sizing well discharge line

ratio

I've got a well pump, the old 1-¼ galvanized is I believe rusting closed—the pump comes on, pressure builds quickly & bounces on & off until I get tired of watching it. Once the pump shuts off the pressure drops rapidly to about 20#. If I hold the contactor on, the line pressure stabilizes at above the cut out pressure, & when I let off the static pressure is higher. History: an old school, the original pump was turned by a dinosaurs hide belt that was ran by maybe a steam engine, or an old electric motor. The expansion tank is a well-x-trol WX302, charged to 60#, cut out is around 60#. (I can't really set the cut in & cut out, it bounces too much right now.) The school bldg is unoccupied, & never going to see more than a dozen people in it at once ever again. The tank is about 60' linear (100' developed) from the well, which is a modern 220v pump—I don't know how deep the well is, but it's fused at 20A with Edison style fuses. Am I correct in my diagnosis of restriction between the tank & well? Assuming that's right, would I be able to replace the old piping with 1" PEX, or would I need to stay with 1-¼? Keep in mind that the demand will be minimal, and I'm tooled up for PEX through 1", I'd have to purchase more equipment to terminate the larger sizes. Also, I should be able to pull the run in without fittings other than the transitions.

Robert_25

Your pressure tank is way over charged. Should be about 2 psi below the cut-in. Depressurize the water side, set the tank air pressure at 38 psi and try again.

ratio

It's not a house, it's a three story school building. 60# is kinda high, but that's what it was originally-been marked on the wall for decades. I'll work on lowering it, I only need about 30-40' of lift, but right now I can't run it without my finger on the contactor to fill the tank.

Jamie Hall

The 1" pipe will do fine -- you don't have enough of it to make any difference, and if the old pipe is corroded (if? well... yeah) it will actually flow better.

However.

I have to ask: where is the pressure switch located in the system? Part of your problem might be coming from having the pressure switch too far from the pressure tank, or too close to the pump. It is very very important, particularly with newer pumps which start fast, that the pressure switch be at or as close as possible to the pressure tank as it can be, even if that means additional wiring. What happens is that when the pump starts, the water column isn't moving and the pump can build up to close to its shutoff head -- but the pressure at the tank hasn't changed yet. If the pressure switch is close to the pump, it will sense that and shut off the pump. At which point the pressure will drop and the switch will cut in again. And so on. Kind of hard on the pump...

EBEBRATT-Ed

Think about it.

If cut out is at 60 and the tank is pressurized to 60 you have no compression, it's like hitting a brick wall your cutting off before you have started to compress the bladder.

isolate the tank from the system and lower the tank pressure

ratio

The pressure switch is appx 8-10' from the well. The expansion tank is maybe 50' past that; but the bouncing on & off just started happening. It's worked fine (more or less, replaced the pressure switch a few years ago) for the last ten years. I'm guessing that something came loose & caused enough restriction to start the pump cycling, & water hammer did the rest.

In any case, it sounds like the 1" PEX will be fine, so I'll plan on that. Thanks.

JUGHNE

If you turn off the power to the pump and run all the water out of the system is the tank empty? Can you rock it around so it seems completely empty?

Jamie Hall

ratio said:

The pressure switch is appx 8-10' from the well. The expansion tank is maybe 50' past that; but the bouncing on & off just started happening. It's worked fine (more or less, replaced the pressure switch a few years ago) for the last ten years. I'm guessing that something came loose & caused enough restriction to start the pump cycling, & water hammer did the rest.

In any case, it sounds like the 1" PEX will be fine, so I'll plan on that. Thanks.

I'd still move that pressure switch. You can run new control wires when you run the new pipe. But that's just me...

JUGHNE

It always seemed logical to me to have the pressure switch, gauge and tank in one place. Of course never a valve to isolate the switch and tank from the pump. But a valve for the supply line to the building. Then I could open a wall hydrant, operate the building valve to dump water to observe operation while sitting my butt on a bucket . The 10 dollar gauge might last only one year, but people don't ever look at it anyway until there is no water.

ratio

Yes, the tank's empty, & I'll look into moving the switch. What's a good target for the cut in & cut out settings? 30# at the highest faucet, 20# diff?

Jamie Hall

Personally I wouldn't think you'd need more than 20 psi at the highest faucet at pump cut in -- unless you have flush valves on the toilets. Then you need 30. 20 psi differential is good.

hot_rod

A well tank tee setup makes a nice clean way to read, control and protect the system. Even the box stores sell these now.

ratio

Ok, I replaced the old 1¼" galvanized with 1" Uponor PEX. I was a little concerned since the few places I cut the pipe weren't all full of rust, & yup no change, at cutout terrible water hammer. I changed the system settings to 40# cutout, 20# ∆P, & set the expansion tank to 38#. (That I did with a Fluke pressure calibrator, so I'm confident it's ±0.1#.) No change. It still seems to me to be a restriction getting water into the expansion tank. Pressure at the pump (& switch location) run ≈16-18 psi higher than the system settles to after the pump is switched off. This doesn't seem to happen at the expansion tank (as noted above, appx 65' distant.) I suppose it's possible that I cut out a rusty, obstructed fitting somewhere that I didn't know about & just happened to add a similar amount of restriction by switching to 1" PEX, but really...? Not too plausible, is it?

The tank hold air, when I set the pressure that was with the tank physically disconnected via a union. That means it's good, right? Is it possible for the inlet on the tank itself to be rusted shut? @JUGHNE mentioned moving the switch to beside the tank, I'll be doing that shortly and expect it to fix the issue since the water pressure seems stable there, but this worked before! I've been around this building for nearly a decade, this most assuredly wasn't happening before. There have been no changes made (I would have been the one to make them). I don't know when it started, except that the water hammer was violent enough that it couldn't have been happening long without a mechanical failure occurring. I first noticed it after a field day in the spring, we had a water slide set up & water flowing for several hours, but that was through some 200' of garden hose, & we never ran out of water. Could the pump somehow have gotten damaged in such a way as to cause water hammer? I can't see how it could.

Jamie Hall

First, as @JUGHNE and, I believe, I mentioned, the pressure switch must be at the expansion tank. Second, there is -- or should be -- a check valve at the top of the pump. If that is leaking and there is another check valve in the system, that will allow air into the drop pipe which could be the source of at least some of the hammer (note that some older setups, with an automatic hydropneumatic tank, had no check on the pump -- but the hydro tank was very close (a few feet max) to the pitless adapter -- or the pump was a slow start type; either situation would be sufficiently unusual these days to require on-site troubleshooting).

ratio

I plan on moving the switch as soon as I have time. There are no additional check valves in the system. The check valve at the pump appears to work, in that the pressure doesn't just drop continuously after the pump shuts off—but it does drop a (repeatable) 16-18 psi after the pump stops. I've been blaming that on head loss of the piping, but I've never watched the pressures at the tank as the pump was running.

I don't know what a slow start pump is, but there is a noticable delay between when the switch closes & the water starts flowing in the pipe of about one second.

I still can't understand why it used to work but doesn't now. The only things left are the tank and the pump. Both of those are high-dollar items, so I'm hoping that just moving the switch will hide the problem, but still! The last time I couldn't figure out the problem after this many tries was June 5th 2004, about 5:23 in the afternoon. It's driving me bananas!!1!

JUGHNE

Ratio, as I read your above posting about pre-charge setting it didn't sound right.
Found some literature: "The pre charge of air should be 2 PSI less than the cut-in pressure of the switch" This air pressure check is with the tank disconnected from anything.

Robert and Ed commented on the pre charge above.

If you check the label on the pressure switch it might say 30/50, which is common for submersible pumps. Maybe good for a 3 story building. Supposedly these switches can not be adjusted much outside of their stamped range.
So if a 30/50 switch I would try setting the tank at 28 PSI of air.

IIRC I did read that the goal is to push as much water into the tank as possible and to have the pre charge air push it out until it is just about empty before the pump would start again. This would prevent short cycling and maybe water hammer.

I would still move the switch as discussed above.....just don't isolate the switch from the pump, even with a valve that no one might ever close. Just a valve between tank and building piping supply. Then the hose bib outside open you can watch operation.

ratio

Ahhhhh, less than the cut-in pressure. I saw the recommendation for 38# above & apparently stopped reading. That fits with what I was experiencing before, as I was lowering the tank pressure without a pressure gauge the last time I was on site, & I had about 26# in there yesterday when I showed up to "fix it". 20# cut in should be adequate, it's a three story building but there's no water to the third floor, so total elevation from the switch to the highest faucet is in the 15-20' range. That's give me, what, about 15 psi at the 2nd floor at cut-in? That should be fine.

JUGHNE

Old piping may have build up and give low delivery IMO.
After all the grief you have had I would put a new pressure switch on, (30/50 IIWM) set the tank to the 28 and see what happens.
Pressure switch contacts get a little burned after a few years and can create another call back.

Jamie Hall

Square one. What is the flow rating of the pump? If you don't know, find out. OK. What are your desired cut in and cut out pressures? I'd go for a minimum of 20 psi at cut in and no flow at the highest faucet in the building (in fact, if I were still inspecting plumbing, I'd require it...). Pressure switch and gauge at the pump. Now. What size is your tank? Amtrol has a neat widget (http://www.amtrol.com/support/well_sizing.html) to get a recommended size. On the time scale, I would set the time to at least two minutes; the quickest way to kill a pump is too frequent starts. Is your tank at least that big? If not, it's too small; there's no harm to a tank which is too big, but too small is a real problem. If your tank is big enough, are you sure that it is accepting and releasing water? The best and simplest way to check is to run the pump to cut out and then run a handy tap into a bucket (so you can measure volume) until the pump cuts back in.

If the tank pressure is correct, and it is accepting and releasing water, it's probably OK. If it doesn't release the rated amount, it's toast. Time for a new one -- unless there is an obscure valve closed somewhere

Basically, if the pressure switch is at the tank it won't chatter, provided the tank has air in it and is at the correct pressures and is available to the pump. Anywhere else and it might -- or might not, depending on the exact dynamics of the system.

Water hammer is a completely different problem. Somewhere up there I read something about water hammer; if it's a water hammer problem when the pump starts -- which is very unlikely, as very few submersibles start fast enough to cause hammer -- we need to think about this some more.

ratio

JUGHNE, occluded piping was my initial diagnosis, proven false (I believe) by me replacing all piping between the well and expansion tank, less a few feet on each end with no change. There was a new pressure switch sitting on the shelf, preset to 40/20 (it claims), so I installed that, as the old one had seen some hard service before I found the contacts banging in & it and shut it down.

Jamie, the flow rate of the pump is unknown, but I think I can make an educated guess. This was a township school with 250-300 students. The pump has a 1½" discharge, it's fused with 20A fuses. The expansion tank is a Well-X-Trol WX-302, the Amtrol table says this is appropriate for 25-30 GPM.

That table also has the acceptance at various pressures, I'll verify that. I'm sure it is accepting some water however, as I do get good run times as long as I hold the switch through the bouncing.

Maybe water hammer isn't the right word. What happens is the pump comes on & runs up towards the cut-out nearly immediately. Then it reaches cut-out, drops out, & immediately the pressure drops below the cut-in & the pump starts back up. The cycle is fast enough that it's nearly impossible to switch it off with the disconnect before it's back on; and the PEX (& the galvanized before) is bouncing all over the place.

All in all, it sounds like I still have the tank pressure wrong. I'll start with that & we'll see where it leads.

Thanks for your help everyone, this was really driving me nuts!

Jamie Hall

I'm going to bet from your description that moving the switch will fix the problem. Why didn't it do it before? Hard to say -- too many variables in the system!

JUGHNE

I would say your water hammering was caused by the short cycling/chattering of the pressure switch.....caused by lack of expansion tank. In your case of having the pressure tank air at 60 PSI, as said above that was like no tank at all.

Most controls I see are preset pretty well right out of the box.
The cover has the rating labeled on the inside. Remember the covers will fit all models so things could have been switched. There is a physical difference in the spring sizes/strength.

Do you have an above ground control box (start components OL, etc) for the pump motor. These components suffer from short cycling just as the pressure switch would. If down the well then are a challenge to change.
Those often will give you the horsepower but not necessarily the GPM dependent on number of stages which I believe dictate the GPM. HP might be an indicate of lift or head the pump could overcome. Most of the few pumps I have dealt with were quite oversized, (just like HVAC equipment), but often the owner wants the added GPM/HP.

For your install it sounds like that Tank would be OK....the main thing is to limit start/stop cycling.

EBEBRATT-Ed

As @JUGHNE mentioned you have to get the expansion tank and pressure switch set properly.

You are running with no air cushion so it's like you have no expansion tank at all

ratio

@Jamie Hall, I had one of those hose bib gauges with the high level needle attached a few feet away from the tank, after I had shut off the pump & walked over, the pressure was only a few #s below the red needle. I'm guessing it'll fix the problem too, but I was hoping to avoid running the wires. The current setup switches the 208 volts directly on the pressure switch. I could get a contactor & switch low voltage, but I'm unsure if the contacts on the pressure switch will reliably switch 24 volts at a few 10s of VA's max.

@jugune, everything's down the hole. IDK how deep it is and don't have enough (any!) experience to hazard a guess. With any luck, getting the tank pressure more in line with what I need will solve the problem. If not that alone, moving the switch should fix it.

Thanks again for all your help!

ratio

Moving the switch & setting the pressures correctly (18 tank, 20 CI 40 CO) solved it. There's still some shimmy in the PEX when the pump starts, but the flutter at the switch is down to just a few lbs. & the switch handles that fine.

One other question: I heard a lot of air going in to the tank when I first restarted the system. Is that a concern, or will it slowly migrate out?

JUGHNE

Good to hear the ordeal is over.
That air will most likely come out with the water after some usage in the building.

ratio

Just a follow-up. A week after the last changes, found the tank full of water & empty of air. After pricing a new tank, I decided to change the Schrader valve instead. Recharged the tank & she's been working fine ever since. Whew! I think it's finally over!

JUGHNE

Maybe, did you get any water out of the Schrader valve, I assume you just changed the core.
If the bladder is leaking then water could sneak back into the air side.
This is punishment.......are you on a school board for this place?

ratio

No water on the air side. Seemed like a leaky valve, it's been born out (so far!) by the fact that it's still working.
And it's worse than on the board—we own the place. So not only do I get to fix everything, but not even a chance to get any moolah for it. It's all good though, we home school in a real school building!