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4.5 Slope

Slope refers to the angle, or grade, of an incline. Slope can be upward or downward. Slope is typically expressed as a percent, and corresponds to the amount of rise, or vertical distance, divided by the run, or horizontal distance. Percentage means per 100. Slope can also be expressed as an angle, which gives the amount of deviation from flat as a number of degrees. Conversions between slope percent and slope angle can be done using a scientific calculator and the inverse tangent (arc tan) function.

4.4 Degrees and Protractor

Degrees are the unit of measure used for angles, just as feet are used to measure distance. The symbol for degrees is "°". There are 360° in a full circle, and 90° in a right angle. A protractor is used for measuring angles. As shown below, a protractor is a half or full circle measuring device, marked in degrees along the outer edge, with a straight line running from 0° to 180°. There is a small hole in the center of the protractor. To use a protractor: 

4.3 Angles

Angles are formed when two or more lines come together at a point. The angle in the image below is 45 degrees. A right angle, where the two lines are perpendicular to each other, is 90 degrees. The closer together the two lines, the smaller the angle.

Angles

Table 3.2 Comparative Diameters and Weights (100-foot lengths) of Coupled Fire Hose

Type of Hose FS SPEC Jacket ID (in) Factory Proof Pressure (psi) Burst Pressure (psi) Max Dry Weight (lb) Water (gal) Weight Water (lb) Max Total Weight (lb)
Garden synthetic jacket, lined (50 ft only) It

Table 3.1 Water Handling Unit Estimations

Description
ID = Inner Diameter		 Rounded Values
Used in
U.S. Measure
Field Estimations
GOOD TO MEMORIZE
ID = Inner Diameter
Volume (Capacity)		 U.S. Measure

3.5 Drafting Guidelines

It is important to know the difference in elevation between the pump and the water source when drafting water from a pond or stream. When drafting water, the air at atmospheric pressure is removed from the hose line, creating a vacuum (negative pressure) within the pump chamber. The atmospheric pressure (weight of air) on the water's surface forces the water up through the suction hose to the pump.

3.4 Calculating Engine Pump Pressures

To achieve a desired nozzle pressure (DNP), a few factors must be considered. First, you must note the head loss (HL) or head gain (HG). Water head is the height of the water column (lift) due to imposing pressure. The head pressure is positive (gain) if the hose lay is downhill because the force of gravity is helping push the water down, consequently increasing the pressure. The head pressure is negative (loss) if the hose lay is uphill, since the force of gravity is pulling the water down, when it needs to be pumped up.

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