Small Components with an Important Job
A practical guide to understanding what steam traps do, how the different types work and where they are used.
Steam is widely used in industry to transfer heat. As steam gives up its heat, it cools and turns back into water. This water is called condensate.
The condensate needs to be removed from the system without unnecessarily allowing valuable steam to escape.
That is the job of a steam trap.
A steam trap automatically removes condensate and, depending on its design, air and other gases while keeping useful steam inside the system.
If condensate is not removed properly, it can reduce heating performance, interfere with temperature control and contribute to problems such as water hammer. If steam is allowed to escape unnecessarily, energy is wasted.
Although a steam trap may be a small component, it plays an important role in keeping a steam system working efficiently.
1. Why Does a Steam System Need a Trap?
Think of steam as the heat carrier.
Steam travels through the system to equipment such as a heat exchanger, heating coil or process vessel, where it transfers its heat to the process.
Once the steam has given up enough heat, it turns back into condensate.
That condensate now needs somewhere to go.
If it is allowed to collect where steam should be working, it can reduce heat transfer and affect the performance of the equipment. Air can also become trapped in the system, particularly when equipment starts up.
A steam trap provides an automatic way of letting the condensate out while keeping the steam in.
Different types of steam traps achieve this in different ways.
2. The Main Types of Steam Traps
One of the easiest ways to understand the different types of steam traps is to look at what makes each one open and close.
Mechanical Steam Traps – Respond to Condensate Level
A ball float steam trap contains a float that rises and falls with the level of condensate inside the trap.
As condensate enters and the level rises, the float moves upwards. This movement opens the outlet and allows the condensate to drain away.
As the amount of condensate changes, the float responds automatically.
Within the AVS steam-trapping range, ARI CONA® S, CONA® SC and CONA® SC-Plus use ball float technology.
In simple terms:
Condensate rises → float moves → condensate is released.Thermostatic Steam Traps – Respond to Temperature
Thermostatic steam traps use temperature to control when condensate is released.
A temperature-sensitive element inside the trap responds as the condensate cools. This allows the trap to open and discharge the condensate. When hotter steam reaches the trap, the element responds to the higher temperature and closes the outlet.
These traps are useful in applications where the condensate can be allowed to cool slightly before it is removed.
The AVS/ARI range includes the CONA® B bimetallic steam trap and CONA® M thermostatic steam trap.
In simple terms:
Condensate cools → trap opens → condensate is released.Thermodynamic Steam Traps – Respond to Flow and Pressure
Thermodynamic steam traps use changes in flow and pressure to control when they open and close.
A common design uses a small disc inside the trap.
Condensate flows beneath the disc and out of the trap. As hot condensate passes through the trap and enters an area of lower pressure, some of it can quickly turn back into steam. This is called flash steam.
The change in pressure causes the disc to close. As that pressure drops again, the disc opens and the cycle repeats.
The ARI CONA® TD uses this thermodynamic operating principle.
In simple terms:
Changes in flow and pressure → disc opens and closes → condensate is released while steam is kept in the system.
3. Where Are Steam Traps Used?
Steam traps are used wherever condensate needs to be removed from steam lines or equipment that uses steam for heating.
Typical applications include:
- Steam distribution lines
- Heat exchangers
- Process heating equipment
- Heating coils
- Steam tracing systems
- Dryers and other steam-heated equipment
- Condensate collection and return systems
The same type of steam trap will not necessarily suit every application.
One piece of equipment may need condensate removed as soon as it forms, while another may allow it to cool slightly before being discharged. The amount of condensate produced can also vary depending on the equipment and whether the system is starting up or running normally.
This is why the application should determine the type of steam trap selected.
4.Choosing the Right Steam Trap
There is no single type of steam trap that is right for every steam system.
Choosing the right one starts with understanding the job it needs to do.
How much condensate needs to be removed?
The trap needs to handle the amount produced during normal operation as well as the larger amount that may be produced when the system first starts up.
What are the pressures before and after the trap?
There needs to be enough difference in pressure to move the condensate through the trap and into the system after it.
How quickly must the condensate be removed?
Some equipment needs condensate removed as soon as it forms. In other applications, it can be allowed to cool slightly first.
Does air need to be removed from the system?
Air can collect in steam equipment, particularly during start-up, and can reduce heating performance. The ability to remove this air may therefore be important when choosing a trap.
Where will the trap be installed?
The position of the trap, type of pipe connection, available space and access for future inspection and maintenance all need to be considered.
Will the operating conditions change?
The amount of condensate and the steam pressure may change while equipment is operating. The trap needs to continue working correctly as these conditions change.
Selecting a steam trap therefore involves more than simply choosing one that matches the size of the pipe.
5. What Happens When a Steam Trap Stops Working Properly?
Steam traps work continuously and, like other working components in a steam system, can wear or develop problems over time.
If a steam trap does not close properly, live steam can pass through when it should remain in the steam system. This wastes steam and energy.
If a steam trap does not open properly or becomes blocked, condensate cannot drain away as it should. It can then build up and reduce the heating performance of the equipment.
A problem with a steam trap may not always be obvious from the outside. Regular inspection and testing can help identify traps that are no longer working correctly.
The ARI range also includes CONA® Control, a monitoring system designed to identify problems such as steam leakage and blocked steam traps.
A Practical Steam Trap Selection Checklist
Before selecting a steam trap, ask:
☐ What equipment or steam line needs to be drained?
☐ How much condensate will it produce?
☐ What pressure will the trap operate at?
☐ What pressure will there be after the trap?
☐ Does the condensate need to be removed immediately, or can it cool first?
☐ Does air need to be removed from the system?
☐ Where and in what position will the trap be installed?
☐ How will the trap be inspected and maintained?
The Right Steam Trap Starts with the Application
The basic purpose of a steam trap is simple: let condensate out while keeping useful steam in.
The difference lies in how each type knows when to do it.
A ball float trap responds to the level of condensate. A thermostatic trap responds to temperature. A thermodynamic trap responds to changes in flow and pressure.
Each type works differently, and each has applications where it is particularly well suited. Choosing the right steam trap therefore starts with understanding what the system needs the trap to do.
AVS provides steam-trapping and condensate-management solutions for industrial steam systems, together with technical support to help customers select suitable equipment for their application.
Not sure which steam trap suits your application? Talk to Allied Valve Specialists about your steam and condensate requirements.
