Plots of the power input to this pump show that the input power increases as the liquid
viscosity increases.
Related Calculations. Use this procedure for a regenerative-type pump han-
dling any liquid—water, oil, kerosene, gasoline, etc. A decrease in the viscosity of a liq-
uid, as compared with the viscosity of water, will produce the opposite effect from that of
increased viscosity.
EFFECT OF LIQUID VISCOSITY ON
RECIPROCATING-PUMP PERFORMANCE
A direct-acting steam-driven reciprocating pump delivers 100 gal/min (6.31 L/s) of 7O^0 F
(21.1^0 C) water when operating at 50 strokes per minute. How much 2000-SSU crude oil
will this pump deliver? How much 1250 F (51.7^0 C) water will this pump deliver?
Calculation Procedure:
- Determine the recommended change in pump performance
Reciprocating pumps of any type—direct-acting or power—having any number of liquid-
handling cylinders—one to five or more—are usually rated for maximum delivery when
handling 250-SSU liquids or 7O^0 F (21.1^0 C) water. At higher liquid viscosities or water
temperatures, the speed—strokes or rpm—is reduced. Table 1 shows typical recommend-
ed speed-correction factors for reciprocating pumps for various liquid viscosities and wa-
ter temperatures. This table shows that with a liquid viscosity of 2000 SSU the pump
speed should be reduced 20 percent. When 1250 F (51.7^0 C) water is handled, the pump
speed should be reduced 25 percent, as shown in Table 1. - Compute the delivery of the pump
The delivery capacity of any reciprocating pump is directly proportional to the number of
strokes per minute it makes or to its rpm.
When 2000-SSU oil is used, the pump strokes per minute must be reduced 20 percent,
or (50)(0.20) = 10 strokes/min. Hence, the pump speed will be 50 - 10 = 40 strokes/min.
Since the delivery is directly proportional to speed, the delivery of 2000-SSU oil =
(40/5O)(IOO) = 80 gal/min (5.1 L/s).
When handling 125
0
F (51.7
0
C) water, the pump strokes/min must be reduced 25 per-
TABLE 1. Speed-Correction Factors
T.. j. • oj Water temperature
Liquid viscosity, Speed Speed
SSU reduction, %^0 F^0 C reduction, %
250 O 70 21.1 O
500 4 80 26.7 9
1000 11 100 37.8 18
2000 20 125 51.7 25
3000 26 150 65.6 29
4000 30 200 93.3 34
5000 35 250 121.1 38