Pumping Apparatus Driver Operator (1st Edition)
Chapter 6 - What is Water & Where Does it Come From?
Test Review
NOTICE: Be sure to check out the "By the Numbers" section as this chapter contains many important numbers.

  • Modern extinguishing agents include dry chemical, dry powders, foam concentrates, and halogenated hydrocarbons.
  • Water cannot be seen in vapor form and can only be seen as it condenses.
  • Water is considered incompressible.
  • Water extinguishes fire primarily by cooling but may also be used to smother a fire by excluding oxygen.
  • Water used as an extinguishing agent is affected by the Law of Specific Heat and The Law of Latent Heat of Vaporization.
  • Specific heat is a measure of the heat absorbing capacity of a substance.
  • Latent Heat of Vaporization is the quantity of heat absorbed by a substance when it changes from a liquid to a vapor (boiling point).
  • The rate heat is released from an object depends on physical form, surface area, and air/oxygen supply.
  • Water absorbs heat at a speed proportional to its surface area (finer droplets-faster absorption).
  • Steam expansion is rapid and careful use of ventilation must be used to prevent steam or fire from rolling back on attack crews.
  • Water can be used to smother liquids (by floating on top) such as carbon disulfide which is heavier than water but may not work on materials that are water soluble such as alcohol.
  • Viscosity is the tendency of a liquid to possess internal resistance to flow (water=low, oil=high).
  • The higher the viscosity of a combustible liquid, the longer an emulsion produced by water on top of the liquid will last (the emulsion suppresses vapors).
  • Water has a relatively high surface tension which causes it to not soak into dense materials readily.
  • Water allows radiant heat to pass through it because of its properties of low opacity and reflectivity.
  • Pressure is defined as force per unit area and may be expressed in pounds per square foot (psf) or pounds per square inch (psi).
  • Force is a simple measure of weight, usually expressed in pounds and is directly related to the force of gravity.
  • The speed at which a fluid travels (velocity) through hose or pipe is developed by the pressure placed upon the fluid.
  • Fluid pressure is perpendicular to any surface on which it acts.
  • Fluid pressure at a point in a fluid is the same intensity in all directions.
  • Pressure that is transmitted to a confined fluid from without is transmitted equally in all directions.
  • The pressure of a liquid in an open vessel is proportionate to its depth and density.
  • The pressure of a liquid on the bottom of a vessel is independent of the shape of the vessel.
  • Atmospheric pressure is greatest at low altitudes and least at higher altitudes.
  • The weight of the atmosphere is commonly measured by comparing it to the weight of a column of mercury.
  • PSIG means pounds per square inch "gauge" (reading minus 14.7 psi), while PSIA means pounds per square inch "absolute" (actual atmospheric pressure).
  • Head refers to the height of a water supply above the discharge orifice.
  • Static (at rest) pressure is stored potential energy available to force water through pipe, fittings, fire hose, and adapters.
  • Normal operating pressure is pressure found in a water distribution system during normal consumption demands.
  • Residual (remainder) pressure is the part of the total available pressure not used to overcome friction loss or gravity while forcing water though pipes, fire hose, fittings, and adapters.
  • Flow pressure is the forward velocity at a discharge opening while water is flowing (commonly measured with a pitot tube).
  • Elevation refers to the level above or below the center line of the fire pump.
  • Altitude is the position of an object above or below sea level.
  • Pressure loss or gain caused by nozzles being above or below the level of the pump is referred to as elevation pressure.
  • Friction loss is the part of total pressure lost while forcing water through pipes, hose, fittings, and adapters.
  • Coefficient of friction refers to the roughness of a hose or pipe lining.
  • Friction loss varies indirectly with the length of the hose or pipe.
  • Friction loss varies approximately with the square of the increase in velocity of the flow on like hose sizes.
  • Friction loss varies inversely as the fifth power of the diameter of the hose, for the same discharge.
  • Friction loss is approximately the same, regardless of pressure on the water, for a given flow velocity (same amount of water flowing.
  • The smaller the hose, the greater the velocity needed to deliver the same volume.
  • Critical velocity is when the practical limit of a streams velocity has been reached and agitation occurs which creates considerable friction loss.
  • Suddenly stopping water moving in a hose results in an energy surge in the opposite direction that can damage hose, appliances, pipes, and pumps, and is called water hammer.
  • Water systems consist of a water source, means of moving water, water processing/treatment, and a distribution system including storage.
  • Primary water supplies are obtained from surface water (rivers, lakes) and/or ground water (springs, wells).
  • The amount of water a community needs is determined by an engineering estimate.
  • Methods of moving water include direct pumping (pumps provide pressure), gravity systems (gravity provides pressure), or both (used by most communities).
  • Water may be treated by coagulation, sedimentation, filtration, or the addition of chemicals, bacteria, or other organisms.
  • Fluoride or oxygen may be added to water during the treatment process.
  • When hydrants are supplied from more than 1 direction, pressure loss in the distribution system is less.
  • Primary feeders are large pipes (mains) with relatively widespread spacing that convey large quantities of water to various points of a local distribution system.
  • Secondary feeders are a network of intermediate-sized pipes that reinforce the distribution grid within the various loops of a primary feeder system and aid in the concentration of the required fire flow at any point.
  • Distributors are grid arrangements of smaller mains serving individual fire hydrants and blocks of consumers.
  • Valves should be located at frequent intervals within a distribution system to stop flow at specified points and should all be operated at least once yearly.
  • Water system valves are either indicating (visually shows if valve is open) or non-indicating (no visual confirmation if valve is open) types.
  • Common indicating valves include Post Indicator Valves (PIV) which consists of a hollow metal post that is attached to the valve housing and contains the words OPEN and SHUT, and the Outside Screw & Yoke (OS&Y) valve which contains a yoke that when out, shows the valve is open and when the yoke is in, it is closed.
  • OS&Y valves are commonly used on sprinkler systems.
  • PIV valves are commonly used in private water supply systems.
  • Non-indicating valves are typically buried or installed in manholes and are the most common type of valves used in public water distribution systems.
  • Control valves in water distribution systems are either gate valves or butterfly valves.
  • Non-rising stem gate valves and non-indicating butterfly valves require a special valve key to operate.
  • Underground water pipe is generally made of cast iron, ductile iron, asbestos cement, steel, plastic, or concrete.
  • Private water supply systems commonly receive their water from municipal systems.
  • In many cases, a private source of water used for fire protection is non-potable (not for drinking).
  • Private water supply systems maintain separate piping for fire protection and for domestic/industrial services.