Spot on from Alex
Tosh mentioned something almost identical to that as I was musing with him why mine and squeaks systems seem to vary.
It was really bugging me
Mine is perfect, with the inline on/off valve (that is always at my waist) I can turn my flow down to little more than a trickle if i want, and the pump continues to flow smoothly, flat out I have jets of water going over 15ft through the air.
It is really good to know that you can actually fine-tune the actual pump, as this then does away with the need for a bypass or varistream controller.
I can't help thinking that it is a lot of messing around turning flows up and down. I do put a control on for people wanting to reduce the flow, but that is more to do with how fast a person can work. A fast worker would have it on full flow, and a slow worker would have the flow reduced. A slow worker on full flow will waste water, and a fast worker on a low flow will wast time. If you want less water on the glass move the brush faster. All I want to do is turn the water on or off.
Peter
totally agree with Peter too, succinctly put Peter
Ian