The fittings (pipe joints) in a UPVC drainage system are the functional hubs strictly matched with the pipes. Their design directly determines the pipeline routing, branching logic, and sealing performance. According to the GB/T 5836.2-2018 standard, these fittings are primarily produced by injection molding, using materials consistent with the pipes to ensure the chemical stability and lifespan uniformity of the system.

I. Classification by Function and Structure (Core Dimension)

This is the most commonly used classification logic in engineering selection, directly corresponding to specific actions during construction.

1. Direction-Changing and Flow-Diverting Fittings

Used to alter fluid paths, forming the basis of pipeline layout.

● Elbow: The most common fitting for changing direction. For indoor drainage, 45° elbows are primarily used (reducing flow resistance, promoting smooth drainage) and 90° elbows (used for transitions between vertical stacks and horizontal runs or fixture connections). In special scenarios, there are also 90° elbows with a cleanout, facilitating future maintenance and clearing.

● Tee (Straight / Wye): Used for flow splitting or combining. Wye tees (typically 45° or 88°) are the preferred choice in drainage systems. Their streamlined design significantly reduces hydraulic resistance and noise, avoiding the "water hammer" phenomenon common with straight tees.

2. Reducing and Connecting Fittings

Used to handle pipe diameter changes and straight extensions.

● Reducer (Bushing): Commonly known as a "reducer," it connects pipes of different diameters (e.g., DN110 to DN75) to achieve system diameter transition.

● Coupling: Used to extend straight runs of same-diameter pipes. If it includes a rubber ring, it forms an expansion joint, used to compensate for pipe length changes due to thermal expansion and contraction.

3. Special Function Fittings

Address specific functional requirements within the drainage system.

● Trap (P-Trap / S-Trap): The key component for odor prevention. It uses a water seal retained in the trap's bend to block sewer gases. Must be installed beneath fixtures like sinks, floor drains, etc.

● Access Fitting and Cleanout: The "maintenance doors" of the system. An access fitting is typically installed on a vertical stack with a removable cover. A cleanout is often placed at the end of a horizontal run for clearing blockages.

● Floor Drain: A special fitting combining drainage and odor prevention, usually containing an internal water seal or mechanical seal.

II. Classification by Connection Method

The fitting's interface design dictates the installation process and must strictly correspond to the pipe connection method.

III. Key Points for System Matching of Fittings and Pipes

When selecting fittings, consider not just the individual part but also system compatibility:

● Material Consistency: Fittings must be selected from the same brand or standard as the UPVC pipes to prevent joint leakage due to differences in shrinkage rate or temperature resistance.

● Sound Attenuation Compatibility: If using spiral sound-attenuating pipes, it is essential to pair them with specialized low-noise fittings (with internal flow channels) to preserve the noise-reducing effect of the spiral flow.

● Environmental Attribute: According to GB/T 5836.1-2018, lead-free fittings (using calcium-zinc stabilizers) should be prioritized for indoor drainage to meet green building requirements.

Summary

UPVC drainage fittings are the "joints" that build an efficient drainage network. The selection logic follows a "function-oriented" approach: elbows for turns, tees for branches, traps for odor control, and access fittings for maintenance. During installation, it is imperative to ensure precise matching between the connection method (solvent cement / rubber ring) and the pipe type (solid wall / spiral) to achieve the operational goals of a zero-leakage, low-noise, and long-lasting system.