How to Measure Your Well Pump GPM
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- Опубликовано: 8 сен 2024
- In this video, Chris shows you how to determine the flow rate of your well pump using the stopwatch method.
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Your equation is wrong. You wrote Time(min.)/Drawdown=GPM while it should be Drawdown /Time(min.)=GPM. In your equation as written, the units on the left side of the equation is min/gallon and the units on the right side is gallon/min. In the example, you are calculating MPG (minute per gallon) not GPM (gallon per minute). 4 min/21.7 gal is ~0.2 MPG while 21.7 gal/4 min is ~5 GPM.
i had to come to the comments to make sure I wasn't the only one...
@@bouy33 Ok, glad to see I wasn't the only one on this. I checked the math, then decided to check the comments. Thank you.
I think you need to change the equation to drawdown over time (min)=gpm
Back by popular request it’s Dr. Worst at the podium... We just got schooled! Nice job. Hey, Inquiring minds want to know when you’ll be showing us your residential water pressure booster pumps?
Thanks Robert! That video has been on our list for a while, but we haven't had time to shoot it properly. Hopefully towards the end of summer we'll get a chance!
Shouldn't it be drawdown divided by time?
Great job, keep em coming !!!!!
Thanks! :)
But how do you measure the total volume of what your pump puts out at 45 psi or whatever? It seems like as the pump gets toward 60 psi it is probably able to pump much gpm than when it first starts refilling the tank at 40 psi
Thank you. How is well yield determined?
Thanks but, you never explained how you got the drawdown numbers? Or maybe from the chart.
I have a 44 gallon WX 250 pressure tank.
I didn’t understand this guys math. How do I measure what type of pump do I have?
I think you may have omitted an important step, and that’s to turn off the hose bib when the pressure pump kicks on.
I initially tried this method and left it open the whole time. It was never able to build up to the 50psi to turn the switch off.
At 3:50 we cover it, but I agree that we should have mentioned it sooner in the video. I appreciate the input!
Why does it need to be open in the first place?
G P , to drop pressure and get to the pump to kick on.
@@mattdeloff4348 OK, thank you. If I simply add a 2nd pressure tank do both tanks have to be sized exactly the same?
Can you clarify what flow rate is this process measuring - is it the flow rate of the well pump or the flow rate of the pressure tank? Do i need to turn off the water valve downstream of the T that feeds into the house during the draw down of the water in the pressure tank? To measure well pump gpm could I not just put the garden hose from the T valve into a 5 gallon container and check how many seconds it takes to fill without messing with the tank pressure at all or will that not work?
You are calculating the flow rate of the pump in GPM (gallons per minute)... and doing that by timing how long it takes for the pump to refill the pressure tank with a known volume of water. You want to be sure no fixtures are using water during the test (like a washing machine or flushed toilet). If you don't know the "drawdown" then you can measure it. I suggest you measure it yourself even if the drawdown is provided on a document, because the drawdown is dependent on your 40/60 cut in and cut out being set exactly at those PSI values like they were at the pump manufacturer's when they calculated the drawdown. It is simple to measure the drawdown... and do your stopwatch work at the same time. Get a 5 gallon bucket and empty 5ea one gallon jugs of water into it... mark the 5 gallon water level on the 5 gallon bucket with a marker. Empty the bucket. Get your stopwatch ready. Be sure the washing machine isn't running or anything else that will use water. Open a spigot and let the water run onto the ground until the pressure gets low enough for the pressure switch to cut in (turning on the well pump). Turn off the spigot and start the stopwatch at the same instant in time that the pressure switch cuts in (watching the pressure gauge will help, just as Mr Worst noted... as the pressure gets close to 40psi then shut the spigot down to a very small flow so you can turn it immediately off when the pressure switch cuts in). Allow the pressure tank to fill until the pressure switch hits the cutoff value (60 psi in the example) and stop the stopwatch at the instant the pressure switch cuts off (the pump stops). Remember/write down the minute(s) and seconds shown on your stopwatch (this is the time it took to fill the pressure tank with a certain volume of water). You are done with the stop watch. Now let's determine what the volume of water was; Fill the bucket to the 5 gallon mark, shut off the spigot, empty the bucket, fill the bucket again, etc... as many times as needed until the pressure switch kicks back on at the cut in value (40psi in this example). Be sure to shut the spigot off right when the pressure switch kicks on. You are done with the pressure tank. Now measure how many gallons of water are in the partially filled 5 gallon bucket... by pouring the water into 1 gallon jugs... add that number of gallons to the previously emptied full 5 gallon buckets and you know how many gallons were emptied from the pressure tank before the well pump kicked on. This is the volume of water we were looking for, and is termed your "drawdown". Now you know the number of gallons pumped in a certain period of time... in other words you now know the gallons per time (gallons/time). Just adjust the time you measured into minutes (for example, 2 mins 30 seconds = 2.5 minutes). Now divide the gallons that went into the bucket by the minutes of time that elapsed and you have the gallons per minute (GPM) that your well pump is pumping. So if 23.5 gallons were pumped in 2.5 minutes (23/2.5) then the well pump would be producing 9.4 GPM.
Chris: I have a wellxtrol pressure tank that has rusted on the bottom third of the tank that is near failure. Only the bottom third of tank is rusted. There is chlorine injection system in the well house that maybe the problem. Looking at a poly tank to eliminate the rust issue. What shall I do?
Put injection system downstream of pressure tank
Math is wrong but this was still helpful!
Wait wait. What is drawdown? How do I find that number?
i looked at your chart i have a 52gal tank so i used your 62 gal tank numbers it was 16 of draw down gallons, my thing is my time from pressure switch clicking on at 50 to off at 70 is less then one min its more like 25 seconds so how do i get the gpm sence its under a min
Use 60s / 1min and cancel the units.
(52gal / 25s) * (60s / 1min). Cancel the seconds leaves you with 52 * 60 / 25 gpm.
If I wanted more constant stable gallons per minute and to stay in the 40/60 psi range without cavitation on my farm irrigation system when more than one zone is running that now has a Gould’s J5s jet pump would it be possible to install a second J5s in parallel? Would I run both pumps with separate 40/60 switches? And would there be any issue if they both came on with only one zone running? Would it just refill the pressure tank with a faster cycle? Right now my entire system is 1 inch and 3/4 poly pipe zones and I would like to increase my main zone right at the pump from 1 inch to 1-1/2 But my pump outlet is 1 inch Thanks
Ben, give us a call or send this in an email over to us: 855.329.4519 or Customer.Service@Rcworst.com
? you started by saying to measure the time it takes to fill an empty tank. Then you say it took 4 minutes to draw down the tank
You have are wrong in your calculation. You have it upside down. The gallons should be on top on the time on the bottom. Please check your math!
You are correct, we had it flipped. Good catch!
I am not the best at math the weekend after Memorial Day. I'm sure you see I did get the right answer, just setup the formula a little goofy. :)
This does not take in to account how much water your pump is lifting..... If it is 4 GPM so is the system once the pressure tank is low.......
Dave, regardless of how deep your well pump this method works. Water does not escape the system and thus must all pass through the tank. This method is best applied when trying to determine a rough nominal flow rate.
@@chrisworst8353 Chris, If you were buying a home with a well, are you advising to use this method to calculate well yielding when in fact the well test should be over a period of time? Are there not variables one should be aware of when calculating available water in a well?
@@amyogren3326 The method described in this video is to determine your GPM more or less for equipment sizing, not well yield. Well yield is a much more complicated topic that put simply, the more critical the water supply, the more in depth productivity test you might consider. This might be a good topic for me to do a discussion video on.