Description
The Elbow That Connects, Not Just Turns
Most elbows do one job: change direction. A connection elbow does two: change direction AND provide a serviceable joint at an equipment interface, inspection point, or transition between duct types. The connection function — flanged, socket-fit, or compression — determines how the elbow is specified and installed. A standard butt-weld elbow that’s welded into the middle of a duct run is permanent. A flanged connection elbow at a fan inlet is removable — and that removability is the reason for specifying it.
Connection elbows serve where duct meets equipment, where duct changes material or cross-section, and where future access for cleaning or inspection is required. For standard elbows, see our PP Duct Elbow main page; for specific angle options, see 90 Degree and 45 Degree product pages.
Connection Types for Elbows
| Connection Type | Elbow Ends | Best For |
|---|---|---|
| Weld-end both sides | Both ends plain (butt-weld) — permanent joint to straight duct | In-line direction changes in continuous duct runs where no future disassembly is needed |
| Flanged one end | One end flanged, one end weld — flanged end connects to equipment flange; weld end joins duct | Equipment connections: fan inlet/outlet, scrubber nozzle, damper flange, filter housing |
| Flanged both ends | Both ends flanged — removable elbow for equipment access | Elbow at equipment inlet that must be removed for equipment extraction or internal cleaning |
| Socket one end | One end socket (slip-fit with seal), one end weld — quick-connect to small-diameter branch | Lab bench connections, instrument vent lines, temporary or reconfigurable setups |
Round and Square Connection Elbows
Connection elbows are produced in both round and square cross-sections, with transition elbows available for round-to-square connections:
- Round connection elbows. Standard for most industrial ventilation. Round flange faces are easier to seal than square — uniform bolt circle provides even gasket compression. Round socket connections use O-ring seals for quick assembly. Available in 45deg and 90deg, DN15-DN500 injection-molded.
- Square connection elbows. For rectangular duct systems. Square flanges require careful bolt spacing to maintain uniform gasket compression — the flat sides between corner bolts tend to have lower compression than the corners. Thicker flange material or closer bolt spacing compensates.
- Square-to-round transition elbows. Changing direction AND cross-section in one fitting. One end square (matches rectangular duct), one end round (matches round fan inlet or scrubber nozzle). The transition through the bend must manage both the direction change and the cross-section change without flow separation — the elbow length and internal contour are engineered for the specific dimensions.
Gasket Selection for Flanged Connection Elbows
The gasket is the sealing element in a flanged connection elbow. Selecting the wrong gasket material for your chemical environment means the joint leaks — not from flange failure, but from gasket degradation:
- EPDM. General service. Good for mild acids and alkalis, water, and non-aggressive ventilation. Temperature range -30 to 120degC. Most cost-effective. Not suitable for solvents or oils — EPDM swells on contact with hydrocarbons.
- FKM (Viton). Chemical service. Excellent resistance to solvents, oils, chlorinated compounds, and aggressive chemicals. Temperature range -20 to 200degC. Higher cost than EPDM. The standard choice for chemical plant, pharmaceutical, and solvent-handling exhaust systems.
- PTFE. Universal chemical resistance. For the most aggressive mixed-chemical exhaust where no elastomer is adequate. Higher cost, requires higher bolt load for sealing due to lower compressibility. Used where gasket replacement access is difficult and maximum service life is essential.
For flange kits including gaskets and fasteners, see our Air Duct Connections & Flanges page.
Send your connection requirements to xicheng023@outlook.com. We’ll specify the right connection type, gasket material, and provide a quotation. WhatsApp: +86 18927456906.
