Author Topic: Formula for pump math?  (Read 961 times)

Tyler Coressel

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Formula for pump math?
« on: September 13, 2023, 07:48:59 PM »
First off, i am not a professional, so this is probably elementary for you guys that work with it everyday. But i was wondering how the math works to figure out your submersible pump pressure on the poly drop line. I want to get a CSV to install under my pitless adapter, but am concerned about the pressure. I just replaced my pump that went bad with a Simer 1/2hp 10gpm. My static water level is 25ft, my pump is 50ft down from the surface. What is the formula that figures the back pressure at 50ft of head?

Probably irrelevant details: 40/60 PS, 7 gal pressure tank. Poly line is 1 inch with no markings that i can find. Im sure its old. Probably cant take whatever its rated pressure used to be.

My current system cycles all the time, like 3 or 4 cycles for every toilet flush. Ridiculous. Im glad i found the CSV! I just need to make sure I know what I am doing before I order and install it.

One last thing, we have sulfur water in my area in Northwest Ohio. The water releases hydrogen sulfide gas which is murder on copper and brass. Kills electronics in my house all the time. Does the CSV contain copper or brass components?
« Last Edit: September 13, 2023, 07:51:50 PM by Dieselpowerstroke »

Cary Austin

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Re: Formula for pump math?
« Reply #1 on: September 15, 2023, 08:06:48 AM »
Just need to know how much pressure your pump can build.  Most 1/2HP, 10 GPM pump build 90 to 110 PSI max.  2.31' equals 1 PSI.  So, you can take off 10 PSI from having a static level of 25'.  It is not that your pump builds too much pressure, but barely build enough to work with a 40/60 switch.  Cycling 3 times to fill a toilet sounds like your tank is bad.  Get one of the PK1A kit with the 4.5 gallon size tank to replace what you have.  Everything in the PK1A is Stainless or plastic except the tank.  If you want to supply your own tank get the PK1ALT, which the LT means less tank.

Tyler Coressel

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Re: Formula for pump math?
« Reply #2 on: September 16, 2023, 07:33:45 AM »
Thank you for the information!

I understand about the pressure tank maybe being bad, that makes sense. When it cycles 3 times to fill a toilet, it runs 2 or 3 seconds each time and has things back up to 60psi. I thought that was okay since it builds up pressure so quickly. I do understand that short cycling will kill it. Do you think my pump is too small for the well depth? You said it barely makes enough pressure to work with 40/60, so that concerns me. I might have something incorrect in the system.
 
I was considering the CSV125 to thread into the bottom of the pitless adapter, but had another thought. Is there any reson i couldn't thread a pipe nipple into the pump outlet and put the csv125 there, then a hose barb to poly pipe? In my mind, that would keep the back pressure off the poly pipe and keep it in the pump housing. Or is that a bad idea?

I will consider all options and suggestions. Sometimes what we think we know about things isnt correct, and I am willing to relearn anything that I may have misunderstood for years. I will surely replace the pressure tank at this point. Just wondering if I did okay on pump choice and my thought process. If something I mentioned could be done better, I am all ears.

Cary Austin

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Re: Formula for pump math?
« Reply #3 on: September 19, 2023, 01:27:41 PM »
"it runs 2 or 3 seconds each time and has things back up to 60psi."

This makes me think you have a different problem.  The cycling I am talking about happens as the tank fills to 60 and drains to 40 PSI.  If the tank is bad and has no air charge, it changes from 40 to 60 every few seconds as the pump cycles on and off quickly.

What you just said makes me thing the pump is not reaching 60 until the pump has cycled on about 3 times.  That would be the overload in the motor tripping, and resetting after cooling off for a minute or so.

A Cycle Stop Valve can help when the pressure is going from 40 to 60 over and over, but it can't help at all unless the motor is operating properly and not tripping the overload. 

A CSV125 in the well needs to go as high up as possible.  Just a couple feet below the pitless is best.  The lower in the well the CSV is installed, the lower the pressure it delivers by 1 PSI for every 2.31'.

Tyler Coressel

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Re: Formula for pump math?
« Reply #4 on: September 19, 2023, 04:55:35 PM »
I think maybe my last description wasnt very good lol! I took a video of my pressure gauge with my sink running to show what im talking about but i cant find a way to upload the video here. But it kicks in at 40, pump runs two seconds and kicks out at 60. Pressure drops as faucet runs, 5 seconds to get down to 40 then kicks pump in, 2 seconds and system is back to 60, kicks out. Process repeats. Same with toilet flushes. Keeps doing that until the toilet tank is refilled, hence the 3 or 4 cycles.

I am thinking you were correct the first time about the pressure tank being bad.  Doesnt seem to be tripping the pump overload. Its only a 7 gallon tank, but it also could be bad. It has been here the 7 years I have lived here and the system has always acted this way.

And yes, you're right, i forgot about the 1 psi per 2.31ft. Not a good idea to put the CSV right in the pump 50ft down. I will purchase one and put it below the pitless. Thank you for your time and for allowing me to ask my questions here! This is an amazing forum that i have learned a lot from already!

Cary Austin

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Re: Formula for pump math?
« Reply #5 on: September 19, 2023, 08:06:43 PM »
The tank is certainly bad. Look at the PK125.