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FIG. 14-36 Typical moving valve tray pressure-drop profile. (From G. F. Klein, Chem. Eng., May 3, 1982, p. 81; reprinted courtesy of Chemical Engineering.)

The velocity at which the valves start to open (point A) is given by

where closed = hole area at point A, m/s; tv = valve thickness, mm; = ratio of valve weight with legs to valve weight without legs, given in Table 14-11; Kc = orifice coefficient with all valves closed (see above), s2-mm/m2; pM = valve metal density, kg/m3 (about 8000 kg/m3 for steel); pG = gas density, kg/m3.

The velocity at which all the valves are open Uhopen can be calculated from

Pressure drop through the aerated liquid [h'L, in Eq. (14-100)] is calculated by hL = Phd, (14-106)

where P = aeration factor, dimensionless hds = calculated height of clear liquid, mm (dynamic seal)

The aeration factor P has been determined from Fig. 14-37 for valve and sieve trays. For sieve trays, values of P in the figure may be calculated from

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