Page 77 - Fluid mechanics, heat transfer, and mass transfer

PIPING, SEALS, AND VALVES
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FIGURE 3.14 Symbols for some common types of valves.

. What are the symbols used for different types of valves? . “A ball cock is used to prevent overflow from an
Illustrate with diagrams. overhead tank.” Illustrate how it works.
& Symbols of some commonly used valves are given in & Ball cock is connected to a float, which is a plastic
Figure 3.14. ball. As liquid level rises, the float moves up over the
. What type of valves do you recommend for gas lines liquid surface. When the tank fills up to its prede-
requiring tight shutoff? termined level, the lever attached to the ball closes
the valve stopping the flow.
& Globe valves are most commonly used for gases for
control and when tight shutoff is required. . “Pressure drop in a Y-type globe valve is less than that
for a standard globe valve.” True/False?
& Where the valve is to function for fully open or fully
closed conditions requiring no flow control, gate & True.
valves are used. . “In a laboratory experimental setup, gate valves are
. What types of valves do you recommend for use on installed for varying water flow rates.” Is it the correct
slurry lines? arrangement? Explain.
& Pinch valve is claimed to be one of the best valves & No. Not suitable for flow control. Reason is explained
available for slurry service. This type of valve can elsewhere. Gate valves are operated either in fully
handle abrasive slurries such as lime, minerals such open or in fully closed condition.
as alumina, rejects from pulp stocks, titanium diox- . What are safety, relief, and safety relief valves?
ide, cement, and sand. & Safety valve is an automatic pressure-relieving de-
& Diaphragm valves are used for slurries for a long vice actuated by the static pressure upstream of the
time. Diaphragms require frequent replacement, es- valve and characterized by full opening pop up
pecially for abrasive slurries. action.
& Ball valves are used for nonabrasive slurries, as ball ➢ It is used for air, steam, or vapor service.
moves across seats with a wiping action. ➢ Rated capacity is reached at 3%, 10%, or 20%
. “Friction losses are more for a gate valve compared to overpressure, depending on applicable code.
globe valve both being under fully opened conditions.” & Relief valve is an automatic pressure-relieving de-
True/False? vice actuated by the static pressure upstream of the
& False. With a gate valve, flow direction will not valve that opens further with the increase in pressure
change whereas in a globe valve flow direction over the opening pressure.
changes increasing DP. ➢ It is used primarily for liquid service.