Test Requisites

Operating Conditions The primary factors affecting the operation of a pump are the inlet (suction), outlet (discharge or total head), and speed. The secondary factors are phys-

Calibrated limit

Quantity to be of accuracy plus measured Measuring device or minus, %

Capacity Venturi meter %

Nozzle 1 Pitot tube

Orifice 1M

Disk 2

Volume or weight—tank 1

Propeller meter 4

Head Electric sounding line %

Air line lA

Liquid manometer, 3- to 5-in (75- to 127-mm) deflections %

Liquid manometer, over 5-in (127-mm) deflections H Bourdon gage—5 in (127-mm) min dial:

full scale 1

Power input Watt-hour meter and stopwatch IK

Portable recording wattmeter VA Test precision wattmeter:

scale %

Clamp on ammeter 4

Speed Revolution counter and stopwatch 1%

Handheld tachometer 1%

Stroboscope l1^

Automatic counter and stopwatch A

Voltage Test meter:

Rectifier voltmeter 5

FIGURE 4 Limits of accuracy of pump test measuring devices in field use ical and climatic variables, such as the temperature, viscosity, specific weight, and turbidity of the liquid being pumped and the elevation of the pumping system above sea level. In some installations, it is impossible to measure discharge or even head accurately. In these instances, good shop tests are essential. It follows then that, in order for the shop test to predict the field performance of a pump, the field operating, installation, and suction conditions should be simulated.

The inlet passages are critical, and the sump where used on the suction lift must be duplicated as closely as possible. During the shop tests, no total suction head less than specified should be permitted, nor should the suction head exceed the specified amount in cases where cavitation or possibly operating "in the break" could occur.

For field installations above sea level, the difference in elevation between the shop test site and the field installation must be taken into account by reducing to the barometric pressure at the specified elevation. This is especially true if a suction lift or negative suction head is involved. Standard tables of barometric pressures are available for use in computing the data, and the tables to be used should be acceptable to all interested parties.

FIGURE 5A through C Typical arrangement for determining cavitation characteristics (Hydraulic Institute Standards, 13th Edition—out of print2)

Cavitation Tests Cavitation tests should be run if required by the specifications (provided such tests are needed and have not been previously conducted on similar pumps and certified by the manufacturer) or if needed to assume a successful pump installation.

The suction requirements that must be met by the pump are usually defined by the cavitation coefficient s. Plant s is defined as NPSHA (net positive suction head available) divided by total pump head per stage:

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