Straight Union

A straight union is a three-piece pipe fitting designed to join two sections of pipe in a straight line while allowing quick and easy disconnection without disturbing the surrounding pipework. It is an essential component in utility, process, and instrument piping systems where maintenance access, equipment removal, or line modifications are required.

Three-Piece Design

The straight union consists of three components that work together to create a secure, leak-free joint that can be assembled and disassembled repeatedly:

• Body Half A — the upstream body piece with a female threaded end that connects to the incoming pipe.
• Body Half B — the downstream body piece with a female threaded end that connects to the outgoing pipe.
• Union Nut — a threaded collar that draws the two body halves together, compressing the seat seal to form a pressure-tight joint. Unscrewing the nut allows the two halves to separate instantly.

This design eliminates the need to cut or unthread pipe runs when servicing inline equipment such as valves, meters, or filters.

Materials

Straight unions are available in a range of materials to suit different service conditions and fluid compatibility requirements:

• Brass — suitable for water, gas, compressed air, and general utility services.
• Carbon Steel (CS) — used in higher-pressure industrial and process piping applications.
• Stainless Steel (SS) — ideal for corrosive media, hygienic applications, and instrument lines.
• Galvanised Iron (GI) — provides corrosion resistance for water distribution and general plumbing systems.

Thread Standards & Size Range

Straight unions are available with BSP (British Standard Pipe) or NPT (National Pipe Taper) threaded ends to suit regional piping standards. The size range covers 1/4" to 4", accommodating small instrument lines through to larger process and utility headers.

Seat & Seal Options

The sealing interface between the two body halves is critical to leak-free performance. Two seat options are available:

• PTFE O-ring — excellent chemical resistance, suitable for a wide range of process fluids and temperatures.
• Rubber O-ring — cost-effective sealing for water, air, and general utility services.

Typical Applications

• Utility piping systems (water, compressed air, steam)
• Industrial process piping for chemicals, oils, and gases
• Instrument piping for pressure gauges, transmitters, and control valves
• HVAC and building services pipework
• Maintenance connections where frequent disassembly is required