Thanks for all your replies,
i have just attached my backpack to my 50 m half inch garden hose..... attached my pole and cleaned upstairs windows....
so the 40 psi will work using it for a van mount, the only thing that concerned me was that although i could still clean on the No.2 setting, the pump was louder and sounded under strain, i also think the battery will wear out quicker as they are only small,
So although it does work, i think Mac gold is right in that the pump is a boy doing a mans job and wouldnt last the pace.
Thanks again for all your input lads.
Gary.