probably nothing wrong with the CSV or kit. Check to see if the pressure gauge is holding steady 50 PSI or so while you are using water as described. If the pressure drops very far below 50 when more than one tap is on, the pump is just not producing as much water as you are using. If the pressure stays steady at about 50 as it should, the pump is large enough and most likely you have a restriction in the lines after the CSV. If you have multiple outlets on the same 1/2" line, the shower pressure will drop even though the CSV is holding 50 PSI constant. With a 3/4" line you would not see the low shower pressure when a toilet is flushed on the same line.
