Valves: ball globe

Figure 5.5. (c) Ball valve (d) Globe valve (e) Diaphragm valve... 

Per hardware globe control valve (sin e port or double port), rotaiy ecwjtrol valve (ball, plug, or butterfly), angle control valve. 

Angle valve,open Ball check valve, open -Swing check valve, open, 45°-Y Globe valve, open l80 close screwed return. ... 

Valves with pocket areas or closing devices (e.g., ball, plug, gate, and globe) that move into and out of flow area should be avoided. 

The flow area will depend on the valve travel, with a characteristic dictated by the geometry of the plug and cage in a globe valve or by the detailed shape of the disc or notched ball in a rotary valve. Hence, in general, the valve opening is a function of the valve travel y = / (x). The geometrical basis for the valve characteristic means that the function, /, is applicable equally to liquid and gas flow. 

Globe or stainless steel ball valves with Teflon trim are recommended where throttling is desired. Gate valves are suitable only in locations where the valve operations are either fully open or fully closed. Valves should have all-metal seats and disks. The use of aluminum is not recommended. 

There are many different types of valves used in safety instrumented functions. Typical valve t)rpes include ball, butterfly, offset butterfly, gate, globe and other special designs that are not readily categorized into the standard design groups. 

Binding may occur between the closure member and the seat or between the stem and the stem bore. The sensitivity of binding between the closure member and the seat depends on the amoimt of contact the two surfaces maintain. Because of this, ball valves have a higher incidence of this failure compared to a butterfly valve. Binding failures are non-existent in a globe valve. 

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