What Is a Ball Valve?

Quick Answer

A ball valve uses a hollow, perforated sphere rotated 90 degrees to open or close flow. Ball valves provide bubble-tight shut-off, fast operation, and low maintenance. They are the industry standard for pipeline isolation in oil and gas, available in floating (small sizes) and trunnion mounted (large sizes/high pressures) designs per API 6D and API 608.

Key Specifications

Feature	Details
Function	On/off isolation (quarter-turn operation)
Sealing	Ball-to-seat contact (soft or metal seats)
Bore types	Full bore (FB), reduced bore (RB), V-port
Design types	Floating ball, trunnion mounted
Body styles	Monolithic (one-piece), 2-piece, 3-piece
Entry	Side entry, top entry
Pipeline standard	API 6D
General standard	API 608
Pressure-temperature	ASME B16.34 Class 150-2500
Face-to-face	ASME B16.10
Body materials	A216 WCB (cast CS), A105 (forged), A351 CF8M (SS), F51 (duplex)
Sizes	1/2” to 60”+

How a Ball Valve Works

The ball sits between two seat rings inside the body. When the handle is parallel to the pipe, the bore of the ball aligns with the flow path and the valve is open. Rotating the handle 90 degrees turns the solid side of the ball toward the flow, blocking it completely. The seats press against the ball surface to create a bubble-tight seal.

Quarter-turn operation means fast opening and closing. A pipeline ball valve can be cycled from fully open to fully closed in under one second with a pneumatic actuator.

Floating vs Trunnion

In a floating ball design, the ball is not mechanically fixed. Line pressure pushes the ball against the downstream seat, creating the seal. Simple and effective for sizes up to about 8” and Class 300. Above these limits, the operating torque becomes excessive because the full line pressure acts on the ball.

In a trunnion mounted design, the ball is anchored on a fixed shaft (trunnion) at top and bottom. Spring-loaded seats press against the ball. This reduces operating torque dramatically and allows ball valves to be built in sizes up to 60” and Class 2500. Trunnion designs are standard for pipeline applications per API 6D.

Body Configurations

• One-piece (monolithic): body cast or forged as a single unit. Ball is installed during manufacturing. No in-line maintenance possible.
• Two-piece: body split at one joint. Ball can be removed from one end. Most common for general process service.
• Three-piece: body in three sections bolted together. Ball and seats can be removed without disturbing the piping. Preferred when regular maintenance or seat replacement is expected.

Typical Applications

Ball valves serve as block valves on pipelines, equipment isolation in refineries and gas plants, subsea shut-down valves, fire-safe emergency isolation, and instrument root valves. Their tight shut-off and low maintenance make them the preferred choice over gate valves for many modern installations.

Pro Tip

For sour service (H2S-containing fluids per NACE MR0175), specify trunnion ball valves with double piston effect (DPE) seats and body cavity relief. This prevents pressure buildup in the body cavity that could damage seats or cause unsafe conditions.

Read the full guide to valve types