Do undersink AIR EXPULSION VALVES exist like AIR ADMITTANCE VALVES?

[Montreal]

[SOLVED] Hello, My girlfriend lives in the country in an old house whose plumbing was remoldeled 30 years ago. All the new plumbing fixtures are located within 15 feet of the main sanitary drain that connects to the outdoor septic system and these drain well. However there is a kitchen sink located 57 feet from the main sanitary drain which is giving us a problem. This 57 foot drain is composed of 2 vertical feet of 1.5" pipe under the sink to the basement, 15 feet of 1.5"pipe @ 2% slope, a backflow valve, 2 feet of 1.5" pipe @ 2% slope, 8 feet of 2" pipe @ 2% with two 90 degree shallow elbows, and finally 30 feet of 2" pipe @ 1% slope with two 45 degree elbows. Unfortunately when the kitchen was remodeled, no ventilation stack was installed for the kitchen sink due to the exterior walls being made of cement block. Since a few weeks the kitchen sink was draining slowly, so I ran a fish through all of the 2" pipe and found no blockage. Today I installed an Air Admittance Valve under the kitchen sink hoping that it would increase the drain flow. After I filled the sink half full and pulled the stopper, it still drained very slowly. But as soon as I unscrewed the Oatey AAV from its mating collar, the sink quickly drained, albeit with some water over flowing out of the fitting where the AAV was previously connected. I placed a plastic bag over the open fitting where the AAV was and as I drained the sink a second time, the bag filled up with air. Conclusion: In order for the kitchen sink to drain well, any trapped air in the 57 feet of sloped drain pipe needs to evacuate in order to let the sink water take its place. In my situation, this air cannot evecuate easily unless I create a vent under the kitchen sink with no AAV attached. Sewer gases are not a problem for the kitchen sink because the flap on the backflow valve in the drain path is sealing cleanly. My only risk is if I fill up the kitchen sink and pull the stopper, then sink water will finds its way back to the fitting for the missing AAV and overflow into the under sink cabinet. Just running water into the sink with no stopper works well. What I need is an Air Expulsion Valve which would allow air to flow in both directions but block water from escaping through the valve. Such a valve could be made of a cage with a ping-pong ball which would float upwards and seal off the device. Otherwise I would have to raise my new under sink vent so that the top of this vent would be above the highest level of water in the sink. That would require extending the vent through a new hole drilled into the kitchen counter top. It is easy to suggest that if I increase the slope of my 30 feet section of 2" pipe from 1% to 2%, then all my problems would be solved, but I`m not so sure. Any other suggestions would be appreciated. Thanks for reading.

 

[Reach4]

To your title question, yes. But wait.

Today I installed an Air Admittance Valve under the kitchen sink hoping that it would increase the drain flow. After I filled the sink half full and pulled the stopper, it stilled drained very slowly. But as soon as I unscrewed the Oatey AAV from its mating collar, the sink quickly drained, albeit with some water flowing out of the fitting where the AAV was previously connected. I placed a plastic bag over the open fitting where the AAV was and as I drained the sink, the bag filled up with air.

The ideal way to vent is with a real through-the roof vent. If you are going to release pressure indoors, it's going to smell.

But bad venting does not cause bad drainage from a sink by itself. There is another problem. I expect you have a belly in your piping, or septic is full, or something else.

There is one more thing. Is the drain on a garbage disposal? If so, try poking one of the rubber flaps down, and see if you then get good draining.

 

[Sponsor]

 

[Montreal]

To your title question, yes. But wait.


The ideal way to vent is with a real through-the roof vent. If you are going to release pressure indoors, it's going to smell.

But bad venting does not cause bad drainage from a sink by itself. There is another problem. I expect you have a belly in your piping, or septic is full, or something else.

There is one more thing. Is the drain on a garbage disposal? If so, try poking one of the rubber flaps down, and see if you then get good draining.

Thanks Reach4 for your suggestions.

There is no garbage disposal.

There is no risk of smell since the weight of the plastic flapper in the backflow valve is heavy enough to seal the drain pipe going to the nearby kitchen sink.

I agree that there could be a belly in the 30 feet of 2" drain pipe with an undersized slope of 1%.

Even a slight belly could reduce the flow of air.

When I shine a flashlight along the 20 foot straight run of 2" pipe, I can`t see a belly.

I determined the slope of 1% by measuring the position of this pipe relative to the basement ceiling joists.

If the ceiling is not level, then I will have an error in the estimated drain pipe slope.

Since the bathroom sink and and tub all drain properly, I will have to rule out the septic tank being full.

It is not a compicated task to increase the 1% slope to 2%, but I have no garanty that my problem will be solved whereas I know with certainty that if I raise my under kitchen sink vent outlet by a foot to place it above the kitchen counter top, then my problem will be solved.

 

[Reach4]

This is a sketch of an exaggerated belly. The AAV is represented by the blue rectangle. So anyway, since removing the AAV lets water flow, I expect there is some standing water between your sink and the through-the-roof venting.

But wait, what is this backflow valve you mentioned? Is that for the kitchen sink, or the whole house?

 

[Montreal]

This is a sketch of an exaggerated belly. The AAV is represented by the blue rectangle. So anyway, since removing the AAV lets water flow, I expect there is some standing water between your sink and the through-the-roof venting.
View attachment 76147

But wait, what is this backflow valve you mentioned? Is that for the kitchen sink, or the whole house?

Thanks for the sketch.

If there is standing water between the kitchen sink and the one and only through the roof vent located 60 feet away from the kitchen sink, then that would easily explain the air being trapped in the system.

About this backflow valve located 15 feet downstream from the sink, it is only for the benefit of the sink, not the whole house.

At 25 feet from the sink and 10 feet downstream from the backflow valve, there are entry points into the 2" drain pipe for the basement sump pump and the backwash drain of the water softening machine.

I suspect that this backflow valve was put in so that if the sump pump debit or the water softening machine backwash debit was too much for the drain system, then the excess would not back up into the kitchen sink on the floor above.

Yes indeed there are such creatures as Air Expulsion Valves, but they seem to be used on the water supply side where the working pressures are greater than 10 psi.

In my installation, I would need an AEV that can block water from passing through at only a few psi.

Tomorrow I plan to increase the 2" drain pipe slope from 1% to 2%, for all the obvious and hidden avantages.

 

[Montreal]

Today I ncreased the slope of the last 30 feet of drain pipe from 1% to 2% and this did not allow my kitchen sink to drain any faster.

I am beginning to believe that there is a limit to how easily air can travel in a long, thin, empty, tube regardless of the slope.

The assembly of my 57 feet of 1.5" and 2" drain pipes offers an internal volume of 1.2 cu. ft.

If I had 17.5 feet of 3" drain pipe instead , then this new pipe would have a near identical internal volume.

If I fill up my kitchen sink with 4" of water, and then pull the stopper, about a one-third cu. ft. of water will try to enter my 57 feet of drain pipe.

Since the water has a long way to travel and with a 2% slope and only 3 feet of vertical drop, I expect that most of the water will be out of the sink and still in the pipe before any of it has a chance to reach the septic tank.

All this water in the pipe reduces the path for air to flow since the only through-the-roof vent is located 57 feet from the unvented kitchen sink.

Today I blew into 35 feet of empty 2" pipe and it felt like I was trying to blow up a balloon.

I now understand why it is so important for the drain pipe that joins the trap under the sink to the nearest vent stack be as short and as fat as possible.

In my case, I have the opposite situation.

Air admittance valves may be the ideal solution in some installations, but not the answer for me.

There is an air release (expulsion) valve designed for working pressures above 10 psi selling for over $450.

What I need is a air release valve designed for 0-1 psi selling for the same price as the air admittance valve I bought for $25 in Canada.

Otherwise it looks like my only solution is a vent tube coming through a hole in the kitchen countertop next to the sink.

Thanks for reading.

 

[Reach4]

Air admittance valves may be the ideal solution in some installations, but not the answer for me.

There is an air release (expulsion) valve designed for working pressures above 10 psi selling for over $450.

An open pipe would be better than a valve that would open to relieve pressure. No way you you are developing anything like 10 psi.

How about running a pipe outside and up, so that you have a real vent?

Is there a plumbing vent on your roof?

Have you had your septic pumped in the last few years?

 

[Montreal]

An open pipe would be better than a valve that would open to relieve pressure. No way you you are developing anything like 10 psi.

How about running a pipe outside and up, so that you have a real vent?

Is there a plumbing vent on your roof?

Have you had your septic pumped in the last few years?

I agree that the working water and air pressures are very low, way below the minimum rating of 10 psi for the ARV product currently for sale.

The exterior wall behind the sink cabinet is concrete block, I am not ready to make a hole in that just to pass a 1.5" pipe outside and then up to the eave.

Since the bathroom fixtures all drain properly, the septic tank can`t be full otherwise it would stink everywhere, indoors and outdoors.

Fortunately the stainless steel kitchen sink has a spare hole which currently accomodates a second water faucet (for water not treated by the softening machine). We don`t really need this second faucet, so I can remove it and pass a tube through what I hope will be a standard 1-3/8" dia. hole in the sink rim. I will probably get a adaptor with a hose barb to attach to the end of the 1.5" pipe where the AAV would have been.

Thanks for all your comments.

 

[John Gayewski]

I think the backwater valve may have more to do with your drainage problems than air. I would try to remove it first. They aren't supposed to be in a drainage system anyway. Other than for a main drain that is. Even then if it isn't necessary then get rid of it. See if that helps the problem.

 

[Montreal]

I think the backwater valve may have more to do with your drainage problems than air. I would try to remove it first. They aren't supposed to be in a drainage system anyway. Other than for a main drain that is. Even then if it isn't necessary then get rid of it. See if that helps the problem.

Thanks John for your suggestion.


The backwater valve located 2 vertical feet and 15 horizontal feet downstream from the sink has a removable flapper. When I take out the flapper, the sink does not drain any faster.


The backflow valve is essential. Located 10 feet downstream of this valve are where the basement sump pump hose and the water softener machine backwash hose are attached. Water from these two sources is pumped into the drain pipe under pressure and since the remaining 30 feet of 2" drain would have difficulty passing the necessary debit, there would be a backup into the kitchen sink, so this backflow valve prevents this backup.


I have no problem with running the kitchen tap into the sink with no stopper. The faucet is at 50 psi and the debit from the spout with aerator is slow enough that water and air can negotiate adequately in the drain pipe even with the presence of the flapper in the backflow valve that apparently is pushed open wide enough to allow water to pass in one direction and air in the other.


However when I fill up 4 " of water in the sink and then pull the stopper, suddenly a 2 foot column of water is trying to push its way through the 57 feet of pipe with only 1 psi available to force the air in the circuit to exit at the far end.


After I pull the plug, a large bubble of air comes up into the sink through the standing water. That allows an initial amount of water to enter the pipe. But after that, the 1 psi of working pressure has a hard time pushing the water and air through the 40-50 feet of still empty pipe.


If I unscrew the AAV while the sink is slowly draining, then the sink suddenly drains quickly, but some water shoots out of the opening where the AAV was located.

 

[WorthFlorida]

Montreal, you stated it and explained it in your first post. Using a plastic bag over the removed AAV was a great way to prove your problem. What exasperates the drain problem is a very long drain without an atmospheric roof vent. Does the drain pipe run under any closets or any near by where you can tap into and run a vent pipe through a closet to the roof? That is if it's a one story home?

Cutting through a cement block wall isn't all that hard. You can rent a drill and a cutting head that makes it like your going through butter.

 

[Montreal]

Montreal, you stated it and explained it in your first post. Using a plastic bag over the removed AAV was a great way to prove your problem. What exasperates the drain problem is a very long drain without an atmospheric roof vent. Does the drain pipe run under any closets or any near by where you can tap into and run a vent pipe through a closet to the roof? That is if it's a one story home?

Cutting through a cement block wall isn't all that hard. You can rent a drill and a cutting head that makes it like your going through butter.

Thanks Worth for your suggestions.


Unfortunately, there is no option in the first 25 feet of drain pipe to create a vent connection to the roof via a closet.


The building has a second floor above the kitchen which has no attic crawl space.


I could drill a 1.5" diameter horizontal hole in the concrete block behind the sink and send the vent outside and up to the eave, but there may be electrical wires in the wall behind the sink, so there is some risk in blindly drilling.


Since the sink is protected from sewer gas by the nearby backflow valve, the option of using the soon-to-be-vacant-hole in the rim of the sink to pass a 1" dia. plastic tube extending from the removed AAV is the easiest and least complicated solution at the moment.


This is an old remodelled school house from the 1930’s, so we are not too worried about the sight of a few inches of plastic tubing protruding above the corner of the sink rim.

 

[Reach4]

Since the bathroom fixtures all drain properly, the septic tank can`t be full otherwise it would stink everywhere, indoors and outdoors.

I think you have the wrong idea about pumping septic tanks. You are not supposed to wait until something fails. If there is a change in symptoms, you want to consider things urgent, but you want to get the septic pumped before there are are any symptoms. The expense of pumping too early is minimal. The expense of pumping too late is not.

Don't get me wrong. I am not saying that pumping won't help your symptom. I am saying that if it does, you were way late.

For me, pumping currently runs US$250. So CAN$500 would not shock me. But look at all of the sewer bills or special water service tax that you have not been paying.

 

[Tuttles Revenge]

AEV.. thats a good one. If you do end up doing that farmhouse hack, use a dishwasher air gap as your finished piece. You can hook up air to the inlet and connect the discharge to the sink tail piece. This is not a good alternative to solving the actual problem which may just get worse over time.

However I believe Worth has the correct answer. There is also something else blocking the line or causing backpressure. A belly would be visibly obvious and easily solvable.

Measuring distance from joists to the pipe in an old house is not a really good way to determine slope since its very likely that the house has sunk and shifted over its near 100yrs on earth. Only a level or a laser line will really tell you the slope of the pipe.

 

[Montreal]

I think you have the wrong idea about pumping septic tanks. You are not supposed to wait until something fails. If there is a change in symptoms, you want to consider things urgent, but you want to get the septic pumped before there are are any symptoms. The expense of pumping too early is minimal. The expense of pumping too late is not.

Don't get me wrong. I am not saying that pumping won't help your symptom. I am saying that if it does, you were way late.

For me, pumping currently runs US$250. So CAN$500 would not shock me. But look at all of the sewer bills or special water service tax that you have not been paying.

Thanks Reach4 for wanting to leave no stone unturned.

At one point I disconnected the far end of the 57 feet of drain pipe and put a bucket under the end and tried to drain the sink.

The septic tank was completely out of the circuit but that did not improve the sink draining.

My girlfriend owns this house for 30 years and has lived most of her life in the country with septic tanks. I trust her to know when pumping the septic tank is called for. She can get it pumped for under CAN$300 and plans to in the coming weeks.

As for me, I've spent all of my 70+ years of life with city systems and only owned one house for 28 years.

 

[Montreal]

AEV.. thats a good one. If you do end up doing that farmhouse hack, use a dishwasher air gap as your finished piece. You can hook up air to the inlet and connect the discharge to the sink tail piece. This is not a good alternative to solving the actual problem which may just get worse over time.

However I believe Worth has the correct answer. There is also something else blocking the line or causing back pressure. A belly would be visibly obvious and easily solvable.

Measuring distance from joists to the pipe in an old house is not a really good way to determine slope since its very likely that the house has sunk and shifted over its near 100yrs on earth. Only a level or a laser line will really tell you the slope of the pipe.

Whenever I have seen drawings of a dishwasher air gap device, the device was installed in a hole drilled in the counter top next to the sink. Only after I remove the secondary faucet from my sink will I know what the hole diameter is and if an attractive dishwasher air gap device will fit into the hole.


The first 27 feet of pipe has a slope of 2% easily measured using a spirit level even though it is in the old part of the house.


The last 30 feet of pipe originally with a slope of 1%, is suspended from the joists of the new annex built in 1987.


But you are right not to trust ceiling joists.


What I did to determine the overall slope in the 57 feet of pipe was to cut it free at the far end. I put a bucket under the cut end to catch any draining water. Then I raised the cut end while adding water via the sink until water stopped flowing out the cut end, in other words I created the minimum belly necessary to block the flow of water. Then I measured the position of the cut end of the pipe above where it was originally before I cut it to arrive at the vertical drop. After dividing this drop by 57 feet, I concluded that the last 30 feet of pipe had a slope of 1%, which is OK for 3" drain pipe but not for our 2" drain pipe.


Since all of these 30 feet of pipe was suspended by steel wires every 5 feet, it was easy to adjust the slope along the route in order to avoid any bellies.

Is there something blocking the line you ask? I don't think it is an easy proposition to get a few hundred cubic inches of air to quickly pass through 57 feet of 2" pipe using only 1 psi of pressure at the instant I pull the stopper in the sink.

Thanks Tuttles Revenge for your comment.

 

[Montreal]

............ There is also something else blocking the line or causing backpressure...........

Tuttles, you were right on suggesting that there was a hidden blockage. Today I discovered that there was indeed a hidden blockage. There were chunks of salt blocking the last 15 feet of pipe, a pipe that for 30 years had a 1% slope. The water softeneing machine dissolves 1000 pounds of salt a year and sends the solution into the last 30 feet of drain. If the salt solution moves slowly through the drain, then the salt appears to drop out of solution and the crystals stick together in clumps.


Today for $20 CAN I purchased a 25 foot snake that attached to my drill. I had to cut the last 35 feet of drain in two sections using a saw so that I could clean different sections of the pipe with the snake. The blockage was quite firm and while the snake went through the blockage rather easily, it didn’t clear the blockage. Constant flushing of the pipe section with a garden hose while ramming the snake back and forth eventually sent the crap down the pipe into a bucket. Flushing with about 25 gallons of water eventually turned black waste water into clear.


Now the kitchen sink drains quickly with a powerfull vortex.


No need for an improvised Air Expulsion Valve, it works fine with only the Sure-Vent Air Admittance Valve.


Moral of the story. Keep drain pipes at the slope determined by code and make sure that they can be easily flushed out using cleanout traps or by dismantling pipes assembled with clamped rubber couplings (I now have 4 couplings and 3 access ports in my 57 feet drain system),


Thanks for all the suggestions from all the participants.

 

[Reach4]

If the salt solution moves slowly through the drain, then the salt appears to drop out of solution and the crystals stick together in clumps.

I expect that is not sodium chloride (softener salt) but I suspect it is hardness materials that came out of the softener during regeneration. Sodium chloride is very soluble.

Technically those are all salts, but not the sodium chloride salt we normally mean when we say salt.

 

[Montreal]

I expect that is not sodium chloride (softener salt) but I suspect it is hardness materials that came out of the softener during regeneration. Sodium chloride is very soluble.

Technically those are all salts, but not the sodium chloride salt we normally mean when we say salt.

A closer look at the residue makes me now think that it is 10 years of dishwasher soap from either undissolved powder or tablets. There are some spots of blue mixed in with the white clumps. More like a paste than hard salt crystals. The chunky residue created a belly that allowed water to build up behind the dam and not pass air. Now water and air freely flow as needed.