[Dave Willis]

What determines the pressure rating of a pump? ie. what’s the difference between a 100psi pump and a 60 psi pump? Are the internals the same and are the pressure switches different? Can a 100psi pump be downgraded to 60psi or less and vice versa?

I have another use for a pump besides cleaning windows but for a different application with different settings and was wondering if I could adapt one of my spares.

[P @ F]

I think it is the little screw by the PS one way raises and the other lowers I believe

[Simon Trapani]

Wait for Spruce to come along...

[P @ F]

It’s also possible to dremmel a little bit off the spring , can’t think who it was that did it though !

[Spruce]

Wait for Spruce to come along...

[Spruce]

What determines the pressure rating of a pump? ie. what’s the difference between a 100psi pump and a 60 psi pump? Are the internals the same and are the pressure switches different? Can a 100psi pump be downgraded to 60psi or less and vice versa?

I have another use for a pump besides cleaning windows but for a different application with different settings and was wondering if I could adapt one of my spares.

In the old days of 1/2" hoses our Shurflo pumps were 65psi units.

When minibore and microbore came out they uprated to pump to 100psi. I checked the parts list of both of the pumps and they listed identical part numbers for the motor and pump housing assembly. The only thing they changed was the pressure switch and I presume they used a stiffer spring to give them the extra pressure before it cut off.

I haven't tried it but there were a few cleaners who just used a PWM controller and adjusted the pressure switch to a lower cut off pressure with that screw adjuster on the pump housing.

We were also able to use the old 65psi pump with a Varistream controller that could be set higher. I'm presumimg the reason why Williamson pumps recommend removing the pressure switch from the circuit was because of this 65psi/100psi conflict.
 

[Dave Willis]

Thanks Spruce, the one I want to replace is 11Lpm and 25 psi so looks like our pumps aren’t quite suitable.

[Kinver_Clean]

I would give it a try. The pressure switch should be able to be turned down so the pump cuts at a lower pressure. If not find a pressure relief valve and dump the excess back to tank.

[Dave Willis]

What it is ........ I have a canalboat that has fitted from new some horrible noisy Chinese crap but the specs are quite different. Eleven litres a minute max which is nearly double my nice quiet Shurflows and Flowjets knocking about my garage. I reckon maybe the pressure can be backed down but the flow maybe too little. It feeds an accumulator tank too.

[Spruce]

What it is ........ I have a canalboat that has fitted from new some horrible noisy Chinese crap but the specs are quite different. Eleven litres a minute max which is nearly double my nice quiet Shurflows and Flowjets knocking about my garage. I reckon maybe the pressure can be backed down but the flow maybe too little. It feeds an accumulator tank too.

Low pressure, high volume unfortunately. You would be better replacing the pump with a suitable Shurflo replacement imho. Our pumps are 5lpm. They change the flow of the pump by changing the camber of the pump mechanism. So the 3.8 lpm Shurflo pump has a shallower 'stroke' than the 5lpm pump.

I very much doubt you would get one of our pumps down to 25psi. But without the volume the shower won't work properly, especially if the pump is supplying a hot and cold feed and another tap is opened at the same time.

I would check how the pump is mounted as you might be able to better isolate the vibration transmitted though the steel boat structure.