Pool School 114 Automatic Skimmers

SkimmerDiagramEAlmost every pool has an automatic surface skimmer, this is the device that is on the side of the pool that draws water into it, and it is probably one of the least understood pieces of equipment on everyone’s pool. Don’t feel bad it was years after I got into the pool business before I understood how they worked and why they were there.

So let’s travel back in time, to say the early 1900’s, and pools were coming into vogue with the wealthy. The problem with pools in the early days was there wasn’t a filtration system; the pool was just stagnant, nothing moved. After a week or more the water did not look so good at that point they would open the drain at the bottom of the pool and drain all the water out and refill the pool with fresh clean water. Not a very efficient system but water was cheap and that was the best you could do. Without a filter system you had debris collecting on top of the pool and it had nowhere to go, you had to get a leaf skimmer out and skim the surface of the pool by hand. This is an arduous and boring task. With the advent of filter systems they solved the dirty water problem but the skimming issue was still a problem. Along came the invention of the automatic surface skimmer. The concept is to skim debris off the surface of the pool so you don’t have to, when done properly you will have very little debris to remove from the surface of the pool.

The operation of the skimmer is very simple, at the mouth of the skimmer is what people like to call a flapper, the technical name of the flapper is a weir. The weir has two functions; first it enhances the skimming action on the surface of the pool by creating a drop on the back side of the weir which pulls debris from further out into the pool. The second function is to block the flow of debris out of the skimmer when you turn the pump off. If your weir is missing or not working properly you will not pull debris off the surface of the pool as well as you should, and when you turn the pump off all the debris you collected will end up back in the pool. So it is wise to make sure your weir is in place and working properly. When I say working properly I mean it should float freely on the surface of the water leaning back slightly when the pump is running.

One of the other functions of the skimmer is keeping large debris from getting stuck in the pipe that goes between the skimmer and the pump. Inside the skimmer is a basket that strains the water keeping large debris out of the pipe. Ideally you should never run the pump without the skimmer basket in place. The skimmer is also used to vacuum the pool, when you use it for this purpose you must use a vacuum plate on top of the skimmer basket when you connect to the system. If you don’t use both the vacuum plate and the basket you may pull something into the plumbing that will be too big for the pipe and block the flow of water. The only solution for this is to use a second pump to blow the suction line out backward. Not a pleasant process, so be smart and use the vacuum plate.

As I said earlier the skimmer is one of the most miss understood components on the pool system and one of the most confusing things is when you have more than one skimmer. When you have more than one skimmer there is a balance you need to achieve to get the maximum skimming action from both skimmers. If you don’t balance your skimmers then you will have one skimmer that draws water really well and one skimmer that has very little draw. To equalize the flow you will need to use what is called a trimmer plate. The trimmer plate is located at the bottom of the skimmer and can be slid over the hole farthest from the pool at the bottom of the skimmer. The skimmer closest to the filter system will always draw more water than the far skimmer. So you would slide the trimmer plate over the hole farthest from the pool at the bottom of the skimmer closest to the pump about half to three quarters of the way over the opening, and you would make sure the far skimmer’s trimmer plate is not covering the hole at all. You would play with the position in the skimmer closest to the filter until you feel you have even flow. So you are probably wondering why there is a trimmer plate in the far skimmer. Clearly you are thinking about what is going on and that is excellent! I like that! The purpose for the trimmer plate in the far skimmer is for vacuuming the pool. When you vacuum the pool you usually use the skimmer closest to the pump and we need to block the flow of water into the far skimmer, so you would take the trimmer plate and slide it over the hole farthest from the pool blocking the flow of water from the skimmer and completely uncovering the hole in the skimmer closest to the pump.

Class is over it is time to hit the pool and have fun. Class dismissed!

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