Movable valve trays

K for sieve trays is 0.3 K for grid trays is 0.6. Only an idiot would use movable valve trays. The valve caps stick to the deck and do not greatly retard tray deck leakage. 

Moving valve trays (Fig. 14-18c) have the perforations covered by movable disks (valves). Each valve rises as the gas velocity increases. The upper limit of the rise is controlled by restricting legs on the bottom of the valve (Fig. 14-18c) or by a cage structure around the valve. As the gas velocity falls, some valves close com-... 

A valve tray (Fig. 6.5) is a flat perforated plate, with each perforation equipped with a movable disk. The perforations and disks may be circular (Fig. 6.5a, 6, d) or rectangular (Fig. 6.5c). At low vapor rates, the disk settles over the perforation and covers it to avoid liquid weeping. As vapor rate is increased, the disk rises vertically. 

Valve trays have movable elements in the tray openings for adjusting the free area to the actual gas load. This widens the operating range and reduces the pressure drop at high gas loads. 

IT = 1 for sieve trays and 2.5 for movable and fixed valve trays. The introduction of Kto the spray equation manifests that the valve tray has a better capability in suppressing entrainment than sieve trays. This is achieved by the mechanism of vapor entering the tray horizontally with valves, which reduces the entrainment significantly at low liquid loadings. According Lockett (1986) and Summers and Sloley (2007), spray factor 5p in equation (12.6) must be larger than 2.78 to avoid spray regime. 

Valve trays (see Figure 12-19) are units in which holes are covered with movable caps whose rise varies with gas flow rate. The valve tray is a very widely used device because it represents a useful compromise between the bubble cap and sieve trays. 

Grid tray Similar to a sieve tray. A perforated distillation tray deck, but with no movable valve caps. Represents modern distillation tray design. 

The use of movable valve caps in any service where deposits can accumulate on the tray decks will cause the caps to stick to the tray deck. It s best to avoid this potential problem. Use of grid trays with fixed cap assemblies is preferred for most services. 

Many such columns are equipped with movable valve caps. If the relief valves open, the vapor flow through the trays will be reversed. This will seal the valve caps up against the tray panels. The large downward force exerted by the trapped vapors could then collapse the trays. 

Trays with drilled holes in the base plate, which are covered by movable and adjustable load valves. Liquid flows in a controlled manner across the tray (e.g.. 

Don t use movable caps (i.e., valves). They do not greatly decrease tray deck leakage at low vapor rates. But they do stick to the tray deck and cause premature flooding. 

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