Plumbing and Science.

[bob_2]

Ok - just to be clear. My sink is on the ground floor. There is a ‘U’ bend directly under the waste and then a (more or less horizontal) 1½" pipe, about 6 feet long through the outside wall, a 90 degree bend and a two feet of downpipe to an open drain. There is no other plumbing connected to it so the hose pipe analogy is a good one.

I assume that there has been a build up of something nasty in the ‘U’ bend which has slowed the drain. Until recently, it drained faster (as it should) than the tap could supply water. If I filled the sink using a plug, it tended to form a vortex as it drained which is what you would expect.

My query is why the vortex makes it drain faster now that there is a restriction.

[DSeid]

@Joey_P

… The slug of water heading down your kitchen is creating a vacuum. The vent stack breaks the vacuum. If the vent is blocked, it’s going to draw that air in from somewhere. It might empty out another trap somewhere and suck air in from that drain. But most likely it’ll make the drain you’re using right now burp/gurgle/vortex since that one is the closest and probably easiest to suck air in from since the water is moving through it. If it can’t do any of that, it’ll just drain slowly. …

See here is the disconnect … the relative “vacuum” being created is between the trap and the stack and only exists when water has drained completely out of the sink and the water level sinkside on the trap is down to the top level of the stackside of the trap and some air gets in stackside. Under that circumstance the stack might drain marginally slower and pull air in through the trap or other traps and cause burbling in the trap … but the water would already be drained from the sink! Until water has drained from the sink there is no relative vacuum behind the slug of water … atmospheric pressure is still behind the slug of water from the open sink drain.

[HoneyBadgerDC]

@Joey_P

Did you just reply to yourself? Or contradict yourself? (A “couple of ups and downs” would be a trap). I’m confused.
In the first post you said your money was on it flowing straight down, in the second post you said it would need to burp.
If you fill up a funnel with water, my guess is that’ll it’ll go straight down. However, if you fill up a really big funnel, say, one that holds a gallon or two, it’ll start to vortex. They usually take more than a half a cup of water to get started.

In your home, as water is flowing down the drain it’s trying to pull air in behind it. Remember, it’s not just one pipe from your sink to the city, there’s a lot of other, air filled, pipes in your house. The slug of water heading down your kitchen is creating a vacuum. The vent stack breaks the vacuum. If the vent is blocked, it’s going to draw that air in from somewhere. It might empty out another trap somewhere and suck air in from that drain. But most likely it’ll make the drain you’re using right now burp/gurgle/vortex since that one is the closest and probably easiest to suck air in from since the water is moving through it. If it can’t do any of that, it’ll just drain slowly.

My next guess is that if the funnel experiment does create a vortex, it would be eliminated by adding a vent somewhere in the system (somewhere that makes sense by typical plumbing standards). Add a T and another section of hose going straight up and rising significantly higher than the funnel.

Back to the OP, I’m not saying you don’t have a clog, and like I said, you could certainly pull the trap off, that’s an easy place to start and easy for the homeowner to clean.

When I visualized a trap caused by a loop in the hose I second guessed myself. So yes I did contradict my first post.

[DSeid]

Another possibility … the vortex does not make it drain faster; the vortex occurs when, for some reason such as waxing and waning of the size of the clog, or more water in the sink creating more pressure, the sink is draining faster.

Maybe by angling the water with the swivel tap you are slightly dislodging some small portion of the clog temporarily?