Advice requested re: CSV usage with .75 GPM water usage in home

[Ladd]

My house's 23-year old pressure tank has had a bladder failure (Pro Source PS82T-T05, 35 gallon). When drained, the tank has no air pressure; after filling with air to 2 PSI less than the low cut off, after refiling, I get only about 2.5 to 3.0 gallons of water out of a basement laundry sink faucet between high cut off and low cut off. And a week later there will be no air pressure again as read from the fill valve.

I am considering replacing the pressure tank with a CSV setups, but from what I've read, a CSV is not recommended for my particular situation.

In addition to the well pump and pressure tank sending water to the home, between the pressure tank in my basement and the piping going up to the inside of the house, there is a "T"  that also sends water to a 1,700 gallon cistern buried outside the house, with it's own jet pump, which is used by all the outside spigots for gardening.

Because our well has a low recharge rate of only about 1 GPM (well is 800 feet deep, pump* is 500 feet down, head is 100 feet down), we refill the cistern at about .75 GPM and this refilling is set by timer-activated solenoid for 16 hours per day. All garden irrigation is controlled by other timers set for every three days and the entire yard is done in two days with a day of rest for the cistern to catch up and fully refill.  This setup has allowed the gardens to get the required watering AND for us in the house to never run out of water.

Given that we have multiple 16 hour days of .75 GPM water flow going into the cistern, plus whatever water we use inside the house, it is my understanding that a CSV setup is NOT appropriate as CSV setups require a minimum of 1.0 GPM for satisfactory operation.

I invite any and all questions, advice, suggestions and general wisdom regarding this.

Regards,

Ladd

*I'm not sure of the specs for the current well pump. The old pump was a Sta-Rite Signature 2000, model 5PHE02HL-02, Code 1J96P. I can find no information on this pump so I don't know what horse power it is, nor what is it's GPM.

[Cary Austin]

Doing a little calculating I figure your pump is cycling 72 times during the 16 hours of cistern filling for each day.  That adds up to 26,200 cycles per year.  That is why your bladder is broken, and the cycling is greatly shortening the life of your pump as well.

The problem with a CSV on the well pump is not the .75 GPM draw, as the 1 GPM minimum of the CSV would just lengthen the pressure tank fill times, and actually reduce the cycling considerably.  The problem is the backpressure that a 1HP, 5 GPM pump with a static water level of 100’ can cause.  That pump would produce 259 PSI of backpressure on everything before the CSV.  This would also require two CSV1A valves in series at the well head to stair step the pressure down from 259 Psi to the 50 PSI needed when using a 40/60 pressure switch.

In this way the CSV would work fine, but probably not be much of a benefit to you the way you are filling the cistern, other than just being good for the pump and bladder tank.

I would fill the cistern directly with the well pump and put a CSV on the booster pump.  This way you would use the stored water for the house as well as the irrigation.  This would give you more water and better pressure to the house, as well as being able to irrigate the same way you have before.  Here is a drawing of a similar setup.

[Ladd]

I'll need to ponder your suggestions to see if I understand all the implications; I do have one question though.

In our current setup, the garden irrigation uses one half to two thirds the 1,700 gallon cistern on day 1, refills that day and part of the night at .75 GPM, and then uses more than half the water on day 2, refills that day, part of the night, all the next day and part of the night. Then the cycle starts again.

If the irrigation uses two thirds of the cistern per day, running it down to less than 25% capacity on the second irrigation day and before the full day of rest, I'm not sure there is enough water in it to to avoid running out of water on Laundry Sunday (or some other day). Of course, the well pump would be refilling the cistern at full blast instead of .75 GPM, so that would most likely take care of the household usage also.

But how would I keep the well from running dry during refill, since the cistern holds more water than the full well pipe? Is there some system that will stop the pump relatively immediately, wait half a day and then start up again automatically?

Years ago I ran the well dry deliberately to test the capacity. Using one outside hose bib (back before the cistern was installed and everything ran through the house), I filled four 5.5 gallon buckets in 4 minutes, 15 seconds. That works out to about 5.18 GPM. Continuing to run the hose, the well ran dry in three hours three minutes, which is about 948 gallons, including the one GPM well recharge rate.

So the well holds a lot of water, but still can be run dry.

[Cary Austin]

If your well will run wide open and deliver 900 gallons in 3 hours, that is way more efficient and will deliver more water than letting it fill at .75 GPM, which runs the pump for 20 hours to put in the same 900 gallons.

A Cycle Sensor like the one pictured below looks at amps and knows when the well is pumped dry.   It quickly shuts off the pump and has a timer that can be set from 1 minute to 500 minutes to automatically restart the pump. 

There are two Cycle Sensors in the drawing above.  One on the well protects the well pump while allowing the most production from the well.  The other Cycle Sensor protects the booster pump in case you pump the storage tank dry.