M-type butterfly valve design calculation
1. the minimum wall thickness of "M"-type butterfly valve body
Using ASME B16.34 appendix wall thickness calculation formulas to calculate.
2. Eccentric butterfly valve stem torque calculation
Using the following formula, torque calculation diagram shown in Figure 2.
MD = MM + MT + Mj + Md (1)
in the formula MD ———valve stem torque, unit is N•mm;
MM ——— sealing surface friction torque, unit is N•mm.
qM ———sealing surface necessary specific pressure, unit is MPa (look-up table or calculated)
R ———disc sealing radius, unit is mm
bM ———Sealing surface contacting width, unit is mm;
fM ———sealing surface friction coefficient (for rubber is 018 ~ 110);
h ———the eccentric distance between stem and disc center, unit is mm;
MT ———packing sealing friction torque (it can be negligible due to the stem use "O" ring sealing);
Mj ———hydrostatic torque, units is N•mm (look-up table or calculated)
Md ———hydrodynamic torque, unit is N•mm (look-up table or calculated)
3. disc thickness calculation (Figure 3)
b = 01054 D3 H (3)
in the formula b ———the maximum disc thickness, unit is mm
D ———butterfly valve flow diameter, unit is mm
(Look-up table, the general b / D = 0115 ~ 0125 (Figure 2)
H ———Maximum static pressure water head (water hammer boost medium), unit is m.
H = 100 ( p +Δp) (4)
p ———Design pressure (often taking p = PN), unit is MPa
Δp ———Butterfly valve quick off the valve, produces water hammer step-up value in the pipeline, unit is MPa;
v ———medium flow rate, (look-up table) unit is m / h;
t ———the disc experienced time from fully open to fully closed (look up table for selection), unit is s.
4.Check the strength of cross-section
(1) disc A2A cross-section Strength Check
in the formula σWA ———Verify A2A section bending stress, unit is Mpa.
MA ———A2A section bending torque, unit is N•mm
MA = 01113 pD31 (7)
p———Design pressure (often taking p = PN), unit is Mpa.
D1 ———disc external diameter, unit is mm.
WA ———A－A cross-section anti-bending cross-section coefficient, unit is mm3;
JA ———A－A cross-section inertia moment (look-up table or calculated) unit is mm4.
b ———the maximum disc thickness, unit is mm.
If the A-A cross-section actual bending stress, that is,
σWA < [σWA ] the disc design is reasonable,, [σWA ] is allowable bending stress for the material.
(2) disc B2B cross-section strength check
As the valve adopts upper and lower two-section stem to support, disc deformation is very small, so not to repeat them here.
the key of "M"-shaped butterfly valve design is the calculation of the upper and lower stem of driving pieces, body and disc strength, and the valve body, disc, stem, and pin and other parts rational selection and heat treatment. The valve is a single eccentric butterfly valve, torque is small, the whole disc is coated with a sealing layer, with good sealing performance, do not pollute the environment, demolition and maintenance are very convenient. Driven approach has handle type, worm gear type, electric and pneumatic, etc., is a valve that widely used.
