qcprc said:
Thanks for the information. I guess I'm confused with the pressure vs. volume issue. So what is the difference between, let's say a 1/2 horse pump vs. a 3/4 horse? More volume at a faster rate?
In general terms you could say that pressure is the resistance to flow and volume is how many gallons is delivered by the motor in overcoming the resistance to that flow. The bigger the horse, the more work can be done, but if the wagon is the same size and the same volume of material is in the wagon and the weight is the same..... the bigger horse eats more and takes up more room for no gain. Unless you drive the horse faster, the result is the same.
As to tank size.... The size of the tank is to be sufficient, at the pressure range the pump is operated, to allow the pump motor to be off for at least 60 seconds for motors of up to 1 hp. Over 1 hp up to 2 hp the minimum is 120 seconds; above that the time needed is increased. That is to allow for proper cooling of the motor betwen pump runs. The pressure range used dictates the drawdown gallons provided between pump runs. The higher the pressure the fewer gallons no matter what size tank. I.E. a 20 gal nominal will provide about 6.5 gals at 20/40 psi, about 5.2 at 30/50 and about 4 at 40/60 etc.. The larger the tank the more gallons but... you can go too large and cause water quality problems and/or pump problems depending on the pumping level and recovery rate of the given well and pump or cause a 'dry' well condition at times of heavy water use.
In more or less layman's terms... To size a pump you have to know the peak demand gpm the building requires (your fixture unit count) and how much 'work' is required to provide them, then you apply the horses to get the gpm to where you need them or where they ned to go, or in other words, to get the job done. The hp has little to do with the gpm output of the pump. That's because all pumps have two parts; the wet end or stages, and the motor. The wet end is rated in gpm and the motor in hp. Between the two, they deliver the gpm to where it needs to go at whatever 'head' (elevation/height/pressure) the system has to be able to overcome, including friction pressure losses of the plumbing material used.
Gary
Quaity Water Associates