What's The Purpose Of a Pool Skimmer Door?

What's the purpose of a swimming pool skimmer door?
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Skimmer weirs are often missing from pool skimmers, however, the are an important part of your swimming pool's circulation system.
Pool skimmers with a working weir create a slight waterfall effect which pulls the surface water into the skimmer at a faster rate. This is due to what is called Bernoulli's Principle or the Bernoulli effect. This means your skimmer catches more leaves and top debris while helping to increase the pool circulation. Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy (for the science geeks).
A non-working skimmer will not collect debris and properly circulate your pool chemicals, which can increase your chances of a cloudy swimming pool. Also, your pool pump motor will need to work harder and likely need replacing earlier than designed. This can be a costly mistake. Maintaining your pool skimmer is essential.

[@Lovemynico]

Thank you! I've been looking up everything on the suction of the skimmer and I finally found your video. Thank you for explaining it thoroughly!

[@EagleRockers]

My skimmer door has snapped off. Tried putting it back, that doesn't work. How important is it? Can I just leave it off? Is it costly to replace?