This article on Balanced pressure steam trap provides on information of various aspects of this steam trap such as working principle, design variations, advantages and disadvantages.
Balanced pressure steam trap is a temperature operated trap which means higher temperature of steam compared to condensate is used to close this trap when steam enters this trap.
Working Principle
Balanced pressure steam trap has a thin walled metal below which acts as a stem of internal valve. This bellow has a vacuum with some liquid of boiling temperature lower than water inside it. This liquid is mostly mix of water and alcohol.
Startup Stage :
During startup, air enters balanced pressure steam trap and gets freely released outside the steam circuit. Internal valve of this trap is open when there is no steam in this trap.
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Steam Entry :
When steam enters this trap, it heats up liquid inside below and causes it to quickly boil and create internal pressure inside bellow. As this liquid has boiling temperature lower than water, it creates higher vapor pressure than that of steam circulating outside. This higher pressure expands the below and closes the valve (Trap).
Steam Condensation:
When steam condenses inside this trap, the condensate inside trap has to cool down lower than boiling temperature of liquid inside below so that vapor pressure inside bellow decreases, causing bellow to contract and open the trap valve. This releases condensate from trap.
Advantages of Balanced Pressure Trap:
- Balanced pressure steam traps have high air venting capacity at startup as valve is fully open.
- As balanced pressure steam trap depends on differential pressure between liquid inside bellow and steam surrounding the bellow, it is self-adjusting. So this trap can function satisfactorily under varying steam pressure (within its operating pressure range) conditions without any external adjustments.
- Balanced pressure steam trap does not require freezing protection under subzero ambient conditions when it is discharged as free drain. There is no liquid in this trap when it is cool and open.
- This trap has large capacity with very simple and compact design.
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Disadvantages of Balanced Pressure Trap:
- Balanced pressure steam trap is generally not suitable for super-heated steam.
- This trap has limited resistance to water hammer due to this walled below inside.
- Some amount of sub-cooling of condensate cannot be avoided.
- Balanced pressure steam trap is susceptible for corrosion attack, when handling corrosive condensate.