Piston pump and hydro-pneumatic tank

[Chucky_ott]

Haven't been on here for a while. Too many projects on the go.

At my cottage, I currently have a jet pump and diaphragm pressure tank. It works well except:
1. In the spring when I hook it up. Takes forever to prime and fill intake pipe. And until all the air is pumped out, the pump deadheads until I can purge the line.
2. Air in the line is an occasional problem throughout the season as well.
3. If there is a power outage (happens regularly enough) and someone uses water, pressure will drop and it will lose prime.

Now this is not a big problem right now because I'm usually around to fix any issues that come up. But my wife and kids would have no idea what to do. Ditto for my sister and BIL who have the cottage next to mine and get their water from my pump.

My cousin, who has a cottage next to ours, still uses a 50+ year old piston pump. I set it up in the spring. It self primes and doesn't cause any problems. Ever.

So thinking about the future, I'd like to make my pump as foolproof as possible, I'm thinking of replacing the jet pump with a piston pump.

Now for my question.

I contacted the pump manufacturer to ask about the maximum pressure a particular pump could build (FWIW, it's this one: https://pompco.com/en/products/piston-pumps/regular-model/). They promptly answered but also provided additional information for which I needed clarification.

He essentially said that captive air tanks are not recommended for a piston pump and I should instead use an hydro-pneumatic tank. Not knowing the difference, I googled it and found even more confusing information on what an hydro-pneumatic tank was. Google essentially said that my diaphragm tank (as well as bladder tanks) are hydro-pneumatic tanks. I again asked the vendor for some clarification and he said that you don't want to use a pressure tank that pushes against the pump. Instead, you only want the pump to provide the pressure. He gave me a link to a recommended tank and it is essentially just a reservoir as shown in the picture. He said to keep my pressure tank as it will work and not damage the pump. But he added that when the tank fails, I should consider the hydro-pneumatic tank even though they are generally more expensive.

So exactly what it an hydro-pneumatic tank. How does it work to provide pressure? I'm assuming any air in the tank gets compressed. Is this the same as an air-over-water tank? Are these trouble-free? Anything else I'm missing? Thanks

 

[Valveman]

Hi Chucky. Piston pumps will draw a prime much easier than a Jet pump, but not as easy as a submersible. They have there problems but most can be mitigated.

Hydro Pneumatic just means air over water tank. Bladder and diaphragm tanks qualify as Hydro Pneumatic as well. The difference is captive air or not captive air. Bladder and diaphragm are captive air, meaning the air charge is installed at the factory and can't get out. Most people call diaphragm and bladderless tanks Hydro Pneumatic, because that's all they got. Lol.

All pumps will prime easier into a Hydro tank compared to a captive air tank because Hydro tanks start at zero pressure. Captive air tanks start at the air pre-charge amount. 30/50 switch, 28 PSI pre-charge, pump starts at 28 PSI instead of zero and primes easier.

The downside is you have to keep adding air to a Hydro tank as automatic air volume controls are not reliable. They get waterlogged often. Captive air tanks never water log and don't need regular air charges until the bladder or diaphragm fails. Failing bladders and diaphragms are a common problem for those who don't know how to eliminate cycling, which is what destroys bladders and diaphragms and makes some people think hydro tank are better.

 

[Sponsor]

 

[Reach4]

He essentially said that captive air tanks are not recommended for a piston pump and I should instead use an hydro-pneumatic tank.

To me, that suggests that he is saying that that particular piston pump adds air on a routine basis. That is an advantage to a hydropneumatic tank, and then the tank would have an AVC valve to release excess air.

You may sometimes see hydropneumatic tanks called "conventional" because they were the norm once upon a time.

 

[Valveman]

An AVC on a jet or piston pump adds air to the tank. An AVC for a submersible releases excess air from the tank. Neither are very dependable, which is why the captive air tanks are much more popular than the "conventional" or "hydro" tanks.

 

[RetiredInGueydan]

A properly installed jet pump/diaphragm pressure tank/foot valve combination should never experience any of your issues.

 

[Reach4]

Is this the same as an air-over-water tank?

Yes. They are often also called galvanized tanks, although they can be had in fiberglass, and I presume other construction.

An AVC on a jet or piston pump adds air to the tank. An AVC for a submersible releases excess air from the tank. Neither are very dependable, which is why the captive air tanks are much more popular than the "conventional" or "hydro" tanks.

So would the piston pump work well with the AVC port plugged, and using a precharged tank?

 

[Chucky_ott]

To me, that suggests that he is saying that that particular piston pump adds air on a routine basis.

That would make sense. He did add that if I used a captive air tank, I might see air coming out of the faucets every once in a while. I'll confirm this with the manufacturer

A properly installed jet pump/diaphragm pressure tank/foot valve combination should never experience any of your issues.

Well, I agree. But this is a seasonal cottage so the pump gets disconnected every fall. I usually have those problems when I re-connect the pump and until all the air is purged. Just a tiny amount of air causes the pump to deadhead. It gets close to cutoff but not quite. It's only when I open a valve to let the air out that it stops. Like I said, not a big problem but the spring-time setup is too finicky for the kids to manage.


A few other questions/comments:

1. Would lowering the pre-charge on the diaphragm tank help? Or is that likely to stretch the diaphragm too much ?
2. Why is a conventional tank so much more expensive? The one he linked to is a bit more than $1000 CAD. That's almost twice the cost of a diaphragm tank of the same capacity.

 

[RetiredInGueydan]

The pump should never lose prime or introduce air into the system. Is there a check valve at the pump or foot valve at the bottom of the suction line? When a foot valve is used, the entire suction side of the the pump is filled with water and primes instantaneously. The air pre-charge should be 2psi under cut-in pressure and is likely not your issue.

 

[Chucky_ott]

The pump should never lose prime or introduce air into the system. Is there a check valve at the pump or foot valve at the bottom of the suction line? When a foot valve is used, the entire suction side of the the pump is filled with water and primes instantaneously. The air pre-charge should be 2psi under cut-in pressure and is likely not your issue.

Yes, there's a check valve just above the sand point. Then it's about 100 ft of 1.25" polypipe on uneven terrain. The jet pump is not self priming. The entire suction line needs to be purged of air at the beginning of the season. That's why it's finnicky to setup each spring. It usually settles down after a few weeks of use.

As for issues during a power outage, it's really more a problem with the low-pressure lever on the pressure switch. Someone needs to re-engage it when it trips.

Like I said, it's not a big problem but perhaps too complicated for my wife and daughters to manage. The piston pump that my cousin has is easy-peasy.

Come to think of it, the jet pump sits higher than the tank. Perhaps I should put it lower so that the pump doesn't drain when the tank empties if there's a call for water during an outage.

 

[Reach4]

1. Would lowering the pre-charge on the diaphragm tank help? Or is that likely to stretch the diaphragm too much ?

Do you turn off the power to the pump and empty the water to winterize? If you empty the pump, I think it is going to need priming.

Based on other comments, I now think you leave the pump powered and wet.

2. Why is a conventional tank so much more expensive? The one he linked to is a bit more than $1000 CAD. That's almost twice the cost of a diaphragm tank of the same capacity.

Specialty low-volume item, plus typically physically bigger, so harder to ship and store. Shipping charge is often affected more by volume than weight. A 32 gallon precharged tank replaces maybe a 100 gallon conventional tank (I probably have the ratio off).

The jet pump is not self priming.

So a self-priming jet pump could be an alternative. Those still need some water in the pump to get going.

Come to think of it, the jet pump sits higher than the tank. Perhaps I should put it lower so that the pump doesn't drain when the tank empties if there's a call for water during an outage.

Electrical outage? So electricity is on most of the time while you are away, and the pressure tank capacity would compensate for the leaky check valve. The lower precharge would ensure more water to compensate for the leaky check valve during electrical outage periods. Sounds to me as if lowering the precharge by 5 psi could be worthwhile.

It could also be useful to fill the pressure tank as you leave, if the check valve leak is not so bad. To do that, poke the pressure switch armature to make the pump turn on until cutoff.

Maybe note how often your pump cycles when you are not using water. That could help gauge how leaky your check valve is.

 

[Chucky_ott]

Do you turn off the power to the pump and empty the water to winterize? If you empty the pump, I think it is going to need priming.

Most definitely. -30C here in the winter :-(

Specialty low-volume item

I figured this had something to do with it.

Electrical outage?

Yes. What I meant is that if someone uses water during an electrical outage, it will deplete the pressure tank and trip the lever on the pressure switch. Sometimes the pump loses prime, perhaps because it sits higher than the tank. If I keep the jet pump, I'll move it lower next spring.

Maybe note how often your pump cycles when you are not using water. That could help gauge how leaky your check valve is.

The check valve is fine. When the pump is not running and there's no call for water, the pressure is maintained for a long period.

 

[Chucky_ott]

Oh, and by lowering the pre-charge on the diaphragm tank, I meant doing this instead of using a air-over-water hydro-pneumatic tank with a piston pump. Lowering the pressure would mean it's not working against the pump when it self-primes (if I understood what Valveman said). But I don't know if that would cause the diaphragm to stretch too much.

 

[Reach4]

Yes. What I meant is that if someone uses water during an electrical outage, it will deplete the pressure tank and trip the lever on the pressure switch. Sometimes the pump loses prime, perhaps because it sits higher than the tank. If I keep the jet pump, I'll move it lower next spring.

So the problem you are concerned with occurs in the summer. The best solution is to be rid of the pressure switch that has the lever. So that if the power goes off, somebody uses water, the pump will start pumping when the electricity comes back on at 3 am.

A lever-type cutoff will not necessarily cut off in the case of the well point running dry and sucking air, but can keep the pump running with the pressure tank stuck at half full of water.

If your well point runs dry, consider a device designed to detect this out-of-water condition. Yes, it costs more, but it is more reliable.

Lowering the pressure would mean it's not working against the pump when it self-primes (if I understood what Valveman said).

I don't think Valveman was saying that or would say that. He could say a lower precharge would be better for other reasons-- mainly supplying water while the pump gets going.

A lower precharge would help with false trips, but if a user exhausts the stored water, the precharge level I don't think would have a significant effect on the pump self-priming. And if there was even a miniscule effect, I don't know if it would aid or hinder self-priming. I lean toward hinder.

 

[Chucky_ott]

The best solution is to be rid of the pressure switch that has the lever.

Been there, done that. The system had a regular pressure switch before until I had a power outage, water was depleted, and when the pump came back on, it could not build-pressure. Had a deadhead condition, plastic fittings melted, water all over the place. I agree that the Cycle Sensor would be a great solution but I only have 120V to the pump house and the sensor needs 220V. Running a 3-wire underground is not in the works for now.

don't think Valveman was saying that or would say that. He could say a lower precharge would be better for other reasons-- mainly supplying water while the pump gets going.

His exact words were "All pumps will prime easier into a Hydro tank compared to a captive air tank because Hydro tanks start at zero pressure. Captive air tanks start at the air pre-charge amount. 30/50 switch, 28 PSI pre-charge, pump starts at 28 PSI instead of zero and primes easier.". So what I was suggesting is lowering the pre-charge pressure on a diaphragm tank to mimic the zero initial pressure of a hydro tank IF AND ONLY IF I switch to a piston pump

 

[Valveman]

Lowering the pre-charge will not work the same as a hydro tank during priming. A hydro tank at zero pressure will accept some water as the pressure increases. The diaphragm in a captive air tank is shoved against the inlet/outlet hole, and the tank cannot accept any water until the pressure increases above the pre-charge amount. If a pump cannot push water, it cannot draw water. With a captive air tank a tap needs to be open during priming for there to be a place for water to push. With a hydro tank the pump will usually prime without a tap open.

The lever on the pressure switch (low pressure cut off) is a good idea on jet or piston pumps. You don't want these type pumps to try and re-prime when you are not there. It is a pain to have to go lift the lever, but at least the pump is not melted.

The Cycle Sensor can be set to manual reset and would work well. If there are already 3 wires to the 115V pump, moving the common to a second (double) breaker would make it 230V.

 

[Valveman]

Air Volume Controls are ok if you need them. But if there is anyway to eliminate an AVC, like using a captive air tank, it eliminates several more possibilities for failures. It has been my experience that the extra check valve, tubes, schrader, and other parts needed for an AVC just make a water system less reliable. Tearing a bladder or diaphragm is the biggest drawback of a captive air tank, and when used with a Cycle Stop Valve to eliminate the cycling torn diaphragms are no longer a problem.

Oh, and a little extra stretch won't hurt nearly as much as excess cycling.

 

[Chucky_ott]

With a captive air tank a tap needs to be open during priming for there to be a place for water to push. With a hydro tank the pump will usually prime without a tap open.

Hmmm, maybe that's been my problem all along when it comes to priming. I've always done it with all valves closed. I never realized that I was fighting against the pre-charge pressure.

 

[Reach4]

Hmmm, maybe that's been my problem all along when it comes to priming. I've always done it with all valves closed. I never realized that I was fighting against the pre-charge pressure.

By that logic, opening the drain valve at the pump would help. I am not sure if it is worth doing or not.

 

[RetiredInGueydan]

By that logic, opening the drain valve at the pump would help. I am not sure if it is worth doing or not.

Reach, just exactly how many jet pumps have you primed? Jet pumps move water and are not air compressors.

 

[Reach4]

Reach, just exactly how many jet pumps have you primed? Jet pumps move water and are not air compressors.

Zero.

I am saying that if priming into a galvanized tank is easier than into a pre-charged pressure tank, then starting into an open drain valve would also make things easier. I am afraid I am trying to apply logic. Do you disagree with my logic?

I did not say that priming into a galvanized tank is easier. That was the pump company.

In part that you did not quote, I had discussed a non-priming thing -- the water level of the water drops to the level of the sand point screen while the pump is sucking. I would indeed expect the pump to be pumping a mix of air and water at that point. What would you expect? Jet pumps produce a vacuum. That sucks only water if there is only water at the screen. If the water level dropped, I expect to not suck only water.