How to test the main drain?

[105ex]

Hello,

I just bought a house that has a gunite pool with a single main drain. The pool is probably 40 years old.

I haven't been able to locate valves that deal with the main drain nor the skimmer.

I noticed that dirt around the main drain doesn't get sucked in and also confirmed that the main drain doesn't seem to be working.

The skimmer works just fine.

A pool cleaning guy suggested that I test it by putting in a tennis ball to cover the skimmer hole to see if the main drain would then start to suck.

My questions:

1. Is that safe to do?

2. Is it normal that old pools don't have any valves to control the water flow?

Thank you.

[duraleigh]

#2 is a yes......convenient valves are left off many pools......then and now.

#1 is a qualified yes. If the main drain is blocked, you will be pulling no water thru the pump. safe enough for a short period of time....just don't go to lunch with the pump on.

[matt4x4]

As long as the tennis ball is way bigger than the pipe and there won't be any chance of it getting sucked in, sure, it's safe to do, however, if your main drain is filled with concrete (many people plug them after having issues that are unfixable), then your entire suction side is almost completely shut off (May have a trickle left around the tennis ball fuzz), at which point your pump will start to create quite a bit of suction, leave this going too long and you could cause damage to your 40 yr old plumbing, so my suggestion is:
1. Add some dirt on/around the main drain so suction is very evident right away(you can always vac it back up...)
2. position yourself at the edge of the pool watching the main drain closely and holding the tennis ball in position at the skimmer
3. Get a helper to turn pump on, but not for more than 10 seconds.

[waste]

105, welcome to the forum!! Matt and Dave are right about the possible problem if the skimmer line is the only working line.
Does the skimmer have 2 ports? - some morons plumb the MD through the skimmer and use a special attachment in the skimmer to regulate the flow of the skimmer and the MD If you're not sure just see how many lines come up into the pump - if it's only 1 the MD is probably plumbed through the skimmer and you'll need the special attachment to get any water movement through the drain.

[105ex]

Almost 3 years ago since I posted this thread. Thank you for all the responses.

I believe Ted's description matches the configuration for my pool. The skimmer has 2 holes, one leading to the pump and the other leading to the main drain. And, I thought the saucer-looking thing that I found in the skimmer was a weight for the skimmer basket.

Recently, I was adding water through the skimmer when I noticed that some dirt around the main drain moved. That's what led me to realize that:
1. the second hole basically gets piped to the main drain (as clarified in http://wiki.answers.com/Q/Should_the...r_have_suction) and
2. the saucer-looking thing is a "skimmer diverter"

Anyways, just updating the thread in case there are others who may also be clueless as I've been and may benefit.