Do Lug-type Butterfly Valves Require Gaskets?

Whether lug butterfly valve requires gaskets depends on its sealing structure and specific operating requirements. Here are some details:
1.Lug-Type Butterfly Valve Sealing Structure Types
The sealing design of lug butterfly valve directly influences the demand for gaskets. Common seals include:
Gasketless Seal (Composite)
Structural features:
The contact surface between the valve body and the flange of the pipe is machined with a sealing slot or a a a a convex table. Seals are made of hard metal seal (e.g. stainless steel) or a soft sealing material (e.g. rubber or fluorine rubber).
The lug design uses bolts to clamp the valve between the flanges, using bolts to prefasten and maintain contact with the sealing lid.
Gasket Requirement:
No gasket required: Direct sealing sealing can be achieved if the contact surface between the valve body and flange is finely machined (e.g. surface roughness ≤ 3.2μm) or embedded in a soft seal ring.
Typical applications: low to medium pressure piping systems (e.g. PN ≤ 1.6MPa) and clean media (e.g. water and air). Gasket Seal (Gasket-Assisted Seal)
Structural features:
A gasket shall be installed between valve body and pipe flange. The gasket's deformation fills the small gap between the contact surfaces and improves the sealing effect.
The gasket material shall be selected according to the characteristics of the medium (e.g. temperature, pressure and corrosion). Common materials include spiral wound gaskets, polytetrafluoroethylene gaskets and rubber gaskets.
a gasket:
Gaskets are required if the contact surface between the valve body and flange is not rough or scratched, or if operating conditions require high sealing performance (e.g. high pressure, high temperature or corrosive media).
Typical Scenarios:
(a) (a) (a) Steam or gas pipelines operate at high pressure (e.g. pressure greater than 4.0 MPa);
Hot oil or molten salt pipes operating at high temperatures (e.g. pressure greater than 300°C);
Chemical pipelines operating in highly corrosive media such as concentrated sulfuric acid or chlorine gas.
ii. Key factors affecting Gasket Use
Pressure Rating
Low pressure operating conditions (pressure less than or equal to 1.6 MPa): gaskets are generally not required and are direct sealing between valve body and flange.
High pressure applications (PN > 4.0 MPa): gaskets are required to prevent seal failure due to inadequate bolt pretension.For example, inadequate bolt pretension.spiral wound gaskets are commonly used in high pressure steam pipelines in the petrochemical industry.
Temperature range
Ambient temperature applications (-20°C to 120°C): Soft seal cam-type butterfly valves (such as rubber seals) can be sealed directly without gaskets.
High temperature applications (> 300°C): High-temperature-resistant gaskets (e.g. graphite gaskets) are required to prevent the the sealing material from softening or decomposing. For example, flexible graphite composite gaskets can be used in main steam pipelines in coal-fired power plants.
Media Characteristics
Clean media (such as water and air): No gaskets are required and valve body surface roughness meets specified standards.
Corrosive media (e.g. acid and alkali): Corrosion-resistant gaskets (e.g. PTFE or Hastelloy) are required to prevent corrosion valve body or flange contact surfaces. For example, PTFE-coated gaskets are commonly used in chlorine gas pipelines in the chemical industry.
Vibrations and shocks
Stable application: No gaskets are required; bolts are prefastened to maintain seal. Vibration-resistant gaskets (such as metal toothed gaskets) need to prevent vibration-induced bolt loosening or seal cover dislocation.
III. Lug-Type Butterfly Valve Installation Recommendations
Installation Steps without gaskets
Clean contact surfaces: Make sure there is no oil, dirt or scratches on the contact surface between the valve body and flange.
Pre-evenly tighten bolts: Tighten the bolts gradually in diagonal order to avoid local stress concentration leading to seal failure.
Check for leaks: Stress test after installation to confirm no leaks.
Steps to install gaskets.
Choose the appropriate gasket: Select the material and thickness of the gasket (usually 1-3mm) according to the conditions of use.
Gasket mounting: the gasket between valve body and flange to prevent dislocation.
Pre-tighten bolts: Tighten bolts diagonally in stages to ensure uniform compression of gaskets (usually 15% compression).
Double Inspection: After running for a while, re-check whether the bolt is pre-fastened to prevent the gasket from loosening. IV. INTRODUCTION Introduction 1 -5 2
Scenarios Where Gaskets Are Not Required
Municipal water supply and drainage pipelines: PN1.0MPa cast iron cam butterfly valve is installed directly at pump outlet without gaskets.
Air conditioning cooling water system: PN1.6MPa stainless steel cam butterfly valve, soft seal, zero leakage, no gaskets required.
Washer needed
Chemical industry sulfuric acid piping: a polytetrafluoroethylene gasket between flange and flange of PF 2.5 MPa flourized cam butterfly valve to prevent sulfuric acid corrosion.
Power Industrial Steam Pipeline: PN6.4 MPa High Temperature High Pressure Camouflage Butterfly Valve with a spiral wound gasket to ensure no steam leakage at 350°C.