The Shurflo pump used on the latest Aquamist HFS (High flow system) range utilises three internal by-pass valves, set at 125psi. The pressure does not fluctuate . This is our solution in combating pulsing characteristics of the "demand switch" arrange use on all shurflo based systems. The pump is available separately, complete with 22cc accumulator:
If you look carefully, there is no demand switch on the front.