A plug valve is a valve which uses a closing part or a plug to rotate 90° around the centerline of the valve body so as to achieve the purpose of opening and closing. A plug valve is mainly used for cutting off, distributing and changing the flow direction of the medium in the pipeline. A plug valve can sometimes be used to throttle based on the nature of the medium and erosion resistance of the valve's sealing surface.
The characteristics of plug valves with soft sealing are mainly related to features of valve bodies, valve plugs, sealing of stems, internal leakage and valve sleeves, which are indicated from the following aspects:
1. Valve bodies
Reinforcing ribs are added for the connecting part between the flange and valve body as well as the bottom of the valve body to make the valve body strong and extend the service life.
2. Valve plugs
The valve plug of the spool is a plunge. If the sealing area of the stainless steel plug valve is big, the valve will have a long service life and a good flow capacity, that is, the stainless steel valve of the same size has a high rated Cv value.
3. Sealing of stems
There are two seals for stems. The first sealing is formed by a large area of contact at 360 degrees between the upper part of the plug and PTFE sleeve. The second sealing is a uniquely designed PFA sealing membrane. The unique design of the PFA reverse lip membrane makes the pressure and reverse lip membrane compress the valve stem when the pressure of the membrane is too high, thereby providing an enhanced dynamic seal; at the same time, the reverse lip membrane seal is pressed tightly under the action of pressure so as to form a static seal.
Membrane materials: For a unique sealing structure, in order to achieve excellent sealing results, it is inseparable from the sealing material. The selected material for the membrane is PFA, while most manufacturers use PTFE. PFA has the following advantages:
The elasticity of PFA is better than that of PTFE.The abrasion resistance of PFA is better than that of PTFE.
The permeation resistance of PFA is better than that of PTFE.
PFA has creep resistance, no cold flow, and easily restores to its original state, which has sufficient performance and excellent results in acetic acid assembly.
4. Internal sealing
The tightly fitted conical valve plug and PTFE sleeve form a precision seal. The sleeve surrounds the valve plug port and tightly wraps the upper and lower portions of the valve plug so that there is no cavity and a two-way seal is formed. The seal completely depends on the pipeline pressure. There is no metal to metal contact, and the sealing is precise. Stainless steel valves can rotate freely without lubrication. The sealing can be adjusted. There is no need to remove the stainless steel valve from the pipeline for maintenance. The skirt at the contacting part between the valve plug and sleeve forms a self sweeping effect, which can effectively eliminate impurities in the medium and avoid damaging the valve plug and skirt. It is suitable for working conditions with a slurry.
5. Sealing adjustment of valve plugs and sleeves in the pipeline direction
The characteristic of the plug valve is that after a period of wear of the valve seat, the tapered valve plug can be adjusted downwards to form a new sealing surface, which can be realized under pressure on the pipeline, thereby saving maintenance time and reducing maintenance costs. It is very different from the usual adjustment style.
The usual adjustment uses three bolts to adjust downwards, thereby pressing the valve plug downwards to obtain a new sealing surface. This adjustment style requires that the three bolts must be adjusted uniformly, which is difficult to achieve in actual operation. If the adjustment is not uniform, the plug will be deflected to one side and the valve seat will be damaged in the process of closing; at the same time, the sealing of valve stems will also be damaged; the torque of the stainless steel valve will increase, which causes internal and external leakage of the valve stem.
A rocker arm adjuster adopts the cylindrical section and plane section. The valve plug is adjusted downward by two bolts. Because the contact surface between the rocker arm adjuster and lantern ring is tangential, the adjustment system only requires two bolts, and a uniform vertical downward pressure can be generated for the gland by screwing any bolt, thereby avoiding the displacement of the plug, improving the sealing result and extending the sealing life. After adjustment, the precision sealing result can be regained.
