Fact Checked

What is a Ball Valve?

Katharine Swan
Katharine Swan

A ball valve, one type of quarter turn valve, is quite literally a ball placed in a passageway through which fluid flows. The ball has a hole through it, by which the valve opens and closes. When the ball is positioned so that the hole runs the same direction as the passageway, the fluid simply flows through it, and the valve is open. The ball can also be positioned so that the hole is perpendicular to the passageway so that the fluid cannot pass through, and the valve is closed. It is controlled from the outside, often with a handle that is turned back and forth to open and close the valve.

The basic version described above is a two-way valve. This type has a single, straight passageway bored through the ball, making two openings: one on each side, an inlet and an outlet. A ball valve can also be a three-way valve if a third hole is bored partially through the ball, until it meets the main hole, forming a T. A three-way valve can shut off one or all of the three passageways it connects.

The outside appearance of a ball valve.
The outside appearance of a ball valve.

Because of the nature of this valve, it does not work well in situations where fine control of the valve is needed, such as the valve that controls the throttle in a car. It does work very well for situations in which a flow needs to be completely shut off, such as the shut-off valve on the main water line in a house. Ball valves also do not tend to develop problems if they are not used for long periods of time; they will still work perfectly when needed again.

A trunnion ball valve is suitable for higher pressure valves.
A trunnion ball valve is suitable for higher pressure valves.

There are three different types of ball valve. A full port valve offers no flow restriction, which means that when it is open, the liquid can flow freely through it. This is achieved by making the ball larger than the passage size, so that the hole can be the same size as the passage. A standard port ball valve does not have an oversized ball, and as a result, the hole is one size smaller than the passageway. This creates a small amount of flow restriction as the fluid passes through. A reduced port valve, on the other hand, has an smaller ball and an even smaller hole, which creates significant flow restriction as the fluid passes through it.

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Discussion Comments


Horizontal plane ball valves - most common and most are L-port configuration. Center port is always the common port. Flow goes in center port to and turns left or turns right. Or flow comes from left or right and diverts out the center port. There is no shut off position and there is mixing of the side ports when the valve is in transition.

This can be a desirable feature if you are putting water in two different tanks and don't want to dead head the pump when switching tanks. This valve can also be used as a shut off valve if the ball is rotated and then the handle is repositioned, but it would be less expensive to use a two-way ball valve.

T-port horizontal plane ball valves can be used for a straight through and a divert valve. In the straight through position there is less pressure drop than when using an L port valve.

T-port horizontal plane valve can also be used so that the center port is common and you either have flow to the left port or you have flow to all three ports at once.

Say you wanted to use one paint sprayer or perhaps two sprayers at the same time.

Bottom entry ball valve - can be used much like a horizontal plane three-way L port ball valve or can be ported so that you select from the left port, the center port (off and no mixing) or the right port.


How can you design a ball in a ball valve? Is there any special formula?


Yes, some ball valves have the common opening around the axis of the ball's rotation. However, if you wanted more selections available, a T would also work. Then you could have A connected to B, A connected to B and C, or B connected to C, depending on the rotation of the T.


I disagree with your explanation of how a three way valve operates. I have a three way valve that only takes a quarter turn to direct the flow to either outlet. I have drawn the "T" configuration you propose. It would take a half turn to change the selection from one outlet to the other and at the quarter turn point either all three ports are connected or the two outlet ports are connected. I submit that the three way valve has two separate "L" shaped circuits drilled into the ball. In this arrangement the two outlets are never connected which is usually desirable. A single source, the center port can be directed to either end port or in reverse two sources (end ports) can be connected to one center port. In the latter the two sources would be isolated.

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    • The outside appearance of a ball valve.
      By: Sergey Yarochkin
      The outside appearance of a ball valve.
    • A trunnion ball valve is suitable for higher pressure valves.
      By: alex555
      A trunnion ball valve is suitable for higher pressure valves.