Australian Pipeline Valve - Installation, Operation and Maintenance Manual 14 EXPANDING SEAL PLUG VALVE DOUBLE BLOCK & BLEED API6D - TWIN SERIES b. Remove gear housing cap screws. c. Turn handwheel to further open the valve. This will turn gear housing assembly; continue until handwheel comes to desired position and gear housing mounting holes are realigned. d. Replace gear housing mounting cap screws. 3.1 PRESSURE TEST APV plug valves can be hydrostatically pressure tested after installation, to full API6D limits per Table 1 below. TABLE 1 ASME CLASS 150 300 600 COMMENTS Shell Test Pressure (Valve Open) (psig) (kg/cm2) 450 32 1150 81 2250 158 No leakage permitted. Seat Test Pressure (Valve Closed) (psig) (kg/cm2) 319 22 825 58 1650 116 Test upstream & downstream seats. Supplementary (API598) Air Seat Test Pressure (Valve Closed) (psig) (kg/cm2) 80 6 80 6 80 6 Test upstream & downstream seats. No leakage permitted. 3.2 OPTIONAL - “DIFFERENTIAL THERMAL RELIEF” - BLEED SYSTEM This specification addresses the proper functioning, trouble shooting, and repair of the APV plug valve differential (pressure) thermal relief (DTR) bleed system. Background When APV valve is seated and completely fill with a liquid, any slight variation in temperature due to the sun’s rays or ambient thermal fluctuations will cause drastic changes in body cavity pressure resulting from thermal expansion. While results vary under actual service conditions depending on media, pressure vessel rigidity, and presence of entrapped gas it is known that dangerously high pressures will build up in liquid filled positive shutoff valves. Therefore, the APV in liquid service requires a pressure relief device. The differential (pressure) thermal relief system is one such automatic “device” and should be included on every automated valve. The differential (pressure) thermal relief system is arranged as shown below. A variety of components are used. The relief valve mounted in the centre of the valve body pipes over pressure to the upstream throat of the valve. The standard relief valve is set to open at 25 PSI on all valves regardless of working pressure. With the valve closed, the relief valve will open at 25 PIS above upstream pressure. This system functions only when the valve is closed.