Pump sizing

I replaced our 5 year-old 1/2 HP 5GPM pump this weekend with a Goulds 10GPM 3/4 HP unit and a 44 gal Weltrol 250. I thought I did all my homework to properly size the pump (and more importantly, the new welltrol tank). To give you some history, we built our 4-bedroom, 3-bathroom, 2-story house in 2002 and let the well drillers size the pump, tank, etc. Our well is 180 ft deep, pump set at 160 ft, well produces 8GPM, and no static level (water level is limited to 1 foot below grade by a second pitless adapter that spills a line into the woods). Original pump was 1/2 HP with a 20 gal welltrol tank (202?).

Anyway, my concern is that the new pump only runs for 50 seconds to bring the new tank (44gal Weltrol 250) up to pressure. We used to run the psi at 40/60 but I let some air out of the drained tank and reset the pressure switch to 35/55 psi to try and increase the runtime a bit. We also installed a 10GPM dole valve before the tank (because of our high static water level). Should I be concerned that I oversized the pump (or undersized the tank?) and the pump only takes 50 seconds to fill the tank? I'd hate to have to replace the new pump in 5 years (again).

By the way, drillers didn't even bother to install a torque arrestor (or a dole valve - which I think is required for high static level wells)

A WX-250 at 40/60 should hold 11.78 gallons of water. If you have exactly 38 PSI air charge and a 10 GPM dole valve, you should be getting 1.17 minutes of run time. 50 seconds is not far from that. The average life of a submersible pump is 7 years. That is because they know how many on/off cycles you will get in 7 years, and build that many into the pump and motor design. If your pump is only lasting 5 years, your pump must be cycling about 1/3 more than the average. Every time you cut the number of cycles in half, you double the life of the pump. Double the size of pressure tank, double the length of pump life. Triple the tank size, triple the pump life.

However, the larger the tank, or the more tanks you install, the longer the pressure will be decreasing in the house before the pump comes on. With a Cycle Stop Valve before the pressure tank, you can adjust the run time as long as you want. The Cycle Stop Valve only fills the tank at 1 GPM, when the pressure is above the regulating pressure of the CSV. In other words, you could get 11.78 minutes of run time if you wanted. A CSV set at 55 PSI with a 40/60 switch, would give you about 3 minutes of run time to fill the tank.

With a CSV, run time is not nearly as important, because the CSV will not let the pump cycle while you are using more than 1 GPM. A system without a CSV will cycle 3 or 4 times while you take a shower. A system with a CSV will only cycle once while you take a shower, no matter how long the shower takes. This way the CSV will cut out a few cycles when the ater is used in the house but, it won't make much difference for things like filling the washing machine. The CSV makes a tremendous difference in the number of cycles, while you are running a garden hose or sprinkler outside of the house.

While running a 5 GPM garden hose or sprinkler, the system you have now will cycle on for 2 minutes and off for 2 minutes. This could be 360 cycles in a 24 hour day, or 131,400 cycles per year. With the CSV that would only be 1 cycle. There are lots of other benefits in using a Cycle Stop Valve, including having "constant pressure" in the house. The main reason to use a CSV is to reduce the number of cycles, which has proven to triple the life of most pump systems.

I wouldn't have used a Torque Arrester either. Or a Dole valve regardless of the water level. The pressure in the system will protect the Motor from overheating from overpumping.

At eight gallons per minute, you should have all the water you need for a normal household and the 1/2hp should have done a great job. I'm not sure why you would put in a larger pump just to restrict it down with a Dole valve? Replace the Dole with a CSV and you will be doing your new Pump a favor.

bob...

Thanks for all your help. I wish I had known about CSVs before I decided to do this on my own. When I don't know what I'm doing, I tend to be an "instruction manual" kind of guy. The Goulds installation doc says use a dole valve for high static level wells, so that's what I installed. The Wellxtrol brochure says a WX-205 will give a 10GPM pump 1 minute of runtime at 40/60 - so I went with the bigger WX-250 thinking I'd be getting more than 1 minute. Guess next weekend I'll be switching out the dole. And why don't well drillers offer CSVs as an "upgrade"?

ttracy said:

And why don't well drillers offer CSVs as an "upgrade"?

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The good ones do!

pump

ttracy--I don't think your going to have any problems with your 50 second run time. That 50 seconds is only if your not drawing water while your pump is running. Alot of time you will be using water so pump will run longer to reach kickoff setting. Pump cycle as a concern is overrated. I have run a dairy farm with a standard grade 1 hp Franklin powered pump set at 260 ft. Drawdown is only about 6 gallons so can you count how many cycles this pump has seen? Not only has it been running the milk parlor with auto wash equipment, but watering cattle at an auto water tank. These items do not keep the pump running as the tank valve fills slow so pump is on and off 24 hrs a day. Not for 7 yrs. Over 20 yrs since I have seen this pump. About 1 of those yrs was with a hole in the bladder of the tank and a waterlog condition. Don't choke on the tech side. Just enjoy your new pump. LB

Ever once in a while you will get one that can take the abuse of cycling and last 20+ years. Even the hole in the bladder tank was probably caused by cycling. Take it from someone who has sold and installed thousands of pumps, the average life is 7 years. Cycling on and off is the cause for 90% of all failures. The pumps that were made 20+ years ago had more meat in them, and would last longer than pumps made today. For every pump that last 20 years, there are 3 pumps that did not last 2 years, hence a 7 year average. Anybody who has let a pump cycle like that and got 20 years out of it, is just lucky, and should be sitting at a table in Vegas right now. Replacing a pump that only lasted 5 years is much more common, and is nearly always caused by cycling.

A 10GS07 (10 GPM Rated, 3/4 HP) pump produces about 15 GPM with no drawdown at 50 to 60 PSI tank pressure. You have a tank with about 12 gallons drawdown so you should expect about 12/15ths of a minute which is 48 seconds. I'd say your 50 seconds is pretty close to expectations.

Tha pump will deliver 10 GPM at about 100 psi so it may exceed the control capability of a Dole valve.

With a drawdown of 12 gallons, and you are often drawing some water during the time the pump is running, such as when taking a shower, you might run the pump 15 times per day for domestic water. I would not worry about it.

You said you have it set at 35/55. You could set it for 35/65 and this would let it run for just a bit longer or readjust your air charge and go to 40/70.

prd823 said:

You said you have it set at 35/55. You could set it for 35/65 and this would let it run for just a bit longer or readjust your air charge and go to 40/70.

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You know, I thought about running the tank 35/60 or 35/65 (not that I'd gain much more runtime), but I thought the wellxtrols were only built to handle a 20psi differential.

When we do a system to boost city pressure, sometimes we use a pressure switch with a 40/110 bandwidth. I am sure it stretches the bladder more but, I have never had a problem with this. Again, what ruins bladders is repetitive cycling on and off, just like bending a wire back and forth until it breaks.