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Re: Pressure washers

Typically, small pressure pumps are piston pumps (positive displacement 
pumps. They are cheap to make, and I'm pretty certain that most of the cheap 
car/house cleaner pumps are single or dual piston pumps. New material being 
used today for the cylinder and piston ( pressed ceramic, sintered 
stainless, etc) allow these high performance parts to be made cheaply. 
Furthermore, external/internal gear pumps, lobe pumps, gerotor pumps and 
some vane pumps are typically used for higher viscosity liquids (hydraulic 
fluid). It is unlikely that the pressure water pumps are centrifugal pumps. 
However, multistage centrifugal pumps are typically more reliable at high 
pressures than positive displacement pumps. We have replace our high 
pressure (2250 psi, 150 gpm) positive displacement pumps with centrifugal 
ones.
As far as "dead heading" the pdp, you're right, it will cause high 
temperatures in the cylinder and head regions. Since a PDP reaches it's max 
pressure quite quickly, I would imagine you would have the pressure that you 
desire within less than a minute. If you intend on keeping the pressure for 
any length of time, I would suggest an intensifier. This is a device you can 
make or buy that uses the conservation of energy theory. On one side of a 
piston in a large cylinder you have an area of 15 square inches. On this 
large surface area, you use air pressure at 100 psi. On the other side, a 
shaft of one square inch of surface area in a smaller piston is in contact 
with the water. The pressure at this point is 15*100/1=1500 psi. With this 
process, you can make your hydrostatic test rig. I've used these before 
(commercial units) for performing hydo's on fire water systems (250psi), and 
they work great. Hope I didn't get carried away here, but sometimes I get in 
the mood. Good luck with your chamber. It sounds like something I would try.
Suds


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