Page 135 - Air and Gas Drilling Manual

derived for use with the English unit system and the other set for use with the SI
unit system.

Figure 4-14: Schematic of a two stage compressor [10]. Chapter 4: Compressors 4-21
Equation 4-30 is obtained in English units by substituting the following for P i ,
P o , and Q i (and dividing by 550 ft-lb/hp):

P = p 144 (4-32)
i i
P = p 144 (4-33)
o
o
q
Q = i (4-34)
i
60
where p i is input pressure (psia),
p o is output pressure (psia),
3
q i is the input volumetric flow rate (ft /min).
˙
The expression for theoretical shaft power W in English units (horsepower) is
s
 k−1 
nk pq   p  nk 
o
W = s i i    s −1  (4-35a)
˙
s
k −1 229 .17  p 
  i  
An alternate expression which is convenient for booster compressor calculations is
 k−1 
nk ˙ w g  R T    p  nk 
˙
W = s  i    o  s − 1  (4-35b)
s
k − 1 550  S g   p   

i

where T i is the input gas temperature (˚R).
˙
The expression for theoretical shaft power W in SI units (watts) is
s
 k−1 
nk   P  nk 
˙
W = s PQ i   o  s − 1  (4-36a)
s
k −1 i  P 
  i  