1. Connection structure and installation characteristics
Lug butterfly valve
Lug bolt holes are designed at both ends of the valve body, which can be directly connected to the pipe flange by bolts without penetrating the valve body, simplifying the installation process.
The lug holes are divided into through-hole type and internal thread type, suitable for installation with different bolt specifications. The installation time of valves above DN300 is shortened by 40% compared with the clamp type.
The bolt length is short, which reduces the risk of sealing failure caused by bolt creep.
Double flange butterfly valve
The valve body comes with an annular flange, which needs to be connected by flange clamping. The flange holes on both sides must be strictly aligned during installation.
The probability of flange misalignment is high during installation of large diameters (DN≥500), which can easily lead to bias leakage of the sealing surface.
The bolts need to penetrate the valve body, and the flange welds are easily affected by alternating stress during long-term operation.
2. Sealing performance and material design
Sealing mechanism
Lug butterfly valves mostly adopt a triple sealing structure (double-layer soft seal + metal hard seal), with a leakage rate of ≤0.01% under PN16 pressure;
Double flange butterfly valves are usually double eccentric or centerline seals, and the contact pressure of the sealing surface depends on the flange clamping force, and the leakage rate is generally 0.03%-0.05%.
Heat resistance and medium resistance
Lug butterfly valve seats support EPDM or fluororubber materials, with an upper temperature resistance of up to 200℃8, and are compatible with solid particle media (particle size ≤3mm);
The soft sealing seat of the double flange butterfly valve is generally ≤150℃, and is recommended for clean fluids (such as pharmaceutical and food industries).
Structural reinforcement design
Lug butterfly valves use thickened steel plates or low-temperature carbon steel in the lug area, which increases the shear strength by 30%;
The double flange butterfly valve body is not strengthened for local stress, and the welding between the flange and the valve body is prone to become a weak point.
3. Scenario Adaptation and Economy
Applicable Working Conditions
Lug Butterfly Valve:
Scenarios that require frequent disassembly and maintenance, such as fire protection pipe networks and thermal systems;
Dust-containing flue gas and particle medium pipelines (such as cement plant dust removal systems);
Narrow maintenance areas (lug structure reduces flange extension size).
Double Flange Butterfly Valve:
Petrochemical main process pipelines (standardized flanges have high matching degree);
High cleanliness medium control (such as pure water, sterile fluids);
PN40 and above high-pressure pipelines (the overall flange structure has better pressure bearing).
Cost Comparison
The procurement cost of double flange butterfly valves below DN200 is 10%-15% lower;
The lug butterfly valves above DN300 have significant cost advantages in the entire life cycle (reducing flange loss and maintenance hours).
4. Maintenance and Reliability
Maintenance Frequency
Due to the multiple protection of the sealing surface of the lug butterfly valve, the recommended maintenance cycle is 2-3 years;
The sealing surface of the double flange butterfly valve is easily affected by flange deformation, and the sealing status needs to be checked every year.
Failure Mode
Common problems with lug butterfly valves are uneven bolt preload (which can be avoided by standardized operation with a torque wrench);
Double-flange butterfly valves are prone to local wear of the valve seat due to flange deflection, and flange parallelism needs to be corrected regularly.
The core difference between the two types of butterfly valves comes from the connection method and force design: lug butterfly valves achieve efficient installation and adaptation to complex working conditions through structural innovation, while double-flange butterfly valves maintain stable performance in high-pressure clean scenarios with standardized design. When selecting a butterfly valve, it is necessary to weigh the pressure level, medium characteristics and maintenance costs.
