Installation and Maintenance Methods for Danfoss STC100-125-DN150 Butt-Weld Type Globe Valve

Stem Seal Housing

During maintenance, only replace the stem seal housing assembly as a whole. This assembly is sold as a spare part. Do not remove the stem seal housing while the valve is still under internal pressure. However, if the following precautions are taken, the stem seal housing can be removed even when the valve is pressurized.

Back Sealing (Figure 6)

When back sealing is required, rotate the stem counterclockwise until the valve is in the fully open position.

Pressure Equalization (Figure 7)

In some cases, pressure may build up below the stem seal housing. Therefore, when equalizing pressure, secure the handwheel or a similar device to the top of the stem. Slowly loosen the stem seal housing to equalize the pressure.

Removing the Stem Seal Housing (Figure 8)

The handwheel and stem seal housing can now be removed.

Removing the Valve

Do not remove the bonnet while the valve is pressurized.

- Ensure the O-ring is not damaged

- Ensure the stem has no scratches or impact marks

- If the PTFE plug gasket is damaged, the entire plug assembly must be replaced

Replacing the Plug (Figure 9)

Use a hex key to unscrew the plug screw (Position D)

STC 15-40..........................................2.0 mm A/F

STC 50-65..........................................2.5 mm A/F

STC 80-100 .......................................... 4 mm A/F

STC 125-150 ....................................... 5 mm A/F

(Hex keys are included in the Danfoss Industrial Refrigeration Gasket Set).

Remove the balls (Position E).

Number of balls at Position E:

STC 10-20......................................................10 pcs

STC 25-65......................................................14 pcs

STC 80-150 ..................................................13 pcs

The plug can now be removed.

Place the new plug on the stem and replace the balls. Treat the plug locking screw with Loctite No 648 before retightening to ensure the locking screw is properly secured.

Assembly

Before installing the valve, remove all dust from the valve body. Before reinstalling the plug into the valve body, check that the plug is screwed to the maximum open position (Figure 5).

Tightening

Use a torque wrench to tighten the bonnet onto the valve body to the torque specified in the table (Figure 5b). Use a torque wrench to tighten the stem seal housing onto the valve body to the torque specified in the table (Figure 10). Use only genuine Danfoss parts (stem seal housing, O-rings, and gaskets) for replacement. Before replacing spare parts, confirm that the material of the new spare part is suitable for the relevant refrigerant. If you have any questions, please contact your local Danfoss office.