Ⅰ. Directional Change Fittings:
Elbows: The workhorses of redirection. Standard angles are 90 degrees (sharp turn) and 45 degrees (gentler turn), with variations like 22.5° and 60° for finer adjustments. They come in short-radius (tighter turn, higher friction loss) and long-radius (gentler turn, lower friction loss). Material and connection type must match the pipe.
Tees: Used to create branch lines. Standard tees have all three outlets the same size. Reducing tees have one or more outlets smaller than the main run, crucial for transitioning to smaller branch lines feeding sprinklers or hose connections. Crosses (four-way connections) are also possible but less common due to higher stress points.
Connection & Termination Fittings:
- Couplings: Connect two pieces of straight pipe end-to-end. Rigid couplings create a fixed joint. Flexible couplings (often incorporating rubber gaskets) allow for minor movement, vibration dampening, or slight misalignment, commonly used in seismic zones or where building settlement is expected.
- Unions: Similar to couplings but designed for easy disassembly without rotating the pipe. Essential for future maintenance or component replacement. They consist of a nut connecting two threaded or grooved end pieces.
- Caps: Seal the end of a pipe, permanently or temporarily closing off a line (e.g., at the end of a branch or during future system expansion planning).
- Plugs: Seal the end of a fitting opening (like an unused outlet on a tee or valve).
- Flanges: Provide a bolted connection point. Used to connect pipes to large valves, pumps, tanks, or where sections need to be easily removable for major maintenance. Require gaskets for a watertight seal.
- Nipples: Short lengths of threaded pipe used to extend connections or connect fittings closely together.
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Ⅱ. Flow Control & Branching Fittings:
Reducers: Transition pipe flow from one diameter to another. Concentric reducers maintain a centerline, used primarily in vertical pipes. Eccentric reducers have one flat side, used in horizontal pipes to prevent air pockets (installed flat side up) or sediment traps (flat side down). Essential for matching pipe sizes to flow requirements.
Wyes: Similar to tees but feature a branch connection at a 45-degree angle, offering lower resistance to flow than a standard tee. Often used where smoother flow diversion is critical.
Laterals: A specialized fitting combining a tee and an elbow, essentially creating a 90-degree branch line directly off the main run. Saves space and installation time compared to using separate tee and elbow fittings.
Grooved Fittings (A Dominant Modern Method):
While not a type of fitting per se, grooved mechanical joining is a dominant method for connecting pipes and fittings in modern fire protection. The pipe ends and fittings have precision grooves cut into them.
- Grooved Couplings: Housing segments with a rubber gasket are placed around the grooved pipe ends/fittings. Bolts are tightened, compressing the gasket and creating a rigid, leak-tight, self-restrained joint. This method is faster, safer (no hot work like welding), allows for some flexibility, and is highly reliable. Fittings designed for grooving include elbows, tees, reducers, crosses, caps, and flanges specifically manufactured with grooved ends.
Threaded Fittings (Traditional but Still Used):
Another connection method, involving tapered threads (NPT – National Pipe Tapered).
- Threaded Fittings: Elbows, tees, couplings, unions, caps, plugs, and nipples are manufactured with female or male NPT threads. While still common for smaller pipe sizes (typically 2″ and below), branch lines, and connections to valves/sprinklers, they are labor-intensive to install (requires threading and sealing compounds/tape) and can be prone to leaks if not done perfectly. Galvanized malleable iron is a common material.
Flanged Fittings:
As mentioned under connections, flanges are a connection type. Flanged fittings (elbows, tees, reducers) have integral flanges welded or cast onto their ends for bolting directly to other flanged components. Used for large pipes and critical connections to major equipment.
Material Considerations:
Fire pipe fittings are typically made from robust, corrosion-resistant materials:
- Ductile Iron: Strong, durable, widely used for grooved and flanged fittings.
- Malleable Iron: Traditionally used for threaded fittings.
- Carbon Steel: Used for welded fittings (less common in sprinklers today) and flanges.
- Stainless Steel: Used for superior corrosion resistance in harsh environments or specific system types.
- Bronze/Alloy: Sometimes used for specialized components or marine applications.
Ⅲ. Standards are Paramount:
All fire protection fittings must be manufactured, listed, and approved to stringent standards such as:
- UL (Underwriters Laboratories)
- FM (Factory Mutual) Approvals
- ANSI/AWWA Standards
- ASME Standards
Compliance with NFPA 13 (Standard for the Installation of Sprinkler Systems) and NFPA 14 (Standard for the Installation of Standpipe and Hose Systems) is mandatory. These standards dictate pressure ratings, materials, dimensions, and installation practices.