Relief Valves. Relief valves are the generally preferred method of preventing pressure buildup. Relief valves are discussed below in “When Relief Valves Are Needed.”
Insulation of Lines. Several inches of insulation are needed to sufficiently reduce the heat flow to prevent significant temperature rise. The cost of insulation is the disadvantage of this method.
Gas or Vapor Pressure Chambers. The disadvantages of gas or vapor pressure chambers are: (1) higher cost than relief valves, (2) possible contamination if fluid in line is changed before the pressure chamber is flushed out, and (3) gum formation in some gasolines upon contact with air. However, where maintenance of relief valves is a problem, as in some acid or chemical lines, properly designed chambers may offer advantages.
Partial Draining of Lines Before Blocking. This method is subject to human error. Drilled Holes in Valves. This method is not acceptable because of uncontrolled flow through the hole at times other than when relief is necessary.
Slight “Cracking” of Valves. This method is subject to human error and allows contamination if fluids separated by the valve are different.