Chapter 5 Flashcards
Water may be used on combustible liquids that whose specific gravity is?
Higher than 1, to smother fires in combustible liquids
What does the first principle of pressure state?
Pressure exerted by the weight of water is perpendicular to the walls of the container
What does the second principle of pressure state?
Plus pressure at a point in fluid at rest is the same intensity in all directions.
What does the third principle of pressure state?
Pressure applied to a confined fluid is transmitted equally in all directions.
What does the fourth principle of pressure state?
The pressure of a liquid in an open vessel is proportional to its depth
What does the fifth principle of pressure state?
The pressure of a liquid in an open vessel is proportional to the density of the liquid
What does the sixth principle of pressure state?
The pressure of a liquid at the bottom of a vessel is independent of the shape of the vessel
When is atmospheric pressure greatest?
Atmospheric pressure is greatest at low altitudes and least at very high altitudes. Sea level is 14.7 psi which is considered standard atmospheric pressure.
Any pressure less than atmospheric pressure is called? What is absolute zero called?
Vacuum
Perfect vacuum
In the fire service the term head refers to?
The height of a water supply above the discharge orifice
What is elevation?
The center line of the pump or the bottom of a static water supply source above or below ground level.
What is altitude?
The position of an object in relation to sea level
Does height above or below sea level make the pumper have to work harder to produce the pressures required for effective fire streams?
Above sea level makes the pressure drop which makes the pumper have to work harder
The friction loss in older hose may be as much as how much percent greater than new hose?
As much as 50% greater
What does the first principle of friction loss state?
If all other conditions are the same, friction loss varies directly with the length of the hose or pipe.
What does the second principle of friction loss state?
When hoses are the same size, friction loss varies approximately with the square of the increase in the velocity of the flow.
What does the third principle of friction loss state?
For the same discharge, friction loss varies inversely as the fifth power of the diameter of the hose.
What does the fourth principle of friction loss state?
For a given velocity, friction loss is approximately the same, regardless of the pressure on the water
There is much less pressure loss in a water distribution system when fire hydrants are ?
Supplied in two or more directions
At least how often should water main valves be operated to keep them in good condition?
Once a year
What are the two common types of indicator valves?
post indicator valve (PIV) and the Outside stem and yoke valve (OS&Y)
What are the most common type of valves used on most public water distribution systems?
Nonindicating valves
Where are nonindicating valves normally located? And how can you operate them?
Usually are in manholes or valve boxes, below grade valves if properly installed can be operated above ground with a special socket wrench on the end of a reach rod
If valves are installed according to established standards it will be necessary to close off how many hydrants from service while a single break is repaired?
Only one perhaps two fire hydrants
