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Pressure Test
Twin Seal valves can be hydrostatically pressure-tested after installation, to full API 6D limits per Table 3 below.
Table 3
Valve figure No.
ASME Class
Shell Test Pressure
(Valve Open)
Seat Test Pressure (Valve Closed)
Supplimentary (API 598) Air Seat Test
Pressure (Vavle Closed)
OPERATION
The Twin Seal valve is a non-lubricated, resilient seal, plug-
type valve which has a mechanical means of freeing the plug
before it is rotated from the closed to the open position.
In opening the valve, the plug is raised, thus retracting the
seating segments or slips through their tapered dovetail
connections. Only after the slips are fully retracted perpen-
dicularly from the body seat is the plug rotated to the open
position.
Conversely, in closing the valve, the plug and slips are
rotated freely, with no seal-to-body contact until the slips
are positioned over the ports. Then the plug is driven down
between the slips and the tapered surfaces wedge out the
slips for a positive upstream as well as downstream shut-off.
For maximum upstream sealing, do not back off the hand
wheel. Warning: Do not over torque by using cheater bars.
The small Twin Seal valves are handwheel operated, and
require up to 3 turns to open or close. Up to 2 3/4 turns
expand or retract the slips, while 1/4 turn rotates the plug.
Large valves operate in a similar manner, except that they
have enclosed weather-proof worm gearing.
At the top of the valve, a position indicator flag shows the
exact plug position. It appears in line with the flow when
the valve is open, and perpendicular to the flow when the
valve is closed.
07/2011 / IOM-GEN-TWIN-03
C411; C811; C911;
C421; C821; C921;
8811; C1611; C1500
8821; C1621; C1521
150
300
(pisg)
500
1200
(kg/cm2)
35
85
(psig)
300
800
(kg/cm2)
21
56
(psig)
80
80
(kg/cm2)
6
6
Since Twin Seal valves hold bubble-tight, for ease of
opening in liquid service, it is important to prevent trapped
body pressure from exceeding the working pressure of the
valve. Therefore, a relief system is required to prevent pres-
sure buildup in the body cavity.
5
E N G I N E E R E D & P R O C E S S V A L V E S
C441; C841; C941;
C851; C1651;
C1641; C1541
C1551
600
900
2250
3350
158
235
1600
2400
113
168
80
80
6
6
A
C
Installation, Operation and Maintenance Manual
Comments
No leakage permitted
Test upstream &
downstream seats. No
leakage permitted
Test upstream &
downstream seats. No
leakage permitted
B
D
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