Oil lubrication hard seal plug valve can be classified into conventional oil lubrication plug valve and pressure balance plug valve. Tailor-made grease is injected between body and plug from top of plug, forming oil film to reduce torque of valve, highly improving sealing and service life.
Conventional oil lubrication plug valve
a. For conventional oil lubrication plug valve, the installation of plug cone is forward assembling. To reduce friction between body and plug sealing face, the valve generally adopts the seat lubricated by sealing grease as sealing structure. High pressure sealing oil forms high pressure sealing ring around the plug. A layer of oil film is formed between body and plug sealing face, which can seal and lubricate, easy for on-off.
b. For reducing torque of plug valve further, diameter of plug is decreased generally. So, the passageway of the plug valve is rectangle, which can reduce torque of plug valve and increase fluid resistance of plug valve meanwhile.
c. The sealing part of plug cone is bead welded by using STL alloy materials or adopts surface hardening, improving wearing resistance and corrosion resistance of sealing face, extending service life.
d. The surface of plug cone is finished to mirror plane and grinded with sealing face of body, having lower torque.
Pressure balance plug valve
To reduce torque of conventional hard seal plug valve, pressure balance plug valve is usually adopted. Beside properties of conventional oil lubrication plug valve, pressure balance plug valve also has other characteristics:
a. The plug cone is assembled reversely. There is a check valve on the top of plug cone. When the valve is closed, due upward and downward cross section difference of plug cone, injected high pressure sealing oil impacts upward life on plug so that plug and sealing face of valve can acquire better sealing.
b. When the valve is opened, pressure inside inferior vena of body is balanced with media pressure inside pipe. High pressure sealing oil inside superior vena impacts downward thrust on plug, causing tiny gap between plug cone and sealing face of body. When rotate plug, the torque can be decreased effectively and protect sealing pair.
c. Under high temperature, thermal expansion can be absorbed through lifting, in case of sealing pair being wedged.
Although oil lubrication can reduce torque properly, it may pollute media. Therefore, sealing lubricating oil can be chosen based on actual conditions.
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