MPV (Multi-Port Valves) are the big valves found on DE and sand filters. They do a number of functions as described below. Not all MPVs have all the modes listed.
An MPV valve is specific to a model filter and are usually not interchangeable.
MPVs on DE filters are mounted on the side. MPVs on sand filters may be mounted on the top or the side. Note that side mounted MPVs on DE and sand filter have the in and out pipes reversed - top in for sand filters and bottom in for DE filters. Make sure you have the correct MPV for your filter.
Slide Valves are an alternate to an MPV on DE or sand filters.
Filter is the normal setting for the water to flow through the DE or sand.
BACKWASH changes the water flow to wash water over the DE or sand and the dirt will flow out of the MPV waste line with pool water. DE will also be washed out of the filter and new DE will need to be loaded in after the backwashing is completed. A sand filter does not lose sand during a backwash.
RINSE is done along with backwash. In DE filters you typically alternate between BACKWASH and RINSE modes three times during a backwash.
Use RECIRCULATE if you have a bad algae problem that is rapidly clogging the filter so you constantly need to backwash. Do the initial SLAM Process on RECIRCULATE until you kill much of the algae. Then filter out the dead algae without the algae continuously multiplying as you try and filter.
Or if you use Floc (that we don’t recommend doing) and intend to vacuum it to waste when it settles to the bottom of the pool. Run the filter in RECIRCULATE to not clog the filter with Floc or Clarifier.
Recirculate can be used when the filter is in need of repair - if you can't filter the water, at least you can circulate it
WASTE routes water directly to the waster line to dump water out of the pool.
CLOSED shuts off all flow to the filter and pool. Water flow is stopped at the "PUMP" port
Leaks to Waste Line
If water is leaking to the waste line while in FILTER mode it is likely a leaking spider gasket in the MPV that needs replacement.
Replacement handles are available for many MPVs. The Valve handle can be removed by tapping out the handle pin. A helper may be needed to push down on the lid to compress the spring while you tap the pin in for a new handle.
Leaks Around the Valve Handle
There are O rings on the stem underneath the handle that wear and may need replacement.
"one direction only" rotation of the multiport valve?
It's a common discussion, but not everyone does it. In reality, it shouldn't matter and many manuals do not even touch on it. When the gasket is lubed prior to assembly, the (depressed) valve should slide nicely either way. However some feel that the gasket may become worn or almost trained to allow the valve to move better in the same direction to avoid pinching later, especially with age. By that time, it's probably time to replace it anyways.
You will find the spider gasket glued in and you will need to remove it using an xacto knife, needle nose pliers, or a spudger.
Depending on the specific model of the multiport, Pentair recommends gluing the spider gasket in place. They recommend Loctite 401 or 416, but the Permatex should work as long as you don't get carried away with it.
Grease the spider gasket with a pool lube.