Steam Traps 101

What Is A Steam Trap Valve?

As explained in quoting the ANSI/FCI 69-1-1989 standard, a trap is an automatic valve that automatically drains condensate from steam to the outside of the valve body while maintaining tight contact with live steam, if necessary, allowing steam to flow at a controlled or adjusted rate. Most steam traps are capable of draining non-condensable gases while maintaining close contact with the steam.

In industry, steam is often used for heating or as a driving force for mechanical power. So the main function of a steam trap is used in such conditions to make sure that steam is not wasted.

Why Steam Trap Is Used In Piping?

Steam is created when water vaporizes into a gas. To make the vaporization process happen, the water molecules must be given enough energy to break the hydrogen bonds between the molecules, and this energy to convert the liquid into a gas is called “latent heat”.

The steam-based heating process uses latent heat and transfers it to a given product. When the work is complete, i.e., the steam has given up its latent heat, the steam condenses and becomes condensate. In other words, condensate does not have the ability to do work with steam. Therefore, if condensate is not removed as soon as possible, either in the steam transport piping or in the heat exchanger, the heating efficiency will be compromised.

How Many Types Of Trap Valves Are There?

Steam traps are valves used in steam piping and equipment to automatically discharge condensate, air, and other non-condensable gases, and to prevent steam leakage. Based on the operating principle of steam traps, there are three types of steam traps as follows.

Mechanical Type Steam Trap | Classification of Steam Traps by Sensible to Density Changes

Mechanical type steam traps are operated by the change in condensate level in the steam trap.

1. Float Trap

The CS41H Free Float trap is an automatic valve, especially for steam equipment with low pressure, low drainage, and high stability of temperature. The float steam trap is capable of discharging condensate from steam piping networks and heating equipment and preventing steam leakage. This product is widely used in petroleum, chemical, textile, printing and dyeing, pharmaceutical, pulp and paper, food, and other industries.

What is Difference Between Liquid, Vapor, and Gas?

Features

• Ability to continuously drain stable performance, large capacity, low air leakage rate, and high back pressure rate.
• Stainless steel hollow free float is the main part of the valve, THINKTANK adopts stainless steel ground round float ball.
• All internal parts use stainless steel material which is corrosion resistant, wear-resistant, long service life.

FT44H Lever Float Ball Steam Trap Dimensional Drawing

FT14H Lever Float Ball Steam Trap Dimensional Drawing

FT43H Lever Float Ball Steam Trap Dimensional Drawing

GM/GSB Lever Float Ball Steam Trap Dimensional Drawing

UNA23/26H Lever Float Ball Steam Trap Dimensional Drawing

SF-50WL Lever Float Ball Steam Trap Dimensional Drawing

S41h-50L Lever Float Ball Steam Trap Dimensional Drawing

2. Inverted Bucket Trap

An inverted bucket trap is an inverted bucket that is level sensitive, with the bucket opening downward and connected to a lever to drive the disc to open and close the valve. The inverted bucket trap is capable of discharging air, is free of water shock, and has good dirt resistance.

The steam leakage rate is less than 3%, the back pressure rate is 75%, there are more connections, and the sensitivity is not as good as that of the free float type trap. Because inverted bucket traps rely on the upward floating force of steam to close the valve, they are not suitable for use when the differential pressure is less than 0.1 MPA.

Inverted Bucket Steam Trap Dimensions(mm)

Model	981-3	981	980
Dimension	15．20．25	15．20．25	15．20．25
A	100	100	100
B	190	190	190
C	127	127	127
D	100	100	100
Bolt Qty	6	6	6
Max. Allowable Pressure and Temperature	1.7MPa 232℃	1.7MPa 232℃	1.7MPa 232℃
Max. Working Pressure	1.7	1.7	1.7

Other Model Inverted Bucket Steam Traps

3. Open Bucket Trap

An open bucket trap is an open bucket that is level sensitive, with the bucket opening upward.

---

Thermodynamic SteamTrap | Classification of Steam Traps by Sensible to Velocity Changes

1. Orifice Plate Steam Trap

2. Disc Thermodynamic Trap

Discharge of Water（Kg/h） (Based on Differential Pressure MPa)

Model	DN	0.05MPa	0.15MPa	0.4MPa	0.6MPa	1MPa	1.6MPa	2.5MPa
CS19H-16C CS49H-16C	DN15 DN20 DN25	150	280	400	475	600	800
CS19H-16C CS49H-16C	DN32 DN40 DN50	550	650	900	1200	1700	2100
CS19H-25 CS49H-25 CS69H-25	DN15 DN20 DN25	1717	1828	2536	2701	3202	3581
CS19H-25 CS49H-25 CS69H-25	DN32 DN40	56		119		321	470	534
CS19H-25 CS49H-25 CS69H-25	DN50	1800	2050	2600	3000	3500	4300	5000
CS19H-40 CS49H-40 CS69H-40	DN15 DN20 DN25	56		119		321	470	534
CS19H-25 CS49H-25 CS69H-25	DN32 DN40 DN50	1800	2050	2600	3000	3500	4300	5000

Material List

Body	Forged Steel
Cap	Stainless Steel
Bonnet	Forged Steel
Disc	Stainless Steel
Sealing	Stainless Steel

Model	DN	Connection	Max. Allowable Temp.℃	Body Material	B	H	H1	H2
CS19W-16P	6	Threaded	250℃	0Cr18Ni9	50	48	30	18
CS19W-16P	8	Threaded	250℃	0Cr18Ni9	50	48	30	18
CS19W-16P	10	Threaded	250℃	0Cr18Ni9	52	58	35	23
SLZ Thermodynamic Steam Trap	6	Threaded	250℃	0Cr18Ni9	40	33	24	9
SLZ Thermodynamic Steam Trap	8	Threaded	250℃	0Cr18Ni9	40	33	24	9
SLZ Thermodynamic Steam Trap	10	Threaded	250℃	0Cr18Ni9	52	37	26	11

Model	DN	B	H	H1	H2
ST-16C Adjustable Thermostatic Trap	15	62	162	95	67
ST-16C Adjustable Thermostatic Trap	20	68	162	95	67
ST-16C Adjustable Thermostatic Trap	25	75	168	93	75
ST-16C Adjustable Thermostatic Trap	32	80	175	100	80

Model		BNF1	BNF1	BNF1	BNF2	BNF2	BNF2
Connection		1/2″Threaded Ends	3/4″Threaded Ends	1″Threaded Ends	1/2″Threaded Ends	3/4″Threaded Ends	1″Threaded Ends
Size	DN	15	20	25	15	20	25
Dimension(mm)	L	100	105	105	100	105	105
Dimension(mm)	W	63	63	63	63	63	63
Weight(Kg)		0.8	0.9	0.9	0.8	0.9	0.9

3. Impulse Trap

---

Thermostatic Steam Trap | Classification of Steam Traps by Sensible to Temperature Changes

1. Bi-Thermostatic Steam Trap

2. Thermostatic Steam Trap

STC, STB, ST Series Adjustable Thermostatic Traps

Size: DN15 to DN100

Model: ST Series(Angle Type Threaded Ends), STB(Straight Type Threaded Ends), STC(Straight Type Flanged Ends)

Material: Cast Steel, Stainless Steel

Connection Type: Threaded Ends, Flanged Ends

Suitable Temperature: 80～450℃

Application: City construction, chemical industry, metallurgy industry, petroleum industry, pharmaceutical industry, food&beverage industry.

Model-Size	Dimension	Dimension	Max. Drain(ton/hr)	Model-Size	Dimension	Dimension	Max. Drain(ton/hr)	Flange O.D.
	L	H			L	H
ST8-15	120	65	1.4	STB16-15	90	150	3
ST8-20	120	65	3	STB16-20	100	150	4
ST8-25	130	70	4	STB16-25	120	165	5
ST16-15	120	65	3	STB10-40	140	185	9
ST16-20	120	65	4	STB10-50	160	195	11
ST16-25	130	70	5	STC16-15	150	175	3	95
ST16-40	145	85	9	STC16-20	150	175	4	105
ST16-50	145	95	11	STC16-25	160	185	5	115
				STC10-40	230	255	9	145
				STC10-50	230	255	11	160
				STC10-80	310	285	18	195
				STC10-100	310	355	22	215

Features of Adjustable Thermostatic Trap

STC series adjustable thermostatic trap is one of the products of thermostatic type. The temperature-sensitive element inside the valve is equipped with a temperature-sensitive mixture of a temperature-sensitive material, saturating agent, stabilizer, and filler, which is used to automatically close or open the valve by changing the state of thermal expansion and contraction in response to temperature. The temperature range for T condensate discharge is determined by selecting the appropriate specification, and then can be adjusted within this range with the adjusting screw as required.

BNF1(2)Lv21 Thermostatic Traps

Features

1. BNF1(2)Lv21 thermostatic trap with steam or air insulation, not affected by ambient temperature, reduces operation frequency, and extends service life.
2. Equipped with strainer for self drainage.
3. The valve is sensitive and reliable and has a large drainage capacity.

Principle of Operation

Thermostatic traps use the thermodynamic properties of condensate to evaporate a second time when the condensate discharge is low. Only the viscosity and sealing aspects differ from the steam in driving the opening and closing elements.

How Does A Thermostatic Steam Trap Work?

Thermostatic traps are based on the balance of steam pressure and the internal pressure of the thermostatic membrane capsule, which is filled with a special liquid whose saturation temperature is slightly lower than that of steam at any pressure.

In the start-up position, the steam trap opens fully to remove air and drain condensate. When the temperature reaches the pressure-dependent saturated steam level, the vaporization of the liquid inside the thermostatic capsule membrane generates a differential pressure that causes the orifice to close. As the condensate cools, the condensation of the liquid reduces the internal pressure of the membrane. The resultant differential pressure will benefit the external pressure that acts on the membrane by retracting and opening the orifice, which allows the condensate to drain and the cycle to continue.

NO.	Advantages of Thermostatic Steam Trap
1	Maximum Efficiency: Benefit from the hidden energy of steam.
2	Easy Maintenance: In the event of any failure, only needs removing 4 bolts from the steam trap cover, without having to replace all steam traps.
3	Easy to Installation: Unlike thermodynamic steam traps (which can only be installed on horizontal lines), thermostatic steam traps can be installed horizontally, vertically, or at an angle on steam lines and are capable of operating at 100% efficiency.
4	Drain Air or Other Gases: Due to the action of the thermostatic capsule, thermostatic steam traps are enabled to drain air and other gases that cannot condense, to protect the system from water hammer.
5	Enhanced Discharge Capacity: Condensate discharge capacity can be improved by expanding the number of capsules that are used in the valve body design. The discharge capacity depends on the type and number of capsules, as well as the size of the steam trap.

Disadvantage of Thermostatic Steam Trap

The fluid in the capsule is adjusted to the pressure of the saturated steam temperature, and at superheated temperatures, the capsule may become stuck and not function properly, so it is not suitable for ultra-high temperature steam.

3. Bimetallic Steam Trap

The Bimetallic Steam Trap works by striking a balance between the opposing bi-metal force, which depends on temperature and attempts to close the discharge valve, and the steam force, which depends on pressure and tries to open the valve. The trap is calibrated so that the bi-metal force will prevail at saturated steam temperature while the force of pressure will prevail with under-cooled condensate and air and open the valve.

TB5,TB3,TB6,TB11 Series Bimetallic Steam Traps

The adjustable bimetal trap is operated by a bimetal temperature-sensing element that moves the valve plug to open and close. When the device is first started and low temperature condensate appears in the pipeline, the bimetal is spreading and the valve plug is in the open position under the spring force. When the condensate temperature is rising, the bimetal temperature-sensitive element starts to bend, and pushes the valve plug to the closed position. The trap closes completely before the condensate reaches saturation temperature. There is always high temperature condensate inlet of the valve, no steam leakage, and saves energy.

Application

TB5(3,6,11)F adjustable bimetal traps are used for steam mains, sub-cylinders, steam tracing lines, radiators, low-temperature heating tanks, crumb traps, etc.

Advantages of Adjustable Bimetallic Traps

• Free from water shock
• High-pressure resistance
• Small volume
• Lightweight
• Freeze-proof
• Automatically discharge air
• Can be installed in any position
• The back pressure rate is greater than 80%

TB5(3,6,11)F Adjustable Bimetallic Trap

CS47H Adjustable Bimetallic Trap

CS17H,CS67H Adjustable Bimetallic Traps

Model	Size	Connection	Suitable Pressure	Max. Allowable	Adjustable	Body
	Nominal Diameter	Type	Range	Temperature	Temperature	Material				mm
	DN		（MPa）	℃	℃		L	H1	H2	W
TB6(CS17H-16C)	15-20	1/2“~1” Threaded	0.01~1.6	220	50~180	A105	90	109	35	58
TB6(CS17H-16C)	25	1/2“~1” Threaded	0.01~1.6	220	50~180	A105	95	109	35	58
TB6F(CS47H-16C)	15-20	Flanged	0.01~1.6	220	50~180	A105	150	109	35	58
TB6F(CS47H-16C)	25	Flanged	0.01~1.6	220	50~180	A105	160	109	35	58
TB6F(CS47H-16C)	32-50	Flanged	0.01~1.6	220	50~180	A105	230	109	35	58
TB6W (CS67H-16C)	15-20	Sock welded	0.01~1.6	220	50~180	A105	90	109	35	58
TB6W (CS67H-16C)	25	Sock welded	0.01~1.6	220	50~180	A105	95	109	35	58
TB11 (CS17H-16C)	15-20	Threaded	0.01~1.6	220	60~190	A105	90	109	35	58
TB11 (CS17H-16C)	25	1/2“~1” Threaded	0.01~1.6	220	60~190	A105	95	109	35	58
TB11F (CS47H-16C)	15-20	Flanged	0.01~1.6	220	60~190	A105	150	109	35	58
TB11F (CS47H-16C)	25	Flanged	0.01~1.6	220	60~190	A105	160	109	35	58
TB11F (CS47H-16C)	32-50	Flanged	0.01~1.6	220	60~190	A105	230	109	35	58
TB3 (CS67H-16C)	15-20	Threaded	0.01~1.6	350	50~190	A105	90	85	23	54
TB3 (CS67H-16C)	25	1/2“~1” Threaded	0.01~1.6	350	50~190	A105	95	85	23	54
TB3F (CS67H-16C)	15-20	Flanged	0.01~1.6	350	50~190	A105	150	85	23	54
TB3F (CS67H-16C)	25	Flanged	0.01~1.6	350	50~190	A105	160	85	23	54
TB3W (CS67H-16C)	15-20	Sock welded	0.01~1.6	350	50~190	A105	90	85	23	54
TB3W (CS67H-16C)	25	Sock welded	0.01~1.6	350	50~190	A105	95	85	23	54
TB5 (CS17H-21C)	15-20	Threaded	0.01~2.1	350	50~200	A105	90	85	23	54
TB5 (CS17H-21C)	25	1/2“~1” Threaded	0.01~2.1	350	50~200	A105	95	85	23	54
TB5F (CS47H-21C)	15-20	Flange	0.01~2.1	350	50~200	A105	150	85	23	54
TB5F (CS47H-21C)	25	Flange	0.01~2.1	350	50~200	A105	160	85	23	54
TB5W (CS67H-21C)	15-20	Sock welded	0.01~2.1	350	50~200	A105	90	85	23	54
TB5W (CS67H-21C)	25	Sock welded	0.01~2.1	350	50~200	A105	95	85	23	54

SF-1(2,3),SF-1(2,3)-GF Adjustable Bimetallic Trap

Model	DN（mm）	L	H	D	D1	D2	b	f	Z-Φd
SF-1/2/3-GF	15	230	180	95	65	45	14	2	4-Φ14
SF-1/2/3-GF	20	230	180	105	75	55	14	2	4-Φ14
SF-1/2/3-GF	25	230	185	115	85	65	14	2	4-Φ14
SF-1/2/3-GF	32	250	195	135	100	78	16	2	4-Φ18
SF-1/2/3-GF	40	250	200	145	110	85	16	3	4-Φ18
SF-1/2/3-GF	50	250	208	160	125	100	16	3	4-Φ18
TSF-1/2/3-GF	15	210	140	95	65	45	14	2	4-Φ14
TSF-1/2/3-GF	20	210	145	105	75	55	14	2	4-Φ14
TSF-1/2/3-GF	25	210	150	115	85	65	14	2	4-Φ14

TSF-1(2,3) Adjustable Bimetallic Trap

Model	DN（mm）	L	H	H1
TSF-1/2/3	15	110	130	35
TSF-1/2/3	20	110	130	35
TSF-1/2/3	25	110	130	35
SF-1/2/3	15	155	170	45
SF-1/2/3	20	155	170	45
SF-1/2/3	25	155	170	45

How Does Bimetallic Steam Trap Work?

The primary parts of bimetallic steam traps are a conical end stem valve and a composite material made of two plates with differing expansion coefficients. Bimetal components are crushed due to the cold fluid, and the valve is open. During this phase, condensate, non-condensable gases, and air are released. Bimetallic plates expand in distinct ways as the hot condensate enters the system, pulling the valve toward the seat and causing it to cease discharging. The cycle resumes when cool condensate reenters the steam trap.

Pros of Bimetallic Steam Traps

NO.	Advantages
1	Resistant to Water Hammer: Highly resistant to water hammer and corrosive condensate.
2	Resistant to Freeze: Not being affected by freezing.
3	High efficiency: Condensate discharge is lower than steam temperature. Possibility to adjust the bimetal plate to benefit from the hidden energy of the steam.
4	High-Temperature Condition: It Can be used in high-temperature and superheated steam lines.
5	Non Return function: The valve that is linked to the bimetallic plates serves as a check valve and prevents back pressure buildup in the system.
6	Easy Installation: Bimetallic thermostatic steam traps do not need to be fitted to the steam lines as horizontally to the x-axis, in contrast to thermodynamic steam traps. These steam traps are capable of operating at 100% efficiency and can be positioned horizontally, vertically, or at an angle to the steam flow.

Cons of Bimetallic Steam Traps

NO.	Advantages
1	Long reaction time. When condensate and steam temperatures are very close to each other, the response time of bimetal steam traps may be too long. Long response times for load and temperature changes may cause equipment or system failure.
2	Difficulty in the setting. Adjusting bimetal plate traps may be difficult, especially after valve maintenance.

4. Thermostatic Capsule Steam Trap

Features, Types, and Applications of Thermostatic Capsule Steam Traps

The thermostatic capsules and all other internal parts are made of corrosion-resistant stainless steel. Hastelloy membranes even resist acidic condensate conditions very well. There are generally three different types of capsules for thermostatic capsule steam traps.

a. High-Temperature Capsule

Specially designed for applications that require the use of dry steam, such as the tire industry and the textile industry. These capsules discharge condensate at the relevant steam pressure 5°C below the saturated steam temperature.

b.  Standard Temperature Capsule

Standard design for any application requiring the use of saturated steam. This capsule discharges condensate 10°C below the saturated steam temperature at the relevant steam pressure. 

c. Low Temperature Capsule

Specifically designed for applications where steam is used for heating. At the relevant steam pressure, this condensate is discharged at a temperature 30°C below the saturated steam temperature and allows the equipment to use the enthalpy of hot condensate.

Control Valves 101: Valve Types, Applications, Components, and Accessories

Installation Cautions for Steam Traps

Proper installation of steam traps has a direct impact on the safe operation of traps and the productivity of the equipment. The following are 19 common installation precautions.

1. Be sure to purge the piping with steam to remove debris from the piping before installing the steam trap.
2. A strainer should be installed in front of the trap to ensure that the steam trap is not blocked by debris in the piping, and the strainer should be cleaned regularly.
3. On/off valve should be installed inlet and outlet the trap, in case to easy maintenance of steam trap at any time.
4. The flow direction of condensate should be consistent with the trap installation arrow mark.
5. Traps should be installed at the low point of the equipment outlet to discharge condensate in time,  to avoid steam resistance in the piping.
6. If there is no space to install a trap at the low part of the equipment, a backwater elbow (condensate lifting joint) should be added at the low position of the outlet to raise the condensate level before installing a trap to avoid steam resistance.
7. The outlet pipe of the trap should not be immersed in water. (If it is immersed in water, drill a hole at the elbow to break the vacuum and prevent the sand from sucking back.
8. Mechanical type traps should be installed horizontally.
9. Do not install steam traps in series.
10. Each unit should be installed with its own trap.
11. Thermostatic type traps need to have more than one meter of non-insulated subcooling pipe in the inlet of the steam trap, and other types of traps should be installed as close to the equipment as possible.
12. When you select traps for roller drying (with siphon type) equipment, please specify the trap should with an anti-vapor barrier device to avoid equipment vapor lock.
13. If there is a condensate recovery outlet of the trap, the outlet pipe should be connected to the recovery pipeline to reduce back pressure and prevent backflow.
14. If there is condensate recovery downstream of the trap, different pressure lines should be recovered separately.
15. The condensate recovery main downstream of the trap should not be upward, which will increase the back pressure of the trap.
16. The condensate downstream of the trap should be installed with a check valve before entering the recovery main to prevent the condensate backflow.
17. To install traps on steam piping, the main piping should have a condensate collection well close to the radius of the main piping and then lead to the trap with a small pipe.
18. If a mechanical trap is not used for a long time, remove the drain screw and drain the water from the valve to prevent freezing.

Though the trap is only a small valve in the entire steam system, it has a great impact on the normal operation of the system and the cost of the equipment, so routine maintenance and inspection are essential, and good operating conditions of the trap are necessary to ensure that the energy-saving effect is achieved.

In Conclusion

Steam traps provide the basic function of condensate drainage in a steam system. A typical steam system is probably a complex network, and a trap must be matched to a specific drainage application, and we need to consider the various operating principles of steam traps as well as the specific needs and conditions. 

THINKTANK manufactures a wide range of steam traps, including inverted bucket traps, float, and thermostatic traps, controlled disc traps, and differential condensate controllers. Not only we can provide a quick quote, but also provide technical guidance on how to match the various types of traps and their benefits to your specific application needs.

2 Steps to Selecting the Right Control Valves for Your Steam Systems