Requirements for Flange Parallelism,Coaxiality and Flow Direction During Ventilation Butterfly Valve Installation

The installation precision of ventilation butterfly valve directly determines sealing performance,opening-closing flexibility,driving load,valve plate wear and overall service life.Unqualified parallelism,coaxiality deviation and wrong flow direction will easily cause poor sealing,internal leakage,valve shaft jamming,increased actuator torque,frequent motor overload and burning failure.This paper elaborates the detailed technical requirements,tolerance standards,hazard of deviation and installation specifications of flange parallelism,coaxiality and medium flow direction.

1.Flange Parallelism Requirements

Parallelism refers to the flat fitting degree between two pipeline flanges clamping the butterfly valve.

Technical Tolerance Standard

The parallel deviation between the two flange surfaces shall be controlled≤0.2mm;angular inclination deviation shall be≤0.1°per 100mm flange diameter.The two flange end faces shall be kept completely parallel without uneven inclination and warpage.

Installation Requirements

Calibrate with laser alignment tool before bolt fastening.Fasten connecting bolts evenly and symmetrically in cross sequence to avoid local excessive extrusion force.

Consequences of Excessive Deviation

Uneven compression on sealing gasket,accelerated wear of valve plate sealing surface,serious internal air leakage,additional stress on valve body and shaft bending deformation.

2.Flange Coaxiality Requirements

Coaxiality means the center circle centerline of inlet and outlet pipeline flanges is concentric with the central axis of the butterfly valve body.

Technical Tolerance Standard

Radial coaxial offset deviation between pipeline axis and valve body central axis shall be≤0.5mm for small and medium diameter valves;for large-diameter ventilation butterfly valves,the allowable offset shall not exceed 1.0mm.No obvious eccentricity and dislocation of pipeline centerline.

Installation Requirements

Adjust pipeline position to make inlet and outlet pipe axis coincide with valve body center axis.Install pipe supports within 1.5m near the valve to eliminate pipeline gravity offset and displacement interference.Adopt flexible coupling to compensate slight pipeline deformation.

Consequences of Excessive Deviation

Increased rotation resistance of valve shaft and valve plate,eccentric friction wear,rising driving torque of electric actuator,frequent motor overload,jamming during opening and closing,and shortened service life of shaft bearings.

3.Medium Flow Direction Requirements

Basic Installation Rule

The actual airflow flow direction of the pipeline must be completely consistent with the arrow mark on the valve body surface.The arrow on the valve shell clearly indicates the standard medium flowing direction.

Special Characteristics of Ventilation Butterfly Valve

Most central-line ventilation butterfly valves have weak flow direction restriction theoretically,but reverse installation will change internal airflow field,increase flow resistance,aggravate dust scouring on back side of valve plate,accelerate sealing part aging and reduce adjustment stability.

Additional Installation Specifications

The valve is preferred to be installed horizontally with valve shaft arranged in horizontal direction.

Do not install reversely against the marked flow direction for electric and pneumatic control butterfly valves with precise flow regulation.

Reserve sufficient maintenance space on upper part of valve stem and actuator to avoid pipeline interference.

Consequences of Wrong Flow Direction

Increased wind resistance,uneven dust erosion on valve plate,unstable flow regulation performance,abnormal stress on internal structure,and hidden danger of sealing failure.

General Integrated Installation Precautions

Complete flange alignment calibration before valve clamping installation.

Ensure uniform bolt stress during fastening,and prohibit forced installation by violent jacking.

Keep pipeline stable support to avoid additional external force acting on valve body.

Confirm flow direction mark matching before pipeline sealing connection.

Conduct no-load opening-closing test after installation to verify flexible rotation without jamming.

References

1.GB/T 7714

Shi L,Gao F.Installation Precision Specification of Flange Connected Ventilation Butterfly Valve[J].Fluid Machinery,2022,53(4):126-130.

2.MLA

Baker,David,and Gary Morris."Duct Butterfly Valve Installation Geometric Tolerance Standards."Journal of Pneumatic Control Engineering,vol.34,no.2,2021,pp.85-91.

3.APA

Shi,L.,&Gao,F.(2022).Installation precision specification of flange connected ventilation butterfly valve.Fluid Machinery,53(4),126-130.