Searches on previous threads related to MD & Skimmer problems produced much good information, but no good solution To my current problems. I have lived with this pool for 41 years, and the only real problem occured when the carpenter who was re-building my 1929 garage put a Red-Head through the skimmer suction line, despite my warnings. The dominoes started to fall when I noticed the pump plugging up with Atlas Cedar needles (about 1" long ). The trees were 50' high when I bought the place, so I was surprised that they had suddenly become a problem. I found the 1st dominoe to be the Polaris cleaner, which was failing to pick up the needles due to clogs in all three pick-up jets. the cleaner inlet screen was not plugged up, but when I opened the jets with a sharpened bicycle spoke, I noticed the cleaner was also picking up fine sand, along with the organic material.
By playing with the suction gate-valves I noted that most of the water being drawn by the pump came from the skimmer. When I closed the skimmer valve, the pressure at the filter dropped from 20 psi to 10 psi. With the basket cover off and the skimmer closed, water flow from the MD (gravity) was very low, compared to skimmer flow. Using a Drain King at max ( 50psi ) pressure I was able to partially clear the MD, but the flow problem ( as well as more needles in the impeller ) quickly reappeared. I tried to increase the pressure on the Drain King, and promptly blew it to pieces.
The second dominoe fell, when I noticed the water level falling drastically. I did the bucket test, but it was unnecessary, as the level stopped falling when it reached the edge of the skimmer. Doing a bucket-fill test ( compared with putting the hose directly in to skimmer well ), I concluded that the leak in the skimmer suction line was about 2-1/2 gallons a minute. The skimmer well sits in solid concrete, as does 6' of the suction line ( the north wall of the pool, which is the south wall of the garage is a 9'x21'x2-1/2' barrier ). The only part of the skimmer suction line passing through soil is about 4' long, throug which it descends to the pump-house. My guess is that the leak is either in the soil section of pipe, or the portion of pipe that was repaired when the red-head was driven into it ( hence the fine sand being picked up by the cleaner ).
Subsequent attempts to blow out the MD with a Drain King have been unsuccessful ( same results as above ). When I run the DK, clear the needles from the impeller, ant re-start the pump ( skimmer closed ), the pressure 1st rises to 20 psi, then drops to zero. the basket then fills with "air" due to cavitation. the shaving-cream test on the basket lid & both suction valve-stems show no leaks.
I am open to all suggestions as to what to do next, except asking me to dive to the MD to remove the cover and attack it there.