Picture would be good Ian Giles because most is double dutch on this so far?
I'll do a pic later if I've the time....
I have a cheap, plastic hoselock inline tap in the hose that leads from my van tank to the pump, I have this set so that it gives me the flow I require for working.
This is in the negative pressure side of the pump, ie the pump is 'sucking' the water.
Everyone else has their flow control the other side of the pump, the positive pressure side, and unless you have an ecoflow or varistream setup you run the risk of burning out your pressure switch.
When I first decided to put my flow control in the hose leading from the van tank to the pump I was just keeping my fingers crossed it would work....well 15 months on it still is, so far as I am aware I'm the only person who does this...it just occurred to me at the time that it would be a good way to reduce the strain on the pump's pressure switch.
So far so good

And it cost less than a fiver too :
Ian