Steam Trap Selection Guide: How to Choose the Right Steam Trap
Selecting the correct steam trap requires matching the trap type, material, and capacity to your specific application. This step-by-step guide walks through the key factors for selecting the right trap for your application.
Step 1: Determine the Application
The type of equipment being drained is the single most important factor in trap selection:
- Drip legs / steam mains: Inverted bucket traps—dirt handling, water hammer resistance, intermittent blast discharge clears the line
- Steam tracing: Inverted bucket, especially stainless steel for outdoor durability
- Heating / HVAC: Float & Thermostatic—continuous drainage, high air-venting capacity, vacuum capability
- Process heat exchangers: F&T for continuous drainage or IB for ruggedness, depending on priority
- Compact installations: Disc traps where space is limited
Step 2: Identify System Pressure and Temperature
Match the trap’s maximum operating pressure to your system:
| Pressure Range | Body Material | Armstrong Series |
|---|---|---|
| Vacuum to 30 psig | Cast Iron | B/BI (F&T), 800, 880 (IB) |
| To 250 psig | Cast Iron | 200, 800, 880 (IB) |
| To 400 psig | Stainless Steel | 1000, 1800, 2000 (IB) |
| To 600 psig | Stainless Steel / CD-33 | CD-33 (Disc), 1000 (1022 model) |
| To 650 psig | Forged Carbon Steel | 300, 521 (IB) |
| To 1,000 psig | Forged Chrome-Moly | 400 (IB) |
| To 1,800 psig | Forged Chrome-Moly | 5000 (IB) |
| To 2,700 psig | Forged Chrome-Moly | 6000 (IB) |
Step 3: Estimate Condensate Load
Each steam trap model has a specific maximum capacity. Oversizing a trap can shorten its life (especially disc traps), while undersizing causes condensate backup. As a general engineering practice, apply a safety factor of at least 2x the calculated condensate load when selecting trap capacity.
Step 4: Select the Connection Type
Steam traps are available in multiple connection types to match your piping:
- Screwed (NPT/BSPT): Most common for sizes ½″ to 2″
- Socket Weld (SW): For welded connections in higher-pressure applications
- Flanged: For larger sizes and easy removal
- 360° Connector: Quick in-line replacement
- Integral Strainer Connectors: Quick-change capability with built-in strainer
Step 5: Consider Material Requirements
- Cast Iron (ASTM A48): Economical for low-to-medium pressure (≤250 psig). Standard for heating systems.
- Forged Carbon Steel (ASTM A105): Higher pressure capability to 650 psig. Required for many industrial applications.
- Stainless Steel (ASTM A240 Grade 304L): Corrosion resistance, freeze resistance, 3–4x longer life. Compact size. Three-year guarantee.
- Forged Chrome-Moly: For extreme pressures to 2,700 psig. Power generation and high-pressure process.
- Stainless Steel CA40 (ASTM A743): CD-33 disc trap body material for high-temperature service.
Quick Selection Matrix
| I need to trap... | Best Choice | Why |
|---|---|---|
| Steam main drip legs | Cast iron or forged steel inverted bucket | Dirt handling, water hammer resistance |
| Outdoor tracer lines | Stainless steel inverted bucket | Corrosion/freeze resistance, 3–4x life |
| HVAC heating coils | Float & Thermostatic | Continuous drainage, vacuum capability |
| Industrial heat exchangers | F&T or forged steel inverted bucket | Continuous (F&T) or rugged (IB) |
| High pressure (400+ psig) | Forged steel or chrome-moly inverted bucket | Only IB available at these pressures |
| Tight spaces / quick install | Disc trap or 360° connector style | Compact size, easy replacement |