Determining valves for partial draining

geh

Gold Supporter
Nov 28, 2020
93
New Orleans
I want to drain 1/3 of my 15,600 gallon pool and refill it to bring down the stabilizer level. I plan on using my pool pump in backwash, because I think it can do the job fine, and the hose run to the street for a submersible pump would be well over 100 feet. I've determined which two valves shut off the skimmers, by closing and opening each one successively, but not sure how to verify the bottom drains are open and running. There are three identical valves next to each other, one each for the two skimmers, and one next to it, which I was assuming would be for the two bottom drains. The skimmers are in the on position (vertical), and the third one is in the horizontal position, which I assume would be the off position. I heated the pool so I could go the the bottom with the pump running in normal filter mode, and checked for suction. I felt nothing. I turned the valve in question, and heard a difference in pressure or function, dove to the bottom, and still felt nothing, so I returned it to its original horizontal position.

Should the bottom twin drains be drawing water to the pump like the skimmers do, in normal filter mode, or do they only draw water in backwash or waste mode? Here's a few photos: one is of the valves showing three pipes coming from the ground, one showing them joining one pipe, and that pipe goes straight to the pump. Can someone explain? Thanks.
 

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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
36,296
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
It is very difficult to feel suction on the main drain. You really only have one main drain. The two inlets in the pool are plumbed together to create the anti-entrapment requirement to meet the VGBA law.

Open all the suction side valves fully open with pump on. Close one of the skimmer suction valves. Slowly close the other skimmer suction valve. If the pump stays primed, you can then switch to backwash and drain some water.

Caveat and Warning - losing prime doing what you are doing is quite likely. If it happens, you can damage your pump/motor. I do NOT recommend you drain water this way. I also would be very wary draining water unless you are absolutely sure you have a deep ground water level. Your area tends to have shallow ground water.
 

chiefwej

LifeTime Supporter
TFP Guide
Jun 12, 2011
3,551
Tucson
You are making assumptions about the plumbing, that may or may not be true. Many times the bottom drain line is connected to the skimmer vs ”home run” design where everything has its own run back to the pad. There are two openings in the bottom of each skimmer. If each one of your skimmers has only one of those two plumbed, and the other is plugged then your assumption that each is plumbed individually back to the pad is likely true. If so the third valve could be main drain. But often there is also a dedicated suction line (and valve) for a suction side cleaner.
 

geh

Gold Supporter
Nov 28, 2020
93
New Orleans
It is very difficult to feel suction on the main drain. You really only have one main drain. The two inlets in the pool are plumbed together to create the anti-entrapment requirement to meet the VGBA law.

Open all the suction side valves fully open with pump on. Close one of the skimmer suction valves. Slowly close the other skimmer suction valve. If the pump stays primed, you can then switch to backwash and drain some water.

Caveat and Warning - losing prime doing what you are doing is quite likely. If it happens, you can damage your pump/motor. I do NOT recommend you drain water this way. I also would be very wary draining water unless you are absolutely sure you have a deep ground water level. Your area tends to have shallow ground water.

Ok, I'll take your advice and not use the pool pump to drain. Is there a link to thread to explain what submersible pump to use and proper technique? Or can you advise? And looking at my photos above, seems like the main drain is in the off position and should be on? Or is the drain just for draining and normally in the off position? I had the pool re-plastered this year and they drained it completely, I think opening the main drain to allow some groundwater to percolate up when they then pumped out. I am only draining about a third and then re-filling, to bring my high stabilizer level down. I am thinking that would not be enough to cause to pool to come up.
 

geh

Gold Supporter
Nov 28, 2020
93
New Orleans
You are making assumptions about the plumbing, that may or may not be true. Many times the bottom drain line is connected to the skimmer vs ”home run” design where everything has its own run back to the pad. There are two openings in the bottom of each skimmer. If each one of your skimmers has only one of those two plumbed, and the other is plugged then your assumption that each is plumbed individually back to the pad is likely true. If so the third valve could be main drain. But often there is also a dedicated suction line (and valve) for a suction side cleaner.
Only one of the two openings in each skimmer are plumbed.
 

geh

Gold Supporter
Nov 28, 2020
93
New Orleans
That third valve, the one on the right, do you think that is the main drain and should it be in the on position?
 

geh

Gold Supporter
Nov 28, 2020
93
New Orleans
You are making assumptions about the plumbing, that may or may not be true. Many times the bottom drain line is connected to the skimmer vs ”home run” design where everything has its own run back to the pad. There are two openings in the bottom of each skimmer. If each one of your skimmers has only one of those two plumbed, and the other is plugged then your assumption that each is plumbed individually back to the pad is likely true. If so the third valve could be main drain. But often there is also a dedicated suction line (and valve) for a suction side cleaner.
I do have suction side cleaner for a Polaris, which I just retired, and got a robot instead. Never touched this valve, and the Polaris was working. I can take photos of everything if that will help. By the way I just ordered a submersible pump so won’t be using the pool pump to drain. But I would like to know what this valve is and if it should be open or closed.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
36,296
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Test it. Open all the valves wide open. Close the one on the left, note what that does, then close the middle one, note what that does. If those two valves close the skimmers, then the last valve is the main drain. Also, look under the basket of your skimmers, is there one hole or two open? Your Polaris was a pressure side cleaner so that would not be effected by the suction side valves.
 
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