Suds lock? in kitchen sink drain plumbing

[Snowman9000]

Our fiver, like most, has a separate gray tank for the kitchen sink. The vent going up to the roof is 8 or 9 feet away from the sink.
The P trap is a couple of feet to the right of the left hand bowl, and a foot or so from the right hand bowl. So it is in a lateral instead of just underneath. We use the LH bowl for dish water. The air inlet check valve is 30 inches after the P trap.

Sometimes trying to drain the dish water, if there is a good amount of suds, it just won't drain. I can unscrew and remove the check valve, and it drains right down. (Remember, the check valve is not to let air out, only to let air in. But removing it will create a new vent opening under the counter. So this is not a sign of a bad valve.)

If I leave the valve in place and just wait, usually at some point there will be a big glug sound, and then it all drains.

At first I thought I must have a problem in the vent to the roof. Now I'm thinking it is just the suds somehow getting trapped and having enough resistance that the water sitting on top of them won't go through.

Has anyone encountered the same thing?

[bucky]

Is the strainer closed on the other side of the sink? That causes your problem at our sticks and bricks occasionally.

[Dutch_12078]

The roof vent works both ways. It allows air out of the tank when it's filling, and air in when it's draining. As said, the AAV only lets air in the line to break the suction that would otherwise cause slow drainage from the sink.

[4x4van]

Snowman9000 wrote:

Maybe it is. I was looking at it the other way. Air needs to get out, not in, for the drain line to flow. That is what the main vent is supposed to do. But maybe the lateral needs air going in at the valve.

Wrong. The air admittance valve (AAV) is venting the "line", not the "tank". While the main tank vent (through the roof) allows air out of the tank, the AAV allows air into the drain line, to prevent a vacuum in the drain line.

I would also suggest that the same thing is likely happening without the suds; the suds sitting on top of the trapped water just makes it more obvious.

[Tyler0215]

Suds or no suds won't make any difference. Suds are mostly air. If the water won't drain, you have a bad valve.

[Snowman9000]

Bill.Satellite wrote:
Why is it not a sign of a bad valve. If air can't get in, suction is created and the water won't drain out. You removing the valve makes it work properly. Sure sounds like a bad valve to me.

Maybe it is. I was looking at it the other way. Air needs to get out, not in, for the drain line to flow. That is what the main vent is supposed to do. But maybe the lateral needs air going in at the valve.

It doesn't seem to happen without suds, though. I already replaced the valve a while back. I don't recall if it was happening with that one. That one was leaking odors back out.

I'm going to try some experiments with the two valves, suds and no suds.

[MFL]

Agree with Old-Biscuit. Also, too much suds would not stop water from draining, but would need more water to wash suds down.

Jerry

[GordonThree]

Easiest solution, use less soap? Don't need a tub full of suds to wash dishes.

[Old-Biscuit]

Bill.Satellite wrote:
Why is it not a sign of a bad valve. If air can't get in, suction is created and the water won't drain out. You removing the valve makes it work properly. Sure sounds like a bad valve to me.

X2

If galley tank drains OK when dumping then roof vent is clear

So that leaves the AAV NOT opening which then makes sink draining slow

[Bill_Satellite]

Why is it not a sign of a bad valve. If air can't get in, suction is created and the water won't drain out. You removing the valve makes it work properly. Sure sounds like a bad valve to me.