Water Properties

Question 1

Water

Answer 1

• Water = 2 hydrogen atoms and one oxygen atom
• Due to the positive charges and negative
charges of the atoms it has a strong bond between
molecules = surface tension
• Water is called the universal solvent because it is capable
of dissolving numerous compounds.

Question 2

pH scale

Answer 2

The term pH is a scale that indicates the level of acidity or
alkalinity within a solution (not necessarily water)
When Hydrogen ions (H+) = Hydroxyl ions (OH-) the solution is
neutral = pH7
More H+ = more acidic, More OH- = more alkaline
The pH scale works on a factor of 10.
Each pH increment or decline means 10x
pH6 is 10x more acidic than pH7
pH6 has 10x more hydrogen ions
pH8 is 10x more alkaline than ph7
pH8 has 10x more hydroxyl ions

Question 3

Higher pH vs low pH

Answer 3

• More acidic water corrodes the piping
• More alkaline creates deposits in the piping to obstruct
flow
• Hardness is a term used that indicates the alkalinity of the water
• The amount of dissolved minerals in the water measured as mg/L or ppm

Question 4

States of water

Answer 4

• Water can be a liquid, solid, or gas within the earth’s

normal temperatures unlike any other substance

Question 5

density of water

Answer 5

• It’s densest at 4°C, 39 F
• D=M so if M=1 and V=1, D=1
V
as it gets colder and freezes it’s density decreases because
the volume increases
If M=1 and V=2, D=.5
as it heats up, the mass (in the same volume) decreases so
the density decreases
If M=.5 and V=1 , D=.5

Question 6

Water corrosion
makeup of air
dry systems

Answer 6

• In both situations water expands and can damage piping
• NFPA states the sprinkler systems must be maintained at
or above 4°C, or 39°F 16.4.1.1
• Water contains air, air contains 78% nitrogen and 21%
oxygen and 1% co2 and other gases.
• Dry Systems are very susceptible to corrosion
• Oxygen reacts with metals causing corrosion
• Water is miscible (mixes) with antifreeze, but with
temperature variations it can separate
• Water is lighter than AF

Question 7

Flow

Answer 7

• Flow is the movement of fluids
• Water flows from high pressure to low pressure through
the path of least resistance
• Flow can be produced by a pump or a pressure drop
• The pump produces flow the resistance causes the
pressure
• Flow is expressed as
• either velocity (speed) in feet/minute or feet/second or
• flow rate in gallons/minute or cubic inches/minute
• Flow is laminar or turbulent

Question 8

Viscosity

Answer 8

• Viscosity is like the thickness of the fluid. If the viscosity
is high the fluid is thick and thus is more resistant to flow
• Temperature can reduce the viscosity of a fluid
• Movement of any kind is affected by friction
• Piping, fittings and the water itself causes friction
• From hydraulics, frictional losses cause pressure loss
• Pressure is an energy that must be used to cause flow

Question 9

3 types of pressure

Answer 9

• Pressure causes flow – 3 types of pressure
• Pump pressure – caused by a pump
• Atmospheric pressure – caused by the atmosphere and can create
flow in a siphon
• Pressure Head – caused by gravity
• Head is the measurement of the energy at any location within a
piping system
• 0.433 psi/ft (9.81 kPa/m)
• 1 .433psi/ft=
• 2.31 ft/psi

Question 10

Pressure loss

Answer 10

• Pressure causes flow, flow resists, so pressure is lost
• The amount of energy spent to overcome the resistance to flow (friction) is called pressure drop or pressure loss
• For piping the pressure loss can be calculated with the Hazen
Williams, or use tables
• Different pipe materials have different pressure losses

Question 11

What factors contribute to pressure loss/ pressure drop

Answer 11

• Factors Influencing Pressure and Pressure Drop
• The items that directly cause pressure drop are summarized as follows.
• Pipe Size - The smaller the pipe, the higher the pressure drop.
• Circumference Relative to area
• Pipe length - The longer the pipe, the higher the pressure drop.
• Fittings - The more fittings installed in the piping, the higher the pressure drop.
• Material - The rougher the material, the higher the pressure drop.
• Volume - The more volume/flow (gpm) required, the higher the pressure drop.
• Reaming - Un-reamed pipe or tubing will cause a higher pressure drop.
• Look at Meyer Calculator

Question 12

Sprinkler pressures,

Increasing pressure

Answer 12

• Sprinklers require a certain pressure to operate properly
• If there is insufficient pressure possible solutions are to:
• Increase the pipe size
• Add a pump
• Others???
• Hydraulic calculations take into account the pressure
losses within the system regarding:
• Straight pipe flow friction losses
• Fittings are related to equivalent lengths of pipe
• Pressure head losses due to elevation changes

Question 13

what is pressure head?

Answer 13

the pressure available at some point in the system given in feet

Question 14

c value

Answer 14

If the pipe has lower C value it is more resistant

to flow

Question 15

Equivalent Lengths

Answer 15

• The “equivalent length” of the fitting is the
length of the same size pipe that would create
the same amount of friction loss as what occurs
in the fitting.

Question 16

velocity

Answer 16

• Velocity is the speed of the fluid within a piping system
• If the pressure is equal throughout and the pipe size
changes, the smaller the opening, the faster the flow; the
larger the opening, the slower the flow.
• The rate of flow is the quantity that flows past a point
• to get the same amount of water through a small pipe
compared to a larger pipe in the same period of time, the velocity of the water will have to increase accordingly, and
vice versa
• To increase velocity, pressure (energy) is decreased/used
• To decrease velocity, pressure (energy) is increased/gained

Question 17

Venturi effect

Answer 17

The venturi effect is produced when a fluid is forced
through a narrow opening, resulting in an increase in
velocity and a decrease in pressure

Question 18

Venturi’s

Answer 18

• are used for flow meters to measure the flow output and pressures
of fire pumps
• Are used as a proportioner for foam systems
• Because the pressure is lower at the narrows it requires less pressure
to introduce something into the stream

Question 19

What is pressure?

Answer 19

pressure is the weight/area

regardless of the size of the vessel, the pressure is the same

Question 20

what is force

Answer 20

the weight. Area doesn’t matter

Question 21

Pressure head

Answer 21

• Pressure head is the pressure available at some point in the water
system
• Can measure the pressure by the height of the liquid
• The unit is ft
• Pressure head is the height of a liquid column that corresponds to
a particular pressure exerted by the liquid column on the base of
its container.
• Head pressure is a specific type of pressure used in pump
systems. It is a measurement of the height difference
between the fluid being moved and the discharge point.

Question 22

Head pressure on a pump

Answer 22

how high the pump

can lift/push a column of water

Question 23

Suction head

Answer 23

is when the supply is above the pump intake
and pushed into the pump with gravity
• Think of it as head is on top or above
• Most common installation

Question 24

Suction lift

Answer 24

when the supply is below the pump.
• The impellers moving create a vacuum to suck up the liquid
• Requires a foot valve or check valve

Question 25

Discharge head(in feet)

Answer 25

is the vertical lift from the outlet
(discharge) side of a pump to the point of use.
• The elevation difference is the discharge head
• To convert this to pressure multiply by 0.433psi/ft of head

Question 26

specific gravity

Answer 26

is like the weight of a fluid relative to
water SG water = 1.0
• The higher the SG, the heavier the fluid and vice versa
• Eg., if the SG is .5, the fluid is lighter than water
• The higher the SG the more pressure or head to lift it