Figure 1: Bimetallic steam trap and valve configuration
Bimetallic steam traps
Another type of thermostatic steam trap is the bimetallic trap. Bimetallic steam traps are made using two dissimilar metal strips that are welded together to an element. The element deflects when heated. .
Bimetal steam trap
See the image below, considering this simple element, there are 2 important points to consider:
- Steam traps operate at a certain constant temperature that may not meet the requirements of a steam system that may operate at different temperatures and pressures.
- Because the force exerted by a single bimetallic strip is small, a large mass must be used to react to temperature changes in the steam system.
Bimetal steam traps
The performance of any vapor trap can be measured by its response to the vapor saturation curve, the ideal response follows the curve and just below it, a simple bimetallic element reacts linearly with temperature changes, some They use two different sets of bimetals in one batch that operate at different temperatures. (See image below.)
What is a bimetallic steam trap?
How steam traps work
A more innovative design is the thermostatic element of the spring disc, shown in the figure below. The thermostatic element is made of a set of “bimetallic disks”.
If these discs act directly between the “valve stem” and the seat (as part of the thermostatic steam traps), they will cause the condensate discharge temperature to change linearly with pressure.
Washer spring in steam trap
By inserting a “spring washer” between the discs and a retraction in the seat, it absorbs part of the bimetallic expansion at low pressure until a higher temperature change occurs with the pressure change.
This washer-shaped spring is preferable to a spiral spring, because instead of increasing the force linearly, it increases it exponentially, this effect can occur up to 15 g bar so that the spring deviates to the end of the indentation, and this This means that the condensate discharge temperature follows the vapor saturation curve more accurately.
Types of bi-metal steam traps
Advantages of Bimetal Steam Trap
Bimetallic steam traps are usually compact, yet have a high capacity for condensation.
When the steam trap is cooled, even if it is wide open, it provides a good air outlet and maximum condensate discharge under operating conditions.
Application of steam traps
As the condensate is easily released from the outlet, this type of steam trap does not freeze as long as it operates in a freezing position. The body of some bi-metal steam traps is designed so that they will not be damaged even if freezing occurs.
Steam trap efficiency
Bimetallic vapor traps are usually resistant to the effects of “hammer blow”, corrosive condensation and high vapor pressures. Bimetallic elements can operate in a wide range of vapor pressures without having to change the size of the orifice.
Even if it is located at the bottom of the seat, it tends to resist backflow through the steam trap. However, if there is a reverse current with any possibility, a separate check valve should be installed at the bottom of the trap.
Temperature in the steam trap
As the condensate discharges at variable temperatures below the saturation temperature, some of the enthalpy of saturated water can be transferred to the device if dewatering from the steam room can be tolerated. In this way, the maximum energy of the condensate is released before it disappears and explains why these traps are used in the tracking lines.
Steam trap maintenance
Maintenance of this type of steam trap is such that the inputs can be replaced without removing the trap body from the line. The produced steam steam increases the return pressure in the condensate line whenever the condensate is discharged from higher to lower pressure. Becomes. The cooling base allows the condensate to cool, producing less flash steam in the condensate line and thus helping to reduce the return pressure.
Disadvantages of Bimetal Steam Traps
When the condensate is emptied below the steam temperature, dewatering of the steam space occurs, unless a steam trap is installed at the end of a long cooling base. Bimetallic steam traps are not suitable for installation in processes where immediate removal of condensate is necessary to achieve maximum output.
Some bimetal steam traps are vulnerable to pipe clogging due to low internal flow velocities. However, some bi-metal traps have valve-shaped trims that absorb discharge energy to open the valve further.
If the bimetal vapor trap is discharged at a significant return pressure, the condensate must be cooled to a temperature below the required normal before it can even be opened. A return pressure of 50% may cause the discharge temperature to drop to a maximum of 50 ° C. It may be necessary to increase the length of the cooling base in the face of these conditions.
Bimetallic vapor traps do not respond quickly to load or pressure changes because the element responds slowly.
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