28
Testing the Check Valve
1. Remove the hose from the return fitting. (If the return line
drains at this point, the valve is stuck open).
2. Insert a hose from a pressurized gas source (such as nitro-
gen or compressed air) into the return fitting.
Cup your hand
around the fitting to provide a "seal".
3. Apply a burst of gas into the fitting. You should hear a click-
click sound as the seat flops up and down.
Note: If there is fluid trapped in the return line between the valve
and
the tank, it will drain out during this step.
Figure 19
29
Replacing the Check Valve
NOTE: Any soldering to the check valve body must be done
carefully to avoid melting the Teflon® seat.
1. Open the service access cover.
2. Insert a bent wire such as a
coat hanger to pull the seat
open and secure it. This keeps the Teflon® from contacting
the hot valve body.
3. Wrap the valve body with a damp rag.
4. Use a low temperature solder such as 95/5 or 50/50. Use a
hot flame and work quickly.
5. Do not release the seat until the body is cool.
CHECK VALVE CROSS-SECTION
Figure20
30
Ball and Spring Type Check Valves
Older check valves use a mechanical ball and spring arrange-
ment. Performance of this type can usually be restored by
polishing the ball using Scotch-Brite® or a similar abrasive pad.
Repair
of this type, beyond cleaning, is not practical. If a failed
valve
of this type is found, it should be replaced by the current
Teflon® seat type.
Lubrication
A small amount of molybdenum lubricant (see Coupling Lubrica-
tion) on the access cover threads
will assist in sealing and
provide easier future service.
