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KTM VIRGO SERIES E & U TOP ENTRY TRUNNION BALL VALVE
INSTALLATION, OPERATION AND MAINTENANCE INSTRUCTIONS
12 BODY CAVITY RELIEF OPERATION
Single piston effect seat - self relieving seat
When seats are under pressure in pipeline,
upstream and downstream both, the resultant
thrust from pressure pushes the seat rings
towards the ball.
At the same time, pressure in the body cavity
creates a thrust that pushes the seat rings
away from the ball.
The single piston effect (SPE) permits the
automatic release of overpressure in the body
cavity when the valve is in the fully open or
closed position. In single piston effect design,
seat rings are thus "self-relieving".
Double piston effect seat (DEP) - non relieving
type of seats
When seats are under pressure in pipeline,
upstream and downstream both, the resultant
thrust from pressure pushes the seat rings
towards the ball.
Also, pressure in the body cavity creates a thrust
that pushes the seat rings towards the ball.
When the valve is designed with double piston
effect (DPE), self-relieving does not occur and
hence PR (pressure relief) valve is mandatory
with pre-setting to avoid over pressure building
in the cavity.
FIGURE 18
Square/rectangular type stem packing arrangement
Stem
Gland
Braided
gaskets
One packing set
13 GLAND PACKING ASSEMBLY PROCEDURE
1. In case of packing contain braided graphite, it
shall be placed at bottom and top. Position of
packing arrangement such that the oblique
cut of these braided graphite is 180° apart.
Refer Figure below for appropriate
arrangement for die molded and for VEE type
packing.
2. Place the gland into the housing and disk
spring (for VEE type packing) and the cap
screw / hex bolt.
3. Hand tighten cap screw / hex bolt in
crisscross pattern.
4. Tighten gland cap screws / hex bolt in
crisscross pattern by using 25% torque as
specified in Section 14 against mentioned
fasteners material.
5. Ensure no bottoming up of gland or
otherwise one ring needs to be added in
packing set.
6. Verify that the gland top surface is at equal
depth from top face of housing.
NOTE
Full tightening of screws shall be done during
performance testing depending on leakage observed.
FIGURE 19
VEE type stem packing arrangement
Gland bolt
Disk
springs
Gland
Stem
Braided
gaskets
Die molded gaskets
One packing set
VEE type packing set
15
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