The following is a list of likely causes of a globe
valve seat leak and recommended solutions:
The valve is not being fully closed.
Make sure the valve is being closed fully, but do not
use cheaters.
Valve has a motor actuator with a position limitor set
incorrectly.
Actuator motor stops when valve reaches a position limit
but valve is still partially open. Consult actuator manufacturer's
manual for procedure. Position seating of a wedge gate is a difficult
operation and cannot be done by eyeballing. If you require assistance
verifying actuator position limit switches, please contact Velan Field
Engineering Services.
Circumferential contact between the seat and wedge or
disc is not 100%. Minor imperfections on the either the seat or disc
create paths for fluid to escape.
The seat and disc need lapping. Follow warning instructions
in Section 3 of your maintenance manual. Remove the line pressure
and disassemble the valve. Lap the seat and disc and then perform
a bluing test. Repeat until full circumferential contact achieved.
Reassemble the valve. Procedure for seat lapping is in the valve maintenance
manual. Manuals can be delivered, upon request, to customers via e-mail.
The valve was welded onto the line with the disc open.
This caused either seat distortion or weld splatter resulting in seat
damage.
Misalignment in the piping was overcome during installation
by using valve flange or lugs to force alignment. This can lead to
distortion or body flexing, especially in smaller valves. A full seal
is no longer present between the seat and the disc.
