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Automatic Air Vents for Steam ( LA13L / LA21 )

Automatic Air Vents for Steam ( LA13L / LA21 )


Continuously discharge air and gas that build up inside steam supply pipes

These air vents are used to discharge air that builds up inside steam supply pipes and in steam-using equipment.

The valve operates based on the difference between the temperatures of air and steam. The built-in X-element is used to detect this temperature difference, enabling the vent to discharge not only initial air upon startup, but also air which enters the vent during normal operation. This makes these air vents the ideal choice for batch processes.

Additionally, when temperatures inside the pipes and equipment drop and pressure lowers, the automatic air vent will act as a vacuum breaker, allowing air in and preventing the formation of a vacuum in the system.

Automatic Air Vents for Steam ( LA13L / LA21 )


  • Vents hot air at temperatures approx. 22℃ lower than saturated steam temperature
  • Compact size, large discharge capacity
  • "Fail open" X-element design
  • High heat resistance
  • Allows air into system after steam supply is shutoff, acting as vacuum breaker
Automatic Air Vents for Steam ( LA13L / LA21 )


  • Batch processes requiring large-volume air venting upon startup
  • Applications in which air locking tends to occur during operation
  • Double-jacketed kettles, pressing machines, vulcanizers, etc.

Utilization Examples

Automatic Air Vents for Steam ( LA13L / LA21 )


Purpose of use Compatible fluid Operation pressure (mpag) Max. discharge capacity (l/min) Body material Model Product photo Product specifications
Initial air venting + automatic air venting during operation Steam 0.01-1.3 1900 Forged brass LA13L Automatic Air Vents for Steam ( LA13L / LA21 ) 480 kb
0.01-2.1 2000 Cast stainless steel LA21 Automatic Air Vents for Steam ( LA13L / LA21 ) 119 kb

* When used at maximum operating pressure and with air at atmospheric pressure, 20°C

Operation Animation

At equipment startup, the X-element valve is in the open position and large quantities of air are quickly discharged, thereby greatly reducing equipment startup time. When the inflow of steam begins, the X-element valve immediately closes. The valve remains closed as long as the temperature around it is near saturation temperature. As the inflow of air causes the temperature to drop, the valve once again opens and the air is rapidly discharged.


What is an X-element?

The X-element is comprised of a valve and a diaphragm that transmits the force of a thermoliquid (temperature-sensitive fluid). When surrounded by steam, the valve is closed. When condensate, air or other non-condensable gases are present, the valve is open. It can also discharge high temperature non-condensable gases, something bimetal air vents are unable to do. This is made possible due to the special properties of the thermoliquid.

Automatic Air Vents for Steam ( LA13L / LA21 )

Thermoliquid, like water, is liquid when kept under a certain pressure and temperature, and expands to become a gas when its temperature rises above a certain point. The temperature at which it becomes a gas is approximately 6°C (22°C for air vents) lower than the temperature at which water becomes steam. So when it is surrounded by steam, the thermoliquid is a gas and the chamber containing the thermoliquid expands and pushes on the diaphragm. This causes the gap between the valve and the valve opening on the diaphragm to close.

Automatic Air Vents for Steam ( LA13L / LA21 )

In contrast, when the area around the X-element is at a low temperature (when it is either condensate or air), the thermoliquid is in the liquid phase and the valve is not being pushed closed, so condensate and air are discharged from the gap between the valve and the valve opening.

”Fail Open” Safety Feature

Fail safe features are necessary in quality precision instruments. TLV therefore designed the X-element in such a way that the valve remains in the open position ('fail open' safety feature ) in the event the diaphragm ruptures.

If a steam trap fails, the valve may either remain open (blowing) or it may remain closed (blocked). If the valve remains closed, condensate accumulates in any equipment that cannot be shut down in order to replace the failed trap, and this pooling of condensate impairs the equipment's heating performance. On the other hand, if the valve remains open, the supply of steam continues uninterrupted and the equipment can continue to be productive. Due to this special design, even if the diaphragm ruptures and becomes technically 'closed' (by remaining in contact with the valve opening due to the flow of steam and condensate), condensate, etc. can still flow through the valve opening via the hole in the center of the valve.