Question 10.11: What pressure drop should be used for the steam piping of a ......
What pressure drop should be used for the steam piping of a system if the length of the longest run, including fittings, is 400 ft with an allowance of 400 ft for fittings? Initial pressure must not exceed 5 psig.
The total equivalent length of the longest run is 800 ft. From Table 10-4a the total allowable pressure drop is given as 1.5 psi, at a system pressure of 5 psig. The pressure drop per unit length of 100 ft is
∆P/L = 1.51(100/800) = 0.19 ≈ 0.2 psi/100 ft
This value is in fair agreement with the suggested value in Table 10-4a. The steam piping may then be sized using ∆P/L = 0.2 psi/100 ft, the capacity of the pipe section in lbv/hr, and the velocity criterion cited previously.
| Table 10-4a Pressure Drops Used for Sizing Steam Pipe^{a} | ||
|
Initial Steam Pressure, psig |
Pressure Drop
per 100 ft |
Total Pressure Drop in Steam Supply Piping |
| 0 | 0.5 oz/in.² | 1 oz/in.² |
| 1 | 2 oz/in.² | 1 to 4 oz/in.² |
| 2 | 2 oz/in.² | 8 oz/in.² |
| 5 | 4 oz/in.² | 1.5 psi |
| 10 | 8 oz/in.² | 3 psi |
| 15 | 1 psi | 4 psi |
Equipment, control valves, and so forth must be selected
based on delivered pressures.
Source: Reprinted by permission from ASHRAE Handbook,
Fundamentals Volume, 1997.