Steam traps


Selection of steam traps

Explanation of icons used in this table
 
Icon   Description   Icon   Description
  Ball float steam trap with integral automatic air vent     Inverted bucket steam trap
  Ball float steam trap with adjustable needle valve     Thermostatic steam trap
  Thermodynamic steam trap     Bitmetallic steam trap
  Thermodynamic steam trap with integral automatic air vent        
 
 
Autoclaves Laundrymachines Tanks and vessels indoor
Evaporation device Presses Tanks and vessesls outdoor
Heating Steam distribution  
Kitchen equipment Steam heated drying cylinders  
 
Autoclaves    
Application   1st choice   Alternatives            
Autoclaves                
 
Steam heated drying cylinders   Presses
Application   1st choice   Alternatives   Application   1st choice   Alternatives
High speed drying roller         Vulcanising presses    
Low speed drying cylinder       Multi-plate presses    
 
Tanks and vessels indoor   Evaporation device
Application   1st choice   Alternatives   Application   1st choice   Alternatives
Non-critical processes       Evaporators    
Critical processes       Distilling vessels    
 
Laundry machines   Kitchen equipment
Application   1st choice   Alternatives   Application   1st choice   Alternatives
Ironers       Small cookers    
Garment presses       Large cookers    
Tumblers       Cooking kettles (tiltable)      
            Heating tables    
 
Tanks and vessels outdoor   Steam distribution
Application   1st choice   Alternatives   Application   1st choice   Alternatives
Pre-heaters       Waterseparators    
Storage tanks (continuous use)       Main steam pipes (saturated steam)    
Storage tanks (non-continuous use)       Main steam pipes (superheated steam)      
Winterising tracing       Branches    
Critical tracing       Steam diversion pipes    
 
Heating   Heating (continues)
Application   1st choice   Alternatives   Application   1st choice   Alternatives
Boilers       Convection cabinet heaters
(natural draught)
   
Heat exchangers       Convection cabinet heaters (forced draught with fan)    
Steam radiators       Heating batteries    
Finned tubes       Panel heating    
Air heaters                

The operation of steam traps

On the following pages is explained how steam traps operate.

Float type


 

Operation

The valve mechanism of a float type steam trap is operated by a float inside a float chamber. The principle is based on the difference in density between the steam and condensate. 
 
  • The at the inlet side (E) incoming condensate is filling the chamber and starts pushing the float (S) upwards, at the same time opening the discharge valve (V) will open by means of the attached lever (H).
  • The higher steam pressure on the inlet side is driving the condensate via outlet (A) into the discharge system.
  • The more condensate is building up inside the float chamber, the more the discharge valve will open and the more condensate can be discharged.
  • The modulating action ensures the continuing discharge of incoming condensate.
When the supply of condensate is reduced, the whole process is reversed, so the valve will start closing in accordance with the level of condensate in the chamber, so less condensate will be discharged. The valve will fully close and stay closed until new condensate will enter the chamber.

Water lock
The float mechanism is constructed in such way, that once the valve is closed, the valve and seat are always below the water surface, inside of the chamber. The advantage of this is: There is always a water lock present, which will prevent the leaking of steam.

Higher pressures

The buoyancy of the float (S) normally results in an opening force that is higher than the valve closing force, caused by the pressure differential across the valve seat.
When the steam pressure increases, the closing force on the valve increases as well, until the buoyancy opening force can no longer overcome the pressure differential force across the valve seat. The situation now offers two possible solutions:
 
  • The bore of the valve seat can be reduced, which will decrease the pressure differential force across the closed valve and seat
  • The float and the float chamber can be increased in size, so the buoyance force, applied to open the valve, will be increased.
Both solutions have limitations. Reducing the bore will also reduce the discharge capacity, increasing the dimensions of the chamber and float will make the steam trap bigger and more expensive. Consult Econosto to select the best option in your application!
 

Venting

As the valve and seat are below water level, there always needs to be a solution for the venting of air and non-condensing gases present in the system. This can be achieved by means of an automatic vent, or by an adjustable hand-operated vent. Float type steam traps can be supplied with an integrated thermostatic vent.

Advantages float type:
  • Can discharge high volumes of condensate quickly
  • Very good air venting capacity
  • Modulating operation, direct and continuous discharge of condensate
  • Suitable for many applications
Limitations:
  • When used in outdoor installations, the steam trap must be isolated to prevent freezing during wintertime conditions
  • Relatively voluminous and heavy
  • Relatively expensive

 

Inverted bucket type


 

Operation

As the name indicates: in this steam trap, there is no float but an inverted bucket, thus creating the possibility of buoyancy. The operation is similar to that of the float type as described above. The bucket float (G) is rising and falling on the incoming condensate in the steam trap chamber. The discharge valve (V) in the upper side of the steam trap chamber is operated by the moving float. 
 
  • On system start-up the chamber will be filled with condensate, the bucket (G) will sink and stay on the bottom of the chamber, with the discharge valve (V) fully opened, so condensate can now be discharged.
  • When steam or gases are entering the chamber, they will be building up inside the bucket (G), forcing it upwards, and closing the discharge valve (V). This operation can be compared to effect of a glass that is inverted into water. You will find that the glass delivers an upward (buoyancy) force, when you try to submerge it.
  • When the steam in the bucket condensates after some time, the bucket loses buoyancy, making it sink and at the same time opening the discharge valve again.
  • Remaining air in the bucket however, does not condensate, and so would keep the steam trap closed. To prevent this, there is a small orifice (B) on top of the bucket that will allow the air in the bucket to vent to the chamber, so the bucket will sink anyway and will open the condensate discharge valve.
  • This effectively means that the inverted bucket type of steam trap will have an intermittent operation, meaning that it opens to closes under normal load.
Advantages:
  • Less sensitive to dirt
  • Moderate resistance to water hammer
Limitations
  • At start-up, the steam trap needs to become filled with water/condensate first
  • Small but constant loss of steam
  • Poor air venting
  • Intermittent operation under normal load
  • When used in outdoor installations, the steam trap must be isolated to prevent freezing during wintertime conditions
     

Thermodynamic (TD) type


 

Operation

The thermodynamic steam trap consists of three parts: Body, disc shaped valve, and cover. As shown above, when condensate is entering the body, it will push the valve disc upwards. This will allow the condensate to be discharged into the condensate discharge system. Now how does it work?

  • Start-up. Relative cold condensate and air will come into the body and will lift the disc. Condensate and air will be discharged.
  • When the condensate gets warmer and flowing through the inlet into the chamber the pressure drops. Therefor flash steam will occur moving at high velocity. This high velocity and low pressure will draw the disc towards it seat.
  • At the same time the flash above the disc will build up pressure and forcing the disc down against the incoming condensate and will close the inlet.
  • In time the flash steam above the valve will condensate, which will cause break down of the closing force on the valve, the pressurized condensate below the valve will push it open again.
  • This process will repeat itself time after time.

The operation of the TD type of steam trap is based on the law of Conservation of Energy, also known as Bernoulli’s law. This law poses that the total energy remains conserved. Because of the fact that the total energy (summation of kinetic energy a.k.a. velocity, gravitational energy and pressure) must remain the same. In this equation a higher velocity must result in a lower pressure under the valve.

This can be proven very easily. Take a small sheet of paper in your mouth in such way, that the longer part is hanging down, supported by your hand. If you now blow firmly over the paper sheet, you will notice that the paper lifts itself upwards! Why? Because of the increased air flow velocity over the upper side of the sheet, the air pressure on the upper side of the sheet is decreasing, so, the now higher pressure on the lower side of the sheet, can move it upwards, against the existing gravity!

The TD steam trap is also available with integrated air vent, to make repeated start-ups more efficient.

Advantages:

  • Simple construction
  • Little maintenance
  • Relatively cost effective
  • Well resistant against water hammer, vibrations and superheated steam
  • Works also as a check valve


Limitations:

  • Limited air venting capacity, for repeated start-ups a separate air vent is advisable
  • Ticking noise, can be annoying e.g. in hospitals
  • Intermitted operation, so less suitable to be used on heat exchangers
  • Min. pressure differential required between inlet and outlet, of 0,25 bar (with air vent 0,8 bar)
  • Max. allowable backpressure of 70%-80%
     

Bimetallic type


 

Operation

A bimetallic steam trap belongs to the thermostatic type of steam traps. The bimetallic element consists of several sets of metal plates with distinctive specific expansion coefficients. When bimetal is heated, it will start bending, proportional to the temperature increase. This change in state, this movement, can be utilized to operate the valve of a steam trap.

  • In the above picture you can see one thermal element that consists out of several sets of bimetallic plates (S) that are positioned 2 by 2 opposite to each other.
  • On a temperature increase these bimetal sets expands and thereby lifting the spindle and so the valve will close. The valve will be closed before the steam reaches the steam trap.
  • On a temperature decrease the bimetallic element will shrink, and the discharge valve (V) will be opened, so the condensate can be discharged.

Temperature differential

To be sure that there is no loss of steam, the element is adjusted in such way, that the discharge valve is already closed, before the element reaches the steam temperature. Therefor there is always some degree of condensate sub cooling below the steam temperature, between 10 and 30° Celsius, required to open the condensate discharge valve. Because of hysteresis, this differential depends on the adjustment and the response time of the bimetallic element.

Advantages

  • Compact and robust
  • Less sensitive to water hammer
  • Main valve works as a check valve
  • Relatively cost effective


Limitations

  • Relatively slow operation, so more stalling of the condensate
  • A higher backpressure causes more stall and alters the operation
  • The element is aging, especially when used on superheated steam
     

Thermostatic type

Operation

The balanced pressure steam trap belongs, like the bimetallic steam trap, to the group thermostatic steam traps.
The membrane capsule (T) can be addressed as: “a completely sealed stainless steel box” that’s partially filled with a mixture of usually alcohol and water. The boiling point of this mixture is lower than that of only water.

  • When the capsule is heated above its vapor pressure, the mixture filling will vaporize and the internal higher pressure will cause the capsule to expand.
  • This expansion movement of the capsule is now used to close the condensate discharge valve.
  • By varying the composition of the filling mix, a boiling point can be reached boiling of 5°C to 24°C below the saturated steam temperature.

In this way, also under alternating pressure, condensate is always discharged with the same subcooling. So the steam is stopped even under alternating pressures, without the need of adjustment of the steam trap.

Temperature graph

The operation can easily be explained in the graph below.

Suppose the thermostatic steam trap has a sub cooling of 20oC. The steam trap is used to discharge a cooking kettle with a working pressure of 5 bar and 159oC (saturated steam).

At start-up the steam trap will be fully opened and the kettle is still cold and at zero bar pressure. When the steam is supplied to the kettle (slowly as should be), the air and condensate present will be discharged easy and fast. When the condensate gets hotter, the vapor pressure inside the thermostatic element increases, and follows the dotted curve line in the graph. As you can see, the curve of the vapor pressure (boiling point) follows a trajectory, parallel to that of the saturated steam curve.

Because of the fact, that the boiling kettle heating system fills up with steam, it’s temperature is slowly rising to the saturated steam temperature of 159oC (belonging to the steam pressure of 5 bar in this example). Now the temperature is passing the temperature value of 139oC, being the temperature at which the alcohol/water mixture inside of the thermostatic capsule starts boiling, and the capsule is expanding. This expansion forces the discharge valve to close, before the steam actually reaches the steam trap!



After the steam trap has closed, hot condensate is building up in the steam inlet pipe.
Now this pipe with hot condensate gets time to cool down. As soon as the condensate has cooled sufficiently (in this case 20oC subcooling), the alcohol/water mixture in the thermostatic capsule starts to condensate, hence losing its vapor pressure, which is making the capsule shrink and thus opening the discharge valve again, and the condensate will be discharged. This process repeats itself as soon as the condensate is fully discharged and the capsule heats up again, resulting in the closing of the steam trap.
 
Advantages

  • No adjustments needed on alternating pressures
  • Not sensitive to backpressure
  • Not sensitive to freezing in outdoor applications
  • Good venting of air and gases

Limitations

  • Sensitive to water hammer
  • Stall of condensate. Sub cooling of condensate, depending on the capsule filling, between 4oC and 20oC.
  • Only limited suitability to superheated steam
     

Constructions of steam traps

On the following pages you will find the technical constructions of the commonly used steam traps with their most significant parts.

Float type


Browse our assortment of float type steam traps in our online product catalogue.

Inverted bucket type


Browse our assortment of inverted bucket type steam traps in our online product catalogue.

Thermodynamic type


Browse our assortment of thermodynamic type steam traps in our online product catalogue.

Bimetallic type


Browse our assortment of bimetallic type steam traps in our online product catalogue.

Thermostatic type


Browse our assortment of thermostatic type steam traps in our online product catalogue.

Application of Steam Traps

Ball float steam trap

Ball float type steam traps are used especially in situations where condensate needs to be discharged instantly. Because of the modulating operation the ball float steam trap is ideally suitable for the discharging of condensate from heat exchanger as the condensate is directly discharged without any stall into the heat exchanger. As a result, the capacity of the heat exchanger can work most efficient.

Limitations of the ball float type steam traps include the risk of freezing and the sensitivity to water hammer and contamination of the condensate. By insulating the steam trap and by installing a filter upstream of the steam trap, these limitations can be largely avoided, so the float type steam trap may be applied outdoors and in contaminated systems as well.

Typical applications include:

  • Heating
    • Boilers
    • Shell and tube heat exchangers
    • Plate heat exchangers
    • Convectors (forced circulation)
    • Air heaters
    • Heating batteries
    • Panel heating
  • Vaporisator devices
    • Vaporisators
    • Distilling kettles
  • Drying cylinders
    • Dry rollers
  • Laundry machines
    • Tumblers
  • Oil
    • Oil heaters

Browse our assortment of float type steam traps in our online product catalogue.

Inverted bucket steam trap

As the inverted bucket type steam trap does not need much maintenance, it is particularly useful in mounting locations that are difficult to access. This low maintenance requirement is because of its high resistance against dirt and water hammer. Also this steam trap remains open when faulty. The advantage of this function is, that the process is not interrupted on failure of the steam trap. As the inverted bucket steam trap is maintenance friendly, this type of steam trap is known as a “fit-and-forget” type of product.

The limitations of the inverted bucket type of steam trap are:

  • Risk of freezing in outdoor use. This can usually be overcome by insulating the trap properly.
  • The intermittent operation, which is typical for its design.

Typical applications are:

  • Dryers
    • Short drying coils
  • Oil
    • Oil storage tanks
  • Condensate discharge
    • Draining of steam pipe lines

Browse our assortment of inverted bucket type steam traps in our online product catalogue.

Thermodynamic steam trap

Thermodynamic (TD) steam traps are particularly applied for the discharge of steam pipelines. This is because this type of steam trap is:

  • unaffected by freezing
  • is discharging condensate almost immediately

These properties make the TD steam trap most suitable to be applied on a main steam pipleline, that is located outdoor. Other advantages of the TD steam trap are:

  • small dimensions
  • water hammer resistant
  • easy to check/maintain

There are also some limitations to this principle:

  • sensitive to contaminated condensate
  • use of a strainer upstream the TD steam trap is recommended (there are also models available with a filter element already integrated in the body/inlet).
  • Noise (ticking sound every 20 seconds)

Typical applications are:

  • Stoomdistribution
    • Waterseparators
    • Main steam pipelines
    • Branches
    • Steamdiverters
  • Kitchen equipment
    • Large cookers
  • Dryers
    • Long drying coils
    • Drying cabinets
  • Autoclaves
  • Laundry machines
    • Mangels
    • Garmen presses
  • Tanks and vessels
    • Tanks for various processes
  • Presses
    • Vulcanising presses
    • Multi platen presses

Browse our assortment of thermodynamic type steam traps in our online product catalogue.

Bimetallic steam trap

Bimetallic steam traps are particularly applied when stall of hot condensate is preferred, as in steam tracing or storage tanks.

In tracing applications the advantage of stall is, that the latent heat that is still in the condensate gets time to transfer its energy. This is especially an advantage in tracing applications, where it is not efficient, to return small volumes of discharged condensate to the boiler. If hot condensate is not re-used, now the better strategy is to recover as much heat energy from the condensate as possible. Obviously the energy that remains in the discharged warm condensate is otherwise completely lost.

Another advantage of bimetallic steam trap is the smaller amount of flash steam that will occur, because of the fact that the condensate is already subcooled. As a result, the condensate return pipelines can have smaller dimensions, which is also saving installation cost.

Typical applications

  • Heating
    • Finned tubes
  • Tanks and vessels
    • Small hot water tanks
  • Tracing

Browse our assortment of bimetallic type steam traps in our online product catalogue.

Thermostatic steam trap (bellows capsule)

The thermostatic steam trap is related to the bimetallic steam trap in terms of properties. The thermostatic steam trap differs however, where accuracy and resistance to dirt and water hammer is concerned. The thermostatic steam trap works more accurate, but is more sensitive to dirty condensate and water hammer. The sub cooling can be chosen between 4°C and 20°C by choosing different fillings of the capsule. The thermostatic steam trap is used in applications, where it is essential to maintain a certain temperature very accurately. Because of its fast response, it is also used for air venting and vacuum breaking applications.

Typical applications:

  • Heating
    • Stean radiators
    • Convectors (natural draft)
  • Kitchen installations
    • Small cookers
    • Heating tables
  • Tracing
Browse our assortment of thermostatic type steam traps in our online product catalogue.
 

Important terms using steam and steam traps

Index

Abs - Con Con - Hea Hea - Pre Pre - Ste Ste - Wat Wat - Wet
Absolute pressure (bar/a) Condensate discharge Heat transfer Pressure difference Steam pipe Water treatment
Air discharge / venting Cubic meter Hysteresis of a steam trap Pressure gauge Steam table Wet steam
Atmospheric pressure Dry steam Inlet pressure Saturated steam Steam temperature  
Backpressure Enthalpy (H) Intermittent action Saturated steam pressure Subcooling  
Bellows / capsule Evaporation heat Insulation Saturated steam temperature Superheated steam  
Bimetal element Flash steam Kilocalorie (kcal) Specific density (p) Temperature difference (dT)  
Boiling Force (F) Kilojoule (kJ) Specific volume Thermometer  
Capacity Heat (Q) Litre (l) Stall Vacuum  
Condensate Heat content (U) Modulate action Steam Vapour pressure  
Condensation Heat exchanger Overpressure Steam loss / leakage Water film  
Condensate line Heating surface Pressure Steam pressure Water hammer  

Absolute pressure

Pressure measured against full vacuum (0 bar/a) as a reference.
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Air discharge, air venting

Steam systems can build up air/gases which are undesired as gases cannot condensate. Steam traps can have a built-in air vent or are only used as air-vent on top on a system, mostly thermal steam traps. Removing air that has entered the system during a stop increases heating efficiency, and also makes it easier to start up a steam system. Not removing air from a steam system has 3 disadvantages:
  • The partial saturation pressure of a steam/air mixture is lower, as is the effective temperature of the steam
  • Air is also hampering /delaying the heat transfer of the steam
  • The presence of air in the condensate discharge system invokes the forming of carbon dioxide gas, which is aggressive to the discharge lines.
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Atmospheric pressure

Atmospheric pressure (also named gauge pressure) is the pressure in the atmosphere we live in. This pressure depends on the actual location and height. For technical use this pressure usually is rounded to 1 bar = 1000 mbar (millibar) at sea level.


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Backpressure

Pressure on the outlet side of the steam trap, or valve, in the downstream of the system. If the backpressure is above the inlet pressure of a steam system, it is not possible to discharge condensate. Backpressure is a common source for failures like water hammer. Additionally it hampers the correct operation and the capacity of a steam trap. Common causes of high backpressure are:
  • a too small sized condensate discharge pipeline;
  • discharging via a rising pipe to a higher situated part of the discharge system;
  • leaking steam traps;
  • condensate discharge pipeline too long;
  • the presence of pressure in the condensate collecting tank.
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Bellows/Capsule

Metal capsule filled with a mixed liquid (usually alcohol /water). When the bellows are heated, it’s content will start boiling. This causes pressure to build up which expands the capsule. When the temperature drops the bellows will shrink again. This movement can be used to actuate a device like a steam trap (open and close). Because the behaviour of the liquid filling is comparable with that of water, this bellows/capsule automatically follows the saturated steam curve. For the balanced pressure thermostatic steam traps there is a choice for different fillings, 4 °C, 10 °C or 20 °C below the steam saturation curve.
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Bimetal element

This element consists of at least two metals with different expansion coefficients, melted together as one element. When the element is heated, one of the two metals will expand more than the other. As the metals are fixed together, this will cause the element to bend. The bending caused by heating can be used to actuate a device like a steam trap (open to close). The bimetal element has a linear characteristic and does not automatically follow the saturated steam curve! By using multiple bimetal strips with different lengths the combined characteristic approximates that of the saturated steam curve.
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Boiling

Heating of a liquid at a given pressure, until vapour bubbles appear. The temperature at which a liquid starts boiling, depends on the pressure applied to it.
Pure water will boil at a temperature of 100 oC and an absolute pressure of 1 bara. If the absolute pressure is increased to 2 bara, pure water will boil at 120 oC. The relation between the applied pressure and the boiling temperature, is expressed as the “steam curve”. E.g.: The higher pressure present in a pressure cooker causes a higher boiling temperature. As a result potatoes which are prepared in a pressure cooker are cooked in a shorter time!
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Capacity

The mass of boiling hot condensate (kg) that a steam trap can drain (discharge), per time unit (h) at a given pressure difference. Caution: At start-up the required mass of condensate will be large, while the pressure difference will still be small. When determining a steam trap’s bore, a safety factor of 1,5 to 2 is often used before calculating the expected capacity.
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Condensate

Condensed steam is basically pure and mostly boiling hot water. Condensate contains a lot of energy and can very well be used as boiler feed water. Condensate recovery, or reuse of condensate, increases the efficiency of the complete steam installation.
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Condensation

The transition of saturated steam to condensate, at constant temperature. When saturated steam condenses it releases its heat of evaporation.
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Condensate line

Piping to transport the boiling hot condensate back to the steam boiler. Immediately after a steam trap, flash steam is formed, depending on the steam pressure. This fact must be included in the calculations of the required pipe diameter. A too small size condensate transporting pipelines produce a huge resistance to the condensate flow, and hence are a cause of many failures in a steam installation.
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Condensate discharge

Removal, draining of hot condensate from a steam installation.
Depending on the type of steam trap used, condensate is drained at saturated steam temperature, or at a sub cooled temperature below the saturated steam temperature.
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Cubic meter

Unit of measure. The volume of a cube with edges of one meter in length (1 m3 = 1000 litres = 1000 dm3 = 1000 litres).
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Dry steam

Steam containing a low content (5% of the steam mass) of water. Saturated steam (100% dry) contains 100% of the latent heat energy available at that pressure. In such a case the steam contains the most enthalpy possible for saturated steam. However heat losses of pipes cause the dry steam to condensate, causing the percentage of water to increase.  Because of the formation of condensate a drainage point is required every 30 meters, and just before rising pipelines.
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Enthalpy (H)

Enthalpy is a measure of the energy that is stored in a liquid. Enthalpy is a summation of the internal energy and the energy that is stored by the pressure applied to it. The formula for enthalpy is: (H = U + p * V) ; meaning : H = Internal energy + pressure * volume.
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Evaporation heat

Heat/energy required to evaporate a liquid, at constant temperature.
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Flash steam

When boiling hot condensate is depressurized below vapour pressure, the condensate will partly evaporate into flash steam. This occurs mainly at the outlet side of a steam trap.
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Force (F)

Unit of measure in the SI-System of units, expressed in N (N=Newton). Force is the interaction between objects that results in causing acceleration. An example of force is in a rocket launch. The rocket ignites its engine that now is producing a lifting force. Now the rocket itself starts moving, accelerates, and takes off. 1 Newton is defined as the force required to accelerate an object of 1 kg with 1 m/s2.
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Heat (Q)

Heat is the transmission of energy caused by a temperature difference. E.g.: The heating of water in a heat exchanger is possible by the difference in temperature between the steam and the water.
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Heat content (U)

The total heat energy that is stored in steam. The difference between Enthalpy and Heat content is: The Enthaply also includes the energy that is stored by the pressure applied to the steam, where Heat content does not.
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Heat exchanger

A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The primary medium is often steam and the secondary medium often water, that needs to be heated.
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Heating surface

The surface of an object that is heated by the primary medium. The energy which is absorbed is transferred to the secondary medium.
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Heat transfer

The transfer of thermal energy (or heat) from one material to another (hot to cold).
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Hysteresis of a steam trap

This is demonstrated in practice with a thermostatic steam trap as follows: 

Example:
When the temperature of a steam system decreases to 21 oC below the saturated steam temperature, the steam trap starts to close. However when the temperature of the steam is increasing the thermostatic steam trap will close at 19 oC below the saturated steam temperature. The hysteresis is in this case is thus: 21-19 = 2 oC

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Inlet pressure

Steam pressure at the inlet side of a stream trap or a valve. If the inlet pressure of a steam trap is below the outlet pressure, the condensate cannot be discharged.
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Intermittent action

An intermittent acting type of steam trap opens and closes quickly and repeatedly in normal operation. Such mode of operation makes this type of steam trap unusable in applications where condensate needs to be drained continuously. E.g.: thermodynamic and inverted bucket type of steam traps.
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Insulation

Very effective method of thermal insulation of steam and hot water pipelines. Insulation reduces the energy loss of the system, and reduces the risk to burn yourself.
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Kilocalorie (kcal)

Old unit of measure for labor, energy. (1 kcal – 4,1868 kJ). The kcal was originally defined as the energy required to increase the temperature of 1 kilogram of water by 1 degree Celcius. Because of the fact that this energy also depends on the initial water temperature, the unit 1 calorie was later defined as 4,1869 Joule.
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Kilojoule (kJ)

Unit of measure of labor, energy (1000 Joule = 1kJ = 1000Nm). One Joule is defined as the energy required to apply a force of 1 Newton over a length of 1 meter. An example of used energy is pushing a car for 100 meters. Suppose that a force of 250N is needed to get (and keep) a car moving. When applying the above formula, the energy required is: 250N * 100m = 25.00 Nm = 25,000 Joule = 25kJ.
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Litre (l)

Unit of measure for volume (1 l = 1 dm3 = 0,001 m3). A cube with edges of 10 cm has a volume of 1 litre.
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Modulate action

A modulating action type steam trap opens proportionally to the condensate flow to the device. If the flow to the steam trap increases, the valve will open wider.  The modulate mode of operation makes this type of steam trap especially suitable in applications where condensate needs to be drained continuously. A typical example of such operation is found in the float type steam trap. Because of the continuous operation of modulating steam traps, it is harder to verify whether the steam trap works properly.
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Overpressure

Pressure in a system compared to the pressure in the surrounding atmosphere (approx. 1 bara).
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Pressure

Force working on the surface of an object. In the SI-system of units: 1 bar = 105N/m2 (N=Newton, see also “Force”).  kPa is the ISO unit for pressure (not bar).
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Pressure difference

The difference in pressure measured between the inlet and outlet of a steam trap or a valve. The actual value determines the (discharge) capacity of a steam trap. Pressure difference is usually low at start up.
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Pressure gauge

Measuring instrument to measure the unit pressure. A pressure gauge is used to locally indicate the actual pressure in a system. Pressure gauges usually indicate the system pressure with reference to outside atmospheric pressure. In steam installations the unit bar or kPa (kilopascal) is often used (1 bar= 100 kPa).
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Saturated steam

Saturated steam is steam that condensates, when its temperature is lowered. Saturated steam can also be called wet steam as a percentage of the steam condenses. This is because of the fact that at the smallest of temperature loss, already miniscule drops of water start to emerge, making wet steam. Wet steam is unusable for a steam turbine, but it perfectly meets the requirements of powering a steam engine, and is perfect for the exchange of heat.
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Saturated steam pressure

The pressure at which water starts boiling and becomes gaseous, at a given temperature.
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Saturated steam temperature

The temperature at which water boiling and becomes gaseous, at a given pressure starts.
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Specific density (ρ)

Specific density is defined as an object’s mass per unit volume kg/m3. Specific density is the reciprocal of specific volume.
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Specific volume

The specific volume of a substance is the ratio of the substance's volume to its mass m3/kg. It is the reciprocal of specific density.
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Stall

Build up of condensate in a system (e.g. heat exchanger) at the inlet side of a steam trap.
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Steam

Steam is the gas formed when water passes from the liquid to the gaseous state. Dry steam is invisible.
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Steam loss – leakage

The leakage, loss, spill, volume of steam, passing through a steam trap. Leakage must not be confused with steam vapour that is formed from the evaporating condensate that is correctly drained.
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Steam pressure

Steam compressed under pressure in vessels or pipes, see also Steam. Compressed steam can lead to an explosion, e.g. when pipes or vessels are ruptured.
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Steam pipe

Pipe used for transportation of steam under pressure.
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Steam table

The saturated steam table is an important tool for engineers. It is used to determine saturated steam properties, like steam temperature at steam pressure, or the opposite. Steam tables include other related values such as enthalpy (H) and specific volume (v).
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Steam temperature

Steam temperature is related to steam pressure. See steam table.
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Subcooling

Condensate that has been cooled down before it is drained by the steamtrap. Subcooling can be utilised to open the valve of a temperature controlled steam trap.
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Superheated steam

Steam with a temperature above the saturation temperature according to the steam table. Superheated steam is 100% dry.
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Temperature difference (dT)

Difference in temperature of an object or medium. A good example is the difference in temperature between the two media in a heat exchanger. Example: Heating of water from 20 oC to 70 oC causes a dT (dT = 70 - 20 = 50 oC).
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Thermometer

Instrument used to measure the (steam/condensate) temperature in a system or the temperature of an environment.
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Vacuum

A pressure value below absolute pressure of (approx.) 1 bara. A perfect vacuum exists when a space does not contain any matter, and is thus without pressure (0 bara).
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Vapour pressure

The pressure at which (hot) water/condensate boils and evaporates. Because water will boil sooner, when the pressure is lowered, it is possible to create water vapour by decreasing the pressure, while keeping the temperature constant. A decrease of steam pressure can occur in pumps, and in valves. The forming of steam bubbles in a liquid, by lowering the local pressure, is also called cavitation.
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Water film

Thin layer (film) of water that sticks to the internals of a steam pipe. The water film is created by the condensation of steam.
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Water hammer

Water hammer (or, more generally, fluid hammer) is a pressure surge or wave caused when a fluid in motion is forced to stop or change direction suddenly (momentum change). Water hammer can also occur in steam pipes where water is present. If water is present in steam pipes, the steam flow can pick up a slug (mass) of water in the steam pipes and move it forward at high velocity. A water hammer commonly occurs when such a moving “slug of water mass” collides with an obstruction, like bend or a closed valve downstream in the pipeline. The sudden stop of a water mass releases a burst of kinetic energy resulting in a pressure wave. This is also called “hydraulic shock”.

The impact between a slug of water and parts of the system can cause major problems, from noise and vibration to pipe and valve collapse. The hazard of water hammer is a good reason to use steam traps at the right locations, in order to avoid build up of water in steam pipes. Econosto can advise when engineering steam systems!
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Water treatment

Treatment of raw water with chemicals or additives, to make the water suitable to be used as boiler feed water. Water treatment is used to prevent damage to boiler internals.
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Wet steam

Steam that is not full gaseous, but also contains drops of water. Eventually dry steam, generated by a steam boiler, always becomes wet steam because of pressure losses. Wet steam causes water hammer, erosion to control valves and pipes, and also decrease of capacity. Problems caused by wet steam can be reduced by installing a steam dryer or water separator before any control valves. Additionally it is important to provide sufficient drainage points to the installation. Econosto advises to drain a steam pipe every 30 meters.
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