Steam Traps are automatic valves designed to remove condensate from steam lines, but prevent steam loss by “trapping” the steam; hence the name Steam Trap. Air is usually present for some period of time in a steam line, either during start-up and/or operation. So, depending on the application, air is another fluid that usually requires removal from a steam line.
Steam is formed when water vaporizes to form a gas. In order for the vaporization process to occur, the water molecules must be given enough energy that the bonds between the molecules break. This energy given to convert a liquid into a gas is called 'latent heat'. Steam-based heating processes use latent heat and transfer it to a given product.
When the work is done (i.e. steam has given up its latent heat), steam condenses and becomes condensate. In other words, condensate does not have the ability to do the work that steam does. Heating efficiency will therefore suffer if condensate is not removed as rapidly as possible, whether in steam transport piping or in a heat exchanger.
There are three basic operating principles of steam traps, which are explained below: Thermostatic, Density, and Thermodynamic.
OPERATING PRINCIPLES OF STEAM TRAPS:
1)MECHANICAL STEAM TRAPS
operate by use of a float device connected to a mechanical linkage that reacts upon changes in volume or fluid density. There are two main types of mechanical traps: the float & thermostatic (F&T) trap and the inverted bucket trap.
FLOAT & THERMOSTATIC TRAPS-The float & thermostatic trap uses a float connected by a linkage to the valve plug to discharge condensate from the system. In addition, F&T traps contain a thermostatic air vent to allow the discharge of air from the system. For this reason, these traps have excellent air removal capability, which is advantageous during system start-up when large amounts of air are present in the system. Float & thermostatic steam traps are generally the primary selection for drainage of process heat transfer equipment.
INVERTED BUCKET TRAPS- The inverted bucket trap uses an inverted bucket as a float device connected by a linkage to the valve plug. The varying densities between condensate and steam are used to create a buoyancy force on the bucket to open and close the valve. These traps are primarily used in drip applications on stream mains and steam supply lines. They are generally not used in process applications due to their poor air handling capability. Bucket traps are extremely rugged and resistant to water hammer and also resistant to any dirt and scale that may be present in the system.
2) THERMOSTATIC TRAPS
FLOAT & THERMOSTATIC TRAPS-The float & thermostatic trap uses a float connected by a linkage to the valve plug to discharge condensate from the system. In addition, F&T traps contain a thermostatic air vent to allow the discharge of air from the system. For this reason, these traps have excellent air removal capability, which is advantageous during system start-up when large amounts of air are present in the system. Float & thermostatic steam traps are generally the primary selection for drainage of process heat transfer equipment.
INVERTED BUCKET TRAPS- The inverted bucket trap uses an inverted bucket as a float device connected by a linkage to the valve plug. The varying densities between condensate and steam are used to create a buoyancy force on the bucket to open and close the valve. These traps are primarily used in drip applications on stream mains and steam supply lines. They are generally not used in process applications due to their poor air handling capability. Bucket traps are extremely rugged and resistant to water hammer and also resistant to any dirt and scale that may be present in the system.
2) THERMOSTATIC TRAPS
sense the temperature difference of entering fluids these are designed to open for cool fluid and close for hot fluid. The intention is to open for cool condensate or air, and close for hot condensate.
The closure occurs when the fluid, typically hot condensate, has a temperature greater than or equal to a certain threshold value. The hot temperature causes a thermostatic element to move in such a manner that closes a valve head against a valve seat (“valve”). This temperature threshold value is below that of saturated steam, but the actual specific temperature to open/close is different depending on the type of thermostatic trap. Since air – like cool condensate – has a temperature significantly lower than steam, Thermostatic traps are generally very good at venting large amounts of air.
3) THERMODYNAMIC STEAM TRAPS
Thermodynamic steam traps operate in a cyclic on/off process using the thermodynamic properties of flash steam as it flows through the trap. Thermodynamic traps use only one moving part, the valve disc, which allows condensate to escape when present and closes tightly upon the arrival of steam. These traps have an inherently rugged design and are commonly used as drip traps on steam mains and supply lines. Their solid construction and single moving part make them resistant to water hammer and are freeze proof when installed vertically. Thermodynamic traps will only discharge small amounts of air and therefore are typically not used in process applications.
Types of Steam trap
Mechanical Trap
Mechanical traps operate by using the difference in density between steam and condensate. They can continuously pass large volumes of condensate and are suitable for a wide range of process applications. Types include ball float and inverted bucket steam traps. A float within the trap detects the variance in weight between a gas and a liquid.
Thermodynamic Trap
Thermodynamic Traps use volumetric and pressure differences that occur when water changes state into gas. These changes act upon the valve directly. Thermodynamic steam traps have a unique operating principle which relies on the dynamics of water and flash steam.
Thermostatic Trap
Thermostatic traps detect the variation in temperature between steam and condensate at the same pressure. Thermostatic traps operate in response to the surrounding steam temperature. The sensing device operates the valve in response to changes in the condensate temperature and pressure. The operation and benefits of 3 different types are considered here - liquid expansion traps, bimetallic and balanced pressure thermostatic traps. Each operates in a different way and is suited to specific types of application.
Effectiveness of steam trap
-It makes the hot condensate available for recycling, reducing both waterside care and energy costs at the boiler
The closure occurs when the fluid, typically hot condensate, has a temperature greater than or equal to a certain threshold value. The hot temperature causes a thermostatic element to move in such a manner that closes a valve head against a valve seat (“valve”). This temperature threshold value is below that of saturated steam, but the actual specific temperature to open/close is different depending on the type of thermostatic trap. Since air – like cool condensate – has a temperature significantly lower than steam, Thermostatic traps are generally very good at venting large amounts of air.
3) THERMODYNAMIC STEAM TRAPS
Thermodynamic steam traps operate in a cyclic on/off process using the thermodynamic properties of flash steam as it flows through the trap. Thermodynamic traps use only one moving part, the valve disc, which allows condensate to escape when present and closes tightly upon the arrival of steam. These traps have an inherently rugged design and are commonly used as drip traps on steam mains and supply lines. Their solid construction and single moving part make them resistant to water hammer and are freeze proof when installed vertically. Thermodynamic traps will only discharge small amounts of air and therefore are typically not used in process applications.
Types of Steam trap
Mechanical Trap
Mechanical traps operate by using the difference in density between steam and condensate. They can continuously pass large volumes of condensate and are suitable for a wide range of process applications. Types include ball float and inverted bucket steam traps. A float within the trap detects the variance in weight between a gas and a liquid.
Thermodynamic Trap
Thermodynamic Traps use volumetric and pressure differences that occur when water changes state into gas. These changes act upon the valve directly. Thermodynamic steam traps have a unique operating principle which relies on the dynamics of water and flash steam.
Thermostatic Trap
Thermostatic traps detect the variation in temperature between steam and condensate at the same pressure. Thermostatic traps operate in response to the surrounding steam temperature. The sensing device operates the valve in response to changes in the condensate temperature and pressure. The operation and benefits of 3 different types are considered here - liquid expansion traps, bimetallic and balanced pressure thermostatic traps. Each operates in a different way and is suited to specific types of application.
Effectiveness of steam trap
-It makes the hot condensate available for recycling, reducing both waterside care and energy costs at the boiler
-It keeps the system filled with dry steam (saturated steam without entrained condensate)
-It removes by-products (condensate and air) from the system that form insulating barriers that prevent efficient and effective heat transfer
-It removes by-products (condensate and air) from the system that form insulating barriers that prevent efficient and effective heat transfer