Ask a tradesperson

Anonymous user

This is a conundrum that most people struggle with as the relationship between pressure and flow is not easy to grasp. Without boring you with calculations and the physical characteristics of both, your query can be easily answered as it depends on flow rate, not pressure. When you consider that a meter of 22mm dia pipe holds more than double the quantity of water than 15mm dia pipe, (1mtr 15mm = 0.145ltr / 1mtr 22mm = 0.320ltr), and that the frictional losses of pressure are far less through 22mm than 15mm pipe, it is simpler just to confirm that you will get a far greater FLOW RATE through 22mm pipe than you will through 15mm pipe. In the instance of a bath, the important factor is the time it takes to fill it, not the pressure of the water as this will not 'speed up' the filling time. So, in laymans terms, you will fill a bath far quicker with 22mm pipe than 15mm pipe and the system pressure is not important.