Valve Type

Bubble caps were used almost exclusively as cross-flow-plate dispersers until about 1950, when they were largely displaced by simple or valve-type perforations. Many varieties of bubble-cap design were used (and therefore are extant in many operating columns), but in most cases bell caps of 75- to 150-mm (3- to 6-in) diameter were utilized. 

Several steps can be taken to maximize the run time for the reciprocating compressor. Since wear is a function of rubbing speed, the piston speed can be kept to a minimum. Chapter 3 made recommendations for piston speed. Reliability problems due to valves are reputed to account tor 40% of the maintenance cost of the compressor. Valves are the single largest cause for unplanned shutdowns. Basically, valve life can he increased by keeping the speed of the compressor as low as practical. At 360 rpm, the valves are operated six times a second. At 1,200 rpm, ihc valves operate 20 times a second or 1,728,000 times in a day. It is not difficult to understand why the valves are considered critical. To keep the reliability in mind, valve type, material selection and application considerations such as volume ratio, gas corrosiveness, and gas cleanliness need attention by the experts. One final note is that while lubrication is an asset to the rubbing parts, it is not necessarily good for valve reliability. 

PR Valve Type and Size - For convenience, valves are specified "Crosby or Farris valves equivalent accepted." The appropriate valve should be selected from the latest Crosby or Farris PR valve catalog. Sizes or ratings of PR valves that are not normally available are often obtainable by special order, and manufacturers should be consulted in such cases. 

Valve type and size should be specified by the compressor manufacturer. Normally, the manufacturer will quote a valve velocity, which can be calculated from ... 

A separate table such as the example in Table 15-2 is prepared for each line designation. Each valve is assigned a designation on the flowsheets and explained in this table. The pipe, valves, and fittings table can sp( acceptable valves by manufacturer and model number, by a generic description, or by a combination of the two as shown in the example. It should be pointed out that Tables 15-1 and 15-2 are examples from American Petroleum Institute Recommended Practice (API RP) 14E and are illustrative only. There are almost as many different formats for pipe, valve, and fip "" tables as there are companies, and these examples are in no manner ty or recommended. Often, for. simphcity, valve types are not described i pipe, valve, and fittings specifications but on separate sheets for each. ... 

The following descriptions are meant to briefly describe the various generic valve types. Within each type there are numerous different design details that separate one valve manufacturer s valves from the ne of these speciuc models have good points and bad points all can h correctly and incorrectly. It is beyond the scope of this book to c each valve manufacturer s design. However, the various valve sal will be more than pleased to contrast the benefits of their valve s ft with that of the competition. The reader is cautioned that hight valves do not necessarily mean better valves, and that expensive can result in a significant waste of money when a less expensive but adequate valve will perform satisfactorily. 

Table 15-3 summarizes and compares the different valve types discussed in this chapter and highlights important properties that impact valve selection. 

Tlie second letter identifies valve type ... 

Calculate the total quantity of each isolation valve type. 

Assumed the following valve types are NOT used as Isolation valves Air Operated Dlaphram, Solenoid Operated, Pressure Relief Safety, Swing Check, or Tilting Disk Check. 

E- valve(s) is/are required to isolate each (valve type) valve... 

Klein [201] has evaluated from the literature including manufacturer s, i.e., Glitsch [202], Koch [203], and Nutter [204], design procedures for their respective valve type tray... 

Valve type Flat oriHce, Rvw Venturi orifice, Rvw... 

Figure 9.5 shows a main servo controlled by two thermostatic pilots sensing load temperature (type CVT) and a solenoid valve (type EMV). Any of these pilots may be used separately with the servo valve. 

The gauge cocks provide a backup means to determine water levels. In general, three gauge cocks (globe valve type) are vertically installed at spaced intervals, close to the visible gauge glass. 

Typical pipe-fittings are shown in Figures 3.17 and 3.18 and details of other valve types are given in Volume 6. 

Compressed air line apparatus demand valve type 2000... 

Figure 8.26(A) is an example of a valve type interface [329]. Helium carrier gas is provided to the headspace saiq)ler and is split into two flow paths. One path is flow-controlled and provides a constant flow of carrier gas which passes from the headspace unit through the heated transfer line to the gas chromatograph. The second flow path is pressure-regulated and, in the standby mode, the seunple loop and seuapling needle are flushed continuously by the helium flow. At a time determined by the operator, the sampling needle pierces the septum and helium pressurizes the headspace vial to any desired pressure. The headspace gas is then allowed to vent through the sample loop. Once filled, the sample loop is placed in series with the normal carrier gas flow and its contents are driv Bbhrough the heated...

Details of valve types and standards can be found in the technical data manual of the British Valve and Actuators Manufacturers Association, BVAMA (1991). Valve design is covered by Pearson (1978). 

Pipe fittings are discussed in section 5.5.3, see also Perry et al. (1997). Valve types and applications are discussed in section 5.3. 

Select suitable valve types for the following applications ... 

This equation defines the flow coefficient, Cv. Here, SG is the fluid specific gravity (relative to water), pw is the density of water, and hv is the head loss across the valve. The last form of Eq. (10-29) applies only for units of Q in gpm and hv in ft. Although Eq. (10-29) is similar to the flow equation for flow meters, the flow coefficient Cv is not dimensionless, as are the flow meter discharge coefficient and the loss coefficient (Af), but has dimensions of [L3][L/M]1/2. The value of Cv is thus different for each valve and also varies with the valve opening (or stem travel) for a given valve. Values for the valve Cv are determined by the manufacturer from measurements on each valve type. Because they are not dimensionless, the values will depend upon the specific units used for the quantities in Eq. (10-29). More specifically, the normal engineering (inconsistent) units of Cv are gpm/ (psi)1/2. [If the fluid density were included in Eq. (10-29) instead of SG, the dimensions of Cv would be L2, which follows from the inclusion of the effective valve flow area in the definition of Cv]. The reference fluid for the density is water for liquids and air for gases. 

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