Spirax Sarco MST21 and MST21H Balanced Pressure Thermostatic Steam Traps

The Spirax Sarco MST21 Series Balanced Pressure Thermostatic Steam Trap are designed with a welded Stainless Steel element that is self-adjusting over the entire operating pressure range and will discharge condensate at approximately 18˚F (10˚C) below saturated steam temperature on the standard fill trap. This trap removes condensate from steam systems. Its performance is influenced by surrounding steam pressure, and it is controlled by the concentration of the liquid mixture within its capsule whose boiling point is below that of water. At start-up, when conditions are cold, the capsule remains relaxed and the valve is fully open, allowing unrestricted discharge of air. As condensate flows through the trap, it heats up the capsule. The liquid inside then vaporizes before steam reaches the trap, building vapor pressure that expands the capsule and closes the valve. When heat is lost, the vapor condenses, the capsule contracts, and the valve reopens to release condensate. As steam approaches, the cycle repeats. 

Cooney Brothers is proud to be an authorized distributor of Spirax Sarco, stocking a wide range of MST21 Balanced Pressure Thermostatic Steam Traps and MST21H Balanced Pressure Thermostatic Steam Traps. This series is constructed entirely of Stainless Steel with FNPT end connections. MST21H is the high-capacity version of this series. MST21 Thermostatic Traps are available in ¼” and ½” nominal sizes and MST21H Thermostatic Traps are available in ½”, ¾”, and 1” nominal sizes. Both traps in the series are typically offered with standard fill capsules but they are also available NTS Fill near steam (7.2°F) capsules or SUB fill subcooled (40°F) capsules. This series is rated up to 304 PSIG maximum operating pressure with a 518˚F maximum operating temperature. 

There are 4 available steam trap spare parts for the entire MST21 Series: 

1. STD Capsule Assembly (includes parts 3, 4, 5, 6, and 7)
2. SUB Capsule Assembly (includes parts 3, 4, 5, 6, and 7)
3. NTS Capsule Assembly (includes parts 3, 4, 5, 6, and 7)
4. Gasket Kit (set of 3) 

The typical applications of Spirax Sarco MST21 Balanced Pressure Thermostatic Traps and Spirax Sarco MST21H Balanced Pressure Thermostatic Traps are steam main drainage and steam tracing but they can also be used on drip sterilizers and a low-capacity air vet. This series can resist water hammer and may be installed in horizontal and vertical pipelines. Vertical installations should place the trap so the inlet is at the top and the outlet is at the bottom to ensure self-draining. If fitted on a horizontal line, the trap should precede a short drop leg. Full port isolating valves should be installed upstream and downstream of this trap.

Contact us for technical expertise and explore our selection of Spirax Sarco RT Series Balanced Pressure Thermostatic Steam Traps below which includes spare parts, real-time inventory, spec sheets, and more.