Flow rates describe the speed at which water is flowing. They are described in gallons per minute (gpm). The following test is a simple way to observe a flow rate.

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.

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.

Friction loss is the resulting resistance as water (fluid) moves along the inside wall of either a hose, pipe, or hose fittings.

Points to remember about friction loss:

The volume of a hose allows an estimate of how much water can be delivered to the fire and is important in firefighting. The hose diameter is usually given in inches, with length in feet. The volume of a hose can be computed using the equation for volume of a cylinder in Section 3.1.

Example 1 - A 100-foot length of 1-inch diameter hose is charged with water. How many gallons of water are in that length of hose? 

The following metric system equivalents and approximate conversion factors help meet the requirements of Public Law 100-418. This law requires each Federal agency to use the metric system of measurement by Fiscal Year 1992 in procurements, grants, and other business related activities.