JJ,
I bought this in early 2008 so don't get me to lie about verifying the specs, but as I recall it was rated as 4000psi @ 4gpm. The static pressure (without flow) is around 4300 psi, with trigger pulled and engine full speed with a 25 degree nozzle the working pressure is 4000 psi. I do not have a flow meter for this application so this may be questionable. This is with new nozzles which makes a big difference.
In hydraulics as you and I both know the realtime pressure will be limited to the resistive forces the cylinders impose on the flow of the hydraulic fluid. So the pressure the system is under varies widely (assuming an open gear pump system). In the case of a pressure washer the nozzle acts as a choke of sorts and the resistive force is more steady state. Obviously worn nozzles with an enlarged oriface will allow a higher flow while the pressure would decrease.
At any rate 4000 psi is more than you need for most cleaning jobs and I was more interested in getting the higher flow rating. My prior experience with the small units developing 1.5 to 2.0 gpm was they take too long to clean something.
What is more important when shopping for a pressure washer is the design life expectancy. Most low cost pressure washers will have a shorter life than a top quality commercial model, I feel this is a more important consideration when shopping, I feel the Northern will have a much lower life expectancy when compared to a top of the line commercial unit that sees daily service (and costs alot more).
