Strange well/pressure tank problem . . . Missing Drawdown!

[Drewmcg]

Just moved into a house with an older well/tank, and have been trying to get up to speed. System was cycling constantly (lots of diming lights in the house). So:

I had the tank re-pressurized to 2 lbs psi below cut-in (which was set to 30, with 50 psi cutout).

That helped. I replaced a 10 inch X 2.5 inch filter between the well and water softener with a new, 5 micron filter (blown celluose?). After less than a week, I had almost no pressure in the second floor shower. So I replaced the (new, but now saturated) filter with a poly-spun 5 micron filter about a week ago.

Water pressure upstairs is better, but not great. So:

I changed the pressure settings on the tank to 40/60 psi, and re-charged the air pressure to 38 lbs. Not much improvement.

I in the process of draining the pressure tank to re-charge, I noticed a lot of black sentiment coming out of the drain house. It would come out for 30-45 seconds, then clear. I'd close the drain valve on the pressure tank, and reopen it and get more sentiment for 20 seconds or so before it would clear.

I also noticed when re-setting the pressure range and re-pressurizing the tank that in the one week since I'd had the tank re-pressurized from a waterlogged state, it had already lost pressure.

I started to experiment with the drawdown, and here's what I found:

CFR of pump = 10.5 GPM
Pressure tank = Sears Craftsman 30 to 36 gal total volume (its old, and I found conflicting info on google)
DRAWDOWN = 3.75 gals!

This last item is the main issue. With my pressure settings, my minimal drawdown should be 30 gals X .26 = 7.8 gals. (If its a 36 gallon tank, then I should be getting 9.4 gals drawdown). What gives? Where is the missing 4-6 gallons of drawdown? My pump is cycling twice as much as it should be with this tank/setting.

I pretty much figure that the bladder is shot on the tank, but should that make a difference in drawdown? I thoroughly flushed the tank, thinking sediment might have accumulated there, but could it have filled up with that much silt to reduce the effective volume to 3.75/.26= 14.4 gallons? That would be more than one-half!

I wonder if the system is missing a check valve on the submersible pump (or if that valve has failed). I have no information re. the depth of the well, though it looks like a 4-inch casing and two-wire, 230-volt pump.

Any ideas?

 

[LLigetfa]

It sounds like your bladder is shot if in fact you are losing air over time. Make sure however that your air pressure gauge and your water pressure gauge are both reading the same. If you are getting water trapped on the wrong side of the bladder, it will reduce your drawdown.

My bladderless 30 gallon tank is a precipitation tank for iron removal and it provides about 5 gallons of drawdown.

If your checkvalve in the pump failed, you would be losing water back to the well which would be evidenced as a dropping of pressure when there is no water usage in the house. If the pressure holds, that is not the case.

 

[Sponsor]

 

[LLigetfa]

Oh, at higher pressures, you can expect to get less drawdown. Depending on who's specs you believe, a 30 gallon tank at 20 PSI should net about 10 gallons but at 40 PSI it's closer to 8.

The WM-9 has 8.9 galons of drawdown at 30/50 PSI.

http://www.wellmate.com/en-US/produ...ts/captive-air-and-retention-tanks/wm-series/

 

[Drewmcg]

O.K., I've now checked my captive air tank using the instructions by valveman at his sticky "pressure tank maintenance" in this forum:

"To check the air pressure in a bladder tank the power to the pump must be turned off. Then a faucet should be opened until water stops coming out of the tap. While the pump is off and the faucet is still open, you can check the air pressure at the schrader valve on top of the tank. You will need to use a car tire pressure gauge on the schrader valve. The air pressure in the tank should be 2 to 10 PSI below the "start" pressure of the pump. IE; with a 40/60 pressure switch, the air pre-charge in the tank should be no higher than 38 PSI and no lower than 30 PSI. Use an air compressor to pre-charge the tank to the correct pressure. If the air is coming back out of the open faucet, then the bladder is busted. If while holding the valve core down on the schrader valve, water comes out, the bladder is busted. If the schrader valve will not accept air from the compressor, the bladder is most likely busted."

No air coming out of the basement laundry basin sink faucet (cold), and air pressure checked at Schraeder valve with car tire pressure gauge is 38 psi.

So: the bladder on my captive air tank appears to be intact (good news). (Their might be a very slow leak at the Schraeder valve, but that should not be an issue for present purposes.)

I re-checked the draw down (very carefully): 4 gals. @ 40/60 tank cut in/out setting.

Also, I found an old product manual online for this line of tanks. Sears did not make a 30-gallon tank. By checking the replacement bag part number given to me by sears parts telephone sales with a manual I found online, I have verified that this is in fact a 36-gallon total volume tank.

SO: I should be getting over 9 gallons draw down @ 20/40 psi (36 * .26 = 9.36 gals.) , but am instead consistently getting very neary 4 gallons draw down! What gives?

As to check valve issue: while I do not see a check valve in the well house (and Michigan evidently does not allow them above ground), could there be a second check valve in the well casing, underground but near the top? If their is such a check valve, and if the one on/near the pump has failed (I do have 2.6 ppm ferrous iron in my water), could that explain the missing draw down w/o loss of household water pressure? Any other ideas? Help!

 

[LLigetfa]

Are you sure it is a 36 gallon tank? It could be a smaller tank which is equivalent to a 36 gallon hydro-pneumatic tank. Measure the height and diameter and do the math.

 

[LLigetfa]

As for a second checkvalve, is that a code requirement in Michigan? Many people are dead set against having a second checkvalve on the system near the surface. If there is more than 30 feet between the top checkvalve and the water table, when the lower checkvalve fails, the water column will fall creating a vacuum that then water hammers on pump start. Some advocate a checkvalve every 30 feet which others dispute.

 

[Masterpumpman]

I'd keep it simple. Remove all check valves except the one on or near the pump; Replace the captive air tank with a small WX-102 (or equivelent); add a Cycle Stop Valve http://www.cyclestopvalves.com/index2.html. Then unless you have a leak in the system everything should be fine. The CSV will prevent the pump from cycling, and give you constant pressure in the shower. This would be the simplest, cheapset and the best solution.
The sediment is another problem that with the new system may or may not rectify itself.

 

[Drewmcg]

...but how do I know whether I need a new check valve?

Thanks, Porky. That all makes sense to me, but here's the question:

How do I know whether I need a new check valve?

This is an old well, driven underneath the driveway of an old house, whose casing exits the ground in well room (pit?) about 6x 6x 5.5ft (tall) off of the basement. The ceiling is cement (to support the driveway, I presume) with a hole over the casing, covered by an iron plate. Its a 4" diameter, evidently cast iron casing (rust scale all up and down the exposed portion and cap). I have no idea how deep it goes, but I presume that a well pro would have to

(i) dig up the (shared) driveway to the metal plate (blocking two neighbors from getting in and out of their houses);
(ii) set up a tripod to pull the pump, which might be bonded to the casing due to the iron in the water (2.6 ppm). (Its a two-wire, 110v pump--not a 230v pump as previously indicated).

Is there some test I can do to (a) figure out if there is a second check valve, and/or (b) figure out whether there is a failure of the pump check valve if there is a second vavle? Thanks again.

 

[Drewmcg]

O.K.; checked the volume: 20" diameter X 26.5" height = 36 gallons. I'm still "missing" over 5 gallons of drawdown!

 

[DonL]

You can turn off the output of the tank, then see if the tank pressure drops to tell you if you have a check valve leaking.

The pressure should remain and hold. It is best to have a Good cap on the tank air fill valve.

I think that was your question.

DonL

 

[Drewmcg]

I think the problem is that IF there is a second check valve (closer to surface), and the PUMP check valve fails, then the pressure not falling would only indicate that the second (higher up) check valve is still working--but say nothing about the check valve @ the pump. If that (pump) check valve has failed, that might explain the missing 5 gallons of drawdown, non? I'm now officially lost!

 

[DonL]

You are correct, But short of removing the pump, that is about the only test that you can do.

If their is a check valve up top then you should be able to see and remove it, then run the test, to see if the pump is holding.

How are you measuring the drawdown ?

As long as 1 check valve is holding and water is not going back into the well, then that should not affect Tank Drawdown.

"In keeping with current industry standards, drawdown factors are based on Boyle's law. Actual drawdowns will vary depending upon system variables, including the accuracy and operation of the pressure switch and gauge and operating temperature of the system."


Good Luck on your project.


DonL

 

[Drewmcg]

You are correct, But short of removing the pump, that is about the only test that you can do.

If their is a check valve up top then you should be able to see and remove it, then run the test, to see if the pump is holding.

How are you measuring the drawdown ?

...

DonL

Here's how:

Open basement faucet until pump starts to run, then close;
Let pump cut off (verify w/pressure dial at tank);
Measure air at top of pressure tank/shrader valve (60psi);
place one gallon bucket under faucet; fill one bucket at a time until pump kicks in, then stop flow right away and measure gallons (4 gals. tops).

I also measured air pressure @ shrader valve with the tank empty (38 psi), and the dial on the water tank (which appears to be accurate) reads 40 psi when the pump kicks back in.

If I open the top of the well, I can only see/reach a few inches down. Even if I could see a second check valve, I suppose I'd need a tripod/crew to get at the thing.

The only other possibility I see is that somehow--over the years--the bladder on the tank has filled with sediment, reducing its effective volume substantially. Has anyone ever heard of/seen this? Seems like I would have gotten more sediment when I drained the tank, but perhaps its stuck up in there somehow. There would have to be a lot of sentiment in the bladder to make this 36-gallon tank behalf as if it was a 15-gallon tank (15 X .26 = 3.9 gals)!

 

[LLigetfa]

Drain the tank, disconnect it, and see how heavy it is. Maybe there is water/sediment on the wrong side of the bladder.

 

[DonL]

bladder on the tank has filled with sediment, reducing its effective volume substantially. Has anyone ever heard of/seen this? Seems like I would have gotten more sediment when I drained the tank, but perhaps its stuck up in there somehow. There would have to be a lot of sentiment in the bladder to make this 36-gallon tank behalf as if it was a 15-gallon tank (15 X .26 = 3.9 gals)!

The inside of the bladder should not have sediment, only air. Or it has busted.

Even if it were busted, then it would work just like the old school tanks.

You may be expecting more than your system can provide. Or need a new tank for better performance.


DonL

 

[Drewmcg]

The inside of the bladder should not have sediment, only air. Or it has busted.

Even if it were busted, then it would work just like the old school tanks.

You may be expecting more than your system can provide. Or need a new tank for better performance.


DonL

I'm not an expert, but my research on captive air tanks indicates that normally the bladder holds water; not air (at least for metal tanks). See: http://www.inspectapedia.com/water/Water_Tank_Bladders.htm#Bladders .

I'm back to thinking that there is some issue with the bladder, that has let water seep through the bladder and into the metal portion of the tank, taking up volume but not being able to be pumped out. This is doubly worrisome in that it is possible that contaminated water (sitting above the ruptured bladder) could leak into the clean well water and come into my water supply. Wow.

Sears sells a replacement bladder for $60, but by the time I do all the work to disconnect the tank, etc., I wonder if I'd be better off replacing this thing altogether. Thoughts?

 

[DonL]

You are correct on the sears, My mistake.

It does depend on the tank design. Many are just the opposite.

That is nice that a replacement bladder is available, Sears backs their stuff.

Have a Good Day.

DonL

 

[Cacher_Chick]

For twice that, you can get a new overseas made bladder tank and hook it up. I suppose it all depends on what your time is worth. Who knows what the life expectancy is of the replacement sears bladder and how much trouble it is to change it?

 

[DonL]

You can drain the tank and check the air pressure and let it set for awhile to see if it is holding, with a cap on the fill valve.

If there is a leak, then chances are that the tank may rust out from the inside, because water was leaking into the air pocket.

cacher_chick's idea may be the best bet, they may all be made overseas nowadays.


DonL

 

[Valveman]

Tanks with replaceable bladders or bags, have replaceable bladders or bags for a reason. It all depends on how the bag or diaphragm works inside the tank. If it touches the tank when it moves up and down, it will need replacing soon. Some diaphragm tanks with non-replaceable diaphragms are made so the diaphragm can move up and down without ever touching the tank. In my opinion these type tanks will last many times longer than other type tanks.