Steam & Condensate Introduction
3) Discharging Condensate into an Elevated and/or Pressurized Return Line:
Total Back Pressure (Outlet Pressure) is the Sum of Condensate Return Line Pressure + Equivalent Lift Height Pressure Discharging condensate upward against gravity is the least desirable scenario; however, in certain instances, it may be the only solution possible. Since condensate must be “lifted” to an elevation, it adds additional back-pressure to the discharge (outlet) side of the trap. For this example the condensate return line pressure is 5 psig. We first need to calculate Lift Height Pressure : Height x 0.433 Lift Height Pressure = Steam Pressure “pushes” the condensate up through an Elevated return line (15 PSIG)
Condensate Return Lines are designed to drain by gravity at 0 psig; however, they often contain unintentional pressure from being undersized or from the discharge of failed steam traps.
5 psig
50 psig
23.1 ft. Equates to
23.1 Ft. Lift Height
=
23.1 Ft. X 0.433
10 psig Pressure
= 10 psig
Pressure in the steam main. = 50 psig
Inlet Pressure:
Inlet
Since we are discharging steam trap to a pressurized and elevated condensate return line, we need to add condensate
Outlet Pressure 5 + 10 = 15 psig
50 psig 15 psig
Outlet Pressure:
Total Back Pressure
return line pressure (5 psig) to lift height pressure (10 psig) = 15 psig
TD600 Thermodynamic Steam Trap
Inlet Pressure (Steam)
Outlet Pressure (Condensate)
–
=
Differential Pressure
50 psig
– 15psig
= 35 psi
Calculating Lift Pressure A column of condensate in vertical piping results in additional pressure at the outlet of the steam trap. By knowing the height of the condensate return line, the pressure of this column can be easily calculated as follows: Lift pressure (psig) = Lift height (ft) x 0.433 (psig/ft)
23.1 Ft. X 0.433 = 10 psig
11.55 Ft. X 0.433 = 5 psig
Weight of the water column creates pressure
A column of water exerts a downward pressure of 1 psi for every 2.31 ft. of height
23.1 ft. water column
11.55 ft. water column
2.31 Ft. X 0.433 = 1 psig
5 psig
10 psig
1 psig
2.31 ft. water column
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