Plate valve

Valve, trap, and baffle can be combined in such a manner that elastomers can be used in the valve and contamination is controlled from the valve-actuator mechanisms and from the gasket of the valve-plate seal (Fig. 15) (42). 

Three principal vapor—Hquid contacting devices are used in current crossflow plate design the sieve plate, the valve plate, and the bubble cap plate. These devices provide the needed intimate contacting of vapor and Hquid, requisite to maximizing transfer of mass across the interfacial boundary. 

Fig. 16. Individual valve units used in valve plates (a) Koch Flexitray valve, courtesy of Koch Engineering Co. (b) GHtsch Ballast valve, courtesy of...

FIG. 14-19 Valve-plate dispersers. To convert inches to millimeters, multiply hy25.4. 

Minimum allowable capacity of a column is determined by the need for effective dispersion and contacting of the phases. The types of plates differ in their ability to permit Tow flows of gas and liquid. A cross-flow sieve plate can operate at reduced gas flow down to a point where liquid drains through the perforations and gas dispersion is inadequate for good efficiency. Valve plates can be operated at veiy... 

Figure 14-25 or Eq. (14-92) may be used for sieve plates, valve plates, or bubble-cap plates. The value of the flooding vapor velocity must be considered as approximate, and prudent designs call for approaches to flooding of 75 to 85 percent. The value of the capacity parameter (ordinate term in Fig. 14-25) may be used to calculate the maximum allowable vapor velocity through the net area of the plate ... 

Ratio of slot (bubble cap), perforation (sieve), or full valve opening (valve plate) area A/, to active area A is 0.1 or greater. Otherwise the value of U j obtained from Fig. 14-25 should be corrected ... 

An alternate method for predicting the flood point of sieve and valve plates has been reported by Kister and Haas [Chem. Eng. Progi , 86(9), 63 (1990)] and is said to reproduce a large data base of measured flood points to within 30 percent. It applies to entrainment flooding only (values of Flc less than about 0.5). The general predictive equation is... 

For valve plates, values of K and Ko depend on whether the valves are fully open. They also depend on the shape and weight of the valves. Vendors of valve plates make K and Ko data (or their equivalent) readily available. An analysis of valve plate pressure drop has been reported by Bolles [Chem. Eng. Pmgr. 72(9), 43 (1976)], and typical dry head loss data, shown in Fig. 14-31, are taken from that worlc. 

Sieve plates usually have negligible hydraulic gradient. Bubble-cap plates can have significant gradient because of the blockage by the caps. Valve plates presumably are intermediate, with hydraulic-gradient characteristics approaching those of sieve plates. 

For sieve or valve plates, h = h , outlet weir height. For bubble-cap plates, h = height of static seal. Tbe original references present vaH-dations against laboratoiy and small-commercial-column data. Modifications of tbe efficiency equation for absorption-stripping are also included. 

Valve plate—40-mm (1.57-in) holes, 45 valves per plate, 25.4-mm (1.0-in) outlet weir. 

Curve 4 Sieve-valve plate,, 38-mm weir, 49 valves, 140 holes... 

Adsorbers, distillation colunuis, and packed lowers are more complicated vessels and as a result, the potential exists for more serious hazards. These vessels are subject to tlie same potential haz. uds discussed previously in relation to leaks, corrosion, and stress. However, llicse separation columns contain a wide variety of internals or separation devices. Adsorbers or strippers usually contain packing, packing supports, liquid distributors, hold-down plates, and weirs. Depending on tlie physical and chemical properties of the fluids being passed tlirough tlie tower, potential liazards may result if incompatible materials are used for llie internals. Reactivity with llie metals used may cause undesirable reactions, which may lead to elevated temperatures and pressures and, ullinialely, to vessel rupture. Distillation columns may contain internals such as sieve trays, bubble caps, and valve plates, wliicli are also in conlacl with tlie... 

The valve plates, discs, and springs are mounted in a valve cage, which is inserted in the cylinder. Valve breakage occurs due to fatigue of the metal or improper action. This requires replacement and an evaluation of the materials of construction as well as the basic type of valve. Each manufecturer presents his valve design to match his equipment. Only experience can determine which type of valve works best in a given application... 

Figure 12-6I. Dresser-Rand HPS proprietary valve design, using proprietary blend of PEEK, an advanced non-metallic valve plate material, allowing for temperature ranges greater than previously available nonmetallic plate materials, for lubricated and nonlubri-cated applications for long life. (Used by permission Form 85084, 1992.

Figure 4.6 Reed valves on valve plates (Courtesy of Prestcold Ltd)...

Valve plates are proprietary designs. They are essentially sieve plates with large-diameter holes covered by movable flaps, which lift as the vapour flow increases. 

As the area for vapour flow varies with the flow-rate, valve plates can operate efficiently at lower flow-rates than sieve plates the valves closing at low vapour rates. 

The principal factors to consider when comparing the performance of bubble-cap, sieve and valve plates are cost, capacity, operating range, efficiency and pressure drop. 

Cost. Bubble-cap plates are appreciably more expensive than sieve or valve plates. The relative cost will depend on the material of construction used for mild steel the ratios, bubble-cap valve sieve, are approximately 3.0 1.5 1.0. 

Valve plates are intended to give greater flexibility than sieve plates at a lower cost than bubble-caps. 

Summary. Sieve plates are the cheapest and are satisfactory for most applications. Valve plates should be considered if the specified turn-down ratio cannot be met with sieve plates. Bubble-caps should only be used where very low vapour (gas) rates have to be handled and a positive liquid seal is essential at all flow-rates. 

The mechanical design features of sieve plates are described in this section. The same general construction is also used for bubble-cap and valve plates. Details of the various... 

The mechanical specification of bubble-cap, sieve and valve plates is covered in a series of articles by Glitsch (1960), McClain (1960), Thrift (1960a, b) and Patton and Pritchard (1960). 

A, free diameter of the connection to the chamber B, cylindrical opening by the movement of D C, opening between condenser wall and valve plate D, valve plate, hydraulic valve drive E, condensation surface of the refrigerated coils F, in- and outlet of the refrigerant G, tube connection to the vacuum pump H, water drain during defrosting of the condenser pch and pm pressure in the chamber and in the condenser, respectively. 

To the valve plate 2, bellows 3, valve drive 4, condenser wall (schema from source material by AMSCO Finn-Aqua, D-50354 HUrth). 

The third critical part in a steam-sterilized plant is the valve between the chamber and condenser. Its design should influence the flow of water vapor from the chamber to the condenser as little as possible, and its component must be easily cleaned and sterilized. Several technical solutions are offered for this problem. In Fig. 2.48.1 a design is shown in which the valve plate is moved back-and-forth by a hydraulic cylinder. This fulfils the two requirements ... 

Fixed-roof tanks, 24 288-289 Fixed surface aerators, 26 159, 160 Fixed valve plates, 3 763-764 Fixing agents color film, 19 261 photographic, 19 213 Fixolide, 24 494 Flake... 

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