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.
