Lectrician wrote on Feb 3rd, 2010, 8:53pm:As far as I know, pressure is affected by the length of pipe, the number of bends and the internal diameter.
This is why they would like the 22mm to end as close to the pump.
Size affects volume and not pressure.
The reason you take 22mm as close as possible to the pump is to avoid starvation. Gravity in pumped pressure out, so you need to avoid more trying to get out than can get in.