Steam & Condensate Introduction
DIAGRAM 4 : High Running Load
DIAGRAM 3 : Typical Running Load
When a high flow rate of heated water is required, the control valve will open accordingly to allow more steam (lbs/hr) and steam pressure (psi) to enter the heat exchanger. During times of high water usage, there will also be a significant increase in the condensate load (lbs/hr), as well as higher steam pressure in the shell of the heat exchanger. This high pressure steam will push the condensate through the steam trap .
The temperature control valve will automatically adjust the flow of steam (lbs/hr) to coincide with the flow rate of heated water (GPM). The higher the flow rate, the higher the steam pressure will be. The steam pressure in the shell of the heat exchanger is indirectly determined by the amount of water flowing through the heat exchanger. The steam (lbs/hr) turns into condensate (lbs/hr) and is discharged through the steam trap.
Inlet Steam Pressure varies directly with water flow rate
Inlet Steam Pressure varies directly with water flow rate
50 psig
50 psig
30 psig
10 psig
STEAM
STEAM
STEAM
Typical flow rate of hot water
High flow rate of hot water
Condensate flow through trap matches the steam load
Condensate flow through trap matches the steam load
DIAGRAM 5 : Low Running Load
When the demand for hot water is low, the steam control valve will adjust accordingly, allowing just enough steam to heat the reduced flow of water. The pressure in the shell of the heat exchanger will go into vacuum, preventing discharge of condensate. Therefore, a vacuum breaker is used to allow air to enter the shell and equalize the pressure, allowing drainage of condensate through the steam trap by gravity.
System with Vacuum Breaker
System without Vacuum Breaker
Sub-atmospheric Pressure
0 psig
OPEN Vacuum Breaker
- 5 psig
Vacuum causes Condensate to Back Up into Heat Exchanger
1 psig Head Pressure
1 psig
Low flow rate of hot water
2.31 ft. water column
Condensate will not flow without a vacuum breaker
Condensate flows through trap
0 psig
2.31 Ft. X 0.433 = 1 psig
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Tel: 610-495-5131 • Pottstown PA • USA •• www.watsonmcdaniel.com
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