Characteristics of the Various Kinds of Steam Traps

Type of Trap Type Of Discharge Opening Force Closing Force Temperature of Condensate Discharge Air Withstand Water Hammer
Plain float Continuous Buoyancy Float weight Saturation No No
Trip float Intermittent Buoyancy Float weight Saturation No No
Open bucket Intermittent Weight of bucket Buoyancy Saturation No Yes
Inverted bucket Intermittent Weight of bucket Buoyancy Saturation   Yes
Metallic expansion Semi-continuous Metallic contraction Metallic expansion Pre-set temperature Yes Yes
Liquid expansion Semi-continuous Steam pressure Liquid expansion Pre-set temperature Yes Yes
Balanced pressure expansion Semi-continuous Differential pressure Differential pressure Below saturation Yes No
Relay-float, bucket, bottle Continuous if compensated Outside source unlimited Outside source unlimited Saturation No -
Pumping or lifting Intermittent - - Any temperature below steam temperature No -
Barometric leg Continuous Always open   212°F or less N -
U-tube* Continuous Always open   Saturation at exit pressure No -
Type of Trap Strainer Before Condensate Drained Will Lift Condensate Damage By Frost Check Valve Before Trap Suitable for Superheated Steam Suitable for Varying Pressure
Plain float Highly desirable Instantly Yes Yes No Yes Yes
Trip float Desirable As formed Yes Yes No Yes Yes
Open bucket Not essential As formed Yes Yes yes- Yest yes
Inverted bucket Not essential As formed Yes Yes Yes Yest Yes
Metallic expansion Highly desirable At pre-set temperature Yes No No Yes No
Liquid expansion Highly desirable At pre-set temperature Yes No   Yes No
Balanced pressure expansion Highly desirable After cooling Yes No No No yes
Relay-float, bucket, bottle Desirable As formed Yes Yes No Yes Yes
Pumping or lifting Not essential As formed Yes   In trap Yes Yes
Barometric leg Unnecessary Instantly No - No - Yes
U-tube* Unnecessary Instantly No - No+ - No