The technical difference between the center valve and the eccentric valve and the engineering selection logic

In the valve selection, the choice of center butterfly valve and eccentric butterfly valve is essentially a trade-off between "sealing principle" and "working condition adaptability". The following analysis is carried out from the engineering perspective.

Center butterfly valve

Core difference: Different sealing mechanism

The sealing principle of the center butterfly valve is an elastic extrusion seal. The seat is made of elastic material such as rubber or PTFE. When the butterfly plate is closed, the seat is squeezed to deform and fill the sealing surface gap. Good sealing effect, low leakage, but at the cost of each opening and closing have scratch, seat life is limited, and not resistant to high temperature and high pressure.

Eccentric butterfly valves are designed to do the opposite - to reduce friction by biasing the stem position. Single eccentricity solves the problem of excessive extrusion at the upper and lower ends of the butterfly plate. Double eccentricity allows the butterfly plate to break away from the valve seat at the moment of opening, greatly reducing the scratch; Three eccentric completely changes the seal structure, from position seal to torsion seal, butterfly plate and valve seat in the closing process does not produce friction, relying on the contact surface pressure to achieve zero leakage, and is suitable for high temperature and high pressure and metal hard seal scene.

Quantitative selection basis

From the engineering practice data, DN200 caliber, 1.0MPa pressure conditions, the center butterfly valve sealing life of about 10 to 20 thousand times, eccentric butterfly valve about 40 to 60 thousand times. In terms of torque, the three-eccentric structure makes the torque gradually increase but the peak value is controllable during the closing process through the CAM effect, and the overall opening torque is smaller than the central butterfly valve.

Selection decision framework

According to the working conditions, it is divided into four categories: normal temperature and low pressure clean medium (water supply and drainage, HVAC), selecting the center of the butterfly valve; High temperature and high pressure or containing particles medium (steam, chemical), choose double eccentric or three eccentric butterfly valve; In the case of flow adjustment, the adjustment linearity of eccentric butterfly valve is better than that of central butterfly valve; DN500 above large diameter long cycle operation scene, eccentric butterfly valve torque curve is more gentle, lower comprehensive cost.