The sealing section of the disc and the disc’s rotational center lie on the same straight line, and the rotational center is aligned with the centerline of the valve body. (Stem, disc, and body centerlines coincide.)
Because the valve stem axis penetrates the sealing cross-section of the disc, some impact on sealing performance exists. Therefore, this type is typically used with elastic sealing materials like EPDM or PTFE. Sealing is achieved by the disc pressing against the seat, causing the elastic seat to deform. However, this design results in more wear on the seat. Common centerline models include D371X, D341X, etc.
Key Features of Centerline Soft-Seated Butterfly Valves
✅ Coaxial triple center design enables low operating torque
✅ Reliable sealing performance—zero leakage under low pressure
✅ Lightweight and compact—easy to install and maintain
✅ Low cost—more cost-effective than gate or ball valves
✅ Multiple actuator options—manual (handle/gear), electric, pneumatic
Soft-Seated Butterfly Valve Selection Guide
By Nominal Diameter
|
Pipeline Diameter (DN) |
Recommended Valve Type |
|
DN50–DN300 |
Wafer-type centerline valve |
|
DN350–DN1200 |
Flanged-type butterfly valve |
By Media and Seat Material
|
Medium |
Recommended Seat Material |
|
Tap water, hot water |
EPDM |
|
Oils, air |
NBR |
|
Mild acids and bases |
PTFE |
|
Food and beverage fluids |
Food-grade EPDM |
By Actuation Method
|
Operation Frequency/Need |
Recommended Actuation |
|
Manual control, budget focus |
Handle or gear operator |
|
Remote or frequent operation |
Electric or pneumatic actuator |
|
Limited installation space |
Wafer-type preferred |
Centerline soft-seated butterfly valves (EPDM, NBR, PTFE, etc.) are widely used in low-pressure and ambient temperature systems such as water supply/drainage, HVAC, environmental engineering, and light chemical industries. Though simple and easy to operate, the elastic seat is prone to aging, wear, swelling, or hardening over time and must be regularly maintained.
Installation Steps
Pre-Installation Inspection
Confirm the nameplate specifications (model, size, pressure, temperature) match system requirements.
Disc should operate smoothly with no jamming. The rubber seat must be intact—no cracks or aging.
Installation Orientation
Recommended installation on horizontal pipelines with stem upright or horizontal.
Avoid “stem down” installation to prevent accumulation and corrosion.
For bi-directional flow, use bi-directional sealing structure (must be specified).
Valve Position During Installation
Keep valve in fully closed position during installation to prevent damage from contact with pipe or flange edges.
Wafer-Type Installation Notes
Use short pattern flanges (e.g., EN 1092-1 Type 11, GB/T 9115).
Use at least 8 bolts, tighten crosswise in stages to ensure even loading and prevent body deformation.
Flange Face Check
Ensure flanges are clean, flat, free from scratches, burrs, or welding slag.
Add gaskets (rubber, asbestos, etc.) to improve sealing performance.
Actuator Interface Calibration
For electric/pneumatic units, calibrate open/close limits before installation to avoid seal damage.
Connect limit switches and signal feedback terminals; perform on-site system test.
In end-of-line or frequently cycled positions, consider adding a check valve or slow-closing device to prevent disc/seal damage from reverse flow.
Temperature Effects
EPDM/NBR temperature range: typically -20°C to 120°C (varies by material).
For hot water, steam, or oils: use high-temp rubber or switch to eccentric metal-seated valve.
Pressure Testing & Commissioning
After installation, conduct pressure test (typically 1.5x rated pressure) or water/air test.
Observe disc movement and check for flange seal leakage.
Initial Operation Monitoring
Within the first 24 hours, monitor opening frequency, sealing performance, and actuator feedback for anomalies.
Routine Inspection Table
|
Inspection Item |
Frequency |
Description |
|
Seat elasticity/aging |
Every 3–6 mo |
Check for hardening, cracks, peeling |
|
Stem packing seal |
Every 3–6 mo |
Check gland for leakage |
|
Open/close flexibility |
Monthly |
Manual cycle test for jamming or friction |
|
Sealing performance |
Semi-annually |
Water/air pressure test—check for internal/external leak |
|
Handle/gear condition |
Annually |
Lubricate mechanism to prevent rust and jamming |
Seat Maintenance Tips
Avoid Overpressure: Designed for PN10–PN16 systems. Overpressure can permanently deform seat.
Media Compatibility: EPDM not suitable for oils; NBR unsuitable for strong acids/alkalis.
Regular Cleaning: Flush valve chamber if media contains sand, debris, or scale.
Timely Replacement: Replace damaged or aged seat with OEM parts. Do not use DIY alternatives.
Actuator Maintenance
Gearbox: Lubricate every 6–12 months. Check for smooth rotation.
Handle: Check locking devices (limit screw/pin) regularly.
Electric/Pneumatic Actuator:
Maintain motor, positioner, and seat per manufacturer.
Verify limit setting and feedback signal accuracy.
Ensure stable power, control, and air supply.
Common Faults & Remedies
|
Fault |
Cause |
Solution |
|
Leaking Seal |
Aged seat, debris, improper closure |
Clean/replace seat, check actuator |
|
Difficult Operation |
Shaft rust, bearing wear, gear jam |
Lubricate or replace transmission parts |
|
Handle Falling Off |
Over-torque, loose fasteners |
Replace locking pin, tighten components |
|
Packing Leakage |
Aged packing or loose gland |
Recompress or replace graphite packing |
|
Disc/Pipe Interference |
Misalignment or eccentric flange |
Reinstall with alignment or replace flanges |
Shutdown & Seasonal Protection
Store in slightly open position to avoid prolonged seat compression.
In winter, drain water to prevent freezing and rubber cracking.
In humid environments, apply anti-rust agent or regularly wipe/maintain metal surfaces.
Case 1: Municipal Water Supply
In a DN800 mainline, soft-seated butterfly valve replaced gate valve.
Reduced construction time by 2 days, saved 20% in space, and extended maintenance interval from 1 year to 2 years.
Case 2: Central Air Conditioning System
In a commercial cooling system, DN200 butterfly valve replaced ball valve.
Achieved faster control, 30% cost reduction, and integration with building automation feedback system.
Seal Material Selection Guide
Valve performance largely depends on seat material.
Below is a comparison of common sealing materials:
|
Material |
Properties |
Suitable Media |
Temp Range (°C) |
|
EPDM |
Water-resistant, ozone/aging resistant, optional food grade |
Tap water, hot water, food-grade fluids |
-20 ~ +120 |
|
NBR |
Oil/abrasion/pressure resistant, poor ozone resistance |
Oils, hydraulic fluids, air |
-20 ~ +100 |
|
PTFE |
Excellent chemical resistance, non-stick, heat tolerant |
Acids, corrosive chemicals |
-30 ~ +150 |
|
CR |
Weather/ozone resistant, some oil resistance |
Air, weak acid/alkaline systems |
-20 ~ +90 |
|
NR |
Excellent elasticity, poor oil resistance |
Clean water, air |
-30 ~ +70 |
Water supply systems → Use EPDM
Mildly corrosive media → Use PTFE
Oily fluids → Use NBR
Food/pharmaceutical → Use Food-grade EPDM or PTFE
|
Issue |
Cause |
Solution |
|
Seal Leakage |
Seat aging or deformation |
Inspect and replace seat regularly |
|
Difficulty Operating |
Shaft/disc corrosion or jamming |
Clean/replace parts, apply lubrication |
|
Disc Can’t Fully Open/Close |
Installation misalignment or blockage |
Reinstall correctly and clear obstructions |
|
Actuator Malfunction |
Power/air failure, gear jam, misalignment |
Inspect power/air supply, reset limit switches |
|
Seat Dislodged or Cut |
Fast disc motion, debris intrusion |
Slow actuation, install filters |
Typical Applications
Municipal Water Networks: Used for DN50–DN1200 trunk and branch pipelines due to high cost-efficiency.
Building HVAC Systems: Regulating cooling water and air conditioning loops.
Water Treatment Plants: Installed at inlets, sedimentation tanks, and areas requiring easy maintenance.
Fire Protection Systems: Preferred for rapid actuation in fire water lines.
