Which type of valve operates on the principle that as the pressure in a cylinder increases, the temperature of the gas increases?
a. Direct-acting valves c. Rupture-disk pres-sure-relief valves
b. Fusible-plug pres-sure-relief valves d. Spring-loaded pressure-relief valves
ANS: B
Fusible-plug pressure-relief valves operate on the principle that as the pressure in a tank increases, the temperature of the gas increases, causing the plug to melt. Spring-loaded devices are de-signed to release excessive cylinder pressure and reseal, preventing further release of gas from the cylinder after the cause of the excessive pressure is removed. The rupture-disk will buckle when the pressure inside the cylinder exceeds a certain predetermined limit. Direct-acting valves are not pressure-relief valves; instead, they are controlling devices that seal the contents of a com-pressed cylinder until it is ready for use.
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