This video shows what I am experiencing, but I have longer cycles: I went with a larger Amtrol ST-12 thinking it would help maintain a bigger buffer of pressure and smooth out the pump engagement, but maybe it is taking a little too much work off the pump slowing the feedback loop that the pump depends on. I might give a smaller pressure tank a try. I imagine if I had much higher flow, or a lower set pressure, it might stay on longer or continuously. My theory is now that there is more 'elasticity' in the system that allows pressure to be maintained within the 10psi target band of the pump for longer so it takes breaks. It seemed to cycle a lot less before I introduced the external pressure tank. I just spoke with their distributor and he told me that this seems normal, but my understanding was that the pump should 'slow down' to maintain a constant pressure.

It clearly has speeds, as the pressure settings on the pump create audibly different frequencies. I thought the speed was supposed to be variable and expected it to hold a steady pressure at whatever speed was needed. Maybe it's unnecessarily stressing me out, but I don't like the sound of the pump turning on and off.

My measured pressure seems to ping-pong from 60-70psi as the pump goes on and off.

With 2 taps open wide, the pump clicks on for a mere 5-10 seconds, and then stays off for around 30, before cycling back on. Internal pressure tank, and external pressure tanks set to 70% of that = 50.75psi. Pump outlet pressure set and measured 72.5psi. I had a chance today to drain and triple-check my pre-charges were set to exactly the recommended pressure.

Used Grundfos SCALA 2 Grundfos SCALA2