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Selection and Installation Manual for Centerline Soft-Seated Butterfly Valves

2025-05-20 14:57:47

The centerline soft-seated butterfly valve is a compact, flexible, and reliably sealed control valve, widely used in water treatment, water supply and drainage, HVAC, fire protection, and other low-pressure fluid pipelines. Its core characteristics lie in the symmetrical centerline design and elastic sealing structure, which allow high sealing performance under low operating torque.

 

Structural Principle of Centerline Soft-Seated Butterfly Valve

 

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.

butterfly valve

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

butterfly valve

Installation and Maintenance Guidelines

 

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.

butterfly valve

Water Hammer & Backflow Prevention

 

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.

 

Maintenance Recommendations

 

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.

butterfly valve

Application Cases

 

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

 

Selection Recommendations

 

Water supply systems → Use EPDM

 

Mildly corrosive media → Use PTFE

 

Oily fluids → Use NBR

 

Food/pharmaceutical → Use Food-grade EPDM or PTFE

 

Common Issues & Maintenance Solutions

 

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.

 

 

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