Does this make sense?

[Steve Brown]

I'm thinking of doubling water tank capacity and halving the range, from 30/50 to 40/50, for two reasons. The first to have less water pressure variation between turn-on and turn-off of the pump, and the second is to have a good reserve of water in the tank in the event of a power outage. To do this, I would set the air pressure in the tank to 28 psi when water is drained from the system, then set the pressure switch to turn on at 30 psi and off at 50 psi. After checking to make sure the system is operating normally, I would then adjust the pressure switch to turn the pump on at 40 psi and off at 50 psi. The idea is to maintain at least a 50% reserve of water in the tank. When the power goes out, water from that reserve can be used until the pressure drops to zero.

I'm thinking there may not be a linear correlation between pressure and volume of water in the tank, so the turn-on point may have to be above or below 40 psi to have a 50% reserve of water in the tank when the pump turns on. That point can be ascertained by measuring the gallons of water as the tank slowly drains and plotting number of gallons against pressure. The turn-on pressure would then be set to the point where the tank is half empty or half full, depending on whether you're a pessimist or an optimist.

 

[Reach4]

Your idea works. You would need to use an electronic pressure switch to have the narrower setpoints.

 

[Sponsor]

 

[Valveman]

You can get an electronic pressure switch that will do the 10 PSI on/off here.
http://cpkits.com/collections/all/products/electronic-pressure-switch-1

An 80 gallon pressure tank working at 40/60 only holds 25 gallons of water. So you will only have about 12 gallons of storage doing as you describe. Plus reducing the on/off bandwidth by 50% will cause the pump to cycle twice as much.

Without a CSV the pump will cycle on and off for every 12 gallons of water. The pump will continue to cycle on and off WHILE you are using water. So the tank will most likely be at 51 PSI when you shut off the shower. This only leaves you 12 gallons remaining in the tank for power outages.

One way to have a more constant pressure and to utilize as much of the tank for storage as possible is to use a CSV. When taking a shower or using water for other longer term uses, the CSV will keep the pump running at a steady 55 PSI as long as the shower or any water is running. This will maintain pressure even more constant than letting the pump continue to cycle on/off between 50 and 60. Only when all the faucets have been turned off will the CSV let the tank fill from 55 to 60 PSI and shut off the pump. This assures that your pressure tank is always refilled completely after every use of water, which does not happen without a CSV. Always having 25 gallons of water in the tank during a power outage instead of just 12 gallons can be a real benefit on top of the steady constant pressure and eliminating destructive cycling, which are the primary benefits of a CSV.