Classification and Principles of Mechanical Steam Traps

Core Principles and Classification of Mechanical Steam Traps

Steam traps separate steam and condensate based on three core principles:

• Density difference

• Temperature difference

• Phase change

Corresponding to these principles, three types of steam traps are developed: mechanical, thermostatic, and thermodynamic.

I. Mechanical Steam Traps

Also called float-type traps, they utilize the density difference between condensate and steam. The float rises/falls with condensate level changes to drive the valve disc open/closed, achieving steam retention and condensate drainage.

Key Performance Advantages

• Small subcooling degree

• Unaffected by operating pressure/temperature fluctuations

• Immediate drainage (no water accumulation in heating equipment)

• Optimal heat exchange efficiency

• Maximum back pressure rate: 80%

• High operational reliability (ideal for process heating equipment)

Common Types & Specifications

1. Free Float Type Steam Trap

• Structure: Single precision-ground stainless steel hollow float (serves as both float and opening/closing element; no wearing parts)

• Key Features:

• Equipped with Y-series automatic air vent (high sensitivity, energy-saving with zero steam leakage)

• Minimum operating pressure: 0.01 MPa (stable performance from 0.01 MPa to max operating pressure)

• Minimum subcooling degree: 0°C (drains saturated-temperature condensate)

• Back pressure rate: >85% (continuous drainage)

• Operation Process:

• Startup: Air is discharged via automatic air vent; low-temperature condensate enters, lifting the float to open the valve.

• Normal operation: Float rises/falls with condensate level to maintain steam retention and drainage.

2. Semi-Free Float Type Steam Trap

• Structure: Single semi-float bucket (opening downward; serves as opening/closing and sealing element)

• Key Features:

• Resistant to water hammer; no wearing parts; zero steam leakage

• Back pressure rate: >80%; minimum subcooling degree: 0°C

• Suitable for saturated-temperature condensate drainage

• Operation Process:

• Startup: Bimetallic air release element flicks the bucket open to discharge air/condensate.

• Steam entry: Buoyancy lifts the bucket; bimetallic element contracts to close the valve.

• Condensation: Bucket loses buoyancy, sinks, and reopens the valve (cyclic intermittent/continuous operation).

3. Lever Float Type Steam Trap

• Structure: Float connected to a lever driving the valve core

• Key Features:

• Dual valve seat design for high displacement (compact size with large capacity)

• Maximum condensate flow: 100 tons/hour

• Same basic advantages as free float type

• Application: Ideal for large-scale heating equipment

4. Inverted Bucket Type Steam Trap

• Structure: Inverted bucket (opening downward) connected to a lever driving the valve core

• Key Features:

• Air-discharging capability; water hammer resistance; good anti-fouling performance

• Minimum subcooling degree; steam leakage rate: <3%; maximum back pressure rate: 75%

• Not suitable for operating pressure difference < 0.1 MPa

• Operation Process:

• Startup: Bucket falls due to weight; valve opens to discharge air/condensate.

• Steam entry: Buoyancy lifts the bucket to close the valve.

• Condensation: Steam escapes through a small hole; bucket sinks to reopen the valve (cyclic intermittent drainage).

5. Combined Superheated Steam Trap

• Structure: Advanced dual-chamber design (upper main valve chamber + lower auxiliary valve chamber)

• Key Specifications:

• Maximum allowable temperature: 600°C

• Valve body: Full stainless steel; valve seat: Hard alloy steel (long service life)

• National patent-certified (fills domestic gap for superheated steam applications)

• Operation Process:

• Condensate entry: Float in auxiliary valve seals the steam inlet; condensate rises to main valve chamber.

• Drainage: Inverted bucket sinks to open the main valve.

• Steam entry: Auxiliary valve opens; steam lifts the bucket to close the main valve (cyclic intermittent operation).