Pressure tank cycling with sprinkler recommendations

[Bannerman]

Your pump currently delivers water at 15 gpm or as you now calculate, 13.98 gpm whenever it is running. If you are operating only 1 sprinkler consuming 4.1 gpm, once the system pressure drops to 40 psi, the pump will again pump 13.98 gpm so (13.98 - 4.1) 9.88 gpm will refill the pressure tank until the pump shuts off at 60 psi. The high-low-high pressure cycle will continue to repeat for as long as that sprinkler continues to flow water. The pressure to the sprinkler (or a shower, laundry, DW etc) will continually fluctuate between 40-60 psi.

A CSV will control the delivery from the pump, to satisfy the gpm that is actually being used once the pump is running. With a 40/60 pressure switch, the system pressure will drop as usual to 40 psi to start the pump, but once started, the system pressure will rapidly rise to 50 psi where it will remain consistent @50 psi as long as between 1 gpm - <13.98 is flowing. Once water use is stopped, the CSV will then allow only 1 gpm from the pump to finish filling the pressure tank to 60 psi to cause the pressure switch to shut off the pump.

A pressure tank size is typically determined by calculating the pump's delivery rate, to allow the pump to run for at least 60 seconds minimum once started. Because a CSV will limit the pump's flow rate to 1 gpm when flowing only to the pressure tank, a large tank will not be needed to provide the minimum pump run time.

Because the system pressure will need to drop from 60-40 psi before the pump will start, a large tank will result in longer flow time before the pressure will fall to 40 to start the pump to provide 50 psi consistently. A smaller pressure tank's pressure will fall more rapidly, thereby allowing the pump to run sooner and will thereby deliver a consistent 50 psi quicker than when a larger pressure tank is used.

 

[Ballvalve]

Right, I get that. A CSV would be great for sprinklers OR just run more flow than the pump to keep it running. I'm questioning more daily life without sprinklers. Having a CSV for sprinklers is probably the best option but then it doesn't seem like a CSV would be good for daily life after sprinklers shut off (again, at least for me, my wife and son).

I just watch my pressure gauge when all the sprinklers are on and crank up the shut off pressure a bit until it holds just under shut off ... Pipes take 160 to 500 psi, so I never understood the worries about higher pressures. My dishwasher says 120 psi feed max.

 

[Sponsor]

 

[Valveman]

I just watch my pressure gauge when all the sprinklers are on and crank up the shut off pressure a bit until it holds just under shut off ... Pipes take 160 to 500 psi, so I never understood the worries about higher pressures. My dishwasher says 120 psi feed max.

That will work as long as you use enough water to keep the pressure within limits. With a 14 GPM pump you could probably turn up the pressure switch from 40/60 to 60/80 or so and keep the pump from shutting off when using 10 GPM or more. But using less than 10 GPM would still cycle the pump. That method works well with jet pumps that can't build much pressure, but rarely works with submersibles.

 

[Valveman]

No I completely understand that. Water usage needs to be more than the pump to keep the pump running.

I just emptied my tank and timed how long it took to fill up. FL22 at 40-60 has a 19.1 gallon capacity per the spec sheet. It took 82 seconds to fill up. That means the pump was pumping at 13.98gpm. I would need to run three 5gpm sprinklers to keep the pump running. That's not a big deal. Just need to install another spigot which I wanted to do anyway. Since the sprinklers are being used when we are sleeping, they will be the only things running.

My question though, and maybe I'm not understanding the CSV fully, is during normal daily life if you don't use a lot of water, how does the CSV and small tank benefit you over a larger tank? From the math side of it, it seems like the smaller tank with CSV would cycle more, not less. The CSV is only good when water is constantly running for a long time. Even with a washer machine running, HE ones only use 14 gallons per run. With a CSV and smaller tank, the pump would cycle on once. With a 20 gallon tank, it wouldn't cycle at all. Hell, even throw in a toilet flush, wash your hands and someone cleaning dishes for 5 minutes. With all that going on at once, the CSV would cycle the pump once and keep the water running until the water stopped then filled the tank while the larger tank would cycle the pump once and fill the tank back up. Both systems cycling the pump once. For the CSV and smaller tank to cycle less than a larger tank, I would think a lot of things would need to be using water. Maybe a washing machine with a shower going, someone flushing a toilet and washing their hands and then maybe even doing dishes or running the dishwasher. In that extreme case, I would say the CSV would be the better option. But to me, normal daily life, a larger tank would cycle much less...but maybe my exact situation is different than most. Maybe my wife and I use a lot less water than other houses.

As has been said, irrigation, long showers, and other long uses of water is what causes cycling problems. You really can't get a large enough tank to eliminate the cycling for long uses of water. Plus, the larger the tank, the more obvious the 20 PSI difference in pressure, and the longer you are at the low end and living with low pressure.

The CSV fills the pressure tank at 1 GPM and uses the pressure tank more as a mechanical timer.

A 10 gallon tank only holds 2.5 gallons of water, the same way an 80 gallon tank only holds 20 gallons of water. With the CSV the tank is more a mechanical timer than for water storage. Your water comes from the well and pump, not the tank. With a 40/60 switch, CSV set for 50 PSI, and a tank that holds 2.5 gallons of water, the pump will run for 1.25 minutes to refill the tank from 50 to 60 before shutting off. It doesn't start this 1.25 minute tank fill timer until the toilet is full, the showers are off, and no one is using water. With several people in the house or not, someone will normally use water within this 1.25 minute time, the pump does not shut off, and the timer starts again. It is very common for the CSV to make the pump run continuously 30 minutes to 2 hours, during times when people are home getting ready for school, work, or later to bed. This makes the pump only cycle once, even with a small tank, when it would normally cycle many times without a CSV using a large pressure tank.

The large pressure tank method has worked for a hundred years. But there are many disadvantages to letting the pump cycle on and off. A CSV solves the cycling problem no matter if the water is being used 24/7/365 or just for occasional use.