Union (O-Ring Type), FPT x FPT PVC Schedule 40 4" (498-040)

The 4" PVC Schedule 40 O-Ring Union (498-040) is a full-size, threaded union designed to provide a permanent, leak-free, and fully demountable connection point in a 4" PVC piping system — allowing the pipe run to be broken apart and reassembled at the union joint without cutting pipe, disturbing adjacent fittings, or requiring solvent cement for reassembly. Both ends use female pipe thread (FPT) connections that accept standard 4" male-threaded pipe, nipples, or fittings, and the union body seals across the face joint with a precision O-ring rather than a flat gasket — delivering a more consistent, reliable seal across repeated disassembly and reassembly cycles than a gasket-style union provides.

The O-ring seal is the defining performance characteristic of this union type and a primary reason it is specified over flat-face gasket unions in demanding applications. The O-ring seats in a machined groove in the union body, compressing evenly and consistently when the union nut is tightened — maintaining a leak-free seal across a wider range of torque variation, temperature cycling, and repeated service cycles than a flat gasket that can compress unevenly, take a set, or deteriorate with repeated use. In chemical processing, industrial fluid handling, and commercial mechanical systems where union joints are opened and re-sealed regularly for maintenance, inspection, or equipment service, the O-ring design provides a more dependable long-term sealing solution.

At 4" diameter, this is a large-format union — one of the larger threaded union sizes in the Schedule 40 PVC catalog — and the FPT x FPT connection type makes it a natural fit for systems where the adjacent pipe ends are already male-threaded: threaded nipples on either side of a valve or equipment connection, male-threaded adapters at a pump suction or discharge port, or any system configuration where threaded connections flank the union point. The union nut allows the joint to be broken at the face seal without disturbing either threaded end connection, making equipment removal, valve replacement, and system reconfiguration straightforward operations that do not require pipe cutting or re-cementing.

Manufactured from rigid PVC to Schedule 40 specifications and dimensionally compliant with ASTM D2466, the 498-040 ensures compatibility with Schedule 40 pipe and fittings at both FPT ends. NSF 61 certification confirms suitability for potable water contact across applicable uses.

Specifications:

Industries & Applications:

• Commercial & Industrial Plumbing — demountable union connections flanking large valves, strainers, and equipment in 4" primary distribution headers where regular maintenance access or equipment replacement is anticipated
• Chemical Processing — serviceable union joints in 4" chemical feed, dosing, and process fluid headers where O-ring sealing reliability across repeated disassembly cycles is a design requirement
• Industrial Process Piping — union connections at pump suction and discharge ports, inline instruments, and equipment isolation points in plant utility and process fluid systems where the union must be broken regularly for maintenance
• Water & Wastewater Treatment — demountable connections at valves, meters, and equipment in treatment plant process piping where 4" threaded unions provide access without disturbing the surrounding system
• Irrigation & Agriculture — serviceable union connections in 4" threaded mainline headers at valve stations, filter assemblies, and injection equipment where seasonal or periodic disassembly is required
• Aquaculture & Food Processing — O-ring sealed demountable connections in recirculating systems and sanitary fluid handling installations where reliable re-sealing across frequent maintenance cycles is a performance requirement