Coupling, Slip x Slip PVC Schedule 40 4" x 1-1/4" (429-418)

The 429-418 is a 4" x 1-1/4" Schedule 40 PVC Reducing Coupling with Slip x Slip connections. This fitting joins two different pipe sizes inline — one socket accepts 4" PVC pipe and the opposite socket accepts 1-1/4" PVC pipe, both solvent cemented for a permanent, pressure-rated bond. The reduction from 4" to 1-1/4" is accomplished in a single fitting body, eliminating the need for a full-size coupling plus a separate reducer or bushing to achieve the same size transition in the pipe run.

The 4" to 1-1/4" size step is among the most aggressive inline reductions in the Schedule 40 reducing coupling category — a nearly three-increment drop from a large-capacity main to a small-diameter downstream pipe. At this size differential, the 429-418 is a purpose-specific reduction fitting for applications where a large-diameter supply or collection main must transition directly to a much smaller downstream pipe: equipment inlets significantly undersized relative to the supply main, drainage systems where a large-diameter collection line discharges to a smaller outlet, branch connections off heavily oversized headers, and similar configurations where the upstream and downstream pipe sizes are intentionally and substantially mismatched.

Both sockets are slip connections accepting solvent cement — the 4" socket on the large side and the 1-1/4" socket on the small side — making the entire assembly a fully cemented, permanent, solvent-welded reduction with no threads involved. Proper solvent cementing practice applies to both ends: primer should be applied to both the pipe end and socket interior on each side before cement application, with pipe inserted fully to socket depth and held in alignment through the set period. At 4", the large-side socket requires particular attention to full primer and cement coverage given the larger surface area of the joint.

The 429-418 is a direct sibling to the 429-419 (4" x 1-1/2") in the same reducing coupling series — same large-end size, same fitting type, same schedule, one increment smaller on the outlet. Buyers who need a 4" to 1-1/4" reduction rather than a 4" to 1-1/2" reduction should confirm the outlet size carefully before ordering, as the two part numbers differ by a single digit and the socket size difference between 1-1/4" and 1-1/2" pipe is not always immediately obvious by visual inspection of the fitting alone.

Manufactured in white Schedule 40 PVC, the 429-418 provides solid corrosion resistance across a broad range of fluids, good impact performance under normal service conditions, and a substantially lower installed weight compared to metal reducing couplings of equivalent size. While Schedule 40 carries a lower pressure rating than Schedule 80 at equivalent sizes, it remains the correct specification for the majority of commercial, irrigation, and light industrial applications where system pressures fall within its rated range and the cost and weight advantages of Schedule 40 are the governing specification factors.

Specifications:

⚠️ Note: In a reducing fitting, the smaller end governs the pressure rating. Confirm correct pipe size insertion on each end before cementing — the 4" and 1-1/4" sockets are visually distinct but the 1-1/4" socket is close in appearance to 1-1/2"; verify pipe size before assembly. Use primer on both sockets and both pipe ends before cement application; do not skip priming on the 4" socket. Once cemented, neither end can be disassembled without cutting pipe. Confirm 429-418 (1-1/4" outlet) vs. 429-419 (1-1/2" outlet) before ordering.

Industries & Applications:

• Irrigation & Agricultural Systems — Transitions a 4" PVC supply main down to a 1-1/4" pipe run at a distribution point, equipment inlet, or zone connection where the supply header is substantially oversized relative to the downstream circuit and a compact inline reduction eliminates the need for a multi-fitting bushing and coupling assembly at the transition point
• Water & Wastewater Treatment — Used where a 4" collection or distribution main must transition to a 1-1/4" downstream pipe serving a low-flow sub-circuit, small equipment connection, or minor branch that does not warrant continuing the full 4" main bore to that point
• Industrial Process Piping — Reduces a 4" process line inline to a 1-1/4" pipe run at equipment inlets, instrumentation connections, and process sub-circuits where the upstream pipe is substantially oversized relative to the equipment or downstream system it supplies and a direct inline reduction is the most compact solution
• Commercial Plumbing & Mechanical Systems — Applied in commercial building utility piping where a 4" service main must be reduced to a 1-1/4" branch or equipment connection in a single fitting, particularly in renovation and retrofit scenarios where space constraints preclude a multi-component reducer assembly
• Pump Station & Equipment Connections — Installed where a 4" suction or discharge header transitions directly to a 1-1/4" equipment port or secondary pipe run, concentrating the size transition into a single cemented fitting at the connection point
• Swimming Pool & Aquatic Facilities — Used in pool and spa equipment pad plumbing where large-diameter supply or return lines transition to 1-1/4" equipment connections on older or smaller-capacity filters, heaters, and chemical feeders specified with 1-1/4" pipe inlets