To be fair to Williamsons, the Varistream was never designed to work with micro bore.
Remember it is also in affect the pressure switch.
When you stop the flow, a back pressure builds up and draws more amps from the battery, this increased amperage is sensed by the Varistream and it switches off the pump as it's designed to do.
When you have an unrestricted pump running, as you do with the pump pressure switch removed, everything works fine until that back pressure builds up, and this is what happens with micro bore,
the smaller bore, especially when coiled on a reel builds up a lot of back pressure, the Varistream cannot sense if this is you turning off the flow, or back pressure that's built up running through your system, it will turn your pump off, and as pressure drops, back on again.
It is this rapid cycling that does the damage.
It's hard to see how any device that measures the demand on amperage can overcome this problem.
How do you make a device that will overcome the back pressure, without blowing your connectors off when you want to stop the flow?
You could go back to using the bypass method in conjunction with a pressure relief valve, but that won't stop your pump from running when you stop the flow, so no saving on battery drain.
It's a hard one to crack. Dai