no shut off for main drain?

[pool_girl]

Hi - I'm trying to get to know my plumbing and I've seen references to shutting off the main drain valve (ie, for better suction when vacuuming) and my system doesn't seem to have one. There are no shut-off valves, in fact, that I can detect. Am I missing something? My filtration system looks pretty straight forward - I have no heater so the water just seems to go from the pool, through the pump, through my sand filter and back. (there is a little deviation for the polaris booster pump and automated chlorinator, but I'm guessing that doesn't impact anything.)

Clueless, help?

[Buggsw]

Not all pools have a shutoff valve for the main drain. Mine doesn't.