Types of Toilet Fill Valve

You flush down the toilet and the tank empties just in a few seconds. But have you ever wondered how the tank fills itself? What mechanism refills it every time you flush?

Well, if you have ever looked inside a tank, you will see a fill valve on the left. It is responsible for filling the tank up to the mark. Based on what kind of mechanism is installed, there are three major types of fill valves i.e. ballcock float valve, float cup fill valve, and floatless fill valve. The ballcock valve further has two versions; the older one is equipped with a plunger/piston and the other one with a diaphragm.

Before we get into the details of these fill valves, you need to understand the basic functioning of the fill valve. Then, we will move on to the types of fill valves, and see how to adjust the faulty fill valve.

Basic Functioning of a Toilet Fill Valve

The fill valve or refill valve is a component inside the tank that is responsible for controlling the flow of water and refilling the tank after you flush. It is vertically installed on the left side of the toilet tank. From underneath, it is connected to the shut-off valve, which supplies it with water. It closes the inflow of water into the tank once the tank reaches the right level.

3 Basic Types of Toilet Fill Valve

Now, based on what mechanism is attached, you would normally find three basic kinds of fill valves in toilets. These are a ball cock float valve, float cup fill valve, and floatless fill valve.

Ball Cock Fill Valve

The most common fill valve that has been used for decades is the ball cock fill valve. This old-school fill valve was found in multiple water level adjustment applications. It is often identified by its round floating ball.

Schematic Diagram of Ball Cock Fill Valve
Figure 1-Schematic Diagram of Ball Cock Fill Valve

In this type of valve, a float ball indicates the water level. And it is the movement of the float ball that opens and closes the inlet valve. You will find two different kinds of ballcock assemblies attached to a float. In very old toilets, you will find plunger-based fill valves, while nowadays diaphragm-based fill valves are common.  

Plunger Fill Valve

The plunger fill valve is probably the oldest type of fill valve. It is built from brass and performs a quiet operation.

Plunger/Piston Fill Valve
Figure 2-Plunger/Piston Fill Valve

This plunger/piston fill valve utilizes a plunger or piston device to open and seal the toilet tank’s water entrance.  A floating ball is fastened to the end of a brass rod, which in turn is coupled to the piston.  The ball doesn’t sink or swim, but rather maintains a constant position just above the water surface.

As soon as the toilet is flushed, the ball gets to its lowest position; moving the rod of brass along with it. The piston is pushed open, allowing water to flow.

Similarly, the ball and the rod are both lifted when the water level in the tank rises. Once the tank starts filling, the rod lifts the piston and gradually shuts it until it is entirely closed.

In case, you want to adjust the water level, you can do that by bending the metal rod either upwards (to raise the water level) or downwards (to lower the water level).

Plunger fill valves are almost obsolete. Albeit, some manufacturers like Prier still make them.

Diaphragm Fill Valve (Brass and Plastic Version)

Another type of Ball Cock Valve is Diaphragm fill valve. A ballcock with a diaphragm design may or may not have a vertical shaft made of brass; however, most current ballcocks are constructed of plastic.
The brass design was common in the past. It functions similar to the plunger fill valve. However, the system is controlled by a brass diaphragm instead of a plunger. When the water leaves the tank after a flush, the ball float along with the brass rod moves down. The rod puts pressure on the diaphragm, which causes the water to enter the tank.

When the tank refills, the brass rod, and ball float move upward. This releases pressure off the diagram and the inlet valve closes.  Just like a plunger fill valve, you can adjust the water level by bending the rod.

Diaphragm Fill Valve (Plastic Version)
Figure 3-Diaphragm Fill Valve (Plastic Version)

Next, we have the modern plastic design diaphragms. The complete working principle is the same, one difference is material. And the second difference is its adjustment. Unlike the previous case, you get an adjustment screw to adjust the floating rod. Turning the screw clockwise lowers the float while turning it counterclockwise raises the float/water level.

Float Cup Fill Valve

Float Cup Fill valves have largely replaced the old-fashioned ball cocks. This particular kind of fill valve does not have the conventional floating ball; rather, it has a cylindrical plastic cup that travels up and down the vertical shaft as the amount of water in the toilet tank change.            

Let’s see how it works.

Schematic Diagram of Float Cup Fill Valve
Figure 4-Schematic Diagram of Float Cup Fill Valve

Figure 4, shows the schematic diagram of a float cup fill valve. On the bottom end, you find the valve attached to the water supply, and the top end features a moveable cylindrical float.  When you flush the toilet, the floating cup falls to the bottom of the shaft, where it opens the water inlet. The cup rises as water enters the tank and fills it, eventually closing off the inlet.

You may be wondering can I manually adjust the float’s height if by chance its height isn’t appropriate?

Yes, most float cup valves have a plastic screw mechanism that may be used to regulate the amount of water in the tank. Simply turn it to either raise or lower the cup. Therefore, adjusting the water level. Some models also feature a water level adjustment clip through which you can adjust this cup. 

Floatless Fill Valve / Pressure-Assisted Fill Valve

A very different kind of fill valve is the Floatless Fill valve. The name gives you a hint that this fill valve doesn’t have anything to do with floating. It is a pressure-assisted fill valve that opens and closes based on pressure. Such kind of fill valve is attached to the tank’s bottom, completely submerged in water.

Floatless Fill Valve
Figure 5- Floatless Fill Valve

Floatless Fill Valves were launched basically for low-flow toilets. They are inexpensive, albeit they are not much common these days because there aren’t much reliable.

Since there is a risk of back-siphoning polluted water into the fresh water supply, the use of this type of fill valve is prohibited by the building code in some places.

For adjusting the water level, you can turn the adjustment screw on the top. Turning it clockwise will raise the water level while turning it anticlockwise will lower the water level.

When to Adjust the fill Valve?

You need to adjust the fill valve at instances when the tank overflows, you experience a weak flush, double flush or there is a low water level in the tank.

Tank Overflows

If you see water coming out of the toilet tank, it means the tank has been overfilled. Why? The fill valve is incorrectly positioned. To fix its position, raise the float ball or turn the screw clockwise. 

Weak Flush

A weak flush indicates that there is little water in the tank. One of the reasons behind this is a faulty positioned fill valve. Open the tank, and raise the water level to fix the issue.

Low water level in the bowl

A weak flush results in a low water level in the toilet bowl. If the level of water in the bowl drops soon after you flush, it means the flush is weak due to an incorrectly positioned fill valve.

Double Flush

Lastly, if you experience a strong flush followed by a weak flush. Then, that means that the tank has been overfilled due to the inappropriate position of the fill valve and that’s why it is double flushing. In this instance, again you need to make adjustments to the valve.

That’s it. We hope that this article would have enlightened your knowledge on the type of fill valves, and how they work. Do you want to know which type of valve is installed in your toilet? Hurry up, take off the tank’s lid and find out!!

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