Is my main drain clogged?

[GearHead36]

Recently, I decided to get out my snorkel gear, and play with it some. While playing around, I decided to swim down to my main drain, which is at the bottom of the deep end, 8ft below the surface. I cautiously put my hand on the grate, and I didn't feel any suction. I should be able to feel suction, shouldn't I, even with a grate on the drain? However, I did some searching here, found some discussions on MD's, and found that one of the benefits is reduced temperature variations. I couldn't tell any difference in the temperature of the deep end vs the other parts of the pool. So is my drain actually clogged?

It might help for me to describe my plumbing system. There are 3 returns fed from 2 lines from the pump. Both of these lines have valves. One line goes to the return for the robot cleaner. The other line feeds the other two returns. There is one main drain at the bottom of the deep end, and a skimmer. Separate lines for those two go back to the pump, but only one line has a valve. I think the valve is on the MD line. I tried closing this valve, but not totally. The flow through the skimmer seemed about the same, but the pressure DID go down a bit, making me think that I AM getting some flow through the MD. The amount of air in the line (seen at my pump filter basket) also increased quite a bit. I'm pretty sure I have a suction-side leak somewhere, too, but it's not bad enough to affect priming.

 

[Jimrahbe]

36.

You can't really "feel" any suction at a main drain.. The way to tell if it is working is to turn the main drain on 100% and shut off all other inputs, like your skimmers.. Either the pump will continue to work, or it will quickly run out of water..

Not a big deal, but if you have a pool cleaner that uses suction from the pump, it is not a "Robot".. They look like this...

Thanks,

Jim R.

 

[Rancho Cost-a-Lotta]

There is one main drain at the bottom of the deep end, and a skimmer. Separate lines for those two go back to the pump, but only one line has a valve

The main drain may be connected to the deep end skimmer via the front port at the bottom of the skimmer. The back port, on the deck side, would return to the pump. Do you have a float / diverter valve at the bottom of that skimmer under the skimmer basket? It will kind of look like a UFO. If you have this setup, that would be used to balance suction between the main drain and skimmer.

 

[GearHead36]

36.

You can't really "feel" any suction at a main drain.. The way to tell if it is working is to turn the main drain on 100% and shut off all other inputs, like your skimmers.. Either the pump will continue to work, or it will quickly run out of water..

Not a big deal, but if you have a pool cleaner that uses suction from the pump, it is not a "Robot"..

Thanks for the quick reply. Unfortunately, I can't turn off all the inputs except the drain. There is no valve in the skimmer line.

OK. Missed on the terminology. We have a Polaris cleaner.

I did another dive to the bottom of the deep end, and I can't detect any temperature difference at the bottom. I'm convinced now that the drain is working. I'm just surprised that you can't feel any suction. The skimmer, on the other hand, has a LOT of suction. Of course, it's concentrated in a 2" hole, while the drain grate is MUCH larger, which will reduce the suction effect. It just reduced it more than I expected.

 

[GearHead36]

The main drain may be connected to the deep end skimmer via the front port at the bottom of the skimmer. The back port, on the deck side, would return to the pump. Do you have a float / diverter valve at the bottom of that skimmer under the skimmer basket? It will kind of look like a UFO. If you have this setup, that would be used to balance suction between the main drain and skimmer.

Not sure what you mean by "deep end skimmer". The pool has a single skimmer on the shallow end, and a drain at the bottom of the deep end. No diverter valve. I have a valve in the drain line, but not in the skimmer line. Closing that should increase flow through the skimmer. When I close it partially, the pressure goes down, indicating that the total flow decreases, indicating that the main drain is working.

Thanks for the replies.