# DW air gap



## shan2themax (May 1, 2008)

So... how important is the DW air gap to attatch to my garbage disposal... I previously used the dishwasher... but didnt have a garbage disposal... and had heard people talk about an air gap... but never have I seen one in use... so... please inform me... lol...

couldnt I just attatch a loop of discharge hose to the under side of the counter or something like that?


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## inspectorD (May 2, 2008)

I hate to do it, ....http://www.acmehowto.com/howto/appliance/dishwasher/check/airgap.php
This is the easiest way I could explain it...let someone else do it.


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## majakdragon (May 2, 2008)

Air-gaps were a "hot ticket" item for a while. Many areas made the required by Code. After a while, they found that they caused more problems than they solved. If the DW discharge hose is run up as high as possible and then brought back down to the drainline or disposer, I have never had a problem.


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## mstplumber (May 3, 2008)

I agree.   An air gap fitting is unnecessary.   I have installed literally thousands of DWs without one and have had no problems.   Just loop the discharge as high as possible and fasten it to the cabinet to keep it there.


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## glennjanie (May 4, 2008)

Hello Shan:
The dishwasher air gap is vitally important to your health. The dishwasher can siphon back whatever is in your disposer or your drain, especially if the drain is stopped up and backed up. Typhus, Hepititis, Dissentary and many other germs live in the drain system and can be siphoned back into your dishwasher for you do savor and enjoy along with your next meal. Its called backsiphonage and works just like siphoning gas out of your car or pick-up for the mower. You have stolen gas before, haven't you?
The Most Effective remedy for backsiphonage is an air gap. Did you ever get a straw with a hole in it? I had one night before last and couldn't get any coke out of the cup; same principle.
The loop in the dishwasher hose has to be 32' high to prevent backsiphonage because that is how far atmospheric pressure can push water with a vacum in the hose. True, the loop will keep the water from siphoning from the dishwasher but that's no problem anyway; its when the contaminated water is siphoned back into the dishwasher that gives the problem. You won't hear many people complain about this problem, their families don't either; dead men don't talk (sounds like a Mafia statement).
The dishwasher air gap costs less than $10, takes about 30 minutes extra to install and can save your life. You do the math and make your own personal evaluation. I wish you the best with your project.
Glenn


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## inspectorD (May 4, 2008)

I agree with glenn. They didn't develop them and want us to install them if there was not a reason.
Good advice.


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## shan2themax (May 4, 2008)

I had already purchased it.... just wasnt sure how needed it was and just exactly what it did... but.. I went to the website and read about it... so... adding that to my to do list for the week also... thanks guys for all your answers!!!!!!!!


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## Quattro (May 19, 2008)

I don't understand how water can be siphoned back into a dishwasher through the drain hose. At least on my GE DW, there is a check valve where the water is discharged from the pump. I don't see how anything can "backflow". 

Personally, I did not use an airgap when I installed my new DW and sink. Mostly because my new sink is fired clay ceramic, and drilling a big hole in it for the air gap would have been a nightmare. No problem for a cheap stainless sink, but I didn't want to bung up my double Domsjo. I just looped the drain as high as I could.


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## glennjanie (May 19, 2008)

Hello Quattro:
Thanks for inquiring and I will try to give you my best answer.
1.  Check valves are not dependable because they are in the flow of the waste and can become stuck or 'frozen'.
2.  If the check valve is frozen and the sink drain is backed up, just into the  disposal, it can be siphoned back into the dishwasher; its called *backsiphonage*.
3.  Should the sink be backed up into the bowl and the check valve is frozen the pressure of the water could push back into the dishwasher; its called *backflow*.
4.  The best method to prevent backflow or backsiphonage is with an air gap, the second best method, speaking of water supply lines now, is a reduced pressure principle backflow preventer. The latter is a detailed, two vlalve aparatus with a middle chamber that can open and allow the water to run into an open receptacle of some sort (like a floor drain).
5.  We think of plumbing as 'cut a few pieces of pipe and glue them togather' while we think of electricty as something that can shock you and even kill you. The fact is, more people have died from sewer and fresh water problems than by elecrical shock. Case in point, the Black Plague of London, Rome probably fell in some respects because they invented lead pipe for the fresh water supply. Lead poisioning may have affected many brains, even fatally.
6. You have many 'air gaps' in your home, each faucet has an outlet that can't be reached by the water in the tub or sink without running over the top. Your ice maker has one to prevent freezing the water supply. Then there are other connections that have vacum breakers (the third best method of backflow prevention) such as your commodes.
7.  Many municipalities, such as Louisville, KY require backflow prevention in order to protect their water supply.
8.  If I sound like a teacher here, its because I am. However, the presentation here is in good faith and not meant to scold anyone; I just wanted to give a complete answer to your "I don't understand".
Glenn


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## inspectorD (May 19, 2008)

Basically you are trying to keep the potable supply of water, separated from the waste water. You can only truly do this with an air gap in any system. You need to keep the creepy crawly microscopic germs on the other side of the river. 
That "missing bridge" over the river is the air gap.

Like Glenn said, the best example of this is in your toilet tank. The filler valve inside of that tank does not touch the water in that tank, it sprays into the tube. That tank water is directly connected to the bowl we "aim" into.

That's my spiel for my students when I get to teach plumbing.
Hope this helps to keep your family safe.


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## Quattro (May 20, 2008)

Alright, thanks for the great explanation. But if the check valve doesn't fail, there is little to worry about, right? 

Let's say the sink drain is clogged...which I'm willing to guess happens more often than a DW check valve failing...the DW tries to drain into the trap (or first the disposal), and can't. So, it backs up and flows out the air gap, which then flows into the sink and then is stopped again by the clogged drain. The sink fills, and spills everywhere until the DW is done draining...and until it goes into it's next drain cycle. How does the air gap help that situation? 

In my "non-failing" check valve hypothesis, the DW shuts off if it can't force water out the drain. This, to me, makes much more sense than having the above scenario play out. 

This actually happened to me...and that's how I know my check valve works! Turns out the connection to the garbage disposal was clogged. But the same would have happened had the sink drain been clogged.

Anyway, thanks for the knowledge!


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