Ball Valve Principle, Explained in 90°

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A ball valve is a valve that uses a spherical plug (the ball) with a through-boreas its closing element. The ball has a cylindrical passage (bore) through its center; rotating the ball by handle or actuator opens or shuts off the media flowing in the pipeline. It opens and closes with just a 90° turn, so it is also called a “quarter-turn valve”, and is widely used in water, oil, gas and chemical pipelines.

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Cut a ball valve open, and there are only a few key parts:

▲ Cutaway illustration: blue flow enters from the left, passes through the ball bore and exits on the right — open position

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Pressure-retaining shell that connects to the piping

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Spherical closing element with a through-bore — the “heart” of the valve

3

Holds and seals against the ball; often made of PTFE

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Connects the ball to the handle/actuator and transmits torque

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The control component that drives the stem

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Seals the stem-to-body gap to prevent external leakage

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Opening or closing a ball valve simply comes down to whether the ball bore lines up with the flow path. Compare the two diagrams below:

Open: bore aligned, media passes through

Closed: ball rotated 90°, media shut off

Key move: the handle rotates the ball 90° (a quarter turn) — handle parallel to the pipe means open; perpendicular means closed.

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Opens and closes in a 90° turn; ideal for frequent cycling

Full-open flow path is straight and nearly full-bore; minimal pressure loss

Excellent shut-off performance for water, oil, gas and many chemical media

Small size and light weight; easy to install and maintain

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Floating ball valve: media pressure presses the ball against the downstream seat for sealing; most common for small-to-medium sizes and low-to-medium pressure.

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Trunnion-mounted ball valve: the ball is supported by top and bottom stems, giving low operating torque; suited for large sizes and high pressure.

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By body construction: one-piece, two-piece or three-piece; top-entry ball valves allow internal parts to be removed from the top for easy online maintenance.

Next time you see a ball valve with a lever on a pipeline, remember: handle parallel to the pipe = open; perpendicular = closed. That 90° is the whole secret.