Issue with main drain

[DFRESH333]

I recently bought this house and now I have my first pool! After reading and searching a bunch of threads, I have identified all of my pipes, but seem to be having a problem with my main drain. I have been able to accurately manipulate all of my levers with accurate results, but when I open my main and close everything else, I get some water, but no where near the flow of the skimmer or the spa drain. I have also tried all possible combos of main/spa/skimmer with the same results that include bubbles out of the jets. I can see some wather coming into pump basket, but not a lot, so I am thinking a blockage of some sort. When I got the pool, a service was taking care of it and they just had it set at full skimmer, and it must have been that way for some time because the sun has bleached the lever positions in position. What is the best way to diagnose main drain problems? Scuba gear and a snake?? Of course there could be some other setting/ issue with my set up I am not aware of that is causing my issue, another reason why i'm posting!! two pics attached for info. Currently waiting for my test kit, been going to Leslie's in the meantime. The pool is estimated at 16x32 avg 5 ft deep =19200. Leslie's has me estimated at 15500, which is why im having other issues, but that's another thread. Thanks for the help!

 

[JVTrain]

There could be some blockage in the main drain, especially if it had not been flowing for quite some time through the main drain. Sometimes the "easiest" fix is to force air/water back through the main drain by using a blower. A shopvac can sometimes accomplish this if you set valves to only be open to a skimmer and the main drain. In your case, with the pump off, you would position the valve between the MD and skimmer so that it's open to both, then position the valve nearest to the suction side of the pump to be closed to MD/skimmer flow, open to spa flow. Then put the shopvac hose hooked to the output side of the vacuum into the bottom hole in the skimmer. This will blow water/air through the skimmer line, to the equipment pad valve area then out the main drain. If it's fine, but packed debris it may be able to pass in reverse through the MD cover. If you end up with the clog/material under the MD cover, you may have to remove the cover or break it up carefully with a narrow tool through the MD cover grids.

Otherwise products such as this: Clog Buster can be inserted into the problem line and using a garden hose, force water back through the offending line to attempt to clear the clog.

Worst case scenario, the MD could be abandoned if there is damage to the plumbing or if the plumbing to the MD has a break or leak. Main drains are not required and don't do a great deal for improving circulation, but they do make draining the pool below skimmer level possible without a submersible pump.

 

[DFRESH333]

So here's a new piece of the puzzle - I replaced my filter and pressure guage, and now I notice that if I crack my main drain open even the slightest bit, the pressure drops to zero, and all of the return jets stop completely. Is this indicative of a blockage? Is that why there aren't bubbles coming out of the jets? Even if it is blocked, why would it prevent the water from continuing to come from the skimmer side? Seems strange. Back to 100% skimmer, no problems.

 

[DFRESH333]

thanks

 

[CNJ_EC]

Defresh ... loosing complete pressure when you crack the valve to the MD sounds more like you might have a fractured / broken line between the MD and the pad.

To test for that problem you'll have to plug each of your MD's the insert the your leak kit test plug hopefully you ordered the one that has a pass-through air inlet valve. Not knowing the condition of your other diverter valves ... I would opt to
1) Isolated the MD/Skim valve at the 1st valve near the pump inlet
2) Remove the MD/Skim valve cover(8 screws) and the diverter body
3) Insert the Leak Test plug into the valve port for the MD
4) Start pressurizing the line slowly until you'll reach the max pressure for you specific test plug (working pressure for a 2.5" pipe is about 180PSI and busting pressure is about 870PSI)
5) Once you have reached the max pressure rating of your test plug ... if you can't hold pressure ... continue to step 7
6) If it appears to hold ...lock off the pressure port and see if it continues to hold. If it leaks ... continue to step 7
7) Continue to apply the max constant pressure
8) Using a driven probe & a listen / pickup device ... listen along the pipe run for the air leak at maybe 1' intervals from the edge of the pool

You can perform the same test with the Clog Blaster ... just double or triple check the location of the water gushing sound you're hearing.

I use both of these techniques for locating breaks in buried electrical conduit. Sometimes with enough water flow the ground becomes so wet the water and air will just bubble up to the surface.