Process Air Heaters - Trap

Trap Requirements - Constant Pressure

The steam traps that best suit constant pressure applications:

can operate against back pressure
respond immediately to slugs of condensate
are continuous drainers
conserve energy by operating reliably over a long period of time
vent non-condensable gases at steam temperature
provide abrupt, periodic discharges that purge condensate and non-condensables from the lines

The first two conditions are overriding. If the trap does not fulfill these requirements well, it should not be considered for these applications.

Combined, these requirements make the inverted bucket (IB) the best trap choice for process air heaters. At constant pressure below 30 psig (2 bar), the float and thermostatic (F&T) trap is a good alternative up to its pressure/temperature limitations.

	Characteristic	Inverted Bucket	F&T	Disc	Thermostatic	Differential Controller
A	Method of Operation	Intermittent	Continuous	Intermittent	Intermittent	Continuous
B	Energy Conservation (Time in Service)	Excellent	Good	Poor	Fair	Excellent
C	Resists Wear	Excellent	Good	Poor	Fair	Excellent
D	Resists Corrosion	Excellent	Good	Excellent	Good	Excellent
E	Resists Hydraulic Shock	Excellent	Poor	Excellent	Poor	Excellent
F	Vents Air and CO2 at Steam Temperature	Yes	No	No	No	Yes
G	Vents Air at Very Low Pressure (1/4 psig)(.02 bar)	Poor	Excellent	NR	Good	Excellent
H	Handles Start-up Air Loads	Fair	Excellent	Poor	Excellent	Excellent
I	Operates Against Back Pressure	Excellent	Excellent	Poor	Excellent	Excellent
J	Resists Damage from Freezing	Good	Poor	Good	Good	Good
K	Can Purge System	Excellent	Fair	Excellent	Good	Excellent
L	Performs on Very Light Loads	Excellent	Excellent	Poor	Excellent	Excellent
M	Responds to Slugs of Condensate	Immediate	Immediate	Delayed	Delayed	Immediate
N	Handles Dirt	Excellent	Poor	Poor	Fair	Excellent
O	Comparative Physical Size	Large	Large	Small	Small	Large
P	Handles "Flash Steam"	Fair	Poor	Poor	Poor	Excellent
Q	Mechanical Failure (Open -- Closed)	Open	Closed	Open	Open, Closed	Open


First Choice				Alternative				Overriding condition

	Characteristic	Inverted Bucket	F&T	Disc	Thermostatic	Differential Controller
A	Method of Operation	Intermittent	Continuous	Intermittent	Intermittent	Continuous
B	Energy Conservation (Time in Service)	Excellent	Good	Poor	Fair	Excellent
C	Resists Wear	Excellent	Good	Poor	Fair	Excellent
D	Resists Corrosion	Excellent	Good	Excellent	Good	Excellent
E	Resists Hydraulic Shock	Excellent	Poor	Excellent	Poor	Excellent
F	Vents Air and CO2 at Steam Temperature	Yes	No	No	No	Yes
G	Vents Air at Very Low Pressure (1/4 psig)(.02 bar)	Poor	Excellent	NR	Good	Excellent
H	Handles Start-up Air Loads	Fair	Excellent	Poor	Excellent	Excellent
I	Operates Against Back Pressure	Excellent	Excellent	Poor	Excellent	Excellent
J	Resists Damage from Freezing	Good	Poor	Good	Good	Good
K	Can Purge System	Excellent	Fair	Excellent	Good	Excellent
L	Performs on Very Light Loads	Excellent	Excellent	Poor	Excellent	Excellent
M	Responds to Slugs of Condensate	Immediate	Immediate	Delayed	Delayed	Immediate
N	Handles Dirt	Excellent	Poor	Poor	Fair	Excellent
O	Comparative Physical Size	Large	Large	Small	Small	Large
P	Handles "Flash Steam"	Fair	Poor	Poor	Poor	Excellent
Q	Mechanical Failure (Open -- Closed)	Open	Closed	Open	Open, Closed	Open


First Choice				Alternative				Overriding condition

Trap Requirements - Modulating Pressure

Steam traps that best suit modulating pressure applications:

resist wear
vent non-condensables at very low pressure (1/4 psi/0.02 bar)
can discharge start-up air loads
perform well with very light loads

On variable pressure service, the F&T trap is the first choice, up to its pressure/temperature limitations. An IB with a large vent is a reasonable alternative.

	Characteristic	Inverted Bucket	F&T	Disc	Thermostatic	Differential Controller
A	Method of Operation	Intermittent	Continuous	Intermittent	Intermittent	Continuous
B	Energy Conservation (Time in Service)	Excellent	Good	Poor	Fair	Excellent
C	Resists Wear	Excellent	Good	Poor	Fair	Excellent
D	Resists Corrosion	Excellent	Good	Excellent	Good	Excellent
E	Resists Hydraulic Shock	Excellent	Poor	Excellent	Poor	Excellent
F	Vents Air and CO2 at Steam Temperature	Yes	No	No	No	Yes
G	Vents Air at Very Low Pressure (1/4 psig)(.02 bar)	Poor	Excellent	NR	Good	Excellent
H	Handles Start-up Air Loads	Fair	Excellent	Poor	Excellent	Excellent
I	Operates Against Back Pressure	Excellent	Excellent	Poor	Excellent	Excellent
J	Resists Damage from Freezing	Good	Poor	Good	Good	Good
K	Can Purge System	Excellent	Fair	Excellent	Good	Excellent
L	Performs on Very Light Loads	Excellent	Excellent	Poor	Excellent	Excellent
M	Responds to Slugs of Condensate	Immediate	Immediate	Delayed	Delayed	Immediate
N	Handles Dirt	Excellent	Poor	Poor	Fair	Excellent
O	Comparative Physical Size	Large	Large	Small	Small	Large
P	Handles "Flash Steam"	Fair	Poor	Poor	Poor	Excellent
Q	Mechanical Failure (Open -- Closed)	Open	Closed	Open	Open, Closed	Open


First Choice				Alternative				Overriding condition