Pumping Apparatus Driver Operator (1st Edition)
Chapter 8 - Theoretical Pressure Calculations
Test Review
NOTICE: No notes are taken from steps, examples, equations, or metric pages 165-190.
§ Calculation of friction loss must take into account the length and diameter of hose.
§ Elevation pressure is knows as the pressure loss or gain as a result of changes in elevation of the nozzle in relation to the pump.
§ Total pressure loss is the combination of friction loss and elevation loss.
§ Total pump discharge pressure is the combination of friction loss, elevation loss, and nozzle pressure.
§ Friction loss can be determined by actual tests (most accurate) or by calculations.
§ The only truly accurate way of measuring friction loss is to measure the pressure at both ends of a hose and subtract the difference.
§ When a department determines friction loss in their own hose, the hose used for testing should be hose that is in service, not hose that has never been used.
§ The amount of friction loss in a hose can be affected by differences in construction, fabrics, liners, couplings, and wear.
§ Items for testing friction loss in hose include pitot tube or flowmeter, two inline gauges, hose, smoothbore nozzle (if using pitot tube) or any type of nozzle (if using a flowmeter).
§ Flowmeters provide a direct reading of the volume of water exiting a discharge.
§ Pitot tubes are used to measure the velocity pressure of a stream of water.
§ Hose layouts include single hoselines, multiple hoselines, wyed or manifold hoselines, and siamese hoselines, and are considered either "simple" or "complex" layouts.
§ Simple hose layouts include single lines (most common), multiple lines, equal length wyed lines, and equal length siamesed lines.
§ With multiple hoselines of equal length, friction loss only has to be calculated for one line.
§ To reduce friction loss, two or more parallel lines may be laid and connected to a siamese at a point near the fire.
§ Complex hose layouts include standpipe operations and multiple, wyed, manifold, or master stream hoselines of unequal length.
§ Hard piping such as that used in standpipes has minimal friction loss.
§ The total pressure loss in a hose layout using unequal length or diameter hoses is based on the hoseline with the highest friction loss, not the combination of all lines.
§ When a pumper is supplying lines with different nozzle pressures, pressure pumped should be for the highest pressure needed with other lines gated down to their required pressures.
§ Almost all fire pumps in use today are centrifugal type.
§ Net pump discharge pressure when taking water from a hydrant, it is the difference between the intake pressure and the discharge pressure. When drafting, it is the sum of the intake pressure and the discharge pressure.