Vacuum Breaker for Softener/Filter on Input or Output?

[Reach4]

https://terrylove.com/forums/index.php?threads/softener-media-tank-collapsed-why.63066/ discusses putting a vacuum breaker on a softener when the the tank services lower stories or altitudes.

So for such uses, a vacuum breaker, such as Watts N36 should be used. Should the vacuum breaker be on the input or output. Now either will probably work fine if the softener is in service, but we cannot be sure the softener will not try regenerating at the most inopportune time.

"Votes" are opinions, and they can be changed. Votes display publicly.

 

[ditttohead]

No vote needed, the vacuum breaker goes on the side of the system that is prone to a vacuum. If both sides are prone, a second vacuum break is cheap insurance.

If the system is being fed from a well, between the well and softener is usually the correct location. If the system if feeding a booster pump, then between the system and booster pump is preferred.

On the video below, where does the railing on top of the tank go? I hope they had a lot of distance between the crown and this demo...

 

[Sponsor]

 

[Reach4]

I am thinking that during each softener cycle there is a path, maybe through the injector, to the other side. So that a vacuum breaker on the "wrong" side would still prevent a strong vacuum from developing unless the water flow was very swift.

I guess there could be a transient time during the switching between cycles where a power failure or other failure could be wrong.

Considering that almost any deep well could have the potential for such a failure, it is surprising this is not discussed more often. I guess it could be looked at that if such a failure only had a 0.01% chance of occurring in a well and since the damage would probably not hurt people, spending an extra $50 on each of 1000 installs should save $50000 for each failure.

In the case of downhill users of the well, the odds of a failure that causes a vacuum would be higher (many more points of releasing water, each of which is more likely than a checkvalve or drop pipe fail), then the economics would change a lot in favor of the vacuum relief.

It seems that this is something that might be included in controllers or bypass assemblies in the future. I would hope these are a lot more reliable than the leaky vacuum breakers they often put on hose faucets now.

 

[Gary Slusser]

Reach and others, can you explain why/how a vacuum breaker would be needed on a well using either a submersible or single or two line jet pump? What would the condition have to be to warrant a vacuum breaker?

 

[ditttohead]

Vacuum breakers are required on most industrial systems, steam boiler make up tanks etc, but residential applications usually rely on the experience of the plumber.

Most softeners/filtration systems have the inlet/outlet tied together internally during the regeneration cycle unless the system is designed with a no hard water bypass valve etc, but even then, most of those system designs will have multiple tanks so only the valve that is in regeneration isolates the inlet/outlet during regen, the other side I still tied together. Integrating a vacuum breaker, why bother. A good quality USA made vacuum breaker is only about $50 and is good for up to 2" plumbing in most cases.

 

[ditttohead]

A submersible pump that is 400' deep... the potential vacuum of that is approximately 12 atmospheres. If we tried to calculate that to negative PSI, I am guessing that would be nearly -180PSI.

If the check valve fails and the water were to try to go back down to the bottom of the well, here is the result. This can also be caused by the drain line being run down a hill without a vacuum break, or from a booster pump and a lack of adequate feed water volume/pressure. This is very common, I have dozens of pictures similar to this from over the years. We used to fill 50 gallon drums with steam, plug them, and stand back. I wish I video'd some of those, maybe in the future I will. The tanks would implode within 15 minutes of plugging them.

 

[Gary Slusser]

You don't say what the static water level is in the well or what the dynamic water level is. And the way you have described the condition, it is not possible to cause a vacuum breaker to be needed.

A broken check/foot valve leaking water back into the well will decrease the water pressure to the cut in setting of the pressure switch controlling the pump and thereby turn the pump on. Then the pressure increases to the cut out switch setting and the pump shuts off until the leaking check valve allows the pressure to drop to the cut in setting and everything repeats until the pump burns out or someone finds the pump running when water is not being used etc.. Plus the pressure tank empties (under pressure) its gallons down the well to the leaking check valve which equalizes the pressure to 0 psi if the pump doesn't come on. AND then.... the water level in the well would have to fall below the inlet to the pump where the leaking check valve would allow draining of the drop pipe to create a suction. Otherwise you should have water in the drop pipe equal to the water level in the well.

Now that applies to a rock bore well, a sand and gravel well is a bit different in that some do not have a check/foot valve. Many have more than one sand and gravel water bearing layers and slotted casing in each.

 

[Mikey]

We used to fill 50 gallon drums with steam, plug them, and stand back. I wish I video'd some of those, maybe in the future I will.

No need; hundreds of these on youtube. Search for "youtube: imploding 55 gallon drum"

 

[Reach4]

You don't say what the static water level is in the well or what the dynamic water level is.

The water level is what is important, but for maximum vacuum, the drop only has to be enough to correspond to the atmospheric pressure. The highest atmospheric pressure ever recorded on earth is 32.06 inches of mercury, which is 36.32 feet of water. Any depth to water greater than that cannot make a stronger vacuum. A vacuum cannot go below zero psi. Water at 50 or 60F water boils at about 1/4 PSI absolute, but that is still way more vacuum than it takes to make the tanks fail.

Fiberglass media tanks, as far as I can tell, are typically rated to 5 inches of mercury vacuum (2.46 psi). That is only 5.66 feet of water. I am confident there is some margin in the spec, but it would seem that even a shallow well system could in theory have the problem.

A broken check/foot valve leaking water back into the well will decrease the water pressure to the cut in setting of the pressure switch controlling the pump and thereby turn the pump on.

Yes. The problem scenario only occurs if the pump does not run for some reason, for example power fail or broken pressure switch.

Here is another scenario that does not require the check valve to fail: What if the drop pipe fails? Pump stops for whatever reason, and there is an underwater hole in the drop pipe?

I don't currently plan to add a vacuum breaker. I figure the chance of this occurring is not high, and the failure of my water heater, iron filter and softener in the basement is not catastrophic. I wonder if that would be covered by homeowner's insurance.

Hmmm. Score one for the conventional pressure tank with snifter valve. That valve would seem to work as the vacuum relief. I wonder about using a snifter valve with a diaphragm pressure tank. Would its air path be big enough, I wonder?

 

[Gary Slusser]

I serviced thousands of private and small commercial well water customers plus thousands of other dealers' water treatment equipment customers that I did not sell and I fixed their 'no water' and other pump/pressure tank or switch etc. problems. I advertised 24/7 emergency service. I could pull pumps from 500' as long as they were not on galvanized pipe. I had a 4x4 pickup outfitted for nothing but well work. One of the most common causes for jet pump system problems was a leaking foot valve (loss of prime) with some that burnt out the pump. Short cycling due to a bad pressure tank (little or no captive air pressure) took out a lot of submersible pumps. Most of those people had a water softener or backwashed filter etc. but I never heard of or saw any collapsed tank until an internet customer in Puerto Rico called with one and sent me pictures. That was about 2009 and the problem was road work down the hill from his house.

BTW Reach4, would you mind giving an example of what you mean by "The water level is what is important, but for maximum vacuum, the drop only has to be enough to correspond to the atmospheric pressure." so the average guy reading this can understand how it works?

 

[Reach4]

BTW Reach4, would you mind giving an example of what you mean by "The water level is what is important, but for maximum vacuum, the drop only has to be enough to correspond to the atmospheric pressure." so the average guy reading this can understand how it works?

The average guy reading this? That is a select group, so I think so.

When we refer to 4 PSI vacuum, that is based on what a gauge would read. That would be the same as saying the pressure was -4 PSI on the gauge. That can be abbreviated as PSIG. On an absolute basis, atmospheric pressure is about 14.7 psi. So 4 PSIG vacuum means that on an absolute pressure, the pressure is really 10.7 PSI. If we took the container of air with a gauge on it up in an unpressurized airplane, the vacuum gauge would indicate less vacuum PSIG. If we took that to outer space where the pressure is near zero, the pressure gauge would indicate a positive pressure of 10.7 PSIG.

So on an absolute basis, the pressure can never be less than zero. So the strongest vacuum PSIG that you could get is 14.7 PSI (-14.7 PSI pressure) if the current barometric pressure was 14.7 PSI.

 

[ditttohead]

Simply put, tanks implode on occasion. It is not common, it does happen, and mineral tanks are not warranted against it. A single service guy is unlikely to see this more than a couple times in his career. When I was heading up a large service company years ago with a dozen technicians servicing 6-10 units a day each, we saw this occur rarely, but it was not uncommon. A few times a year at max. Well failure, runaway booster pumps, failed low pressure switches, people capping the air breaks on drain pipes, systems installed on roofs and plumbers shutting down the inlet valves to the systems so they can work on something else, etc. I could probably list at least a dozen different scenarios that caused these failures. On a residential system, the additional equipment cost, plumbing etc. may not be worth it considering the low risk, but in a large commercial application, it is very cheap insurance, especially when you are talking about a 100 CF system, 60" diameter tanks, etc.

Now lets talk about hat water backing up into a system...

 

[Gary Slusser]

Reach4, I know all that stuff, used to fly non pressurized planes and lived in Denver for a time plus recently stayed up above 10,200' in the CO Rockies where our pressure cooker wouldn't work all that well. But many average guys may not. What we should do before someone runs off to buy a few breakers is to see if water can leak out of a bad check/foot valve or hole in a drop pipe and create all this vacuum like the -180 psi that was mentioned.

Let's take that 400' deep pump and say that the static water level is at 200'. The 400' can't be the water level in the well or there would be no water to be pumped... my 200' static level would be about 87 psi (.433 psi per foot of water) at the inlet to the pump and in this case the outlet for the water draining back into the well. Now "... run to the bottom of the well...." isn't going to happen because no well pump or foot valve is set at the bottom of the well and... there is no hole at the bottom of the well so, the water in the well and the drop pipe will be at the same level when the pump doesn't run and the pressure tank empties its content. So how do we get a vacuum?

And if there is a hole in the drop pipe it works the same as a leaking check/foot valve and if it is above the water level in the well, the water in the drop pipe will stay at the bottom of the hole in the drop pipe or, equalize with the water level in the well. And the hole in the drop pipe will prevent a vacuum.

 

[Reach4]

Let's take that 400' deep pump and say that the static water level is at 200'. The 400' can't be the water level in the well or there would be no water to be pumped... my 200' static level would be about 87 psi (.433 psi per foot of water) at the inlet to the pump and in this case the outlet for the water draining back into the well. Now "... run to the bottom of the well...." isn't going to happen because no well pump or foot valve is set at the bottom of the well and... there is no hole at the bottom of the well so, the water in the well and the drop pipe will be at the same level when the pump doesn't run and the pressure tank empties its content. So how do we get a vacuum?

Normally there will be a lot more pressure in the drop pipe at the water level height in the casing than outside the casing pipe. The pressure in the pipe will be 400 ft head=173 PSI. The pressure at the surface of the water in the drop pipe is atmospheric pressure adjusted for the altitude at the water level. The pressure at the outside of the pump would be the 87 PSI. At the surface of the water in the well, the pressure is about 0 PSI and 87 PSI in the pipe at that same altitude.

To get a vacuum, turn off the pump (fail or whatever). Get (or already have) a hole in the drop pipe below the water level in the casing. Water flows out of the pipe into the casing. The water in the pipe falls until the water, at the hole, inside the pipe is at the same pressure as the water in the casing.

As water came down and out of the pipe, and no air could get in to replace it, you get a pretty strong vacuum plus some water vapor. The water in the pipe will stop falling when its top is about 32 feet above the surface of the water in the casing.

This would be comparable to a classic mercury barometer except 13.6 times as dense as water. So the column of water would be 13.6 times as tall as a column of mercury in a mercury barometer.

The video talks about that some. Water is much lighter, so such a barometer made with water would have to be much taller.

This video is not animated.

 

[Mikey]

Good explanation. And this all works (to create a vacuum) only if the hole/leak/whatever is below the water level in the well, or it's a really tiny hole, otherwise air would enter to replace the water leaked out.

 

[Gary Slusser]

Normally there will be a lot more pressure in the drop pipe at the water level height in the casing than outside the casing. The pressure in the pipe will be 400 ft head=173 PSI. The pressure at the surface of the water in the drop pipe is atmospheric pressure adjusted for the altitude at the water level. The pressure at the outside of the pump would be the 87 PSI. At the surface of the water in the well, the pressure is about 0 PSI and 87 PSI in the pipe at that same altitude.

To get a vacuum, turn off the pump (fail or whatever). Get (or already have) a hole in the drop pipe below the water level in the casing. Water flows out of the pipe into the casing. The water in the pipe falls until the water, at the hole, inside the pipe is at the same pressure as the water in the casing.

As water came down and out of the pipe, and no air could get in to replace it, you get a pretty strong vacuum plus some water vapor. The water in the pipe will stop falling when its top is about 32 feet above the surface of the water in the casing.

The total head of the system is more than the 173 psi since it is measured to the highest water faucet/tap/appliance in the building plus the air pressure in the pressure tank but... I'm thinking you made a misstatement when you said "there will be a lot more pressure in the drop pipe at the water level height in the casing than outside the casing.". There is no water pressure acting against the outside of the casing that will impact our discussion. The water table is at the a same level, assuming the well has recovered from any recent pumping if the recovery rate gpm is less than the pumping gpm rate, as the static water level in the casing.

Anyway, recall that we have a leaking check/foot valve so as soon as the pump shuts off that 173 psi plus say 29 psi air pressure in the pressure tank, plus the psi to the highest fixture starts to bleed off but.... without air entering the house plumbing or the drop pipe above the static water level, there won't be more than a drop of water every so often leaking out the bad check/foot valve or... a hole in the drop pipe. Which BTW is quite rare even in rock bore wells where the poly pipe or PVC drop pipe rubs the side of the well below the end of the casing that ends in the bedrock a few feet.

 

[Reach4]

Corrected. Thanks.

Yes, thankfully this failure rare.