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The Difference btw Center line-Type & Single-eccentric Type & Double eccentric type & Triple Eccentric Type Of Butterfly Valve
Dec 12, 2017

The Difference Btw Center line-Type & Single-eccentric Type &

Double-eccentric type & Triple-eccentric Type Of Butterfly Valve

                 These several kinds of butterfly valve through the disc rotor position setting to change  the sealing and the state of opening.

             Under the same conditions, torsion of the valve under various degrees of opening , one is bigger than the other; the angle request of the disc being divorced from the seat when valve is opening, one is smaller than the other. 

             That’s why have the center line-type butterfly valve, single-eccentric type butterfly valve, double-eccentric type butterfly valve and triple-eccentric type butterfly valve. 

(As shown in the figure)

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Center line-type butterfly valve’s structure characteristics is that the axis of stem,centre of disc and body, they are in same position.It has the advantage of simple structure, convenient manufacture. Due to disc and seat always be in state of squeezing and scraping, so it has disadvantage of big resistance and quick wearing. In order to overcome squeezing and scraping, ensure the sealing performance, normally using NBR or PTFE etc flexible materials, but cause these sealing materials, so have working temperature limited .


Single-eccentric type butterfly valve, in order to solve the squeezing problem in concentric disc and seat design, and thus produce single-eccentric type butterfly valve, its structure characteristics is that the axis of stem deviate from the centre of disc, so to make the disc up and down do not to be the axis of rotation .Scatter and reduce the disc up and down with seat’s over squeezing. 


Double-eccentric type butterfly valve further improve on the basis of single type, its construction feature is that axis of stem deviate the centre of disc and deviate the centre of body as well, so double eccentric type's using effect is that when opening,the disc can be quick divorced from the seat, big reduce the unnecessary squeezing and scraping btw the disc and seat,  relieve the resistance , lower the wearing, increase the valve service life. 


Triple-eccentric type butterfly valve: when high temperature resistance is needed, then must use metal to metal seaing, but leakage is big;When zero leakage is needed, then must use soft sealing, but cannot resistance high temperature. In order to overcome the disadvantage of double eccentric type, and thus produce triple eccentric type. Its design means shape of sealing pair not positive cone,  but oblique cone. The unique feature of triple eccentrci type design is that the stem through the disc is a three phase design . This three phase design stem, two phase of them are concentric type, and middle phase deviate centre distance from the up& down phases.The disc install on the middle phase. This design to make disc being ddouble eccentric shape in full open position. When disc turn to close, shape to be single eccentric type. Due to eccentric shaft’s function, when near to close, disc move to seat’s cone a distance, disc and seat’s sealing face meet together to achieve reliable sealing performance. 

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