Valves plugs

Plug valves usually require lubrication on a regular basis to seal. The tend to have a more unpredictable torque than ball valves and are thus hard to automate. 

As with ball valves, plug valves are on/off valves and should only be used infrequently in throttling service. They tend to be less e.xpensive than ball valves, but are not as popular because of their need for lubrication. 

Plug valves are available as lined or unlined. In lined plug valves (Fig. 8.32), the body ofthe valve is lined with FEP or, more often, with PFA. The plug is also lined or encapsulated with the same material or made of solid PTFE. In an unlined plug valve, there is still a solid PTFE sleeve around the metallic plug which provides sealing as well as smooth operation of the valve. Valves are available in sizes up to 12 (30 cm) and in steel classes of 150 and 300. 

Liners are injection molded, or transfer molded in the case of PFA and FEP. In both cases, a locked liner is achieved. 

The problem with the originally developed lubricated plug valves was the low resistance of the lubricants to heat, solvents and chemicals. Other problems were product contamination by the valve lubricants and. the expense and trouble required to lubricate and maintain this type of valve. Present day lubricants and coating of the plug surfaces have considerably reduced these problems. 

Lubricants for plug valves have been developed which contain a dispersion of gas that can be compressed to about half of its expanded volume. When the lubricant is forced into the valve under pressure it is compressed. Later, it expands and feeds automatically into the valve lubricant grooves only as needed, reducing lubrication frequency. 

Manufacturers report that in 99 out of every 100 service calls for plug valves, the only thing that was wrong was that the valve needed lubrication. 

Some basic advantages are cited for lubricated plug valves. 

They are quick acting (one quarter turn to open or close). 

---

Plictran Plioflex Plot plan PLP-DPG-PLP Plug valves Plumbic acetate Plumbing applications PlumbopaHadimte Plumbostanmte Plumbous acetate Plume containment Plummer s disease Plums... 

Purely aqueous polymerization systems give copolymers that are not wetted by the reaction medium. The products agglomerate and plug valves, nozzles, and tubing, and adhere to stirrer blades, thermocouples, or reactor walls. These problems do not occur in organic media or mixtures of these with water. 

Fig. 2. (a) Gate valve (b) plug valve and (c) globe valve. 

Fittings and plug valves with ends to match the various types of pipe are available. 

The flowrate of die regenerated eatalyst to die riser is eommonly regulated dirough die use of eidier a slide or plug valve. The operation of a slide valve is similar to that of a variable orifiee. Slide valve operation is automatie. Its main funetion is to supply enough eatalyst to heat the feed and aehieve the desired reaetor temperature. 

For the twin arrangements, a two-way, six-ported, continuous-flow valve will be required. If it is a tapered plug type, a means of lifting the plug will be required. The purpose of the tapered plug valve is to provide... 

Figure 15-2. Cutaway of plug valve. [Courtesy ofXomox Corp.]...

Figure 2-5D. Lined plug valve for corrosive service. By permission, Dow Plastic-Lined Products, Bay City, Mich. 48707, 1-800-233-7577.

Gas does not have the lubricant qualities of fuel oil. Consequently, whereas a drop-weight valve in the oil supply can be expected to close when called upon, this is not the case with a relatively large-bore gas ball valve or plug valve used for gas. 

Slide or plug valves. Cast-vibrating of the refractory lining and stem/guide modifications have minimized stress cracking and erosion. 

Proper standpipe design is one of the most important factors in obtaining good circulation. The standpipe provides the necessary head pressure required to circulate the catalyst. A standpipe assembly is typically comprised of three major parts hopper, standpipe, and slide or plug valve. The function and design of each part is described below. 

The slide or plug valve regulates the flow of catalyst between the reactor and regenerator. The slide valve also provides a positive seal against reversal of the hydrocarbons into the regenerator or hot flue gas into the reactor. Table 7-6 summarizes typical process and mechanical parameters for designing slide valves. 

Higher catalyst circulation usually requires opening the regenerated and spent catalyst slide (or plug) valves. Higher circulation increases the pressure drop in the riser and in the reactor cyclones, lowering the differential pressure across the slide valves. This causes the valves to open further, until the unit finds a new balance. 

Catalyst circulation can also be limited by mechanical problems with the slide/plug valves. They may have limited travel or will not open fully. This is indicated by the lack of response when an adjustment is made. The differential pressure and the flow will not change. Troubleshooting the valves is a function of the valve design and the vendor will supply troubleshooting information,... 

Slide Valve or Plug Valve is a valve used to regulate the flow of catalyst between reactor and regenerator. 

Plug Cock Plug Valve Check Valve... 

---