Plug valve is a relatively simple structure of the valve, fluid direct flow through, small resistance, easy to open and close, rapid, suitable for slurry, viscosity and corrosive media.
1.Structural characteristics of the plug valve:
The plug valve seal forms are packing type and lubricating type (see Figure 3.4-1). The friction between the valve plug and the sealing surface is large, the opening and closing torque is large, and the sealing effect is good for the fluid with high viscosity. The latter has an oil injection hole, which can be injected with grease, so that a thin oil film is formed between the plug and the valve body to lubricate and assist in sealing. However, it will pollute the medium and cannot be used for process materials.
In addition to the straight-through structure of the plug valve, there are three-way and four-way types.
The plug valve has the following characteristics:
A. When the valve is fully open, the mechanism part of the valve body is not in contact with the fluid;
B. Open and close the valve only need to rotate 90 degrees (1/4 turn);
C. When opening and closing the valve, only a small part of the valve plug is in contact with the fluid;
D. The channel of the valve plug is straight, and there is no deposition or scaling;
E. No flow direction limit.
a .Plug valve structure diagram b.Oil sealed plug valve
1-Plug; 2- packing gland; 3- filler; 4-valve body
2.The drive mode of the plug valve:
When the size of the plug valve is too large, manual is not possible (excessive torque). But it can be geared. Generally speaking:
The PLUG VALVE of 150# NPS≥10 “shall be operated by GEAR;
The 300# NPS≥8 “PLUG VALVE requires GEAR operation.
The operating mechanism can be divided into SPUR GEAR OPERATOR, BEVEL GEAR OPERATOR, and WORM GEAR OPERATOR. Others are electric, pneumatic, hydraulic, chain and other operating modes. Sometimes it is necessary to increase the valve lever for easy operation.
3.The use of the plug valve
A. The straight-through plug valve is mostly used to cut off the fluid, but also can be used to adjust the flow or pressure;
B. Three-way and four-way plug valves are mostly used to change the direction of medium flow or medium distribution, and can only be fully opened and fully closed, and can not be used for adjustment.