A centerline (concentric) butterfly valve rotates a resilient-seated disc 90 degrees to open or close. With a wafer body clamped between two pipe flanges and a hand lever or gear, it is the most common, lowest-cost way to get fast, bubble-tight on/off control in water, HVAC, and low-pressure process lines.
What "Centerline" Means
A centerline butterfly valve is the simplest of the three offset designs. The stem axis, the disc center, and the pipe bore centerline all coincide-there is zero offset. As the disc turns, it presses directly against a soft (resilient) seat moulded or cartridge-fitted in the body. In the closed position the disc squeezes the seat into elastic deformation, which produces a tight seal on both sides (bidirectional, bubble-tight) at low torque.
Specification
| Design |
Centerline / concentric (zero offset), resilient seated |
| Body style | Wafer (also lug / double-flange for the type) |
| Pressure class | PN6, PN10, PN16 (0.6 / 1.0 / 1.6 MPa; ~Class 150) |
| Size range | DN50–DN800 (NPS 2–32) |
| Operation | Lever (small); worm gear (large); pneumatic / electric available |
| Temperature | Seat-limited: see seat table (about −40°C to +230°C) |
Body, Disc, and Seat Materials
| Part | Typical material | Use |
|---|---|---|
| Body | Cast iron (GG25), ductile iron (GGG40 / QT450), carbon steel (WCB), stainless steel (CF8 / CF8M) | Iron for water/low pressure; CS for broader temperature; SS for corrosive or sanitary service |
| Disc | Ductile iron with nylon or EPDM coating, stainless steel, nickel-plated ductile iron | Coating protects the disc and provides the sealing face on some designs |
| Stem | Stainless 416 / 304 / 17-4PH, or plated carbon steel | Sized so it cannot shear at maximum differential pressure |
Seat (liner) materials and temperature limits
| Seat | Temperature | Best for | Avoid |
|---|---|---|---|
| NBR (Buna-N) | −20°C to +80°C | Oils, fuels, greases, hydraulic fluid | Water/steam, ozone, strong acids |
| EPDM | −40°C to +120°C | Water, wastewater, HVAC, low-pressure steam, outdoor | Oils, hydrocarbons, fuels |
| FKM (Viton) | −20°C to +200°C | Chemicals, solvents, hydrocarbons, heat | Low temperatures (<−20°C), amines |
| PTFE | −40°C to +230°C | Aggressive chemicals, steam, near-universal compatibility | Very high pressure (extrusion risk) |
Structure and Features
Wafer body: the valve has no flanges of its own. It is sandwiched between two pipe flanges and held by the flange bolts passing through it. This makes it compact, light, and easy to install in tight layouts.
Manual drive: a hand lever is used for smaller sizes; a worm-gear handwheel is added for larger diameters where lever force would be too high. No power supply is needed.
Quick operation: a 90-degree turn takes the valve from fully open to fully closed, so it is well suited to frequent on/off duty.
Any orientation: the simple, balanced design can be mounted in any position.
Bidirectional shutoff: the resilient seat seals in both flow directions with zero leakage when new.
Standards and Testing
Design & manufacture: GB/T 12238, API 609 (Category A, concentric), EN 593, BS 5155
Face-to-face: GB/T 12221, API 609, ISO 5752 (short pattern), EN 558
Flange drilling: ASME B16.5, GB/T 9113, EN 1092
Testing: API 598, GB/T 13927, ISO 5208 (shell, seat, and back-seat tests)
Where It Fits-and Where It Does Not
Centerline butterfly valves are widely used in water supply and drainage, HVAC, cooling-water systems, wastewater, low-pressure process lines, and chemical service where the seat is chemically compatible. Hygienic (FDA-grade EPDM or PTFE) versions serve food, beverage, and pharmaceutical lines.
Steam: soft-seated centerline valves suit only low-pressure, moderate-temperature steam. EPDM is usable to about 120°C and PTFE to higher temperatures; for high-pressure or high-temperature steam, use a double-offset or metal-seated (triple-offset) valve instead.
Cryogenic (LNG, ~−162°C): standard rubber or PTFE seats are not suitable. Cryogenic service requires special low-temperature elastomers or, more commonly, a metal-seated triple-offset design. Do not specify a standard centerline valve for LNG lines.
On/Off vs Throttling
A centerline butterfly valve can modulate flow, and its inherent flow characteristic is approximately equal-percentage (modified)-not linear. Because the disc stays in the flow path and the soft seat wears, a centerline resilient-seated valve is best kept to occasional or coarse throttling. For continuous or precise regulation, a double-offset (double-eccentric) or metal-seated (triple-offset) butterfly valve is the better choice.
Centerline vs Double-Offset vs Triple-Offset
| Design | Offset | Seat | Typical use |
|---|---|---|---|
| Centerline (concentric) | Zero | Resilient (rubber/PTFE) | On/off, low pressure, water/HVAC/utility |
| Double-offset | Two | Resilient or polymer | Throttling, higher temperature, chemicals |
| Triple-offset | Three | Metal-to-metal | High pressure/temperature, steam, cryogenic, severe service |
Maintenance
For the manual lever or gear version, keep the drive simple: check the flange bolts for tightness, keep the stem and gear lubricated, and inspect the packing and seat for wear or leakage. Replace the cartridge seat or packing if the valve starts to leak at the seat or stem. (Pneumatic and electric actuators add their own checks-power supply, signal, and motor-and are serviced as separate units.)
Manual Wafer Type Centerline Butterfly Valve in stock
FAQ
What is a centerline (concentric) butterfly valve?
It is the simplest butterfly-valve design: the stem axis, the disc center, and the pipe bore centerline all coincide (zero offset). A resilient (rubber or polymer) seat is squeezed by the disc as it closes, giving bubble-tight, bidirectional shutoff with low torque. It is mainly used for on/off service at low to moderate pressure and temperature.
What does "wafer type" mean and how is it installed?
A wafer body has no flanges of its own. It is placed between two pipe flanges and held by the flange bolts that pass through it. This keeps the valve compact and light. Wafer valves are supported by the pipeline on both sides, so they are not meant to hold a dead-ended pipe; for end-of-line service, a lug-type body with threaded inserts is used instead.
What seat materials are available and what temperatures do they handle?
NBR (Buna-N) covers about -20 to +80°C and resists oils and fuels; EPDM covers -40 to +120°C and is the default for water, HVAC, and low-pressure steam; FKM (Viton) covers -20 to +200°C for chemicals and heat; PTFE covers -40 to +230°C for aggressive media and steam. No single seat covers the whole range, so the seat is chosen for the actual fluid and temperature.
Can a centerline butterfly valve be used for throttling or flow regulation?
It can modulate flow, but because the disc stays in the flow path and the soft seat wears, a centerline resilient-seated valve is best limited to occasional or coarse throttling. For continuous or precise control, a double-offset (double-eccentric) or metal-seated (triple-offset) butterfly valve is the better choice. Its inherent flow characteristic is approximately equal-percentage (modified), not linear.
What pressure classes and sizes are typical for a manual wafer centerline valve?
Soft-seated centerline butterfly valves are low-pressure devices, typically PN6, PN10, and PN16 (about 0.6, 1.0, and 1.6 MPa; Class 150 equivalent). Common sizes run from DN50 to DN800 (NPS 2 to 32). A manual lever is practical up to roughly DN150–DN200; larger valves use a worm-gear handwheel, and pneumatic or electric actuators are added for automation.
Which standards apply to centerline butterfly valves?
Design and manufacture follow GB/T 12238, API 609 (Category A, concentric), EN 593, and BS 5155. Face-to-face dimensions follow GB/T 12221, API 609, ISO 5752 (short pattern), and EN 558. Flange drilling follows ASME B16.5, GB/T 9113, or EN 1092, and testing follows API 598, GB/T 13927, or ISO 5208.