[Nameless Drudge]

The question, WS202  at 21l/min with 065 nozzle,3000psi.To use less water(15l/min) i put on a lance with an 045 nozzle.Do you drop the revs and fit a pressure gauge so you can see 3000psi still being produced and the nozzle size limits the water flow down to 15l/min or do the revs stay the same,the nozzle itself is responsible for the reduction in flow and the unloader valve is preventing the pump from being overstressed?
I would be delighted if someone could enlighten me or suggest where to find/understand this scenario.

[BDCS]

Yes and yes.
  Flow is governed by the nozzle size as is the pressure. A pump for a given rpm will give a flow related directly to the rpm's . More revs = more flow.
 The unloader gives the maximum pressure and dumps flow when this max pressure is achieved.
 So you put a smaller nozzle, drop the revs till the flow is just below where the unloader lifts or as you say the guage reaches 3k psi.
  Yes you were right. You could still run the motor flat out but that would beat up the unloader - dropping the revs entends the unloader life.
 Flow is inversely proportional to pressure  :

[Nameless Drudge]

Many thanks Sir,i believe i have grasped it now.