CSV pressure question

[Jacek]

Hello, someone recommend CSV to me as something I might possibly want to install on my plumbing system.  But I had a question, that's not really answered on the site that I could find or a glimpse at the current topics.

Say I install a CSV valve, by my understanding is restricts flow rate to what you are using at a minimum of 1 GPM.

Now say I want to water my garden, and I open the valve to let out exactly 1 GPM.  My well pump has a pumping speed of 7.5 GPM, but is limited by the CSV to 1 GPM.  Will it not build pressure on the pre-CSV side of the pump?  The pump is a submersible and is very deep, so has a flexible hose.  Does the CSV have a built in pressure relief?  What if I run my hose for an hour, what is the maximum possible pressure that the CSV will allow to build up on the well side?  I don't know the pressure rating of the hoses underground, but I assume they max at 125 psi.  What is the risk of over-pressure, and what if any counter measures are built in the CSV?

Please note, I'm not a plumber, but have a working knowledge of plumbing.  I purchased the house with the pump already installed, so have no idea of the brand or model since I could not find any documentation for it in the house.  And I'm not about to pull 400+ feet of hose out of the ground to check the model on the pump unless it breaks down first.  If I knew the model I could figure out the pumps max pressure at the depth it is, but I can't for all I know it could put out 125 psi or more.

[Cary Austin]

Hi, Thanks for joining the forum.

I really doubt that you have "hose" attached to the pump at 400' deep.  Just the 400' depth would put 173 PSI on the hose at the bottom.  It would need to be Sch 80 PVC or at least 200# poly pipe, both of which can handle that pressure.

The pressure on the pipe before the CSV is determined by the pump, less the depth to the static water level.  If you don't have a control box or something with the motor horsepower written on it, there are other ways to determine the size of your pump.  The best way is to do a pump test.  You need to open a big valve or several faucets to let out enough water to lower the pressure below 20 PSI on your gauge.  While running the maximum amount of water the pump can produce, measure it in a bucket, or measure at each faucet and add them together for the total GPM of the pump.  While running this much water you need to put a clip around amp meter on one of the incoming electric lines.  The amperage will tell you the horsepower. 7 amps is 3/4 HP, 9 amps is a 1 HP, and 11.5 is a 1.5 HP.  Then the total GPM will tell you the model of the pump.  15 GPM at open flow says it is a 10 GPM impeller pump.  25 GPM would mean a 20 GPM pump, and so on.

Once you know the horsepower and GPM of the pump, you can look up the pump curve and determine the back pressure while pumping only 1 GPM.  You can subtract the static water level from this amount if you now it.  Or just figure total backpressure on the valve if you don't know the static. 

But you are on the right track, as backpressure is the one thing we need to now when adding a CSV.  The CSV itself can only handle about 175 PSI backpressure, so we really need to figure it as close as possible.

I would be glad to talk you through this test if you would like.  Just call if we can help.

I am guessing it is a 7 GPM pump, but we need to know the horsepower and static water level to figure the back pressure.
Thanks
Cary
800-652-0207

[Jacek]

So, my well pump draws 8.40 Amps at 245 Volts.  It's a dual pole, I tested voltage at the switch when it was running to get an accurate read, and yes it is on a dual pole breaker so high voltage single phase pump.  The pump gives me 7.5 GPM, I tested by running water till pump turned on then closing water.  Timing how long it took for the pump to turn off (56 seconds), then drew water till it turned back on (got 7 gallons).  So 7 / 56 x 60 = 7.5 GPM.

btw, at 8.4 amps and 245 volts I get a wattage draw of 2058, which gives me a 2-3/4 HP pump (746 watts/hp).  Not sure if they sell fractional water pumps like that?  Might be an under worked 3 hp?

The pipe that comes out of the wall into the basement has no markings on it.  But it is hard plastic, black, 1" internal diameter, 1-1/8" external diameter.

Have no idea on the exact well depth and water level.  I didn't receive that information when I purchased the home and don't know how to find out without pulling the well pump out and measuring, which I'm not about to do.

[Cary Austin]

Actually 9 amps at 240V means a 1 HP submersible.  Pumping 7.5 GPM into the pressure tank means you either have a 5 GPM pump with a water level of about 100', or a 7 GPM pump with a water level of about 280'.  A 7 GPM pump would not build more backpressure than the pipe of CSV can handle, but the 5 GPM pump could build 250 PSI backpressure.  Without knowing for sure which pump it is, I am afraid there maybe too much pressure to use a CSV.  The only way to measure for sure is to put a guage before a ball valve, close the ball valve, and see how much pressure the pump can build.  If it is less than 200 PSI, the pipe can handle it.  More than 200 PSI would be too much for the pipe.