A flange is a flat, disc-shaped piece used to create a strong, removable connection between two components. In its most common form, a flange joins pipes, valves, pumps, or other equipment in industrial systems. But the term also shows up in plumbing, breastfeeding, and medical care, where it refers to slightly different objects that all share the same basic idea: a protruding rim or collar that helps attach, seal, or stabilize something.
How Industrial Flanges Work
In piping and mechanical engineering, flanges are the standard way to connect sections of pipe to each other or to equipment like pumps and valves. Two flanges are bolted together face-to-face with a gasket sandwiched between them. The gasket compresses under bolt pressure to create a tight seal that prevents leaks. This bolted design is what makes flanges so practical: unlike welded joints, a flanged connection can be taken apart for cleaning, inspection, or replacement without cutting into the pipe.
The gasket material depends on what’s flowing through the system. Rubber gaskets work well for water and steam lines. Teflon gaskets resist chemical reactions, making them common in pharmaceutical and food processing plants. For extreme heat and pressure, like in power plants or oil refineries, metal gaskets made from stainless steel or soft iron provide the necessary durability. Some gaskets combine both, wrapping a soft filler like graphite inside a metallic shell for a balance of strength and flexibility.
Common Types of Industrial Flanges
Not all flanges are built the same way, and the differences matter for strength, cost, and ease of installation.
- Slip-on flanges slide over the outside of a pipe and are welded in place on both sides. They’re cheaper and easier to install, which makes them a good fit for low-pressure systems like water supply lines and HVAC. The tradeoff is less structural strength, since the flange isn’t integrated into the pipe itself.
- Weld-neck flanges have a long, tapered hub that gets welded directly to the pipe, creating a smooth transition that distributes stress evenly across the joint. This makes them the go-to choice for high-pressure and high-temperature environments like oil and gas pipelines, chemical processing plants, and power generation systems.
- Threaded flanges screw onto pipes without any welding at all. They’re used in smaller, low-pressure systems where a quick, simple connection is enough.
Why Bolt Tightening Matters
Even the right flange and gasket combination will leak if the bolts aren’t tightened correctly. The industry standard since 1938 is a star pattern (also called a criss-cross pattern), where you tighten bolts on opposite sides of the flange in a diagonal sequence rather than going around the circle. This distributes pressure evenly across the gasket. You don’t tighten each bolt to full pressure on the first pass. Instead, you gradually increase torque over multiple passes until every bolt reaches the target specification. For flanges with more than 12 bolts, modified star or quadrant patterns help maintain even compression across the larger surface.
The Toilet Flange
In home plumbing, a flange is the ring-shaped fitting that connects your toilet to the drain pipe in the floor. It sits on top of the finished floor and anchors the toilet in place with bolts. The correct installation height is about 1/4 inch above the finished floor surface. A flange that sits flush with or below the floor is a common cause of toilet leaks and rocking.
If you’re replacing flooring and the flange ends up too low, flange extenders (sold in 1/4-inch and 1/2-inch sizes) raise it back to the correct height. For a flange that’s just slightly below the 1/4-inch mark, an extra-thick wax ring can compensate for the small gap. The key rule: always install your finished floor before setting the flange, and make sure everything is level.
Breast Pump Flanges
In breastfeeding, a flange (sometimes called a breast shield) is the funnel-shaped piece that fits over the nipple and areola on a breast pump. Getting the right size is critical. A flange that’s too small will rub and abrade the nipple, potentially causing wounds at the base. A flange that’s too large lets excess tissue get pulled into the tunnel, causing swelling, stretching, and cracking. A common mistake is repeatedly sizing up to escape the pain of an initial poor fit, which can make the tissue damage worse over time.
Most breast pump flanges are made from hard plastic, though some brands offer versions made from medical-grade silicone. Medical-grade silicone is specifically tested for biocompatibility, meaning it won’t cause irritation, toxicity, or allergic reactions when it contacts skin. It’s also softer and more flexible, which can make pumping more comfortable. The material withstands repeated sterilization through boiling, steam, or other methods without breaking down.
Ostomy Flanges
In ostomy care, the flange (also called a skin barrier or wafer) is the adhesive piece that sticks to the skin around a stoma and connects to the collection pouch. It comes in two main shapes. Flat flanges sit level against the skin and work well when the stoma protrudes enough on its own. Convex flanges curve inward, pressing gently on the skin around the stoma to help it protrude outward. This prevents output from sneaking under the barrier and causing leaks, which is especially useful for stomas that sit flush with or below the skin surface.
The choice between flat and convex depends on individual anatomy, and the fit directly affects both comfort and seal reliability. Like breast pump flanges, ostomy flanges that contact the body are typically made from skin-friendly materials designed to minimize irritation on sensitive or compromised skin.