A quarter-turn valve which has a circular disk as its closing element. The standard design has the valve stem running through the disk, giving a symmetrical appearance. Later designs off-set the stem, so that the disk "cams" into the valve seat. Advantages include less
wear and tear on the disk and seats, and tighter shut-off capacities. Many design types are available including inexpensive? Teflon or resilient seats for use in water(treatment) plants, etc. More expensive metal seats can be used where high temperatures or aggressive chemicals are encountered. So-called "High Temperature" butterfly valves offer zero leakage designs and have been applied in both the chemicals and hydrocarbon processing sectors.

The above attached product's specification is as follow:

 

Features:
1) Standards: API 609, MSS-SP-68, ANSI B16.34
a) Basic design: API 609
b) Test: API 598, BS 6755 MSS-SP-25
2) Size: 2" - 36"
3) Rating: 150lbs-1500lbs
4) Body materials: cast iron, ductile iron, cast steel, stainless steel
5) Operation: hand wheel, gear, motor, pneumatic operator
6) End connection: wafer, lug, double flange
7) Design features:
a) Concentric design
b) 2pc shaft low torque design
c) Bi-directional service
d) Self cleaning
e) Blow-out proof shaft
f) ISO5211 top flange