Quiz 2 Flashcards
Main parts of the water supply system
Building supply (water service): is a large water supply pipe that carries potable
water from the city water system to the building.
Water meter: measures and record the amount of water used.
Building main: is a large pipe that serves as the principal artery of the water supply system. It is normally located in a basement, ceiling, or below the
concrete floor slab.
Riser: is a water supply pipe that extends vertically in the building and carries water to fixture branches. It is connected to the building main and runs
vertically in the walls.
Fixture branch: is a water supply pipe that runs from the riser or main to the fixture being connected. It is usually run in the floor or in the wall behind the
fixtures.
Fixture connection: runs from the fixture branch to the fixture.
A shutoff valve is typically located in the hot and cold water supply at the fixture connection.
Pipe and Fixture Layout
- The hot and cold water distribution pipes are installed parallel one another.
- Hot and cold pipes should be spaced at least 6 in. (150 mm) apart.
- Insulation must be placed between them to prevent heat interchange.
- In top quality work, both pipes should be insulated (hot pipes to minimize
heat loss and cold pipes to prevent condensation) - Water supply and drainage pipes are laid out next to each other.
- Shutoff valves should be used to close off the water supply to a fixture,
appliance, or system. - Valves should be accessible in the dwelling unit they control.
3 types of layouts involving pipes and fixtures
Zone: a branch supplying water to two or more fixtures. It can supply on one floor or on a few floors.
Groups: Fixtures located in clusters (commercial buildings, schools etc).
Chase: is a vertical opening through a floor or several floors which is enclosed with walls between floors. It encloses plumbing system piping and/or electrical
wiring, mechanical systems.
Two types of water distribution systems
- Upfeed (upflow) system
Must overcome:
● Any pressure loss due to friction ( pressure is expended in
friction losses as the water pass through the pipe, meter and
pipe fittings)
● Differences in elevation (pressure is expended to overcome
the gravity since pressure is required to push the weight of water
vertically).
● Flow pressure at outlets or equipment - Downfeed (downflow) system
Residual water pressure
The pressure available at the outlet, just before a fixture.
Pumped upfeed in tall buildings
Pressure reducing stations: Monitor and adjust the variations of pressure to make sure that the pressure at the plumbing fixtures is constant. These stations are located at about every ten floors.
A water system must have a positive pressure to:
● Establish a flow in the distribution system and through the plumbing fixtures
● To prevent water from being contaminated by external sources
Pressure losses due to friction are difficult to compute because they are depend on:
- Flow rate
- Fluid velocity
- Pipe diameter
- Pipe material and surface roughness
- Pipe length
- Number of fittings and valves
What is equivalent length
Pressure loss by fittings and devices is higher than that by straight pipes and we
must estimate it.
The pressure loss is given in the unit of “equivalent length of straight pipe”,
“equivalent length” (EL)
Small vs Large Pipe Diameter
Small pipe diameter:
Cost is low
High velocity
High noise
Erosion of inner pipe walls and valves (due to high velocities)
High pumping cost (due to high pressure losses)
Large pipe diameter:
Low velocity
Low noise
Low erosion of inner pipe walls and valves
Low pumping cost
High installation cost
Cavitation
Cavitation: is a physical phenomenon that occurs in a liquid when it experiences a drastic drop in pressure that causes the liquid to vaporize into a small vapor bubbles. When the liquid vaporizes it expands in volume.
As the low pressure returns to normal pressure, the volume reduces
since these bubbles implode as the vapor changes phase back to a
liquid. This implosion causes noise and high level of erosion on the pipe walls, fitting, pump, or valve. Valves can develop cavitation when they are partially closed and flow is restricted.
Cross connection and its solution
Cross connection: is an arrangement of piping that can cause wastewater to enter the potable water system
To prevent cross connection:
An air gap should be used.
Air gap: is the vertical distance between an opening in a fixture or faucet conveying potable water to the flood level rim of a tank of fixture.
Backflow problem and its solution
Backflow: contaminated water flows backwards into distribution pipes containing potable water.
Backflow can be caused by
● Negative pressure in a potable water system (back siphoning). It can be occurred when
◊ there is a broken water main
◊ there is a fire where the fire department uses large quantities of water
◊ there is a fire hydrant opened for testing
To prevent backflow: A vacuum breaker is installed at the branch connection of an equipment or plumbing fixture
Vacuum Breaker functioning
When the pressure in the piping drops below the atmospheric pressure, the vacuum breaker will automatically open the piping system to atmospheric pressure. This prevents foreign material or contaminated water in the equipment from getting into the piping system.
Water hammer problem and its solution
Water hammer: is a large increase of pressure in a plumbing supply system caused by sudden closing of a valve. The fast-flowing water stops quickly and the pressure increases.
Water hammer can cause a valve to rupture and the pipe walls to burst
To prevent water hammer damage to a building plumbing system the following devices are used:
* Air chambers (expansion tanks)
They are installed vertically above the fixture
water connection.
Air is trapped within the air chamber.
Since air is compressible, it absorbs the
hydraulic shock.
- Water hammer arrestors These devices use trapped air to cushion the hydraulic shock.
One is installed at the end of the branch line
between the two fixtures served.
Additional arrestors should be placed at the
midpoint of the run longer than 20 feet.
