Dishwasher pumps faster than piping can handle gravity flow from airgap


  #1  
Old 09-19-10, 04:38 AM
L
Member
Thread Starter
Join Date: Sep 2010
Location: USA
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
Unhappy Dishwasher pumps faster than piping can handle gravity flow from airgap

I just installed a new dishwasher, sink and PVC setup.
The issue is the air gap overflows when the dishwasher drains.

A few notes:
1) The drain setups and all pipes/hoses are new, and the garbage disposal is not clogged at all.
2) All drain pipes, including the run from the garbage disposal to P-trap are at only slight, but definite downward slopes. I can not have a steeper slope because the wall drain pipe is not as low as it normally is on a home.
3) I purchased the airgap and hose that runs from the airgap to garbage disposal from home depot.
There are 2 issues with this hose that may be causing the problem: a) it is labeled a "dishewasher drain hose", and thus is the smaller diameter, not the larger ones that directly fit the disposal w/out an adapter, and b) it's a thin flimsey hose that came rolled up in the package and already had kinks in it that I can't totally keep removed, thus impeding water flow.

My analysis:
Inspite of the kinks and smaller diameter of the hose, it still flows fairly well.
It seems to me that the real issue isn't so much "does it flow well", it's more, does it allow enough gravity flow to support the velocity/flow rate produced by the dishwasher drain pump that feeds the air gap.

The next, obvious, thing I'm going to try is to find a larger diameter hose from a plumbing supply store that is thicker and willn't kink at all.
This should help the gravitational flow rate, however, is it possible that my dishwasher, an older model, simply pumps too fast for an air gap (e.g. gravitational drain system fromt he airgap) to handle?

This brings me to my main question:
It seems to me that there are 2 ways to approach this issue:
1) increase the gravitational flow ability from for the hoses/pipes leaving the air gap.
2) SLow the flow fromt he dishwasher pump into the airgap to a rate that the gravitational exit flow can handle.

Ofcourse, we 1st do everything possible to make optimize (1), the gravatational flow exiting the airgap.
But what about also addressing (2)?

Can I install an adjustable shutoff valve on the main drain line from the dishwasher to airgap to allow a slight slowing of the drainage from the pump, and thus keep it down to a rate the airgap and drainage after the airgap can handle?
Seems like it makes sense, or are there hidden consequences, like the pump can overheat if any, even slight, obstruction is on the line?

Any thoughts or ideas here?


THanks in advance
-Lee
 
  #2  
Old 09-19-10, 10:45 AM
E
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 8,627
Upvotes: 0
Received 1 Upvote on 1 Post
How much water we talking here - that comes out the air gap? A little that gets on the sink deck? Or does it come spraying out that vent?

Is the correct hose on each one of the airgap's nipples?

Did you knock out the plug completely and thoroughly where the drainhose plugs into the disposer?

Your small diameter factory ribbed drain hose should actually have made your problem better, if you think it is restricting - not worse, if you think about it.

I have installed many dishwashers, and have never run into your problem, caused by said possible reasons. Only from plugged up airgaps or drains. I've installed various barnds of DW's also.
 
  #3  
Old 09-19-10, 11:42 AM
L
Member
Thread Starter
Join Date: Sep 2010
Location: USA
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
Originally Posted by ecman51` View Post
How much water we talking here - that comes out the air gap? A little that gets on the sink deck? Or does it come spraying out that vent?

Is the correct hose on each one of the airgap's nipples?

Did you knock out the plug completely and thoroughly where the drainhose plugs into the disposer?

Your small diameter factory ribbed drain hose should actually have made your problem better, if you think it is restricting - not worse, if you think about it.

I have installed many dishwashers, and have never run into your problem, caused by said possible reasons. Only from plugged up airgaps or drains. I've installed various barnds of DW's also.
Thanks so much for responding ecman51.

To answer your questions:
1, Amount of water:
Some water, probably 30% of the total amount comes out the airgap.
So more like "oozes out", not sprays.
When I lay under the sink and hold the hose that runs from airgap to disposal straight with my hands (e.g. try to straighten the folds and kinks to increase flow), then the amount that comes out of the airgap reduces to very little, still some comes.

2. Correct hose
As I tried to explain in detail in the original writeup, no, I do not believe the hose is correct.
The diswasher drain hose (the larger diameter one) is correct and connects directly to the airgap feed.
The hose from the airgap outlet feeding the garbage disposal however is the one that not one but 2 home depots insist is correct, but I question it because a) it is smaller diameter and required adapters at both ends, and b) it has kinks/wrinkles in it preventing 100% water flow because it is thin rubber and came with kinks from the package.
I don't know how I can explain this better, but I feel it is logical that it is a big part of the issue, and as I explained, I will seek ut a plumbing supply store to get a better hose.

2. disposal plug
Yes, 100% knocked out. Not an issue here.

3. Smaller diameter hose part
I did think about it and I don't see how that can help, only worsen the issue.
Perhaps I didn't explain it clear the 1st round...
The smaller diameter is on the part that flows from airgap to disposal, not the dishwasher drain hose that feeds the airgap.
When I say "feed", I mean the water supply to the airgap from dishwasher.
Again, the "supply" is correct hose, the exit flow hose (to garbage disposal) is smaller. By smaller, I mean it's the exact same diameter as the supply hose to airgap instead of being larger.
TO better prove this smaller restricting hose is an issue, I can try disconnecting it totally and placing a bucket under the disposal, and see if water still comes out the airgap...

As I also mentioned originally, I believe the drainage system is not ideal in that the wall main drain is higher than normal, so there's very little downward slope to work with.
It all drains well, but maybe not well enough for the velocity produced by the dishwasher pump, which is why I suggested to valve to slightly restrict/tune the velocity feeding the air gap.

In the past, before remodling the kitchen, there was a dishwasher there that worked fine, except 2 main chenges now with the new setup:
a) added the air gap
b) installed a slightly deeper sink which moved all the under-sink drain plumbing down a few inches, eliminating much of the downward slope to work with, so now, there's only a slight downward slope and all has to be perfect...


Again thanks so much, and as I said, there are several factors that make this different from a normal situation, such as the slope issues and crappy home depot hose (which I am truing to change).

THe air gap concept is simple however, and it seems to me it all comes down to a question of flow rate in to airgap vs. flow rate out.
If the pumped rate in > gravity flow rate out, for what ever reason, then overflow from airgap occurs. Yes?

So my question is, can I place the adjustable restricting valve on the feed from dishwasher to airgap to thus slow the flow rate into the airgap? --this in addition to doing everything else "naturally" possible to increase the gravity flow from airgap to disposal, and disposal to wall drain pipe...


THanks again
-Lee
 
  #4  
Old 09-19-10, 12:47 PM
steve_gro's Avatar
Member
Join Date: Jan 2004
Location: San Francisco
Posts: 1,092
Upvotes: 0
Received 1 Upvote on 1 Post
Get some some 7/8" ID hose and run it from the air gap to the DW without kinks and sloped toward the GD. Make sure that the GD knockout is completely removed, and that there isn't any debris in the air gap (the top should be removable).

I doubt that the DW is pumping too fast for a correctly installed air gap, and do not think it advisable to try restricting it.

I try to keep all that in mind when trimming a kitchen and avoid facing the GD away from the air gap. If I still have problems, I buy a copper air gap. Pricier, but they seem to work better, and you can make slight adjustments to the inlet (to 'aim' it).
 
  #5  
Old 09-19-10, 01:01 PM
E
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 8,627
Upvotes: 0
Received 1 Upvote on 1 Post
Originally Posted by LeeBirnbaum View Post
3. Smaller diameter hose part
I did think about it and I don't see how that can help, only worsen the issue.
I thought you were refering to the hose that originates from the DW. Obviously you can't restrict the line after the air gap. And you really don't want to restrict any designed line, for that matter.
 
  #6  
Old 09-19-10, 01:54 PM
shacko's Avatar
Member
Join Date: Aug 2005
Location: Baltimore County Maryland
Posts: 2,137
Upvotes: 0
Received 0 Upvotes on 0 Posts
>>>installed a slightly deeper sink which moved all the under-sink drain plumbing down a few inches, eliminating much of the downward slope to work with, so now, there's only a slight downward slope and all has to be perfect...>>The hose from the airgap outlet feeding the garbage disposal however is the one that not one but 2 home depots insist is correct, but I question it because a) it is smaller diameter and required adapters at both ends,
 
  #7  
Old 09-19-10, 10:55 PM
L
Member
Thread Starter
Join Date: Sep 2010
Location: USA
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
Thanks to all of you for the help.

It seems that replacing the hose from AG to disposal solved the problem.
The smaller diameter hose I was using (that home depot insisted was correct), was actually much smaller because it had a ribbed insert to connect the hose to the hose adapter.
That probably cut the ID at least 50%, not just a little bit.

Combine that with the fact that it was kinked and kept folding (because too thin and flimsy), and I had a mess on my hands.

Also, I think someone had previously added the wrong soap to the DW causing more suds than expected, which was also adding to venting out of the airgap.

None the less, using the proper hose, as you all recommended, solved the issue with out need for restricting the DW flow into the AG.

THanks again...
-Lee Beer 4U2
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: