I teach at a school in (old) Mexico. It is a two-story building with a basement. The city sends us water, which we collect, in a large storage tank, the level of water in the tank is about 2 feet above a centrifugal pump inlet. The pump is huge, powered by a 5-hp motor. It has a check valve on the inlet side. The outlet has a tee, which allows water to go into the building piping and over to a bladder tank. The water lines go all the way up to the roof to supply water to 8 large evaporative coolers, so the total height above the pump is about 35 feet. We have vacuum flush bathroom fittings on the second floor and on the first as well. During break or after recess we could have as many 8 toilets flushing nearly simultaneously, with the coolers drawing some water as well as sinks or water fountains. We never seem to hurt for volume/pressure when the pump is running.

Our bladder tank has no actual or useful volume information. Looking at the dimensions (diameter 2 feet, height 5 feet - - 2x 3.14 x 5 = 31.4 cubic feet or 235 gal - say 215 gal actual interior volume), I still have no idea of the useful volume. If the FAQ example works, a 42-gallon volume gives about 6 gallons of useful volume. Does it follow that I could expect about 30 gallons?

We have two main problems:

The first is that the system cycles endlessly. Flush one toilet and with seconds the pump turns on. Turn on the hose outside and just listen to the pump going on and off.

The second is that if we don't keep the system pressure high, 42on-70 off, the pump turns itself off as it tries to start. The pressure switch is attached to the pipe very close to the pump outlet, along with a permanent pressure gauge. The switch turns on the pump a "pressure wave" spikes the pressure to 80+ psi and it shuts off, then on as the pressure drops, ruh . . . ruh . . . ruh. . Very bad for the motor and light bill.

We emptied the precharged bladder tank of all its water and measure the pressure at the top: 40 psi. We turned on the pump with the valve to the building off and it reached 70 psi in seconds. We turned off the pump and measured the water that comes out: about 1.5 gallons.
We emptied the air out of the precharged tank and turned on the pump. It ran for considerably longer, (maybe 90 seconds) making strange whooshing noises, and shut off at 70 psi. We measured this volume: about 11 gallons.

The pump has a 3/4-inch outlet, as does the pressure tank. The pipes expand out to 1.5 inches in between. Could it be that friction in the pipes keeps the pressure tank from ever really filling with water? Would it help to add another tank "in parallel"? We have room for 3 more of the same size. The FAQ said itís not good to use a pressure switch with a centrifugal pump - - but it's what we have. Should we change? To what?

The system has worked marginally for 5 years. When we "tweak" it does not cycle quite as badly, but its time for a change. I'm willing to spend money, but our missionary budget only allows for one shot on this. We can buy stuff down here, that is our preference, or we can import from El Paso, Texas. Any ideas?

If we put an air buffer column between the pump body and the pressure switch, would that help dampen down the cycle start tendency?