Water Handling Equipment Guide - National Wildfire Coordinating ...

APPENDIXES
C—Flow Determination, Pump Testing, and Gauges
By knowing the flow in gallon per minute (Q) and
the pressure in psi (P) the orifice diameter can be
found by the following formula:
d =
Q
29.9*0.62* P
The pressure gauge should be a Grade 1A or
better, and be calibrated annually. A Grade 1A
pressure gauge can have a permissible error of 1
percent of full scale (for example a 200 psi Grade
1A pressure gauge can have a permissible error of
±2 psi anywhere on the scale).
The recommended line and tee size should also be
adhered to (see table C2). Smaller lines and tees
should not be used, as the accuracy will not be
maintained. The ratio of the orifice diameter to the
diameter of the tee has an effect on the flow and
pressure reading. Using a smaller line and tee than
recommended could negatively affect the accuracy
of the test.
Test Procedures
1. Select desired size square-edge orifice and
attach to proper size in-line tee.
2. Attach the in-line tee to the overboard discharge
or pump outlet.
3. Start pump, open desired overboard discharge
or pump outlet valve, increase pump throttle to
maximum.
4. If desired pressure is not reached, the pump
does not pass.
Parts list
• One pressure gauge (grade 1A or better)
• One in-line tee (1 inch, 12 inch, 22 inch, or 4
inch)
• One appropriate size cap, with appropriate
size orifice machined in center.
• One 4-foot length of 300-psi rubber line, with
swivel and 4 inch NPT (National Pipe Thread)
fitting on each end.
• a-inch straight-stream nozzle tip tapped with
4-inch NPT threads.
Additional information about the square-edged
orifice system can be obtained from:
USDA Forest Service
Technology and Development Center
444 East Bonita Avenue
San Dimas, CA 91773
Gauge Accuracy Information
When testing pumps as outlined in the previous
section of this appendix, as well as for performing
standard operations with fire apparatus, the use of
quality gauges is necessary. To assist in meeting
this requirement the following information is
provided when selecting a gauge for pump testing
and general fire apparatus needs.
Accuracy is defined as the difference (error)
between the true value and the indication
expressed as a percent of the span (span is the
range of the gauge). It includes the combined
effects of method, observer, apparatus, and
environment. Accuracy error includes hysteresis
and repeatability errors but not friction error. It is
determined under specific conditions. Normally
73.4 °F (23 °C), and 29.92 inch Hg barometric
pressure.
Accuracy of a pressure gauge may be expressed
as percent of span or percent of indicated reading.
Percent of span is the most common method. For
example, the span of a 0-100 psi gauge is 100 psi.
Percent of indicated reading is usually limited to
precision test gauges.
The following are American Society of Mechanical
Engineers (ASME) B40.1 accuracy grades.
Grade 4A. Gauges offer the highest accuracy and
are calibrated to ±0.1 percent of span over the
entire range of the gauge. The gauges are called
laboratory precision test gauges and are generally
82-, 12- or 16-inch dial sizes. These high-accuracy
gauges may be temperature compensated. They
must be handled carefully in order to retain
accuracy.
Grade 3A. Gauges are calibrated to an accuracy of
±0.25 percent of span over the entire range of the
gauge. The gauges are called test gauges and are
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