What is this spiral-shaped device from my toilet supply line?

Question

I needed to replace my toilet’s tank to toilet gasket, and in the process disconnected the toilet’s supply line. The rubber “screw like” object shown above fell out when I did this.

After finishing the gasket replacement, I forgot to put this back, and everything worked fine with no apparent leaks. But now I want to put it back, but I’m not sure what it does or what orientation it previously had. After researching and watching videos of flush valve and supply line replacements, it appears nobody else has a part like this in their toilets. I’m honestly beginning to think this object wasn’t supposed to be where it was.

Here’s an image of the disconnected supply line:

Here’s an image of the flush valve from inside the tank. Brand name: fluidmaster, probably installed ~2011.

Answer 1

This appears to do a few things.

• A backflow preventer. Note the nub on the "top", that should actually go down. Gravity and back pressure seats it on the inlet pipe to try to prevent tank water from backing up into the supply lines if there's a pressure loss or shutoff.
• A flow limiter. Without it the toilet will flow faster, but will be more susceptible to water hammer. The automatic valve opens and closes quicker than humans, and flowing water has inertia. Changes in inertia cause force. That force can be destructive, which is what water hammer is.
• A shock absorber, if it's made of rubber. This adds some compressibility to an incompressible medium, to help with water hammer effects, especially acting on that valve.

Answer 2

Looks like a fill valve regulator.

Pretty sure the metal washer is at the top when you put it in. Its actually an optional thing, and leaving it out might be just fine. It's weird that it fell out though.

Answer 3

It is a flow limiter.

The cistern will have an overflow pipe in case the inlet valve fails. In an area with particularly high feed pressure the rate of filling in such an event might exceed the rate of drainage through the overflow. To prevent the resultant flooding the flow limiter can be fitted.

It's optional because if the feed pressure is poor you won't want to further inhibit the refill times.

All of the inserts I have encountered were simple plastic types. The device you've got is rather fancy, being in rubber and metal. I think the suggestions by @Harper justify that very well.

Answer 4

OP, I know I'm four years and eight months too late, but for the next person that comes along after searching for weird spiral rubber piece in toilet tank supply line, I have a definitive answer on orientation.

Like you, I had the black rubber thing with the washer fall out after removing the supply line, and like you I tried to find the answer online, but unlike you I happen to have a new spare toilet in its original box.

We bought four of the same toilet around 2012, and only 3 have been installed.

Not being able to find the answer online, I unburied the toilet, pulled out the tank, and confirmed it came with the limiter installed nipple side up (American Standard toilet).

Answer 5

I have had the same problem and wasn't sure whether the nub and washer went face up or down. Based on experimentation and documentation, I can say the nub does go face up.