Water Leaking Through Backwash Port
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Do you have a swimming pool sand filter that has started to leak water from the backwash port when you are running on the filter setting? This is a very common point of failure for sand filters which can have a few different causes. I will outline on this page why this happens, how to avoid it happening, how to (quick fix) repair the problem, and also how to properly solve the problem long term. The short answer to all of these questions is that the multiport valve gasket has experienced a failure and is allowing water to bypass the valve and access the backwash port even when you have the filter set to filter mode.
The multiport valve on the top of your sand filter is just like other valves within your pool system except for it has more than one (or two) options. The multiport valve is essentially a five (or six) way valve. Inside of the multiport valve is a gasket that looks like a wagon wheel and it is called a spoke gasket. Should this gasket become displaced, damaged, flattened or disrupted by foreign material (like sand) then water will escape past the selected port and access all of the other ports as well at the same time. This is how you can end up with water leaking from your backwash line when the filter is running on filter mode.
Only rotate the handle in one direction - If you turn the filter multiport valve handle left or right depending on which direction is closer to your end goal, you should cease doing this. The valve handle should only ever be rotated in one direction, clockwise, and reversing this direction can cause the spoke gasket to snag and become displaced. Always rotate the valve handle in the same direction.
Turn off pump before changing filter settings - You can change filter settings without turning off the pump but you definitely should not be doing this. This puts a huge amount of strain on the filter itself, and it the most likely cause for having water leak from your backwash line for most pool owners. By turning off the pump every time you want to change filter settings you are far less likely to experience a failure of the spoke gasket in the filter head.
Use the "rinse" setting after backwashing - The purpose of the rinse setting on pool sand filters is to help clear any potential physical debris from inside of the valve mechanism where it can cause damage or displace the spoke gasket. Sand in particular is well known for causing leaks from the backwash port and performing a 30 second rinse cycle after backwashing helps to limit the potential for foreign debris to displace the gasket.
Wait 60s after completing backwash (and rinse) - When you backwash most people have either a hard plumbed backwash pipe, or a lay-flat roll out hose. If you are backwashing and then turn off your pump and change filter settings too quickly you could induce a problem. There is still water in the pipe (hose) travelling away from the pool system and since the plumbing system is closed loop this means you can end up with a vacuum being created as the backwash water continues to try to exit the pipe. If you change filter settings too quickly the water traveling away from the pool can create a vacuum force which can displace the filter gasket. It only takes a few pounds of vacuum force to displace the filter gasket on some filter brands. Allow 60 seconds after backwashing and turning off the pump for the water traveling away from the filter to finish before changing filter settings.
It is worth noting that some brands of sand filters have a known reputation for water leaking through the backwash port due to spoke gasket failures. Unfortunately some of these models use contact cement to set the spoke gasket making removal and replacement of the gasket a nightmare. In many cases either the entire filter head or the key assembly must be replaced, which is a shame since the problem is with a $10 gasket, not the whole filter head. You can scrape and remove the old gasket, with much effort, but any imperfections in seating the replacement gasket will result in water continuing to escape through the backwash line.
A work around option that many pool owners go to is to install a manual ball valve on the backwash port. This will prevent water from escaping through the backwash line when not in use, but be sure to remember to open the valve when you are ready to backwash! While this may solve leaking water from the backwash permanently for some pool filters, some will continue to leak more and more until the water is no longer passing through the filter tank, but escaping through the recirculation port (which bypasses the filter). For more information you can check out this YouTube video about water leaking out through backwash port.
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Swimming Pool Steve is an award winning, second generation swimming pool and spa specialist from Ontario Canada. With over 10,000,000 views on the Swimming Pool Steve YouTube Channel, winner of the 2018 Pool & Spa Industry Leadership award and author of hundreds of pool and spa articles both online and in print Steve is committed to helping pool and spa owners as well as pool and spa industry workers learn more about the technical side of building, renovating, repairing and maintaining all types of swimming pools and spas. Follow Swimming Pool Steve on Facebook, Twitter and YouTube.
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