What is a steam trap

What is a steam trap?

Steam trap is called trap, also known as automatic drain or condensate drain, which is divided into steam system and gas system. The steam trap is installed at the end of the pipe heated by steam, and its function is to continuously discharge the condensed water from the steam heated pipe to the outside of the pipe.
Most of the steam traps can automatically identify steam and water (excluding thermal static type), so as to achieve the purpose of automatic steam blocking and drainage. Steam trap is widely used in petrochemical, food, pharmaceutical, power plant and other industries, which plays an important role in energy saving and emission reduction.

Classification of steam trap

The steam trap can be divided into three types according to the principle of action:

Mechanical drain valve:

Mechanical type, also known as float type, is to make use of the density difference between condensate and steam, through the change of condensate liquid level, make the float lift and drive the valve disc to open or close, so as to achieve the purpose of steam blocking and drainage. The mechanical type steam trap has small undercooling degree and is not affected by the working pressure and temperature changes. If there is water, it will be discharged. There is no water in the heating equipment, which can make the heating equipment achieve the best heat exchange efficiency. The maximum back pressure rate is 80%, and the working quality is high. It is the most ideal drain valve for production process heating equipment.
Mechanical traps are free floating ball type, free half floating ball type, lever floating ball type, inverted bucket type and so on.
(1) Free floating ball drain valve:
The structure is simple, and there is only one moving part inside. The stainless steel hollow floating ball is not only the float but also the opening and closing parts. There is no vulnerable parts and the service life is very long. The drain valve is equipped with Y Series automatic air exhaust device, which is very sensitive, can automatically exhaust air and has high working quality. When the equipment is just started to work, the air in the pipeline is discharged through the Y Series automatic air exhaust device, and the low-temperature condensate enters into the drain valve. The liquid level of the condensate rises and the floating ball rises. The valve opens, the condensate is quickly discharged, and the steam enters the equipment quickly. The temperature sensitive liquid of the Y Series automatic air exhaust device expands and the automatic exhaust device is closed. The drain valve starts to work normally, and the floating ball rises and falls with the condensate water level to block steam and drain water. The valve seat of free floating ball drain valve is always below the liquid level, forming water seal, no steam leakage and good energy saving effect. The minimum working pressure is 0.01Mpa, and the range from 0.01Mpa to the maximum working pressure is not affected by the fluctuation of temperature and working pressure. It can drain condensate at saturated temperature, the minimum subcooling degree is 0 ℃, and there is no water in the heating equipment, so that the heating equipment can achieve the best heat exchange efficiency. The back pressure ratio is more than 85%, which is one of the most ideal traps for heating equipment in production process.
(2) Free semi floating ball drain valve:
There is only one semi floating ball type drain valve. The opening is downward, and the bucket is not only the opening and closing part, but also the sealing part. The whole spherical surface can be sealed, with long service life, water hammer resistance, no vulnerable parts, no fault, durable, no steam leakage. When the back pressure ratio is more than 80%, it can drain condensate at saturated temperature. The minimum subcooling degree is 0 ℃ and there is no water in the heating equipment, which can make the heating equipment achieve the best heat exchange efficiency.
When the device is just started, the air and low-temperature condensate in the pipeline enter into the drain valve through the launching pipe. The bimetallic sheet emptying element in the valve will open the ball barrel, and the valve will open, and the air and low-temperature condensate will be discharged rapidly. When the steam enters into the ball barrel, the ball barrel will produce upward buoyancy, and the temperature in the valve will rise, the bimetallic sheet emptying element will shrink, the ball stick will float to the valve port, and the valve will close. When the steam in the drum becomes condensate, the bucket loses its buoyancy and sinks down. The valve opens and the condensate is discharged rapidly. When the steam enters the spherical drum again, the valve is closed again, and the valve works intermittently and continuously.
(3) Rod floating ball drain valve:
The basic characteristics of lever floating ball type steam trap are the same as that of free floating ball type. The internal structure is that the floating ball is connected with the lever to drive the valve core, and the valve is opened and closed with the rise and fall of condensate level. The lever floating ball type steam trap uses double valve seat to increase the condensate displacement, which can achieve small volume and large displacement, and the maximum drainage capacity is 100 t / h. It is the most ideal drain valve for large heating equipment.
(4) Inverted bucket drain valve:
The inside of the inverted bucket type drain valve is an inverted bucket, which is a liquid level sensitive part. The opening of the bucket is downward, and the connecting lever of the inverted bucket drives the valve core to open and close the valve. Inverted bucket drain valve can exhaust air, not afraid of water hammer, good anti pollution performance. The super cooling degree is small, the steam leakage rate is less than 3%, the maximum back pressure rate is 75%, and there are many connections, so the sensitivity is not as good as that of the free floating ball drain valve. Because the inverted bucket type drain valve is closed by steam upward buoyancy, when the working pressure difference is less than 0.1MPa, it is not suitable for selection. When the device is just started, the air and low-temperature condensate in the pipeline enter the drain valve, and the inverted bucket falls down by its own weight. The connecting lever of the inverted bucket drives the valve core to open the valve, and the air and low-temperature condensate are quickly discharged. When the steam enters the inverted bucket, the steam of the inverted bucket will generate upward buoyancy, and the inverted bucket will rise and connect the lever to drive the valve core to close the valve. There is a small hole on the inverted bucket. When a part of the steam is discharged from the small hole, the other part of the steam generates condensate. The inverted bucket loses its buoyancy and sinks by its own weight. The connecting lever of the inverted bucket drives the valve core to open the valve, circulates and discharges water intermittently.
(5) Combined superheated steam trap:
The combined superheated steam trap has two isolated valve chambers, which are connected with the upper and lower valve chambers by two stainless steel pipes. It is a combination of floating ball type and inverted bucket type steam trap. The valve has advanced and reasonable structure. Under the working conditions of overheating, high pressure and small load, it can timely discharge the condensate formed when the hot steam disappears, effectively prevent the leakage of superheated steam, and has high working quality. The maximum allowable temperature is 600 ℃. The valve body is made of stainless steel and the valve seat is made of cemented carbide steel. It has a long service life. It is a special steam trap for superheated steam. It has obtained two national patents and filled in the domestic blank.
When the condensate enters the lower valve chamber, the floating ball of the auxiliary valve rises with the liquid level, and the floating ball closes the steam inlet pipe hole. The condensate rises to the main valve chamber through the inlet pipe, and the inverted bucket falls down by its own weight, driving the valve core to open the main valve and discharge the condensate. When the condensate level in the auxiliary valve chamber drops, the float ball decreases with the liquid level, and the auxiliary valve opens. The steam enters the inverted bucket in the upper main valve chamber from the steam inlet pipe. The inverted bucket generates upward buoyancy, and the inverted bucket drives the valve core to close the main valve. When the condensate level in the auxiliary valve chamber rises again, the next cycle starts again, and intermittent drainage is carried out.

Thermal static type steam trap:

This kind of steam trap is to use the temperature difference between steam and condensate to cause the deformation or expansion of temperature sensing element to drive the valve core to open and close the valve. The super cooling degree of the thermal static type steam trap is relatively large, which is generally 15 to 40 degrees. It can use part of the sensible heat in the condensate. There is always high-temperature condensate in front of the valve, no steam leakage, and remarkable energy-saving effect. It is the most ideal drain valve in steam pipe, heat tracing pipeline, small heating equipment, heating equipment and small heating equipment with low temperature requirements.
Thermal static type steam trap has bellows, bimetallic:
(1) Bellows type drain valve:
The stainless steel bellows is filled with a liquid whose vaporization temperature is lower than water saturation temperature. With the change of steam temperature, the valve is equipped with adjusting bolts, which can adjust the service temperature according to the needs. Generally, the adjustment range of undercooling is 15 ℃ – 40 ℃ lower than the saturation temperature. Back pressure rate is more than 70%, not afraid of freezing, small volume, can be installed at any position, can discharge non condensing gas, long service life.
When the device is started, cooling condensate appears in the pipeline, the liquid in the bellows is in the condensation state, and the valve core is in the open position under the spring force. When the temperature of condensate water gradually increases, the filling liquid in the bellows starts to evaporate and expand, the internal pressure increases, the deformation and elongation, which drives the valve center to move towards the closing direction. Before the condensate water reaches the saturation temperature, the steam trap starts to close, and the valve switch is controlled with the change of steam temperature to stop steam and drain water.
(2) Bimetallic trap:
The main component of bimetal trap is bimetal temperature sensing element, which is heated and deformed with the rise and fall of steam temperature to push the valve core to open and close the valve. The bimetallic steam trap is equipped with adjusting bolts, which can adjust the operating temperature according to the needs. Generally, the adjustment range of undercooling is 15 ℃ – 30 ℃ lower than the saturation temperature, and the back pressure rate is greater than 70%. It can discharge non condensable gas, is not afraid of freezing, has small volume, can resist water hammer and high pressure, and can be installed at any position. Bimetallic sheet is fatiguing and needs to be adjusted frequently.
When the device is just started, there is low-temperature condensate in the pipeline, the bimetallic sheet is flat, and the valve core is in the open position under the spring force. When the temperature of condensate water increases gradually, the bimetallic temperature sensing element begins to bend and deform, and push the valve core to the closed position. Before the condensate reaches the saturation temperature, the trap starts to close. The bimetallic sheet controls the valve switch with the change of steam temperature to stop steam and drain water.

Thermal power steam trap

This kind of trap is based on the phase change principle and the different thermodynamic principles of the flow rate and volume change when steam and condensate pass through, which makes the valve plate produce different pressure difference and drives the valve plate to open and close the valve. Because the working power of thermal power steam trap comes from steam, so the waste of steam is relatively large. It has the advantages of simple structure, water hammer resistance, 50% maximum back, noise, frequent operation and short service life.
Thermal power type steam trap has thermal power type (disc type), pulse type, orifice plate type:
(1) Thermal power steam trap:
There is a movable valve plate in the thermal power steam trap, which is not only a sensitive part but also an action actuator. According to the different thermodynamic principles of the flow rate and volume change of steam and condensate passing through, different pressure difference is generated between the upper and lower valve plates, which drives the valve plate to open and close the valve. The steam leakage rate is 3%, and the subcooling degree is 8 ℃ – 15 ℃.
When the device is started, cooling condensate appears in the pipeline. The condensate is pushed open by the working pressure and discharged rapidly. When the condensate is discharged, the steam is then discharged. Because the volume and flow rate of the steam are larger than that of the condensate, the pressure difference between the upper and lower valve plates will be generated, and the valve plates will close quickly under the suction of the steam flow rate. When the valve plate is closed, the valve plate is subjected to pressure on both sides, and the stress area under the valve plate is smaller than that on the upper part. Because the pressure in the steam chamber of the steam trap comes from the steam pressure, the force on the upper part of the valve plate is greater than that on the lower side, and the valve plate is tightly closed. When the steam inside the steam trap chamber is cooled to condensate, the pressure in the steam chamber disappears. The condensate pushes open the valve plate by the working pressure, and the condensate continues to discharge, circulates and discharges intermittently.
(2) Disc type steam insulated steam trap:
The working principle of disc type steam insulated steam trap is the same as that of thermal power steam trap. It adds a layer of shell outside the steam chamber of thermal power steam trap. The inner chamber of the shell is connected with the steam pipe, and the main steam chamber of the steam trap is insulated by the steam of the pipe itself. The temperature of the main steam chamber is not easy to cool down, the steam pressure is maintained and the drain valve is closed tightly. When condensation water is produced in the pipeline, the shell of the steam trap will cool down and the drain valve will start to drain; if there is no condensate on the superheated steam pipeline, the steam trap will not be opened and the working quality will be high. The valve body is made of alloy steel and the valve core is made of cemented carbide. The maximum allowable temperature of the valve is 550 ℃, which is durable and has long service life. It is a special steam trap for high pressure and high temperature superheated steam.
(3) Pulse type drain valve:
The pulse type steam trap has two orifices to adjust the valve switch according to the change of steam pressure drop. Even if the valve is completely closed, the inlet and outlet are connected through the first and second small holes, and are always in the incomplete closing state. The steam constantly escapes and the steam leakage is large. The operation frequency of the trap is very high, the wear is severe and the service life is short. Small volume, water hammer resistance, can discharge air and saturated temperature water, close to continuous drainage, maximum back pressure of 25%, so few users.
(4) Orifice plate drain valve:
According to different water displacement, the orifice plate with different aperture is selected to control the displacement. Because of its simple structure, improper selection will result in insufficient drainage or a large amount of steam, which is not suitable for the steam consumption equipment of intermittent production or large fluctuation of condensate water

How to choose the right steam trap?

When selecting the steam trap, we should not only select from the maximum discharge, but also pay special attention to: it is not allowed to apply the steam trap only according to the pipe diameter. It must be selected according to the selection principle of steam trap and the specific situation of condensate system. Generally, it should be selected according to the following three aspects.
1. Firstly, the type of steam trap is selected and determined according to the requirements of heating equipment and condensate discharge.
For the heating equipment with the fastest heating speed and strict heating temperature control requirements, it is necessary to keep the condensation water not accumulated in the heating equipment. As long as there is water, it is necessary to drain, and the mechanical steam trap which can drain saturated water is the best choice. Because it is a drain trap with water, it can timely eliminate the adverse consequences caused by ponding in the equipment, and quickly improve and ensure the heating efficiency required by the equipment.
For the heating equipment with large heating surface and not strict requirements on heating speed and temperature control, water accumulation can be allowed, such as steam heating drainage, process heat tracing pipeline drainage, etc. The thermal static trap is the best.
For the medium and low pressure steam transmission pipeline, the condensate generated in the pipeline must be quickly and completely removed, otherwise it is easy to cause water hammer accident. With the increase of moisture content in steam, the temperature of steam is reduced, which can not meet the process requirements of steam consuming equipment. Therefore, the mechanical steam trap is the best choice for medium and low pressure steam pipeline.
2. According to the highest working pressure and temperature of steam consuming equipment, the nominal pressure and valve material of steam trap are determined; the connection mode and installation mode of steam trap are determined.
The nominal pressure of steam trap is generally divided into: 0.6MPa, 1.0MPa, 2.0MPa, 2.5MPa, 4.0Mpa and 5.0mpa. In selection, the nominal pressure of steam trap should not be lower than the maximum working pressure of steam using equipment. At the same time, the material of the valve body is selected according to the nominal pressure, maximum working temperature and installation environment of the steam trap. For nominal pressure ≤ 1.0MPa, cast iron or carbon cast steel shall be selected; for nominal pressure > 1.0MPa, carbon cast steel or alloy cast steel shall be selected.
The maximum working temperature of steam trap shall be determined according to the steam used by steam using equipment, and the selection shall not be lower than the temperature of steam used.
The steam trap has two installation methods: horizontal and vertical, which is determined by the connection position of pipeline and steam trap. The connection mode of steam trap includes thread, flange, welding, clamp, etc., which must be determined according to the maximum working pressure and temperature of steam trap and the requirements of corresponding connection parts of steam using equipment.
3. Finally, the performance parameters of the steam trap are determined according to the displacement.
In addition to the pressure, temperature and other parameters of the steam trap should match the conditions of the equipment used, the drainage capacity under various pressure differences of the steam trap is an important factor in the selection of the steam trap. If the drainage capacity of the selected steam trap is too small, all condensate that has reached the trap can not be removed in time, which will hinder the backflow of condensate, and eventually cause blockage, which will significantly reduce the heating efficiency of the equipment. On the contrary, choosing the steam trap with too large displacement will lead to premature wear and failure of valve closing parts. With the increase of valve body, its manufacturing cost will also increase, which is uneconomical. Therefore, the condensate water produced in the equipment or pipeline must be measured correctly or calculated according to the calculation formula, so as to provide conditions for the correct selection of steam trap.

Principle of steam trap

When selecting the steam trap, first select its characteristics to meet the best operation of steam heating equipment, and then consider other objective conditions, so that the selection of the trap you need is correct and effective.
The free floating ball steam trap uses the buoyancy principle. According to the amount of condensate water, the floating ball will rise and fall with the change of water level. It will automatically adjust the opening of valve seat hole and continuously discharge condensate. When condensate stops entering, the bottom of floating ball will return to the closed position, and the drainage will stop. Because the drainage valve seat hole is always below the condensation water level, the shape of the valve seat is always below the condensation water level Water seal, water and gas are separated naturally to avoid steam leakage.

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Bellows steam trap

The main action element of bellows steam trap is metal bellows, which is filled with a liquid whose gasification temperature is lower than the saturation temperature of water.
When the device is just started, there is low-temperature condensate water in the pipeline, and the liquid in the capsule is in the condensation state. The valve is in the open position. When the temperature of condensate water gradually increases, the filling liquid in the diaphragm box begins to evaporate, the pressure in the diaphragm box rises, and the diaphragm drives the valve center to move toward the closing direction. Before the condensate water reaches the saturation temperature, the drain valve is completely closed. The diaphragm box controls the valve switch according to the change of steam temperature, which plays a role in preventing steam and draining water.

Inverted bucket drain valve

The inside of the inverted bucket type drain valve is an inverted bucket, which is a liquid level sensitive part. The opening of the bucket is downward, and the connecting lever of the inverted bucket drives the valve core to open and close the valve. Inverted bucket drain valve can exhaust air, not afraid of water hammer, good anti pollution performance. The super cooling degree is small, the steam leakage rate is less than 3%, the maximum back pressure rate is 75%, and there are many connections, so the sensitivity is not as good as that of the free floating ball drain valve. Because the inverted bucket type drain valve is closed by steam upward buoyancy, when the working pressure difference is less than 0.1MPa, it is not suitable for selection.

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Bimetallic steam trap

Bimetallic trap is driven by bimetal temperature sensing element to open and close the valve core.
When the device is just started, there is low-temperature condensate in the pipeline, the bimetallic sheet is flat, and the valve core is in the open position under the spring force. When the temperature of condensate water increases gradually, the bimetal temperature sensor begins to bend and deform, and push the valve core to the closed position. Before the condensate reaches the saturation temperature, the drain valve is completely closed. There is always high temperature condensate in front of the valve, no steam leakage and good energy saving effect.

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Thermal power steam trap

Thermal power type steam trap is a kind of very strong and simple working mode of steam trap. This kind of trap works by the dynamic action of flash steam passing through the trap.
In the start-up stage, due to the pressure, the disc is jacked up, and the condensate and air pass through the inner valve seat and are discharged from the three small holes in the peripheral outlet through the lower part of the disc. There is a movable valve plate in the thermal power steam trap, which is not only a sensitive part but also an action actuator. According to the different thermodynamic principles of the flow rate and volume change of steam and condensate passing through, different pressure difference is generated between the upper and lower valve plates, which drives the valve plate to open and close the valve.

Source: China Steam Trap Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@ugsteelmill.com

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what is a steam trap - What is a steam trap
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What is a steam trap
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Steam trap is called trap, also known as automatic drain or condensate drain, which is divided into steam system and gas system.
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www.ugsteelmill.com
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