How Toilet Fill Valves Work & Types

It’s a harmonious mechanism whereby you flush the toilet and, when you come back, you simply flush it again and there’s always the same amount of water to do the job right. Inside the toilet tank is a system of interrelated parts working to ensure you always have enough water to keep the toilet clean.

Among the parts in this setup is the toilet fill valve. It works by letting in water into the toilet tank after flushing and, when the tank is filled to a chosen level, sealing off the water inlet. The mechanism itself is a simple one yet very effective in keeping the tank filled always.

There are various types of toilet fill valves although they all do the same job which is keeping the toilet tank filled. Understanding how each type works is important in solving the issues that may arise when using the toilet.

What is a Toilet Fill Valve?

The toilet fill valve is a series of interconnected parts inside the toilet tank that’s responsible for controlling the water flow that refills the tank.

It doesn’t take part in the flushing of the toilet as this role is for the flush valve. However, the two are interrelated as flushing the toilet also activates the fill valve to allow water into the tank.

It’s made up of a mechanism to measure the level of water which in most cases is a floater that moves up and down with the level of water. Others use a pressure-sensing mechanism to detect when the water is present or absent from the toilet tank.

How does it Work?

The floating mechanism keeps at pace with the level of the water in the tank.

When the level drops below a certain maximum point, the fill valve lets in water until the maximum level is attained again.

While all fill valves do the same job, they do so using many different approaches and mechanisms.

Types of Fill Valves

Fill valves are named after the main mechanisms they depend on as you will learn in the sections below. The main types of fill valves include the following:

Plunger/Piston Type Fill Valve

The plunger/piston fill valve uses a plunger or piston system to open and close the water inlet into the toilet tank. The inlet is the bottom-fill type which means that water is injected into the tank from below rather than from above.

Plunger type of fill valve

The piston or plunger is attached to a brass rod which is in turn attached to a floating ball at its end. The floating ball stays on top of the water surface at all times.

When the toilet is flushed, the ball drops to its lowest level. As it does so, it moves the brass rod with it. The brass rod moves the piston which opens the water inlet.

As the water flows into the toilet tank and its level raises up, the ball is raised as well as the rod it is attached to. The rode raises the piston and slowly closes it until it’s completely closed when the tank is full.

To change how much water flows into the toilet tank, you bend the brass rod either up to raise the water level, or downwards to lower the water level. Keep in mind that you should keep the water level within a given maximum level.

Diaphragm Type (Brass & Plastic)


The diaphragm type fill valves are almost similar to the piston type as they also feature a brass rod which has a float ball at its end. This also floats in sync with the water level.

However, instead of the brass rod changing the setup of a piston, it moves a button at the top of a diaphragm setup. The brass part refers to the material the diaphragm is made from as there’s a plastic version of it.

When the toilet is flushed, the floater moves downwards and moves the brass rod with it. This brass rod presses on top of the diaphragm which then opens the water inlet into the toilet tank.

As the water fills up, it moves the floating ball upwards with it. The ball moves the brass rod which releases the pressure on the diaphragm. In this way, the diaphragm slowly closes the water inlet inlet until it’s closed.

To adjust the amount of water that goes into the toilet tank, you bend the brass rod connecting the floating ball to the diaphragm up for more water and down for less water.


The setup for this type of fill valve is the same as that of the brass diaphragm fill valve.

diaphragm fill valve

It even works in a similar manner with the downward movement of the ball opening the diaphragm and upward motions closing the diaphragm and water inlet.

The main difference is that the diaphragm is made of plastic material rather than brass.

Also, instead of bending the brass rod to adjust the water level in the tank, you turn the floating rod adjustment screw at the top of the diaphragm setup.

A clockwise turn lowers the water level while a counterclockwise turn increases the water level in the tank.

Float Cup Type Fill Valve

This type of fill valve lacks the traditional floating ball and instead has a circular cup made of plastic that moves up and down a shaft with the level of water in the toilet tank.

Float Cup Ballcock

It’s one of the most reliable types of fill valves as it has fewer moving parts and is very easy to adjust.

When the toilet is flushed, the floating cup drops to the base of the shaft and opens the water inlet. As the water flows into the toilet tank, it raises the cup upwards until it reaches a point where the inlet is closed again.

To adjust the level of water in the toilet tank, you identify the metal spring clip at the top of the plastic cup and pinch both of its ends together to release it. You then move it either upwards or downwards to lower or raise the water level respectively.

Internal Float Type Fill Valve

The internal float fill valve is named so as it has an internally floating mechanism with a small floater and lever to open and close the water inlet in the toilet tank. Given that the water inlet is also inside the fill valve, it’s very quiet and has been named the QuietFill valve.

The valve fill and everything in it is contained within the head which can be moved up or down to raise or lower the water levels in the tank. You first turn the head counterclockwise to unlock it, move in up or down as needed, then lock it with a clockwise turn.

These are the most known types of fill valves, how they work and how to adjust them when you need more or less water in the toilet tank. The internal float fill valve is the newest of them all and is gaining lots of popularity.

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