Page 344 - Industrial Power Engineering and Applications Handbook

Appendix A1323

Power requirements for pumps A 125 mm pipe has a friction loss of nearly 33 m per 1000 m
and a 150 rnm size of pipe, 13 m per 1000 m.
USGPM H, p :. Total frictional head for a 125 mrn pipe = E
hp = x 33
4000 q
Alternatively. = 37.125 m
IGPM Hb p and for a 150 rnm pipe -- x 13
-
3300 q 1000
= 14.625 rn
where
US GPM = discharge in US gallons per minute A friction loss of 37.125 m in a total length of 1000 m is quite
I GPM (UK) = discharge in imperial gallons per minute high and will require a larger motor. Therefore, a 150 mrn
main pipeline will offer a better and more economical design
H, = head (in feet) compared to a 125 mrn pipeline such as the reduced cost of
= suction head + static delivery head + the prime mover and lower power consumption during the
frictional head (105s) in pipes and fittings life of pumping system, in addition to a longer life span of a
+ velocity head 150 mm pipe compared to a 125 mm pipe.
For determining the frictional head, refer to friction loss Power requirements for lifts
in pipes. bends, elbows and reducers and valves as
provided in Tables A. 1 and A.2: (i) For linear motion drives
p = specific gravity of liquid in g/cm3 Where the weight of the cage and half of the
passengers load is balanced by the counter weight
q = unit efficiency of pump
0.746 x W x V
LPS H, . p P= 2.75 x q (A.2)
or h.p. =
75 ' q
where
LPS = discharge in litres per second P = kW required
H,, = head (in metres) W = passengers load in kg
V = speed of lift in m/s
Friction loss in pipes q = unit efficiency of the drive.

Table A. 1 provides. for a particular rate of discharge in (ii) For rotary motion drives
GPM. the friction loss in pipes for every 100 feet of Using equation ( 1.8).
straight pipe length, reasonably smooth and free from p=- T.N
incrustation. 974 ' q (A.3)
where
Friction loss in bends, reducers, elbows etc. are provided P = kW required
in Table A.2 in equivalent pipe length. T = load torque in mkg
To determine the size of pipe N = speed of drive in r.p.m.
q = unit efficiency of the drive
The economics would depend upon the smoother flow
of fluid without excessive friction loss. A smaller section Power requirements for fans
of pipe may not only require a higher h.p. for the same
suction and lifting head due to greater frictional losses, LPS ' p
but may also cause the pipe to deteriorate quickly as a p=- 75. q (A.4)
result of the additional load on its surface. Losses due to
bends and valves should also be added in the total friction where
loss. P = kW required
LPS = quantity of air in litres per second.
Example p = back pressure of air at the outlct in metres of a
Consider a discharge of, say, 20 LPS against a total suction column of water.
and delivery head of 150 m through a mains 1000 m long.
Considering an average of 25 bends, elbows, tees and reducer Note These are actual power requirements for various applications.
fittings in the total length of pipe, then from Table A.1. Add 10-154 to these figures to select the size of the motor to
account for unforeseen lowx during transmi\\ion from motor to
Total equivalent length of pipe (assuming that every fitting load and other frictional losscs. Too large a motor will give a poor
has an average 5 m of equivalent pipe length, to account for power factor and a poor efficiency. while too sinall a six will run
friction) = 1000 + 25 x 5
overloaded (Section 1 .E). These concideration\ must he kcpt in
= 1125 m mind while selecting the motor rating.