Fluidmaster Flush Valve fill extremely slow (built in flow restrictor).

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The wife is still training me.
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Orlando, Florida
Just like to pass on some information. Today at my son's house I replaced the diaphragm on a Fluidmaster 400A flush valve. It was taking about 5 minutes to fill the tank for water was barely flowing. The diaphragm was not the issue. I then tried a new flush valve as I only changed the top half. Save the hassle if disconnecting the water line, removing the stem, emptying water from the tank, etc. That still did not resolve the issue. Looking things over on the unit, I saw a flow restrictor at the bottom of the stem where the water line connects. Well this 12 year old or older American Standard toilet original flush valve had a slightly different flow restrictor. With a long screwdriver coming in from the top, i was able to pop out the old one. As you can see the old one on the left was made of a soft rubber like material that was collapsing under pressure. The new one is made of a plastic material. Inserting the new one resolved the problem. The flow restrictor is like a screw where the water travels along the threads. I assume without one the valve would be very noisy on fill and it probably reduces water hammer on shut off. I've used 400a forever and it is the first time I've seen this or knew of this part. The packaging and specs of the 400a has no mention of it.

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