Question about Skimmer Diverter and Main Drain

[Option]

Hello, I’ve done a fair amount of reading on these forums regarding how main drain flow can be controlled by skimmer diverters (assuming the pool was plumbed for it). However, there is one part that I am still not understanding.

From what I’ve read, it seems that when the diverter in the skimmer is open, the pump will pull from the skimmers and not the main drain since that is the path of least resistance. Then when the diverter in the skimmer is closed, the pump can no longer pull water through the skimmer so it pulls from the main drain instead.

If that sounds about right, can anyone explain what the second hole at the bottom of the skimmer is for? People have said that it goes down to the main drain but I am not understanding why that is necessary. Thank you!

 

[borjis]

But then how else could it access the main drain, if the hole is not going to the main drain?

Did you think the main drain accessed the skimmer suction, hidden underneath the plumbing?

on some setups, the second hole is either plugged (like mine) or has what's called an equalizing port
if I'm not mistaken. I had that at my last pool, but the main drain was on it's own plumbing
entirely to the equipment pad.

 

[Option]

But then how else could it access the main drain, if the hole is not going to the main drain?

Did you think the main drain accessed the skimmer suction, hidden underneath the plumbing?

on some setups, the second hole is either plugged (like mine) or has what's called an equalizing port
if I'm not mistaken. I had that at my last pool, but the main drain was on it's own plumbing
entirely to the equipment pad.

Thank you for the reply,

When you say "How else could it access the main drain..." are you asking how the pump can access the main drain? If so, I just sort of assumed it was plumbed like this:

 

[jmastron]

Thank you for the reply,

When you say "How else could it access the main drain..." are you asking how the pump can access the main drain? If so, I just sort of assumed it was plumbed like this:

View attachment 64782

I think when people talk about "skimmer diverters", they're talking about the main drain being plumbed into a port in the skimmer itself (and not directly to another valve at the pad or a Tee like you show). Then, inside the skimmer there's a doohickey that allows you to cover the main drain port (pulling all water from the skimmer) or sometimes to cover both ports together (pulling all water from the main drain). Something like this: http://blog.poolcenter.com/designdocuments/skimmer-u3-main-drain-combo-skimmer-plumbing-2.gif

My pool, on the other hand, has the main drain pipe terminating in a port on the upper side of the skimmer (below the basket), so there's no control. I plugged that port with a 1.5" cap so during the summer I get all the water pulled from the skimmer. I'll remove it in the fall when I have to worry about the skimmer basket filling enough to block the flow.

 

[Option]

I think when people talk about "skimmer diverters", they're talking about the main drain being plumbed into a port in the skimmer itself (and not directly to another valve at the pad or a Tee like you show). Then, inside the skimmer there's a doohickey that allows you to cover the main drain port (pulling all water from the skimmer) or sometimes to cover both ports together (pulling all water from the main drain). Something like this: http://blog.poolcenter.com/designdocuments/skimmer-u3-main-drain-combo-skimmer-plumbing-2.gif

My pool, on the other hand, has the main drain pipe terminating in a port on the upper side of the skimmer (below the basket), so there's no control. I plugged that port with a 1.5" cap so during the summer I get all the water pulled from the skimmer. I'll remove it in the fall when I have to worry about the skimmer basket filling enough to block the flow.

Thank you, I think I have it now! My diverter is actually a float valve assembly and I was not correctly understanding how that worked. Assuming I've got it right, the main drain is connected to the bottom of the skimmer right next to the return pipe leading to the pump. If the water level ever drops low enough, the float valve drops which seals off the two pipes from the air in the skimmer and forces the pump to pull from the main drain connection at the bottom of the skimmer instead.

 

[Option]

I guess my next question would be, is there any easy/safe way to force water to be pulled from the main drain to ensure that it's not clogged? With my VS pump running at its usual low speed, I couldn't feel any pull through the bottom drain even if I practically covered it with my hands. Maybe I could try that again after bumping up the speed and closing off the other skimmer via the three-way-valve? I'm thinking that if I get enough flow through the skimmer that is connected to the main drain, maybe I can get some flow from the main drain itself?

 

[pooldv]

You can't feel the flow in a bottom drain. It is designed to have low suction so that people don't get trapped against it. It is unlikely that it is clogged unless the cover was removed for a while. Nothing can get through the cover that would clog it. You can use some red dye to test for water flow.

 

[Option]

You can't feel the flow in a bottom drain. It is designed to have low suction so that people don't get trapped against it. It is unlikely that it is clogged unless the cover was removed for a while. Nothing can get through the cover that would clog it. You can use some red dye to test for water flow.

Great idea, thank you!

I also just realized that the diverter plate has always been broken off from my float valve assembly. If I get a new one, I could use the plate to partially (or fully) close the diverter so that the pump has to pull from the main drain instead of the skimmer. I'm thinking that should increase flow to the main drain enough to detect it.

Here's a couple of illustrations in case anyone else finds this thread and has the same confusion I did.