Goulds Pumps 3498 - IOM - Manual (Page 35)

FIELD TESTS
PERFORMANCE CURVE
A typical performance curve for a specific pump can be
obtained from Goulds Pumps. This can be used in
conjunction with a field test, if one is required. All Goulds
Pumps pump tests, and curves, are based on the “Hydraulic
Institute Standards.” Any field test must be conducted
according to these Standards. Unless otherwise specifically
agreed, all capacity, head, and efficiencies are based on
shop tests when handling clear, cold, fresh water at a
temperature not over 85° F and under suction conditions as
specified in the contract.
DEFINITIONS
To aid in calculating pump performance, the following test
information and definitions are included for reference. See
Appendix III for other useful formulas, and Appendix IV for
a Field Test Report Sheet.
NOTE: Complete procedure for testing pumps is
given in the “Hydraulic Institute Standards”
Centrifugal Pump Section.
Gauge Datum
The datum for all gauge readings is taken as the centerline
of the pump shaft for all horizontal shaft pumps and as the
eye of the impeller for vertical pumps.
Head Measurement
The unit for measuring head should be feet; therefore, all
pressure readings of the pumped liquid should be converted
to feet. The relationship between a pressure expressed in
pounds per square inch (psi) and that expressed in feet of
head is:
Head in feet = psig x 2.31
sg
Where sg = specific gravity of the liquid pumped
Where sg = 1.0 for water at 70°
Total Head
Total head is the algebraic difference between the total
suction and the total discharge heads.
1. Where suction lift exists, total head is the sum of the
total discharge head and the suction lift.
2. Where positive suction head exists, the total head is
the total discharge head minus the total suction head.
Suction Lift
Suction lift exists where the total suction head is below
atmospheric pressure. Total suction lift is the reading of a
liquid manometer at the suction nozzle of the pump,
converted to feet of liquid, and referred to the datum minus
the velocity head at the point of gauge attachment.
Positive Suction Head
Suction head exists when the total suction head is above
atmospheric pressure. Total suction head is the reading of a
gauge at the suction of the pump, converted to feet of
liquid, and referred to datum plus the velocity head at the
point of gauge attachment.
Velocity Head
Velocity head is figured from the average velocity obtained
by dividing the discharge flow (in cubic feet per second) by
the actual area of the pipe cross-section (in square feet),
and is determined at the point of gauge connection. It is
expressed by the formula:
h
v
= V 2
2g
Where g = the acceleration due to gravity, and is
32.17 feet per second squared at sea level
and 45° latitude.
V = velocity in the pipe in feet per second.
Volume Measurement
The method of volume measurement should be made by
some accurate and accepted method and converted to
gallons per minute. For easy reference, refer to the
following:
1. The standard U.S. gallon contains 231 cubic inches.
2. One cubic foot equals 7.4805 gallons.
3. The specific weight of water at a temperature of 60°
shall be taken as 62.34 pounds per cubic foot.
Horsepower
1. The formula for horsepower required at the pump shaft
is:
Bhp = Total head x GPM x specific gravity
3960 x Eff.
2. The true motor brake horsepower, once the efficiency
is determined from dynamometer tests, can also be
calculated from the following formula:
Bhp = kw input x Eff.
0.746
Where Bhp = Brake horsepower delivered
Kw input = Real input power (kw)
Eff. = Motor efficiency
32
3498 IOM 12/04