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Trap principle and structure form

2022-11-14

Trap in the steam heating system plays the role of steam drainage, select the appropriate trap, can make the steam heating equipment to achieve the highest efficiency. To achieve the best results, it is necessary to work on various types of traps performance, characteristics of a comprehensive understanding.

 

Many varieties of traps, each with different performance. When choosing a trap, first of all should choose its special performance to meet the best operation of steam heating equipment, and then consider other objective conditions, so choose what you need the trap is correct and effective.

 

Trap to be able to "identify" steam and condensate, in order to play the role of steam drainage. "Identifying" steam and condensate is based on three principles: density difference, temperature difference and phase change. So according to three principles to create three types of traps: classified as mechanical, thermal static type, thermal power type.

 

1. mechanical drain valve

 

The mechanical type is also called float type, which uses the density difference between condensed water and steam to make the float lift and drive the valve flap to open or close through the change of the condensed water level to achieve the purpose of steam blocking and drainage. Mechanical type trap subcooling degree is small, not affected by the working pressure and temperature changes, there is water that is discharged, heating equipment does not store water, can make the heating equipment to achieve the best heat transfer efficiency. The maximum back pressure rate is 80%, and the work quality is high. It is the most ideal trap for production process heating equipment.

 

Mechanical traps are free float type, free semi-float type, lever float type, inverted bucket type, etc:

 

1. Free floating ball trap

 

Free float trap structure is simple, internal only a moving parts of fine grinding stainless steel hollow float, both float and opening and closing parts, no vulnerable parts, long service life, "HG" trap internal with Y series automatic evacuation device, very sensitive, can automatically exhaust air, high quality work.

 

When the equipment is just started, the air in the pipeline is discharged through the Y series automatic evacuation device, the low-temperature condensed water enters the trap, the liquid level of the condensed water rises, the floating ball rises, the valve opens, the condensed water is discharged rapidly, the steam enters the equipment quickly, the equipment heats up rapidly, the temperature sensing liquid of the Y series automatic evacuation device expands, and the automatic evacuation device is closed. The trap starts to work normally, and the float rises and falls with the condensate level to block steam and drain. The valve seat of the free float trap is always below the liquid level, forming a water seal, no steam leakage, and good energy saving effect. The minimum working pressure is 0.01Mpa, from 0.01Mpa to the maximum working pressure range is not affected by temperature and working pressure fluctuations, continuous drainage. Can discharge saturated temperature condensate, the minimum degree of subcooling is 0 ℃, no water is stored in the heating equipment, so that the heating equipment can achieve the best heat exchange efficiency. The back pressure rate is greater than 85%, which is one of the most ideal traps for production process heating equipment.

 

2. Free semi-float trap

 

The free semi-float trap has only one semi-float ball barrel as the movable part, with the opening downward. The ball barrel is the opening and closing part and the seal. The entire spherical surface can be sealed, has a long service life, can resist water hammer, has no wearing parts, is trouble-free, durable, and has no steam leakage. The back pressure rate is greater than 80%, the condensate can be discharged 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 the trap through the launch tube. The bimetallic sheet emptying element in the valve bounces the ball barrel, the valve opens, and the air and low-temperature condensate are quickly discharged. When the steam enters the ball barrel, the ball barrel produces upward buoyancy, while the temperature in the valve rises, the bimetallic sheet emptying element shrinks, the ball drifts to the valve port, and the valve closes. When the steam in the ball barrel becomes condensed water, the ball barrel loses its buoyancy and sinks, the valve opens, and the condensed water is discharged quickly. When the steam enters the ball barrel again, the valve is closed again, intermittent and continuous work.

 

3. Rod float trap

 

The basic characteristics of the lever float trap are the same as the free float type. The internal structure is that the float is connected with the lever to drive the valve center and switch the valve with the rise and fall of the condensate level. Lever float trap using double valve seat to increase the condensate displacement, can reach the volume of small displacement, the maximum hydrophobic capacity of 100 tons/hour, is the most ideal for large heating equipment trap.

 

4. Inverted bucket drain valve

 

Inside the inverted bucket trap is an inverted bucket as a liquid level sensitive part. The opening of the bucket is downward, and the inverted bucket connecting lever drives the valve core to open and close the valve. Inverted bucket trap can exhaust air, not afraid of water hammer, good anti-fouling performance. The degree of undercooling is small, the steam leakage rate is less than 3%, the maximum back pressure rate is 75%, the connection is more, and the sensitivity is not as good as the free float trap. Because the inverted bucket trap is closed by the upward buoyancy of steam, 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 trap, the inverted bucket falls down by its own weight, the inverted bucket connecting lever drives the valve center to open the valve, and the air and low-temperature condensate are quickly discharged. When steam enters the inverted bucket, the steam of the inverted bucket generates upward buoyancy, and the inverted bucket rises to connect the lever to drive the valve core to close the valve. There is a small hole on the inverted bucket. When part of the steam is discharged from the small hole, the other part of the steam produces condensed water. The inverted bucket loses its buoyancy and sinks by its own weight. The connecting lever of the inverted bucket drives the valve heart 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 by two stainless steel pipes to the upper and lower valve chambers. It is a combination of float type and inverted bucket type trap. The valve structure is advanced and reasonable. Under the working conditions of small load, the condensed water formed when the superheated steam disappears can be discharged in time, effectively preventing the leakage of superheated steam, and the working quality is high. The maximum allowable temperature is 600 ℃, the valve body is all stainless steel, the valve seat is hard alloy steel, and the service life is long. It is a special steam trap for superheated steam. It has obtained two national patents and filled the domestic gap.

 

When the condensate enters the lower valve chamber, the float ball of the auxiliary valve rises with the liquid level, and the float ball closes the inlet pipe hole. 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 condensate. When the condensate level of the auxiliary valve cavity drops, the float drops with the liquid level, and the auxiliary valve opens. The steam enters the inverted bucket in the upper main valve cavity 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 of the auxiliary valve cavity rises again, the next cycle starts again, intermittent drainage.

 

2. thermo-static type steam trap

 

This kind of trap is the use of steam and condensate temperature caused by the temperature difference between the components of the deformation or expansion drive valve heart opening and closing valve. Thermostatic trap supercooling degree is relatively large, the general supercooling degree is 15 degrees to 40 degrees, it can use part of the sensible heat in the condensate, the valve always has high temperature condensate, no steam leakage, energy saving effect is remarkable. Is in the steam pipeline, heat tracing pipeline, small heating equipment, heating equipment, temperature requirements are not high on the small heating equipment, the most ideal trap.

 

Thermal static type steam trap has a bellows type, bellows type, double metal sheet.

 

1. Membrane type trap

 

The main action element of the diaphragm type trap is the metal film box, which is filled with a liquid with a gasification temperature lower than the saturation temperature of water. There are two options for opening the valve at a temperature lower than the saturation temperature of 15 ℃ and 30 ℃. The response of the diaphragm type trap is particularly sensitive, not afraid of freezing, small size, resistance to overheating, any position can be installed. The back pressure rate is greater than 80%, it can discharge non-condensing gas, the diaphragm is strong, the service life is long, the maintenance is convenient, and the use range is very wide.

 

When the device is just started, low-temperature condensed water appears in the pipeline, the liquid in the bellows is in a condensed state, and the valve is in the open position. When the temperature of the condensed water gradually rises, the liquid filled in the membrane begins to evaporate, the pressure in the membrane rises, and the diaphragm drives the valve heart to move in the direction of closure. Before the condensed water reaches the saturation temperature, the trap begins to close. The diaphragm box controls the valve switch with the change of steam temperature, which plays the role of steam blocking and drainage.

 

2. Bellows drain valve

 

Corrugated pipe trap spool stainless steel bellows filled with a vaporization temperature is lower than the water saturation temperature of the liquid. The valve switch is controlled with the change of steam temperature. The valve is equipped with adjusting bolts, which can adjust the operating temperature according to the needs. Generally, the adjustment range of supercooling degree is 15 ℃ ~ 40 ℃ lower than the saturation temperature. Back pressure rate is greater than 70%, not afraid of freezing, small size, can be installed in any position, can discharge non-condensing gas, long service life.

 

When the device is started, the cooling condensate appears in the pipeline, the liquid in the bellows is in a condensed state, and the valve core is in the open position under the elastic force of the spring. When the temperature of the condensed water gradually increases, the liquid filled in the bellows begins to evaporate and expand, the internal pressure increases, and the deformation elongates, driving the valve core to move in the direction of closing. Before the condensed water reaches the saturation temperature, the trap begins to close, and the valve switch is controlled with the change of steam temperature to block steam drainage.

 

3. Bimetallic steam trap

 

The main component of the bimetal trap is the bimetal temperature sensing element, which is heated and deformed with the rise and fall of the steam temperature to push the valve core to switch the valve. Bimetallic steam trap is equipped with adjusting bolts, which can adjust the operating temperature according to needs. Generally, the adjustment range of supercooling degree is lower than the saturation temperature of 15 ℃ ~ 30 ℃, the back pressure rate is greater than 70%, it can discharge non-condensing gas, is not afraid of freezing, is small in size, can resist water hammer, is resistant to high pressure, and can be installed at any position. The bimetallic strip is fatigued and needs to be adjusted frequently.

 

When the device is just started, the pipeline appears low-temperature condensate, the bimetal is flat, the valve core is in the open position under the spring force. When the temperature of the condensed water gradually rises, the temperature sensing element of the bimetallic strip begins to bend and deform, and push the valve core to the closed position. Before the condensate reaches saturation temperature, the trap begins to close. Bimetallic strip with the change of steam temperature control valve switch, steam drainage.

 

3. thermal power trap

 

This kind of trap according to the principle of phase change, by steam and condensate through the flow rate and volume change of different thermodynamic principles, so that the valve plate up and down to produce different pressure difference, drive the valve plate switch valve. Because the working power of the thermal power trap comes from steam, so the waste of steam is relatively large. Simple structure, water resistance, the maximum back of 50%, noise, frequent valve work, short service life.

 

Thermal power type steam trap has thermal power type (disc type), pulse type, orifice plate type.

 

1. Thermal power drain valve

 

There is a movable valve plate in the thermal power trap, which is both a sensitive piece and an action execution piece. According to the different thermodynamic principles of the flow rate and volume change of steam and condensate, the valve plate generates different pressure differences up and down to drive the valve plate to switch the valve. The steam leakage rate is 3%, and the supercooling degree is 8 ℃ ~ 15 ℃.

 

When the device is started, the cooling condensate appears in the pipeline, and the condensate pushes the valve plate by the working pressure and is discharged quickly. When the condensate is discharged, the steam is subsequently discharged. Because the volume and flow rate of the steam are larger than that of the condensate, the pressure difference is generated up and down the valve plate, and the valve plate is quickly closed 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 force area below the valve plate is less than the force area above. Because the pressure in the steam chamber of the trap valve comes from the steam pressure, the force above the valve plate is greater than the force below, and the valve plate is tightly closed. When the steam trap steam chamber inside the cooling into condensed water, the pressure inside the steam chamber disappeared. Condensate by working pressure to push the valve plate, condensate and continue to discharge, cycle work, intermittent drainage.

 

2. Disc type steam insulation trap

 

Disc type steam trap heat preservation type working principle and the same thermal power trap, it is in the thermal power trap steam outside the increase of a layer of shell. The inner chamber of the shell is connected with the steam pipeline, and the main steam chamber of the trap is insulated by the steam of the pipeline itself. Make the temperature of the main steam chamber not easy to cool down, keep the steam pressure, and close the trap tightly. When the pipeline produces condensate, the trap shell cools down, and the trap begins to drain; if there is no condensate on the superheated steam pipeline, the trap will not open, and the work quality is high. The valve body is alloy steel, the valve core is hard alloy, the valve maximum allowable temperature is 550 ℃, durable, long service life, is a high pressure, high temperature superheated steam trap.

 

3. Pulse trap

 

Pulse trap and two orifice according to the change of steam pressure drop valve valve switch, even if the valve is completely closed inlet and outlet is through the first, second small hole communication, always in the incomplete closed state, the steam continuously escape, large amount of steam leakage. The trap action frequency is very high, wear and tear, short life. Small size, resistant to water hammer, can discharge air and saturated temperature water, close to continuous drainage, the maximum back pressure of 25%, so few users.

 

4. Orifice trap

 

Orifice trap is based on different displacement, choose different aperture orifice plate to control the purpose of displacement. The structure is simple, inappropriate selection will result in insufficient drainage or a large amount of steam running, not suitable for intermittent production of steam equipment or steam equipment with large fluctuations in the amount of condensed water.