The ball valve is celebrated in fluid control for its quick, quarter-turn operation and reliability as an on/off isolation device A Guide to Ball Valves: How They Work, Their Types, and Why They Dominate the Industry. However, not all ball valves are built the same way. The construction of the valve body—specifically whether it is a single-piece, two-piece, three-piece, or a union design—has enormous implications for its installation, serviceability, and suitability for various applications.
This guide focuses on the three most common multi-piece designs, highlighting how their assembly simplifies critical maintenance tasks.
A Single Union Ball Valve features one union end connection and one fixed end connection (either threaded or socket fusion).
The Double Union Ball Valve, often called a True Union Ball Valve, is the gold standard for maintenance-friendly installations.
While plastic union valves dominate plumbing and lower-pressure industrial uses, metal valves—particularly the Three-Piece Ball Valve—offer the same maintenance benefits for high-pressure, high-temperature fluid control.
When selecting a ball valve, the decision often comes down to budget and service requirements.
| Valve Type | Key Feature | Primary Advantage | Typical Cost |
|---|---|---|---|
| Single Union | One disconnect point | Valve removal without major pipe cutting | Mid-Range |
| Double Union (True Union) | Two disconnect points | Full in-line repair or replacement of the body | Highest |
| Two-Piece/Flanged | Bolted end caps | Removable for maintenance when paired with unions | Mid to High |
| Three-Piece | Swing-out center | Quick in-line maintenance for metal valves | Highest (Metal) |
In highly cycling or abrasive environments, the savings from reduced downtime and simplified maintenance justify the investment in a True Union or Three-Piece design. For long-term performance, always select valves in line with recognized benchmarks like ASME B16.34 standard, covering materials, pressure ratings, and testing.
Routine inspections and maintenance—facilitated by these designs—are the most effective way to ensure valve reliability and extend service life.
