Author Topic: CSV1A, fill time & rolloff, strange operation  (Read 3688 times)

joea

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CSV1A, fill time & rolloff, strange operation
« on: July 30, 2016, 05:35:56 PM »
Hi, I just installed a new CSV1A system and am seeing rather unexpected operation. I'd appreciate any input or suggestions on actions I might take. System is as follows:
500ft well, static level 90ft, yield 3gpm.
1HP Goulds pump (model M10422) placed at 480'. Don't have info on water-end but crudely measured about 12gpm.
WellXtrol WX103 7.6g tank, about a 2gal draw-down (verified by measuring it), precharge at 48psi
50 - 70 psi switch
CSV1A adjusted to 55psi at 1.7gpm, drops to 48psi at 3.5gpm, 44psi at 5gpm. About 4x the rolloff vs. the spec.

I went with the slightly larger tank with the objective of having about a 2min tank fill time and was expecting to achieve this with a 50-65psi switch setting. However even after pushing the switch to 70psi I only get a 1min fill time when the water demand is turned off just as the pump starts. If I leave demand for some time after the pump starts the tank will then complete filling in less than 30sec. Also as noted the reduced pressure rolloff is much higher than I expected.

Lastly, if I turn on a single faucet and let the pump start the valve will settle in at 55psi as expected. If I turn on a second and third faucet the pressure rolls-off as noted. Now if I turn off these additional faucets and just leave the one on the pressure slowly rises but continues on past the set point until reaching 70psi at which point the pump shuts off. Seems very strange.

As full disclosure, I'm pushing the valve differential pressure limit to about 130psi. I'm wondering if the closed valve flow rate and rolloff curves are specified for a much lower differential or if they're expected to be valid up to the 125psi differential. If it's the latter I wouldn't expect such a difference from pushing to 130psi. I'm willing to get a second valve to split the differential, but don't want to take that step if it's not likely to resolve these issues.

Thanks for any advice or suggestions.
Joe

Cary Austin

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Re: CSV1A, fill time & rolloff, strange operation
« Reply #1 on: July 31, 2016, 04:34:16 PM »
From the 90' depth of static water, 12 GPM wide open, and 130 PSI differential pressure, I can tell from the pump curve this is a 7 GPM series pump.  When you open enough fixtures to use more water, the pump pressure is falling off, because the well level is dropping.  If the pumping level is 350', 5 GPM is more than that pump can produce and still keep the pressure up.

But the differential pressure is what closes the CSV1A.  So the higher the differential pressure the more reduced pressure fall off there is.  This is usually only a pound or two difference.

The high differential pressure does two more things.  One is that the 1 GPM differential figured in the CSV1A is at about 80 PSI differential.  So at 130 PSI differential the minimum flow is probably closer to 2 GPM.  This means using 1.7 GPM is not quite enough to set the CSV1A, which is why it continues to fill the pressure tank and shut off when water is still being used.  Also 2 GPM will be your tank fill rate.  So to get even get close to one minute of run time in a tank that my calculations show to hold 1.9 gallons at 50/70 pressure, you would need to set the CSV1A for 48 PSI while running about 3 GPM. 

This will ensure that the CSV1A is closed down to the minimum 2 GPM by the time the pressure reaches 50 PSI.  Then it would fill the entire 1.9 gallon tank at 2 GPM, and should take just under 1 minute. 

However, if the amp draw of the motor reduces by as little as 20%, as it should, the motor is running cooler and does not need the old rule of thumb of 1 minute of run time.  20-30 seconds is enough.  For one thing the CSV1A makes the pump run WHILE you are using water PLUS the other 30 seconds to fill the tank.  So normally the pump runs for more than a minute or two anyway.  Another thing is that the CSV1A doesn't let the pump shut off until you have finished using water.  So it is usually off for more than a minute or two as well, and has plenty of time to cool down.

The second thing the high differential pressure will do is eat the guts out of the CSV1A much sooner than it should.  It should still last several years and you can just drop in a new gut pack when the old one wears out, but splitting the differential pressure between two CSV1A's would last much longer. 

However, increased differential pressure through a CSV1A increases the minimum flow for a reason.  A 1HP, 7 GPM pump has 17 impellers.  And the more impellers in a pump, the more flow it needs to remain cool.  You probably need about 2 GPM to keep that pump cool. 

So I would not add another CSV1A, because it would also reduce the minimum flow back close to 1 GPM.  The only problem with having a 2 GPM minimum, is the pump will cycle during times when you are using less than 2 GPM.  If any of your showers on anything you use for very long require less than 2 GPM, you should probably add a little larger tank.  I am not talking about a very much larger tank, maybe 20 gallons total volume.  You could add a 14 gallon to the 7 gallon you have, or replace the 7 gallon tank with a 20 gallon size.

A 20 gallon size tank would hold about 5 gallons of water.  So when you are using 1 GPM, the CSV is letting 2 GPM pass.  1 GPM goes to the faucet you are using and the other gallon goes into the pressure tank until it is full and the pump shuts off.  Setting the CSV1A in the middle of your pressure switch setting, you should get about 2.5 minutes of run time, and 5 minutes of off time as long as you continue to use 1 GPM at the faucet. 

This is better for the pump than 1 minute on and two minutes off, which is the best you can do with the 7 gallon size tank.  But really 1 minute on and 1 minute off is all the motor company says it needs.  And with the low amp draw created by the CSV1A, it really doesn't need that much.  So if you can set it up to get at least 30 seconds of run time, I wouldn't add another tank unless you have a 1 GPM drip system or something that uses less than 2 GPM for long periods of time.


joea

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Re: CSV1A, fill time & rolloff, strange operation
« Reply #2 on: August 01, 2016, 03:58:00 PM »
Thanks for that input Cary. The 2gpm min at high differential explains what I'm seeing with the 1min fill time as well as gradual tank fill when only 1 faucet is on. I still don't understand where the higher than expected psi roll-off is coming from. In looking at the CSV1A curves, combining both friction and reduced pressure rolloff, I expect to see about 3psi change when going from 2gpm to 5gpm. You indicate there could be an addition 1 or 2 psi because of the 130psi differential, but I'm seeing about 10psi change which is twice what we've accounted for. I understand that the pump pressure will drop as the well water level drops, but that's not what's happening in the few minutes I'm running the test and seeing the change.

I understand what you're saying about reduced current, cooler motor, and less need for even a 1min run time. That's consistent with what I've read in these forums and I'm comfortable with that. My rationale for targeting a 2min run time was actually based on our water use patterns and to try to reduce pump cycling. We draw water in a rather conservative on-off fashion. Meal prep for example is on-off while washing veggies, filling pans, wiping counters, etc. Likewise bathroom routine on-off for tooth-brushing, shaving, so-forth. So a lot of on-off, but these come in bursts of activity. If there is a 2min run time there's a rather good chance that all the individual on-off cycles spreads out to the point the pump may only see a single cycle, or at least a minimal number. That's not so likely as the run-time falls below 1min. Also because of the on-off nature there's a fairly good chance that the tank will empty just as demand is turned off, so it's likely the pump will run the minimum fill time on a regular basis. Just to complete the picture our outdoor water use is minimal. No regular irrigation or car-washing, normally just an occasional spot watering of plants and perhaps a deck washing a couple times a year.

Prior to your input I was thinking of going with the dual valve, and perhaps using a CSV125 to limit the rolloff. The statement about 2gpm for cooling flow on my pump setup is really new information for me though, hadn't seen that discussed in other threads. If that's out my options seem to be go back to a traditional tank on a 40-60 switch or keep the current csv setup, although I don't really like the 70psi cutoff and will likely reduce that to 65psi which will lower my fill time to under 1min. I suspect I'm to the point of over-thinking this and will just go with the latter.

You say the high differential pressure will eat the guts out of the CSV sooner, what symptoms can I expect to see when that starts happening?

Thanks again, Joe

Cary Austin

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Re: CSV1A, fill time & rolloff, strange operation
« Reply #3 on: August 02, 2016, 07:18:29 AM »
A little larger tank like a 20 gallon size would solve all those problems.  When the guts get worn in the CSV1A it will start having more minimum flow.  If it is 2 GPM now it will be 2.1 then 2.2 and so on as the gut pack wears down.

valley ranch

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Re: CSV1A, fill time & rolloff, strange operation
« Reply #4 on: September 24, 2016, 03:19:40 PM »
Greetings, I have a question. In the firs post dated July 30, 2016, Joea mentioned he just installed a CSV1A.

Your answer:   A little larger tank like a 20 gallon size would solve all those problems.  When the guts get worn in the CSV1A it will start having more minimum flow.  If it is 2 GPM now it will be 2.1 then 2.2 and so on as the gut pack wears down.

If he just installed this valve and has ware that will be increasing, How fast can we expect these CSV to ware out?

Is his valve in very acid conditions of something of that nature? I'll re read the posts to see if my answer in here.

Thank you
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I re read the above, so it's the pressure differential that causes the ware, I guess because it's a rather large differential?

I don't understand much yet, I have to admit.  but  I'm working on it.

Richard

« Last Edit: September 24, 2016, 04:02:06 PM by valley ranch »

Cary Austin

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Re: CSV1A, fill time & rolloff, strange operation
« Reply #5 on: September 25, 2016, 08:58:25 AM »
Staying within the 125 psi differential the CSV1A should last 30 years.  But running water 24/7 with 200 psi differential may wear out the seat in 6 months.  It all depends on the differential pressure and how many hours you run water at very low flow rates.