Balanced Pressure Thermostatic Steam Trap L21S / L32S – Fail-Open Design for Industrial Steam Systems

In industrial steam systems, efficient condensate removal without live steam loss is critical to maintaining heat transfer performance and operational safety. The L21S/L32S Balanced Pressure Thermostatic Steam Trap is engineered with precise temperature-controlled operation and a fail-open safety design, ensuring reliable condensate discharge, reduced water hammer risk, and long-term protection of equipment under high-pressure and high-temperature conditions.

1. Product Overview

The Balanced Pressure Thermostatic Steam Trap is designed to automatically discharge condensate from steam systems without allowing live steam loss.

Models L21S and L32S are engineered for a wide range of industrial applications, including:

• Steam mains
• Steam tracing systems
• Dryers
• Process heaters

With a forged steel body construction, these models provide high durability and reliable performance under demanding pressure and temperature conditions.

2. Operating Principle – Balanced Pressure Thermostatic Mechanism

The balanced pressure thermostatic steam trap operates based on the temperature difference between saturated steam and condensate.

Inside the trap, a temperature-sensitive X-element (C6) contains a specially formulated liquid. The operating cycle is as follows:

• When cool condensate enters the trap → the element contracts → the valve opens → condensate is discharged.
• When steam approaches saturation temperature → the element expands → the valve closes → live steam is retained.

This cyclic operation ensures controlled condensate discharge at a consistent subcooling level (up to 6°C below saturation temperature).

3. Fail-Open Design – Operational Safety Advantage

The Fail-Open design ensures that, in the unlikely event of element failure, the valve remains in the open position.

Key advantages:

• Prevents condensate accumulation in the steam space
• Reduces risk of water hammer
• Protects downstream heat transfer equipment
• Enhances overall system safety

This is a significant advantage compared to traps that may fail closed, potentially causing dangerous condensate backup.

4. Key Features of Models L21S / L32S

• Forged steel body construction
• Stable cyclic operation across the full pressure range
• Does not retain condensate in the steam space
• Excellent air venting capability
• Resistant to superheat and water hammer
• Compact design with high discharge capacity
• Hardened stainless steel valve seat
• Built-in strainer with large surface area
• Easy cleaning and maintenance
• Optional built-in check valve available

5. Technical Specifications

Specification	L21S	L32S
Nominal Sizes	15, 20, 25 mm	15, 20, 25 mm
End Connections	Screwed, Socket Welded, Flanged	Screwed, Socket Welded, Flanged
Max. Operating Pressure (PMO)	2.1 MPaG	3.2 MPaG
Min. Operating Pressure	0.01 MPaG	0.01 MPaG
Maximum Back Pressure	90% of inlet pressure	90% of inlet pressure
Subcooling	Up to 6°C	Up to 6°C
X-element Type	C6	C6

6. Operating Limits

• Maximum Allowable Pressure (PMA): 3.2 MPaG
• Maximum Allowable Temperature (TMA): 300°C
• Operating temperature follows the saturated steam pressure curve.

These limits ensure suitability for medium- to high-pressure industrial steam systems.

7. Construction & Materials

Major components are manufactured using high-quality materials:

• Body & Cover: Carbon Steel (ASTM A105 equivalent)
• Valve Seat: Stainless Steel SUS420F
• X-element: Stainless Steel SUS304
• Gasket: Graphite / SUS316L
• Strainer: SUS304 / SUS430

This robust material selection ensures:

• Long service life
• High corrosion resistance
• Strength under high pressure and temperature
• Reduced maintenance costs

8. Typical Applications

The L21S/L32S steam traps are suitable for:

• Steam distribution mains
• Steam tracing lines
• Heat exchangers
• Industrial dryers
• Tank heating systems

Their superior air venting capability makes them especially effective during system start-up conditions.

9. Comparison with Other Steam Trap Types

Criteria	Thermostatic (L21S/L32S)	Mechanical	Thermodynamic
Air Venting at Start-up	Excellent	Moderate	Limited
Temperature Sensitivity	High	Low	Low
Superheat Resistance	Good	Moderate	Good
Fail-Safe Behavior	Fail-Open	Design dependent	Not guaranteed
Suitability for Tracing	Highly suitable	Not optimal	Not recommended

10. System Benefits

By installing the L21S / L32S balanced pressure thermostatic steam trap, you can achieve:

• Improved heat transfer efficiency
• Reduced water hammer risk
• Minimized live steam loss
• Enhanced operational safety
• Extended equipment lifespan
• Lower long-term maintenance costs

11. Conclusion

The L21S / L32S Balanced Pressure Thermostatic Steam Trap provides a reliable and safe condensate removal solution for industrial steam systems requiring:

• Accurate temperature-based condensate discharge
• Excellent air venting performance
• Fail-Open operational safety
• High durability under demanding pressure conditions

It is an ideal solution for industries such as food processing, textiles, chemicals, power generation, and general manufacturing.