When talking about the pool pump what is 'backwash'?

Im not sure of this answer as I am a new pool owner but I believe when the term backwash is used, it regarding cleaning a sand filter system. I think this is the only way to clean a sand filter without replacing the sand. That answer is pretty much spot on. Backwashing reverses the flow of water in the filter - instead of going from top down, it goes bottom upwards. The purpose of this is to dislodge dirt from the sand filter and send it out the waste pipe. This is the correct way of cleaning a sand filter and should be done every 2 weeks or so, or when the pressure gauge reading INCREASES. Yes, backwash reverses the flow of water in a sand filter to clean the sand. You should backwash when the pressure increases by 5PSI (roughly every week). The sand only needs to be replace every 10 or 15 years. People often confuse the pump with the filter. The filter is the big tank with the valve on top marked filter/backwash/rinse, etc. The pump is what moves the water and has a small basket to catch leaves.

I would only add to the above answers -- If you have a very small sand filter back washing the filter every two weeks may seem adequate because of the volume or capacity of the tank. Larger filters more adequately sized and matched with the rest of the system better serve you, possible use less water in backwashing, can wait to be backwashed up to 4 or 5 weeks. A sand filter that is slightly dirty will work better at cleaning the water than an extremely clean one. Again the pressure on the gauge is the best indicator with the exception of the occasional filter unit and gauge that will not register an increase until the filter is absolutely packed. As the saying goes in the industry "bigger is better" applies to most cases here.

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