What is Effective Working Pressure (EWP) on Pressure Cleaners? What is Maximum Pump Pressure? What is Operating Pressure?

Maximum Pump Pressure (or Maximum Rated Pressure)

Max. Pump Pressure (in psi) is the maximum pressure the pump can take or which it is rated at – using in our case an Industrial Water Blaster. If you put too big an engine/motor on a pump and you drive it above this max pump pressure, you can
damage or ‘blow up’ the pump. Maximum Pump Pressure is the Maximum Rated
Pressure the pump can operate at.

This has nothing to do with the OPERATING PRESSURE (or ‘pressure at the nozzle’ or
‘working pressure’, except to know that the OPERATING PRESSURE must be below
the MAXIMUM PUMP PRESSURE otherwise you will damage the pump and lose your

Most companies only give you this Max Pump Pressure and not the OPERATING PRESSURE – which is the important one. Unlike other companies, we put Operating Pressures on our Spec Shhets and other documentation because that is the important one – the REAL pressure. This OPERATING PRESSURE can often be changed on the request of the customer depending on customer needs or application.

Example: A pump might have a MAXIMUM PUMP PRESSURE of 3500 psi, 15 lpm
which may require 10hp to drive it to this pressure. We might put a 10 hp
engine/motor on it but still only set it up at an OPERATING PRESSURE og 3000
psi, even though there is enough pressure to drive it to 3500 psi. Why? Because
for most general cleaning of painted surfaces you don’t want a set-up pressure
of more than 3000 psi because you will damage the paint.

Now if you only put a 5 hp motor/engine on this pump which requires 10 hp, you will still get 15 lpm running at the same revs (because for every stroke of the piston a certain volume of water is pumped which does not change) but the pressure will only get to half of 3500 psi, which is an OPERATING PRESSURE of 1750 psi.

Operating Pressure in Industrial Pressure Cleaners

As we’ve explained above, the OPERATING PRESSURE (or Set-up Pressure) is the
pressure at the nozzle, which can be read on a proper Pressure Gauge fitted to
the machine.

Operating pressure is firstly dependent on the power of the engine/motor that drives it
and secondly on the application.

EWP – Effective Working Pressure

*EWP = Effective Working Pressure (using a Turbo Nozzle) – is a
theoretical figure. Because the water stream from a turbo jet does not fan out
and the force of the jet stream does not dissipate as is the case with a fan
jet/nozzle by the time the water hits the cleaning surface, the concentrated
pencil jet stream hitting the surface is equivalent to a cleaning effect around
60% higher than with a fan jet.

And because the turbo nozzle /roto jet spins in a circular motion at a very high
speed, it still covers the same surface area as with a normal fan jet/nozzle
giving you:

  • Better pressure where it hits the surface (~60%)
  • ~60% better cleaning
  • Same cleaning surface area
  • Much faster cleaning speed

But it is not really 6960 psi.
It really says: If you compare a normal fan jet at 4350 psi’s performance,
a Turbo Nozzle’s performance is 60% better and it is almost like using a fan
jet at 6960 psi.

EWP is very confusing and we only quote that figure because some opposition
companies do that – giving people a false sense of expectations from their
Industrial Pressure Cleaners – which is even more of an issue when it comes to
Domestic Pressure Cleaners which are not fitted with pressure gauges – or which
are fitted with some sort of gauge which doesn’t give you psi, just numbers
which can be mistaken for psi and again misleading the buyer.

We are slowly deleting EWP off all our documentation.