This article on Bimetallic Steam Trap provides information of various aspects of this stem trap such as operating principle, design variations, advantages and disadvantages.
This trap is a temperature operated trap i.e. thermostatic steam trap. It uses the fact that temperature of steam is higher than condensate. Higher temperature of steam is used to close this steam trap.
This trap is most robust design of steam trap among all steam traps. This trap contains bimetallic strips of dissimilar metals stacked together in pairs.
Following figure shows steam trap in open state. When steam trap contains condensate, bimetallic strips are in flat position and valve is open. Condensate drains freely out of system.
When steam enters the trap, its higher temperature causes bimetallic strips to bend and close the valve. Thus no steam goes out of the system.
Invert Disc Valve
This is an improved design of bimetallic steam trap. It contains an inverted disc valve and the bimetallic strips arranged in a reverse manner.
Multiple Prongs Type Bimetallic Steam Trap
A further improvement in the response line of the bimetallic steam trap is possible by utilizing a modified design of the bimetallic element with multiple prongs as shown in the blue sketches above.
Advantages of the bimetallic steam trap:
- Bimetallic steam trap is fairly robust and has a compact design.
- Bimetallic steam trap has fairly high air venting capacity.
- This steam trap has fairly high resistance to Water Hammer.
- Bimetallic steam trap has reasonably good performance against super-heated steam.
- This trap has fairly high thermal efficiency when set to discharge sub-cooled condensate. Possibility of flashing of sub-cooled condensate in bimetallic steam traps is minimal.
- Bimetallic steam traps do not require freezing protection under subzero ambient conditions when its discharge is piped as a free draining line.
Disadvantages of the bimetallic steam trap:
- Some amount of sub-cooling of condensate cannot be avoided in bimetallic steam traps.
- This trap has modest response to temperature variations.
- Bimetal characteristics of bimetal strips used in this trap may change after being in use for some time. Hence these traps may require servicing at periodic intervals.