Plumbing a second bladderless pressure well tank

[Gohot]

I currently have a 5 hp well pump 170 feet down, feeding a 385 g bladderless tank, with a 2 inch pipe. Ok for the home, but now have irrigation demands. The set up is ok for the sprinklers, stay on at approximately 45 psi while the sprinkler banks are working. However, when running the drippers, the pump cycles too frequently. So, I added a second tank, twice as large in capacity, on it's side, with the center at the same level as the upright first tank. The tanks are connected with a T after the pressure valve. Both tanks have a side mounted air bleed valve to let out extra air. The tanks are connected to each other from the top of the lateral tank to near the top of the upright tank with a 3/8 line to equilibrate the air pressure above the water line. In theory I expected this set up to work. In practice, I do not believe I am using the water in the lateral larger tank. It seems the larger tank waterlogs while the smaller one is working well. I may be over theorizing, but I suspect the same pressure (adequate in the smaller tank) is insufficient in the larger tank because there is more surface area in the larger tank to spread the pressure coming from the connected small tube from the smaller tank. Does anyone have experience in hooking up multiple bladderless pressure tanks and can shed a little light? Appreciated. ts

 

[LLigetfa]

The tops, not the centre of both tanks would have to be at the same elevation.

 

[Sponsor]

 

[Gohot]

The tops, not the centre of both tanks would have to be at the same elevation.

Would it matter or not matter where the level of the water is, as I envisioned the water level being the same in both tanks, as long as they were connected top and bottom. Therefore, if one tank was higher than the other at the top, the water levels would still be the same? Similar to using a long clear tube for adjusting height on a long brick wall.

 

[Gohot]

Would it matter or not matter where the level of the water is, as I envisioned the water level being the same in both tanks, as long as they were connected top and bottom. Therefore, if one tank was higher than the other at the top, the water levels would still be the same? Similar to using a long clear tube for adjusting height on a long brick wall.

Sorry, I meant a long tube filled with water, to see where the level was on either end.

 

[LLigetfa]

It is only the amount of air above the water that would matter. The lower tank would be 100% full of water and not have any value.

 

[LLigetfa]

If you have two tanks connected at the bottom and at the top by a tube, the water will have the same level on both tanks. The air will rise to the highest point and since there is only a small amount of air, it will compress into a small space at the top of the taller tank. When you draw down water, the air expands until the pressure drops to turn on the pump. If there is not enough air to displace all the water, what water is left in the tank is just wasted space.

 

[Texas Wellman]

Install a schreader valve into the 2nd tank and supercharge it with air.

 

[Gohot]

It is only the amount of air above the water that would matter. The lower tank would be 100% full of water and not have any value.

The smaller tank is roughly 2 feet diameter, and upright. The one it's side tank is almost three feet diameter. The middle of the larger tank, the center level if you will, is even with the level at where the water would be in the smaller tank when it cuts off at 55 lb. The top of the larger tank is 10 inches below the top of the smaller upright tank, but because it is larger in diameter, it's "water line" when charged is approximately even with the expected water line of the smaller upright tank when charged. However, the larger tank still water logs.

I will experiment and allow more and more air to get into the smaller tank to see if it allows air in the larger, before the side valve float is opened at the low water level in the smaller tank.
Is there a plumbing diagram somewhere showing the proper way and level to hook up two bladderless pressure well tanks?

 

[Gohot]

Install a schreader valve into the 2nd tank and supercharge it with air.

Thanks for the suggestion. Placement of a valve for charging the larger tank is my fall back plan. I am trying to work it out so it works automatically without my having to interfere. I am thinking raising the on it's side tank so it's top(side) is level with the top of the upright tank.

 

[Valveman]

The automatic air injector only works when the pump cycles on. By adding a larger (additional) tank, the number of cycles will be reduced along with the number of times the air gets injected. At the same time you have tripled the size of the tank and tripled the amount of air needed to keep the tanks charged. You can triple the amount of air being injected with each pump cycle by lowering the bleeder orifice in the well three times deeper. You have to use a special bleeder orifice to be able to do that, as the standard bleeder will not open when installed more than about 10' deep.

Without pulling up the pump to put the bleeder deeper, adding air with a compressor and a Schrader valve maybe your best option.

A 1000 gallons worth of pressure tanks only holds about 100-150 gallons of water. You might consider using a 1000 gallon cistern storage tank that will hold 1000 gallons of usable water, and using a little 1/2HP booster pump to handle the drip system. The well pump would only cycle once to fill the cistern tank for 1000 gallons of drip use.

 

[Texas Wellman]

With your set-up I would suggest looking at a whitewater compressor, that automatically adds air to the tank. I haven't messed with one in years but they are available.

 

[Gohot]

The automatic air injector only works when the pump cycles on. By adding a larger (additional) tank, the number of cycles will be reduced along with the number of times the air gets injected. At the same time you have tripled the size of the tank and tripled the amount of air needed to keep the tanks charged. You can triple the amount of air being injected with each pump cycle by lowering the bleeder orifice in the well three times deeper. You have to use a special bleeder orifice to be able to do that, as the standard bleeder will not open when installed more than about 10' deep.

Without pulling up the pump to put the bleeder deeper, adding air with a compressor and a Schrader valve maybe your best option.

A 1000 gallons worth of pressure tanks only holds about 100-150 gallons of water. You might consider using a 1000 gallon cistern storage tank that will hold 1000 gallons of usable water, and using a little 1/2HP booster pump to handle the drip system. The well pump would only cycle once to fill the cistern tank for 1000 gallons of drip use.

Excellent suggestions from all. I went out and completely emptied both tanks bone dry, then refilled. After the pump stopped, I could sound the tanks and estimate the water line. I believe this is what is happening:
The cut off pressure is 55 lb, and that is the pressure of the compressed air in both tanks when full. The pounds of pressure is the same in both tanks, per square inch, but since the pressure is the same, the amount of square inches of surface area of water must in fact be smaller in the larger tank , ie, closer to the top of the tank , until the square inches pressed on is the same for both tanks. The upright tank does not change sq inches with water level, but the lateral tank does because the cross sectional area changes in the larger one with the level of the water. Therefore, the bubble of air is in fact smaller in the larger tank, although both read the same pressure. At the poster above pointed out, the tops must be level in order for both to share in the air bubble. So, I am either going to have to stand the larger one upright and lower it, thus making both the same sq inches of surface area, and same level at top, or raise it up while laying on it's side. Cannot simply add air to the larger, as the air will go to the smaller and equilibrate regardless of which one it is pumped into. I believe a quick fix may help, which is to tighten the valve at the outflow air valve, to somewhat make the system keep extra air. Hoping the air level will not drop too far in the smaller tank to pass bubbles to the hopuse. I think the larger tank will flow water in to prevent that. I will keep allposted.

At this time, I would not advise a customer to add a 2X larger tank on its side to the existing system (least until we have this figured out !)

 

[Texas Wellman]

Listen, you can orient the tanks any which way you like. It had zero to do with the'pressure' of the air- it's all about the volume. Add air via an air compressor to the second tank until you get at least half water and half air.

As long as the headspace in each tank is not directly connected it should keep its air charge.

 

[Reach4]

So, I added a second tank, twice as large in capacity, on it's side, with the center at the same level as the upright first tank. The tanks are connected with a T after the pressure valve. Both tanks have a side mounted air bleed valve to let out extra air. The tanks are connected to each other from the top of the lateral tank to near the top of the upright tank with a 3/8 line to equilibrate the air pressure above the water line. In theory I expected this set up to work.

Interesting and fun problem. I am thinking that the level of the two bleeders should line up presuming both bleeders are similar. If the tanks are at that height, it seems like either bleeder could optionally be removed and plugged.

 

[LLigetfa]

As valveman said, your airmaker is probably inadequate to service both tanks and you will probably need to add air periodically with a compressor. I would disconnect the air crossover, disable the AVC in the first tank, and plumb the second tank in series. That way if there is too much air in the first tank, it will burp across to the second tank at the bottom of every pump cycle.

 

[hj]

Do NOT connect the tops of the tanks together. You want the second tank's air to be pressurized by the incoming water. Feed in to the bottom of the tank so you capture the maximum amount of air volume.

 

[Texas Wellman]

I failed to see this in your original post. Get rid of this line.

he tanks are connected to each other from the top of the lateral tank to near the top of the upright tank with a 3/8 line to equilibrate the air pressure above the water line

 

[Reach4]

I presume this is a non-standard configuration without an established standard method. These are some thoughts that may or may not have merit. They are certainly not based on experience. If my logic is flawed, please point it out.

1. As discussed earlier, the amount of air added over time needs to be enough to make up for air that dissolves into the water. This was discussed early in the thread.

2. If the extra air pressure equalization line is removed, then each tank needs its own bleeder vent system. It is not clear to me in that case that the altitude matters. What is clear I think is that the incoming air would have to be divided up somehow, or else one tank gets waterlogged-- (eventually have no air). That splitting up up of the incoming air may not be easy.

3. If you put the two tanks in series as LLigetfa suggests, and the bleeder vent on the first tank is disabled, then the extra air pressure equalization line would be important. I think the height of the active and disabled vents should be the same pretty much the same.

 

[LLigetfa]

3. If you put the two tanks in series as LLigetfa suggests, and the bleeder vent on the first tank is disabled, then the extra air pressure equalization line would be important. I think the height of the active and disabled vents should be the same pretty much the same.

No, I don't agree. There is no problem with having too much air in the tank just so long as it doesn't move forward into the downstream plumbing. The AVC on the second tank if suitably plumbed would act as the air separator so the first tank would not need an AVC and excess air from the first tank would service the needs of the second tank, assuming of course there is enough air to begin with. If there isn't then topping it up with an air compressor may be needed.

 

[Reach4]

No, I don't agree. There is no problem with having too much air in the tank just so long as it doesn't move forward into the downstream plumbing. The AVC on the second tank if suitably plumbed would act as the air separator so the first tank would not need an AVC and excess air from the first tank would service the needs of the second tank, assuming of course there is enough air to begin with. If there isn't then topping it up with an air compressor may be needed.

I see your point. My thinking was that the air/water ratio for each tank was optimized when it was designed to work alone. So the 2-tank system should have a similar air/water ratio. I now think that may well be wrong.

I have been thinking that the air release valves are usually fairly close to the middle of the tank. Now I wonder why -- why are they not nearly at the bottom of the tank. So that in a 40-60 system, when the air+water gets down to 40 PSI, the release could release some excess air, keeping only a small reserve of water to allow for the delay of the pump bringing new water.

Clearly in the system you describe, there would be a higher air/water ratio than with a single tank. Maybe that is desirable. Maybe the standard tank leaves less than ideal amount of air. In that case, the system you describe would be better than a single bigger tank with the release near the middle. I now think that the release valve on a big hydro-pneumatic tank should be positioned to keep only a few gallons of water in place before air is released.

The equivalency rating of a diaphragm/bladder pressure tank is over 2 x the size of the that tank. If the air were to fill the whole hydro-pneumatic tank at 38 PSI, the equivalency would be almost 1:1. I am guessing that they leave a whole lot of water in the hydro-pneumatic tank to minimize the air blast that would occur if the electricity went off or if the pump did not start for some other reason.