The trap plays a role of steam resistance and drainage in the steam heating system. Choosing the appropriate trap can make the steam heating equipment achieve the highest working efficiency. In order to achieve the best results, it is necessary to have a comprehensive understanding of the performance and characteristics of various types of traps.

There are many kinds of traps with different performances. When choosing traps, first of all, the characteristics should be selected to meet the optimal operation of steam heating equipment, then other objective conditions should be considered, so that the selection of traps you need is correct and effective.

The steam trap must be able to "identify" steam and condensate in order to play the role of steam resistance and drainage. "Identifying" steam and condensate water is based on three principles: density difference, temperature difference and phase change. So three types of traps are made according to three principles: mechanical type, thermostatic type and thermodynamic type.

I. Mechanical traps

Mechanical type, also known as float type, is to use the density difference between condensate water and steam, through the change of condensate water level, make float lift to drive valve disc open or close, to achieve the purpose of steam resistance and drainage. Mechanical traps have low supercooling, and are not affected by working pressure and temperature changes. Water is discharged immediately and there is no water in the heating equipment, which can make the heating equipment achieve the best heat transfer efficiency. The maximum back pressure is 80%, and the working quality is high. It is the most ideal trap for the production process heating equipment.

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

1. Free floating ball trap

Free floating ball trap has a simple structure. It has only one fine grinding stainless steel hollow floating ball. It is not only a float but also an opening and closing part. It has no vulnerable parts and has a long service life. The inside of HG trap has 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 up, the air in the pipeline is discharged by Y series automatic air exhaust device. Low temperature condensate water enters the trap. The liquid level of condensate water rises, the float ball rises, the valve opens, and the condensate water is discharged rapidly. The steam enters the equipment quickly, the equipment warms up rapidly, and the temperature-sensitive liquid of Y series automatic air exhaust device is discharged rapidly. Expansion, automatic air exhaust device closed. The trap starts to work normally, the float ball rises and falls with the condensate level, and the steam is blocked and drained. The valve seat of the free float ball trap is always below the liquid level, forming a water seal, no steam leakage and good energy saving effect. The minimum working pressure is 0.01 Mpa, and the range from 0.01 Mpa to the maximum operating pressure is not affected by the fluctuation of temperature and working pressure. It can drain condensate water at saturated temperature, and the minimum undercooling is 0 C. There is no water in the heating equipment, so that the heating equipment can achieve the best heat transfer efficiency. Back pressure ratio is more than 85%, which is one of the most ideal traps for production process heating equipment.

2. Free Semi-floating Ball Trap

Free semi-floating ball trap has only one semi-floating ball bucket as a moving part. The opening of the bucket is down. The bucket is both an opening and closing part and a sealing part. The whole spherical surface can be sealed, long service life, water hammer resistance, no vulnerable parts, no fault, durable, no steam leakage. The back pressure ratio is more than 80%. It can drain condensate at saturated temperature. The minimum undercooling is 0 C. There is no water in the heating equipment. It can make the heating equipment achieve the best heat transfer efficiency.

When the device is just started, the air and low temperature condensate water in the pipeline enter the trap through the launching pipe. The bimetallic disc emptying element in the valve springs the barrel open, the valve opens, and the air and low temperature condensate water are discharged rapidly. When steam enters the barrel, the barrel generates upward buoyancy, while the temperature in the valve rises, the bimetallic disc emptying element shrinks, the ball drifts to the valve mouth, and the valve closes. When the steam in the barrel becomes condensate water, the barrel loses buoyancy and sinks, the valve opens, and the condensate water is discharged rapidly. When the steam enters the barrel again, the valve closes again, working intermittently and continuously.

3. Rod floating ball trap

The basic characteristics of leveraged floating ball trap are the same as that of free floating ball trap. The inner structure of the leveraged floating ball trap is connected with the leverage to drive the valve core, and the valve is switched on and off with the rise and fall of condensate level. Leveraged floating ball trap uses double seats to increase condensate discharge, which can achieve small volume and large drainage. The maximum drainage is 100 tons/hour. It is the most ideal trap for large heating equipment.

4. Inverted bucket trap

The inner part of the inverted bucket trap is an inverted bucket which is a liquid level sensitive part. The opening of the bucket is downward. The inverted bucket connects the lever to drive the valve to open and close. Inverted bucket trap can discharge air without fear of water hammer and has good anti-fouling performance. The supercooling degree is small, the leakage rate is less than 3%, the maximum back pressure is 75%, and the connection parts are more, so the sensitivity is not as good as that of the free floating ball trap. Because the inverted bucket trap closes the valve by steam buoyancy upward, when the working pressure difference is less than 0.1 MPa, it is not suitable for selection.

When the device is just started, the air and low temperature condensate water in the pipeline enter the trap, and the inverted bucket falls by its own weight. The inverted bucket connecting lever drives the valve core to open the valve, and the air and low temperature condensate water are quickly discharged. When the 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 in the inverted bucket. When some steam is discharged from the small hole, another part of the steam generates condensate water. The inverted bucket loses buoyancy and sinks down by its own weight. The inverted bucket connects the lever to drive the valve core to open the valve, circulate and drain intermittently.

5. Combined superheated steam trap

The combined superheated steam trap has two separate valve chambers, which are connected by two stainless steel pipes. It is a combination of floating ball trap and inverted bucket trap. The structure of the valve is advanced and reasonable. Under the working conditions of superheating, high pressure and small load, the condensate water formed when superheated steam disappears can be discharged in time. Effectively prevent the leakage of superheated steam, high quality of work. The maximum allowable temperature is 600 C, the valve body is stainless steel, the valve seat is carbide steel, and the service life is long. It is a special trap for superheated steam. It has obtained two national patents and filled the domestic blank.

When the condensate water enters the lower valve chamber, the float ball of the auxiliary valve rises with the liquid level, and the float ball closes the intake pipe hole. The condensate rises to the main valve chamber through the intake conduit, and the inverted bucket falls by its own weight, which drives the valve core to open the main valve and discharges the condensate. When the condensate level of the auxiliary valve chamber drops, the float ball drops with the level and the auxiliary valve opens. Steam enters the inverted bucket in the upper main valve chamber from the intake 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 chamber rises again, the next cycle starts again and the drainage is interrupted.

Ⅱ. Thermostatic trap

This kind of trap uses the temperature difference between steam and condensate to cause the variation or expansion of temperature sensing elements to drive the valve core to open and close. Thermostatic trap has a high degree of supercooling. Generally, the degree of supercooling is 15 to 40 degrees. It can make use of some sensible heat in condensate water. There is always high temperature condensate water in front of the valve. There is no steam leakage. The energy saving effect is remarkable. It is the most ideal trap in steam pipeline, heat tracing pipeline, small heating equipment, heating equipment and small heating equipment with low temperature requirement.

Thermostatic traps are diaphragm box type, bellows type and bimetal sheet type.

1. Diaphragm box trap

The main action element of the diaphragm trap is metal diaphragm box filled with a liquid whose gasification temperature is lower than the saturation temperature of water. There are two options for the open valve temperature to be lower than the saturation temperature of 15 C and 30 C. Diaphragm trap is very sensitive, not afraid of freezing, small size, heat resistance, any location can be installed. Back pressure ratio is more than 80%. It can discharge non-condensable gas. The diaphragm box is strong, has long service life, easy maintenance and wide application range.

When the device is just started, the condensate water appears in the pipeline, the liquid in the diaphragm box is in the condensation state, and the valve is in the open position. When the temperature of condensate water increases gradually, the liquid filling in the film closure begins to evaporate, the pressure in the film closure rises, and the diaphragm drives the valve center to move towards the closing direction. Before the condensate water reaches the saturation temperature, the trap begins to close. The diaphragm box controls the valve switch with the change of steam temperature, and plays the role of steam resistance and drainage.

2. Corrugated pipe trap

The spool of bellows trap is filled with a liquid whose vaporization temperature is lower than water saturation temperature in stainless steel bellows. With the change of steam temperature to control the valve switch, the valve has adjusting bolts, which can adjust the operating temperature according to need. Generally, the adjusting range of supercooling is lower than the saturation temperature of 15 ~40 C. Back pressure ratio is more than 70%, not afraid of freezing, small size, can be installed at any location, can discharge non-condensable gas, long service life.

When the device starts, cooling condensate water appears in the pipeline, liquid in the corrugated pipe is in condensation state, and the valve core is in the open position under the elastic force of the spring. When the temperature of condensate water increases gradually, the liquid filling in the bellows begins to evaporate and expand, the internal pressure increases, the deformation elongates, and the valve center moves towards the closing direction. Before the condensate water reaches the saturation temperature, the trap starts to close, and the valve switch is controlled with the change of the steam temperature to prevent the steam from draining.

3. Bimetal sheet trap

The main component of bimetal sheet trap is bimetal sheet temperature sensing element, which is heated and deformed with the rise and fall of steam temperature and drives the valve core to switch on and off. The bimetal sheet trap has adjusting bolts, which can adjust the operating temperature according to the need. Generally, the adjusting range of supercooling degree is lower than the saturation temperature 15 ~30 C, and the back pressure ratio is more than 70%. It can discharge non-condensable gas, not afraid of freezing, small size, water hammer resistance, high pressure resistance, and can be installed at any position. Bimetal sheet has fatigue property and needs to be adjusted regularly.

When the device is just started, low temperature condensate appears in the pipeline, the bimetal sheet is flat, the valve core is in the open position under the spring elasticity. When the temperature of condensate increases gradually, the bimetallic temperature sensing element begins to bend and deform, and pushes the valve core to the closed position. Before the condensate reaches saturation temperature, the trap starts to close. The bimetal sheet controls the valve switch with the change of steam temperature, and resists steam and drains water.

The working principle of the disc steam insulation trap is the same as that of the thermodynamic trap. It adds a shell outside the steam chamber of the thermodynamic trap. The inner chamber of the casing is connected with the steam pipeline, and the main steam chamber of the trap is insulated by the steam of the pipeline itself. The temperature of main steam chamber is not easy to cool down, the steam pressure is maintained and the trap is tightly closed. When condensate water is produced in the pipeline, the trap shell cools down and the trap begins to drain; if condensate water is not produced in the superheated steam pipeline, the trap will not open and the work quality is high. The valve body is alloy steel and the valve core is carbide. The maximum allowable temperature of the valve is 550 C. It is durable and has a long service life. It is a special trap for high-pressure and high-temperature superheated steam. The orifice plate trap is to select orifice plate with different aperture to control the drainage according to different drainage volume. Simple structure, inappropriate selection will lead to less drainage or a large amount of steam run-off, not suitable for intermittent production of steam equipment or condensate water fluctuation of steam equipment.

Ⅲ. Thermodynamic trap

According to the principle of phase change, this kind of trap relies on different thermodynamic principles of flow rate and volume change when steam and condensate pass through, which causes different pressure difference between the upper and lower parts of the valve sheet, and drives the valve sheet to switch on and off. Because the working power of thermal power trap comes from steam, the waste of steam is relatively large. Simple structure, water hammer resistance, maximum back of 50%, noise, valve piece work frequently, short service life.

Thermodynamic trap has thermal power type (disc type), pulse type and orifice type.

1. Thermal power trap

Thermodynamic trap has a movable valve plate, which is both a sensitive part and an action actuator. According to the different thermodynamic principles of the flow rate and volume change of steam and condensate water passing through, different pressure differences are generated between the upper and lower parts of the valve sheet to drive the valve sheet to switch on and off. The leakage rate is 3%, and the undercooling is 8 ~15 C.

When the device starts up, condensate water appears in the pipeline, and the condensate water pushes the valve sheet open by working pressure and discharges rapidly. When the condensate water is discharged, the steam is discharged afterwards. Because the volume and velocity of the steam are larger than that of the condensate water, the pressure difference between the upper and lower parts of the valve sheet is produced, and the valve sheet closes rapidly under the suction of the steam flow rate. When the disc closes, the disc is subjected to pressure on both sides. The area under the disc is less than the area above. Because the pressure in the steam chamber of the trap comes from the steam pressure, the force above the disc is greater than the pressure below, and the disc is closed tightly. When the steam in the steam trap chamber cools down to condensed water, the pressure in the steam chamber disappears. The condensate is pushed open by the working pressure, and the condensate is discharged continuously. The condensate is circulated and drained intermittently.

2. Disc steam insulation trap

The working principle of the disc steam insulation trap is the same as that of the thermodynamic trap. It adds a shell outside the steam chamber of the thermodynamic trap. The inner chamber of the casing is connected with the steam pipeline, and the main steam chamber of the trap is insulated by the steam of the pipeline itself. The temperature of main steam chamber is not easy to cool down, the steam pressure is maintained and the trap is tightly closed. When condensate water is produced in the pipeline, the trap shell cools down and the trap begins to drain; if condensate water is not produced in the superheated steam pipeline, the trap will not open and the work quality is high. The valve body is alloy steel and the valve core is carbide. The maximum allowable temperature of the valve is 550 C. It is durable and has a long service life. It is a special trap for high-pressure and high-temperature superheated steam.

3. Pulse trap

Pulse trap has two orifices to adjust valve switch according to the change of steam pressure drop. Even if the valve completely closes the inlet and outlet, it is connected through the first and second orifices. It is always in an incomplete closed state. Steam escapes continuously and the leakage is large. The trap has high operating frequency, severe wear and short service life. Small size, water hammer resistance, can discharge air and saturated temperature water, close to continuous drainage, maximum back pressure 25%, so few users.

4. orifice plate trap

The orifice plate trap is to select orifice plate with different aperture to control the drainage according to different drainage volume. Simple structure, inappropriate selection will lead to less drainage or a large amount of steam run-off, not suitable for intermittent production of steam equipment or condensate water fluctuation of steam equipment.