10
Forbes Marshall Thermodynamic Trap
7.4. Procedure to service trap: [Refer figure 1]
1. Remove the Isotub if fitted and unscrew the main bore cap (2) using a spanner. Do not
use a pipe wrench which may cause distortion of the main bore cap (2).
2. Any minor or major damage / scratch on the seating surface of the disc (3) or body seat
(1) will cause the steam trap to pass steam. Since the disc is less hardened than the body
seat (1), fine particle passing through the steam trap (along with the condensate) could
damage the disc (1). This damage will be in the form of scratches on the disc (1) surface
area. If the scratch depth is not much this can be cured by lapping the disc (3) and the
steam trap can be made functional. If the body seat(1) is slightly worn out it can be
refaced by lapping individual on a glass surface plate. The amount of material to be
removed by lapping should not exceed 0.25mm (0.01”).
Lapping Procedure:
a)
Requirement: Emery paper, glass surface, lapping paste and oil.
b) First, lap the disc (3) on a piece of emery paper (grade 220) to eliminate scratches
on the disc (3) and to prepare the surface for further fine lapping.
c)
Apply the lapping paste and oil on to the glass surface and rotate the disc (3) in the
shape of the numeric “8” (Eight).
d) Lapping should be done till all scratches on the disc (3) disappear.
Note
: If the scratches on the disc (3) are not curable then the disc (3) should be replaced.
3. When re-assembling main bore cap (2), the disc (3) is normally placed in position with
the grooved side in contact with the body seating face (1). No gasket is required but
high temperature anti-seize grease should be applied to the threads. Tighten the main
bore cap (2) to the recommended torque as mention in Table 1.
7.5. Procedure to replace the strainer screen: [Refer figure 1]
1. Unscrew the strainer cap (5) using the spanner, withdraw strainer screen (4) and clean
or if damaged replace with new one.
2. To re-assemble, insert the strainer screen (4) in the strainer cap (5), then screw strainer
cap (5) into the place with recommended torque as mention in Table 1.
3. No gasket is required but a finer smear of Molybdenum Disulphide grease should be
applied to the threads.
7.6. Steam traps testing:
Following methods can be used to determine the operating condition of a trap and
determine if its working properly:
1. Testing traps through visual inspection.
2. Testing traps using temperature gun / equipment
3. Testing traps using sound/ultrasound.
4. Testing traps through online monitoring
.
