Valve body types

Fig, 6.45. Continuous valve-body type refractometer suitable for measuring concentration of dissolved solids... 

Nickel is usually alloyed with elements including copper, chromium, molybdenum and then for strengthening and to improve corrosion resistance for specific applications. Nickel-copper alloys (and copper-nickel alloys see Section 53.5.4) are widely used for handling water. Pumps and valve bodies for fresh water, seawater and mildly acidic alkaline conditions are made from cast Ni-30% Cu type alloys. The wrought material is used for shafts and stems. In seawater contaminated with sulfide, these alloys are subject to pitting and corrosion fatigue. Ammonia contamination creates corrosion problems as for commercially pure nickel. 

High Pressure Valves used for pressures nominally above 760 bar (11,000 psi, pressures above ANSI Class 4500) are often custom-designed for specific applications. Normally, these valves are of the plug type and use sped ally hardened plug and seat assemblies. Internal surfaces are polished, and internal corners and intersecting bores are smoothed to reduce high localized stresses in the valve body. Steam loops in the valve body are available to raise the body temperature to increase ductility and impact strength of the body material. 

A lower capacity is required at critical flow for a valve with less pressure recovery. Although this may not lead to a smaller body size because of velocity and stability considerations, the choice of a more economical body type and a smaller actuator requirement is attractive. The heavy-duty angle valve finds its application generally on flashing-hydrocarbon liquid service with a coking tendency. 

The valve body is machined from a carbon-filled Teflon block (75% Teflon, 25% carbon) (Ebolon), and the spools are made of polycarbonate with Viton O rings for seals. Teflon tubing is attached to the ports via Teflon 0-ring compression fittings. Two 24-V DC push-type solenoids position the spool. 

FIGURE 8.1 Pyrolysis unit, Scientific Glass Engineering (SGE) Pyrojector. 1. Sample loading area, 2. Quartz sample tube (reaction zone), 3. Sample loading cover interlock, 4. Valve body, 5. O-ring type seal, 6. Carrier gas inlet, 7. Check valve, 8. Carrier gas vent, 9. Valve spindle, 10. Heat deflectors, 11. Micro furnace,... 

Valve bodies for the most part are basically of the same metal as the piping. Many different types are in caustic service. Globe valves have several useful safety features. These include ... 

Both types can be made in multi-port form, that is the hole in the ball or plug may be T or L shaped and the valve body has three or four outlets (Fig. 3.15). The careful selection of a single, multi-port valve will not only eliminate two or three valves but it will also eliminate the dead leg of material that remains in a branch above the conventional valve (Fig. 3.16). 

Control valves consist essentially of three parts. The valve body is used to obstruct the flow to a desired degree to obtain a specified fluid passage. Figure 3.7 shows a balloon-type valve, where the amount of flow that passes the valve is determined by how far inside the seat the cap is, indicated by numbers 1 and 2. 

Table 22-1 summarizes symbols used to identify material types. These symbols are usually permanently marked on piping, flanges, and valve bodies at the time of fabrication. 

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