After checking mine over today the motor still has the Clarke plate on so it original.I did check mine and it is the same model, SE14A150. the motor looks identical so it is original, single phase 3hp, 150l receiver. mine is dated oct 1989.
If it doesnt cut out maybe its just adjusted too high - pull the cover off the pressure switch and wind the nut down a bit
Also I though the pump had been replaced, but looking at others on google the pump looks the same so guess that’s original too.
Mine is date stamped as July 1986. Clarke have already responded to me to tell they don’t do any spares for it anymore due to age so I’ll have to get gasket paper for the pump to rebuild it