I'm confused, why do some controllers use the pumps pressure switch whilst others don't?
Because it's cheaper to make a controller that still utilises the pump's cutoff switch. The controller just reduces the speed at which the motor turns so the pump delivers less water but once you dead end the water flow the pump's pressure switch will cut the pump at what it is set at - say 95psi.
Other controllers that are more expensive do away with the operation of the pressure switch and allow you to regulate the flow and pressure that suits you electronically - hence less wear and tear on the pump, fittings etc. The pump in my son's van is 5 years old and the pump in my van is nearly 7 years old - both Shurflo pumps with Varistream controllers.
I once put a water pressure gauge on the pump on my van to see out of interest where I had set it to my requirements - It was around 55 psi.
Spruce
Some good points here. That show how using a purpose designed control can give years of service, I have come across some of our early analogues that are going strong after 5 - 6 and 7 years. These units perform a basic funtion very much as described by spruce EG they slow the pump down reducing wear and tear and water use.
As our understanding of how a WFP systems works, in particular pressure when in DE.
We made an engineering decision to design a controller that would run with a pressure switch. It took a lot of time and coding of the processor to achieve this, The cheap option for us would have been not to include this in the design.
We found that disconnecting the pump pressure switch could lead to high pressure build up while in DE.
With some controllers the pressure will just continue to build up with nothing to stop it.
Left in this DE situation with no pump pressure switch, can mean that hoses connectors will blow or hoses split.
It is also creating a lot of strain on the motor as the pressure has to go somewhere, This can lead to the pump turning - and dumping water somewhere.
By taking the technical route of designing in the pump pressure switch, The pressure switch becomes helps protect the whole system, as the pressure will never get so high that it blows something or dumps water in your van through leaks.
It was important to us that the controller was able to protect the whole system, this is an area we continue to develop. This is one of the differences between our and other controls.