Description
Spirax Sarco MST21 stainless steel balanced-pressure thermostatic steam traps are repairable balanced-pressure steam traps designed for relatively low condensate discharge applications, such as tracing lines. Constructed from stainless steel for corrosion resistance, MST21 provides standard capacity for tracing lines, while MST21H offers higher capacity for special applications. The fill capsule type must be specified when ordering. Standard capsules are marked “STD” and discharge condensate at approximately 10°C below saturated steam temperature. Optional capsules marked “SUB” discharge condensate at approximately 22°C below saturation temperature, while capsules marked “NTS” discharge condensate at approximately 4°C below saturation temperature.
Available Models
| Model | SKU |
|---|---|
| MST21 1/4” BSP STD Polished | 11250660 |
| MST21 1/4” BSP NTS Polished | 11251660 |
| MST21 1/2” BSP STD Polished | 11250860 |
| MST21 1/2” BSP NTS Polished | 11251760 |
| MST21H 1/2” BSP STD Polished | 11251460 |
| MST21H 1/2” BSP NTS Polished | 11251860 |
| MST21H 3/4” BSP STD Polished | 11251960 |
| MST21H 3/4” BSP NTS Polished | 11252160 |
| MST21H 1” BSP STD Polished | 11252260 |
| MST21H 1” BSP NTS Polished | 11252460 |
Standards
This product fully complies with the European Pressure Equipment Directive 97/23/EC. Test reports are available; specify certificate requirements when ordering.
Sizes and Pipe Connections
-
MST21: ¼”, 3/8” and ½” threaded NPT or BSP connections, EN228-1.
-
MST21H: ½”, ¾” and 1” threaded NPT or BSP connections, EN228-1.
Operating Range
-
PMA - maximum allowable pressure: 25 bar g@300°C
-
TMA - maximum allowable temperature: 400°C@23 bar g
-
Minimum allowable temperature: 0°C
-
PMO - maximum operating pressure: 21 bar g@270°C
-
TMO - maximum operating temperature: 270°C@21 bar g
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Minimum operating temperature: 0°C
-
Note: Consult Spirax Sarco for lower operating temperatures.
-
Maximum designed cold hydraulic test pressure: 38 bar g
Materials
| No. | Part | Material |
|---|---|---|
| 1 | Body | Austenitic stainless steel ASTM A743 CF16Fa |
| 2 | Cover | Stainless steel 420A UGIMA AISI 420 |
| 3 | Capsule | Stainless steel |
| 4 | Spring | Stainless steel BS 2056 302 S26 |
| 5 | Baffle | Stainless steel BS 1449 304 S15 |
| 6 | Strainer (0.8mm aperture) | Stainless steel ASTM A240 316L |
| 7 | Gasket | Stainless steel BS 1449 304S15 |
| Note: Materials shown in parentheses correspond to the applicable standards. |
Weight (Approximate)
| Size | Weight (kg) |
|---|---|
| ¼” | 0.34 |
| ½” | 0.48 |
| 3/8” | 0.48 |
| ¾” | 0.48 |
| 1” | 0.48 |
Capacity
Includes cold-water and hot-water capacity data; detailed values are not specified.
Safety Information, Installation and Maintenance
See the installation and maintenance guide supplied with the product (IM-P125-07).
Installation Instructions
Install this steam trap vertically, with the capsule horizontal and the inlet at the top. For horizontal installation, it is preferable to install a suitable drop leg upstream. Install suitable isolation valves upstream and downstream of the trap to ensure safe maintenance or replacement. Remove all packaging before installation. Open the isolation valve slowly until the system reaches stable operation, and check for leaks. Note that the body/cover gasket contains a stainless steel support ring; handle it carefully.
Disposal
This product is recyclable and, when disposed of properly, does not present an ecological hazard.
Ordering Information
Example: 1 - Spirax Sarco ½” MST21 balanced-pressure steam trap with NPT threaded connections. “STD” capsule, discharging condensate at approximately 10°C below saturated steam temperature.
Ordering Spare Parts
Order spare parts according to the descriptions in the table above, specifying the trap size and model together with the capsule type. Example: 1 - Internals for ¼” MST21 steam trap, “STD” capsule, discharging condensate at approximately 10°C below saturated steam temperature.