There are numerous varieties of steam traps available on the market. Every steam trap differs in capabilities, processing requirements, benefits, and drawbacks. However, in all of them, a steam trap’s primary function is to release condensate accumulated in the steam distribution line promptly. Steam traps can be divided into several groups based on their design and operation.
Types of Steam Trap
Each steam trap falls into one of these 04 categories depending on how it functions, and the different types of steam traps are as follows within each category:
- Thermodynamic Steam trap
- Disc-type steam trap
- Piston-type steam trap
- Mechanical Steam Trap
- Float type
- Inverted bucket
- Thermostatic steam trap
- Liquid Expansion
- Balanced pressurized
- Bi-metallic
- Bellowed
- Venturi Nozzle steam trap
Thermodynamic Steam Trap
The difference in dynamic pressure between steam and condensate serves as the basis for a thermodynamic steam trap’s operation. Condensate is discharged here at the same temperature as steam. Steam from the body enters the trap and rapidly swells as it reaches the disc’s backside.
High flow velocity and a drop in disc pressure result from the steam expanding on the disc’s backside. High-pressure force is applied to the steam above the disc, and the action of balance being forced on the disc aids in closing the trapped disc on its seat.
A type of phase detector is a thermodynamic steam trap. They can easily distinguish between liquids and gases, but they cannot do so when distinguishing between steam and air or other non-condensable gases. As a result, they are less able to release these gases, and some steam is also released throughout the process.
Disc Type Steam trap
A metallic disc covers a small opening in the trap’s body in disc-type steam traps. The steam trap is a disc-type trap because it has a disc. A low-pressure zone is produced when steam travels quickly, which closes the disc.
This pressure rises as condensate forms, causing the disc to break free from the trap body’s surface and allow condensate to be discharged.
Disc Steam Trap Operation
The working theory of a disc-shaped steam trap is based on Bernoulli’s theorem. Bernoulli’s law states that a system’s total static and dynamic pressure remains constant throughout all sites of fluid flow.
Low-temperature condensate pours into the steam trap during startup, forcing the valve disc higher and allowing the condensate to exit the trap body’s outlet hole. Condensate heats up, and pressure builds as the startup period progresses.
The steam trap body between the seat and the disc is where a portion of the static pressure is later transformed into velocity. As a result, the disc stops discharging steam and traps it.
Advantages of Disc Steam trap
- No calibration adjustments are necessary.
- Body design that is lightweight, basic, and compact.
- Can be applied to steam at high temperatures and pressures.
- There is no set prerequisite for installation orientation.
- Highly resilient and able to tolerate water battering
- In the field, performance may be assessed.
- The disadvantage of Disc steam trap
- Its air handling capacity at startup is deficient, which can result in a stuck disc.
- The disc may not close if there is too much back pressure in the return system.
- Condensate discharge causes a lot of noise.
- Dirt can speed up the work cycle, which increases disc wear.
- Sensitive to the environment. The trap may not operate well in cold weather.
Piston-type Steam Trap
The interior design of a piston steam trap is similar to a piston valve that rests on its seat to prevent steam release. The piston in a piston steam trap is propelled from its place by the kinetic energy of steam and the heat of condensate.
A piston steam trap is a phase detector that distinguishes between liquid and gas, much like a disc steam trap. However, this thermodynamic steam trap has drawbacks, including the inability to distinguish between steam and other non-condensable gases.
Operation of Piston Type Steam Trap
Condensate pressure lifts the piston valve, permitting condensate discharge during the initial charging of the steam system. Because of the control hole in the piston, the pressure in the control chamber drops during this procedure.
More condensate can now be fed to the control chamber through the first orifice of the trap, thanks to the control orifice of the second orifice. According to the rules of thermodynamics, condensate in the control chamber turns into flash steam as its temperature approaches steam.
Condensate flashing in the control chamber interrupts the flow of steam through the control orifice, increasing the pressure in the area around the control chamber. The piston valve shuts the chamber and becomes stuck to its seat due to the increased pressure, stopping steam from passing through the trap.
When the cooled condensate reaches the trap, the pressure in the control chamber decreases, the flashing stops, the trap opens to release the condensate, and the cycle is repeated.
Advantages of Piston Type Steam Trap
- Suitable for systems that use high-pressure steam
- Adapts well to changes in the condensate load condition.
- Highly resilient and able to tolerate water hammer.
- self-draining and resistant to freezing damage.
- When steam is overheated, the function is unaffected.
- Excellent air handling capacity.
- Lightweight and compact.
Disadvantages of Piston Type Steam Trap
The trap may not close if the return mechanism experiences too much backpressure
- Unquiet operation
- Significantly more significant steam loss
Mechanical Steam Trap
A float that reacts to changes in fluid density and condensate level is a feature of mechanical steam traps. Condensate is detected by the mechanical steam trap using the difference in densities between steam and condensate.
The outlet port of the trap body is where the mechanical steam floats hinges, allowing or disallowing condensate flow depending on the level of the trap body.
Float Type Steam Trap
The operating principle of a float-type steam trap is the fluid density difference within the trap body. Neither steam nor non-condensable gas can flow through the steam trap in the image above because the trap is constantly saturated with condensate.
Therefore, a hand-operated valve was included in the early designs of these traps to expel this air upon commencement manually. Modern traps feature a thermostatic air vent, which allows initial air to pass while the trap is storing condensate, thanks to the most recent technological advancements.
This automatic air vent incorporates a balanced pressure capsule above the condensate level. This remains closed after the initial air is released until no additional air or non-condensable gas builds up in the steam trap.
Working of float-type steam trap
A lightweight portion of the steam trap is hinged to the output nozzle in a float steam trap. For the steam trap, this hinge functions as a gate. Condensate is discharged from the steam trap body through a hinged gate when the float in the trap body slides upward when the trap is filled with condensate.
Here, density is essential to the operation of a steam trap. The density of the float that is fitted in a trap is higher than steam but lower than condensate. Condensate builds up in the steam trap, creating a buoyancy force that causes the float to float above the condensate.
Advantage of float-type Steam Trap
- Condensate can be continually discharged using this. This is a fantastic option for a steam system with a high heat transmission rate.
- Capable of handling both heavy and small condensate loads.
- Not impacted by quick pressure changes.
- Without disturbing the condensate, this can discharge air and non-condensable gases.
- Able to withstand water hammer.
- The disadvantage of float-type Steam Trap
- Can be harmed by frigid temperatures.
- Only one mounting position is available.
- A trap will close and stop passing condensate if exposed to a higher differential pressure than desired.
Inverted Bucket Steam Trap
As its name implies, the Inverted Bucket Steam Trap is made out of an inverted bucket that blocks the flow of steam while releasing condensate and non-condensable gases. This steam trap is also known as an “inverted submerged bucket steam trap” since it is constantly submerged in the condensate.
“A little air vent hole” on the top of the bucket is the most critical component of the inverted steam trap. Due to the bouncing force of steam, this enables accumulating all non-condensable gases, such as CO2, at the top of the trap body and discharging them when the bucket descends from its raised position.
Inverted Bucket steam trap Working Principle
Following installation, the bucket remains at the base of the steam trap, and the lever connected to the bucket maintains the valve’s open position. When steam begins to flow through the steam trap, this raises the bucket and closes the valve with its lever arrangement.
Steam changed into condensate after losing latent heat, and condensate began to fill the trap body and surround the bucket. When condensate reaches a certain level, the steam’s applied bouncing force begins to diminish, and the bucket slowly descends.
When the bucket is at the bottom of the steam trap, a lever linked to it permits the valve gate to be opened. Non-condensable gases are initially evacuated from the trap body through this gate, and condensate is drained into a sound system.
Advantage of Inverted Bucket steam trap
- Simple design, excellent durability, and minimal to no wear.
- This kind of steam trap can endure high steam system pressure.
- Can be utilized with an NRV put at the trap’s inlet in superheated steam lines.
- A defense against a water hammer.
- Corrosion protection.
- Because of the built-in strainer in the bucket, resistant to steam dirt.
- The disadvantage of an Inverted Bucket steam trap
- Cannot survive in low-temperature areas and can freeze in frigid climates.
- Starting up requires priming.
- The potential for steam leaking at low load.
- Losing the water seal in the traps may be due to the increased temperature of superheated steam.
Thermostatic Steam Trap
The condensate’s changing temperature controls a thermostatic steam trap. Saturated process steam is hotter than either its condensate or steam combined with condensable gases, according to the operating theory behind them.
The condensate’s fluctuating temperature controls a thermostatic steam trap. According to their working theory, saturated process steam is hotter than its condensate or steam coupled with condensable gases.
Liquid Expansion Steam Trap
One of the most basic varieties of thermostatic traps is this one. An oil-filled part of this kind of trap stretches and shrinks in response to the heat that steam and condensation absorb. This movement of the steam trap’s element makes it possible for it to discharge condensate and non-condensable gases, making it the perfect choice for large-scale condensate discharge.
The liquid expansion steam trap’s typical operating temperature range is between 60 and 100 degrees Celsius. This trap can be utilized as a “Condensate drain trap” due to its reaction to temperature changes.
The exit of liquid expansion traps is always angled upward to allow for continued immersion of oil-filled components. It can be fitted next to a condensate return line-connected mains drain trap.
Liquid expansion steam trap operation
Because oil expands when exposed to heat, its volume rises correspondingly. Conversely, when exposed to cold, oil’s volume falls. This trap captures steam and discharges condensate thanks to the fundamental properties of the oil.
A piston-like mechanism exists in an oil-filled liquid expansion steam trap chamber. This piston’s tip is designed so that as it moves sideways, it will open and close the valve gate as necessary.
When this oil comes into contact with steam, it expands, increasing volume. Because of the oil’s expansion, the piston can move laterally and rest on the valve seat to close the valve. The piston returns to its initial position to open the condensate trap after losing latent heat and transforms into a condensate trap, allowing condensate and non-condensable gases to escape.
Advantage of Liquid Expansion Steam Trap
- Adaptable to drain even in frigid temperatures.
- This is resilient to water hammer and vibration.
- When inundated with cooler condensate, this fully opens and aids in the quick and thorough drainage of condensate during startup load.
- Can quickly release a large amount of condensation.
Disadvantages Liquid Expansion Steam Trap
- Due to condensation and high temperature, the flexible tube arrangement is vulnerable to corrosion and destruction.
- Ineffective when the outside temperature is low.
- This cannot be applied to a steam system when the trap must be removed immediately.
Balance Pressure Steam Trap
The steam trap’s operation changed due to technological advancements to better manage steam and utilize it. The balanced pressure steam trap is a liquid expansion steam trap developed for use in industry.
The surrounding steam pressure impacts how well a balanced pressure trap works. A sealed capsule (Capsule) with a unique liquid-water mixture is inserted in this trap. That mixture has a lower boiling point than water.
The capsule is relaxed in cold weather or during startup, which means that there isn’t any pressure buildup inside the capsule due to the liquid-water mixture. The valve is not on its seat, and the trap is open in this situation. With no steam loss, this balanced pressure steam trap feature is ideal for air venting during startup.
Working of Balance Pressure Steam Trap
The liquid-water mixture of the capsule absorbs heat when condensate travels through the balanced pressure steam trap. Before the steam reaches the steam trap, that combination begins to evaporate. This is forced to expand and close the valve by the vapor pressure of the capsule.
The water next to the capsule is cooled by heat loss from the trap. The cycle repeats as the steam reaches the trap again and the vapor created in the capsule condenses, the capsules contract, the valve opens, and condensate and air are discharged.
Advantages of Balance Pressure Steam Trap
- The valve is small and tightly closed.
- During startup, the valve remains fully open, enabling air to escape.
- Very little likelihood of freezing.
- Self-adjustment following the steam pressure for the permitted maximum pressure.
- Simple upkeep and repair.
- Able to tolerate water battering and vibration.
- The disadvantage of Balance Pressure Steam Trap
- When the condensate pressure reaches a level below the boiling point of the liquid-water mixture, this trap opens.
- An earlier balanced pressure steam trap has a bellow that is vulnerable to damage from corrosive condensate and water hammer.
Bi-metallic steam trap
The metal expands when heated to a given degree, and each metal expands differently depending on the temperature. This type of metal is used for the bimetallic steam trap to function.
As the name implies, a bimetallic steam trap is created by joining two separate metal strips by welding to create a single strip.
Regarding this straightforward process of bimetallic strips, there are two key points to keep in mind:
- After reaching a preset temperature, the steam trap begins to operate. This circumstance might not meet a steam trap’s pressure and temperature requirements.
- Many other metals react to the temperature change due to the force created by the bending moment of a single bimetallic strip. Differing properties of the two metals, the early expansion in one metal strip will result in a bending moment in the entire welded strip when both are heated.
Bi-Metallic Steam Trap Operation
Conical end steam serves as a gate to open and close the valve in a bi-metallic steam trap in response to metal strip motion. The essential parts of this trap are two metallic plates with varying expansion coefficients that make up the composite strip.
The bimetallic strip is compressed when steam enters the trap body chamber, and the lever linked to it assists the conical gate in closing the discharge door. The compressed bimetallic strip returns to its original position as the temperature drops after steam is converted to condensate, allowing the gate to be opened and the condensate and air to exit the system.
Advantage of Bi-Metallic Steam Trap
- Despite being small, it can manage a lot of steam system condensation.
- have practical air venting abilities and thorough condensate draining.
- Steam traps are impervious to damage, even in subfreezing temperatures.
- This can withstand corrosion, high steam pressure, and water hammering because of the metallic strips.
- Any desired orientation for installation of this is possible.
- Can function effectively at higher temperatures and pressures.
- Tough, energy-saving, and self-draining.
The disadvantage of the Bi-Metallic Steam Trap
- Waterlogging in the trap body might result from condensate discharge below the steam temperature.
- Steam is lost because of its slow reaction time.
- The valve may not be able to close tightly if it is covered in dirt.
- Condensate must be cooled to a temperature 50% lower to be discharged against the back pressure.
Bellowed steam trap
Bellow steam traps are thermostatic traps that react by opening and closing the valve in response to changes in the temperature and pressure of the steam. In this trap, the liquid-vaporizing bellow acts as the valve’s actuator.
The valve opens or closes in reaction to a change in pressure caused by the liquid inside the bellow. One end of the bellow is fixed, while the other is free to move. Corrugated bellows are the actuation material most typically used for bellow steam traps. Here as well, single diaphragm capsules are employed.
Operation of Bellowed Steam Trap
The balanced pressure steam trap and the bellows type steam trap operate on a similar principle. Since the liquid is inside the trap element, pressure is also generated, controlling the valve stem.
During startup, the bellowed steam trap is initially in the open position. As a result of the bellow’s internal liquid gaining heat, steam evaporates as it reaches the trap, expanding the bellow as it does so. This causes the valve’s cone-shaped gate to rest on its seat and seal tightly, trapping steam inside.
As condensate begins to form, the temperature drops, the bellow’s internal pressure reduces, and the valve opens, allowing air and condensate to be discharged from the trap.
Advantages of Bellowed Steam Trap
- Excellent ability to handle air.
- Self-draining, energy-efficient, with a range of discharge temperatures.
- Can be installed in several ways.
- Simple internal pieces that are also simple to repair and maintain.
- Light weight and size.
The disadvantage of Bellowed Steam Trap
- Bellows components frequently break, especially when hit by water hammers.
- Checking is challenging when the engine is being throttled.
- Commonly unsuitable for higher pressure.
- Limited capacity for superheating.
- The design of the short-stroke diaphragm is prone to failures brought on by dirt.
Venturi Nozzle steam trap
Venturi Nozzles function as an effective condensate removal device in steam trap types by using the actual physical differences in specific volume between steam and condensate. This type of steam trap has a venturi-shaped nozzle inserted at the steam trap’s exit that aids in separating condensate and steam.
Working of Venturi Nozzle steam trap
Compared to live steam, condensate is denser and moves much slower. Condensate’s slower speed makes it impossible for steam from the venturi to get through. Condensate from the venturi nozzle’s diverging section might cause some of it to start flashing, which raises a specific volume and has the effect of choking, making it difficult for steam to escape the steam trap.
Advantage of Venturi Nozzle steam trap
- The steam trap is without moving parts.
- Suitable for use in high-pressure steam systems.
- Extremely robust and resistant to water battering.
- No harm is done by freezing.
- The steam that has been overheated can also be effectively handled without losing effectiveness.
- Able can be deployed anywhere.
The disadvantage of the Venturi Nozzle steam trap
- Each steam trap requires specific consideration depending on its position and size, so care must be taken while choosing the venturi size.
- This is unable to adapt to changing condensate loads.
- The steam trap may become ineffective with a large venturi.
- Dirt particles impact the performance of steam.
- Steam can escape from the outlet without condensation in the trap body.
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