**This information is presented in a format that will hopefully help you understand the limits of your equipment, give you a guide to follow when operating fire streams, and helpyou best manage your water delivery system.**

**Understanding the principles will help you apply them to practical solutions. The principles of fluid pressure are part of the foundation of understanding and, when coupled with an application, help you to solve some field problems.**

1. Fluid pressure is perpendicular to any surface onwhich it acts.

2. Fluid pressure at a point in a fluid at rest is of the same intensity in all directions.

3. Pressure applied to a confined fluid from without is transmitted equally in all directions.

4. The downward pressure of a liquid in an open vessel is proportional to its depth.

5. The downward pressure on a fluid in an open vessel is proportional to the density of the fluid.

6. The downward pressure of a fluid at the bottom of a vessel is independent of the shape of that vessel.

__ $$ Moving water through hoses, pipes, fittings,etc.__

Just as there are principles of fluid at rest and under pressure, there are principles that apply to moving fluids through hoses, nozzles, pipes and fittings. Energy is necessary to move fluids through whatever means is used. There are conditions where energy losses occur and we must take these into account when moving water.Friction and elevation create two sources of energy loss. There are four principles of friction loss to consider when moving water.

**1. If all other conditions are the same, friction loss varies directly with the length of hose or pipe. **Double the length, double the friction loss.

**2. When hoses, etc., are the same size, friction loss varies approximately with the square of the increase in the velocity of the flow. **Double the speed of the water and increase friction loss by 4 times.

**3. For the same discharge, friction loss varies inversely as the fifth power of the diameter of the hose. **At a given GPM, friction loss is cut by 4 times when you increase the diameter of hose from a 2½" hose to a 5" hose.

**4. For a given velocity, friction loss is approximately the same, regardless of the pressure on the water. **Thus, friction loss is velocity based. The faster you move it, the more friction occurs.

$$ **Helpful Information:**

**1. One gallon contains 231 cubic inches. **

**2. Fresh water weighs 8.35 lbs per gallon approximately.**

**3. One cubic foot of fresh water weighs 62.5 lbs approximately.**

**4. A cubic foot contains 1728 cubic inches.**

**5. A cubic foot of water contains 7.481 gallons. (7.5 gallons approximately)**

**6. A column of water one inch square and one foot high will create a downward pressure of .434# at the base of the vessel. The symbol # represents pounds per sq. inch.**

**7. One pound of pressure will raise a column of water 2.304 feet in height.**

**8. The largest tip size used on a fire stream is one half the diameter of the hose.**

**9. Class 'A' pumps deliver 100% of their capacity at 150# of discharge pressure, 70% of their capacity at 200#, and 50% of their capacity at 250#, as measured from draft, lifting water no higher than 10 ft. Thus, higher discharge pressures actually reduce the volume of water delivered. **

**Centrifugal pumps are widely used in fire fighting due to their ability to take advantage of incoming pressure. This is most evident when a 1,000 GPM pumper, when connected to a hydrant can deliver 1250 GPM. The pumper can deliver more than its rated capacity up to its critical velocity. Critical velocity is that point where so much turbulence is created that it makes it impossible to move any more water. You have reached the limits of your equipment.**

** $$ Managing Your Water**

**Just like managing your money, you know how much you can spend. On the fire ground there is NO water credit so credit cards are out of the question. You must balance your income with your outgo. To accomplish this, you will need to know how much water you have to spend and how you intend to spend it. If you can get the water to your pump, you can deliver it in some fashion. Remember that someone is dependent on you maintaining his or her fire stream. Pump operators should have a good understanding of pressure and the different kinds of pressure.**

*Atmospheric Pressure is the weight of a column of air at a given location on the surface of the earth. Sea level atmospheric pressure is 14.7# on the average.*

*Static Pressure is pressure on a confined fluid with no water flowing.*

*Residual Pressure is pressure remaining on a system when water is flowing.*

*Discharge Pressure is the pressure of the water at the point of discharge. This can be nozzle pressure, pump discharge pressure or engine pressure.*

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