Steam & Condensate Introduction
DIAGRAM 3: Nearing Set Temperature (Trap Partially Open) As the temperature of the kettle contents
nears set point, less steam will be required and the control valve will modulate toward a partially open position. As this happens, steam pressure decreases in the jacket and therefore the pressure differential across the steam trap will likewise decrease. The steam trap will then adjust to the lower condensate flow generated.
Air Vent CLOSED
Steam Pressure in Jacket of Kettle (low pressure)
Control Valve PARTIALLY OPEN
Trap Partially OPEN
Process Liquid is nearing Set Temperature
DIAGRAM 4: Temperature Set Point Achieved (Steam Flow Reduced; Since Only Required to Maintain Temperature) Once the set temperature is achieved, a significantly less amount of steam is required to maintain the temperature of the product inside the jacketed kettle. The steam supply valve will modulate to a near shut-off condition, dropping the pressure, and the kettle may be operating in vacuum. This action will impede the discharge of condensate as the pressure in the jacket will be less than atmospheric. Therefore, a vacuum breaker is required to allow air to enter the jacket and equalize the pressure. This then allows drainage of condensate through the steam trap by gravity. If the vertical discharge leg from the jacket is 2.3 ft., this will provide 1 psi head pressure to assist with condensate drainage.
System without Vacuum Breaker
System with Vacuum Breaker
Vacuum Breaker OPEN Vacuum breaker equalizes the pressure in the jacket and allows head pressure to "push" condensate through the steam trap
Condensate does not freely drain because of negative pressure differential (i.e. atmospheric pressure at 0 psig is higher than jacket pressure at -5 psig )
Condensate Backs Up into Jacket of Kettle
-5 psig
0 psig
Steam Pressure in Jacket of Kettle (vacuum)
2.31 Ft.
Steam Pressure in Jacket of Kettle (atmospheric) (0 psig)
Control Valve PARTIALLY OPEN
1 psig
Control Valve PARTIALLY OPEN
Condensate
Condensate does not drain freely
0 psig
0 psig
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