ASPE CPD PAPER ACTUAL ANSWERS AND
QUESTIONS SET A+
✔✔Name and describe the two methods of determining peak demand for domestic
water systems in the US. - ✔✔Empirical method and Method of Probability. EM: Based
on arbitrary decisions arrived at from experience and judgement and is useful for only
small groups of fixtures. MP: Based upon the theory of probabilities and is most
accurate for large groups of fixtures. (Never use for a small number of fixtures.)
Remember to add FU values and not GPM values. Add all FUs first, then convert to
GPM.
✔✔Give examples of continuous demand outlets and intermittent demand outlets. -
✔✔Continuous: hose bibbs, lawn irrigation, air-conditioning make up, water cooling, etc.
Intermittent: plumbing fixtures.
✔✔Define Maximum Flow, Average Flow, and Maximum Probable Flow: - ✔✔The flow
that will occur if the outlets on all of the fixtures are opened simultaneously (maximum
possible flow). The flow that is likely to occur in the piping under normal conditions. The
maximum flow that will occur in the piping under peak conditions (peak demand or peak
flow).
✔✔What is an easy way to eliminate noise problems in plumbing? - ✔✔Maintain a flow
velocity under 8 FPS in all parts of the pipe.
✔✔Describe the phenomenon of cavitation. - ✔✔The centrifugal force developed
around a short bend radius at high velocity causes an increase of pressure at the outer
bend with a resultant lowering of pressure at the throat. This low-pressure zone can
drop below atmospheric pressure to a pressure that corresponds to the boiling point of
the flowing fluid. Under this condition, the cavity that forms at the inside of the bend
permits the fluid to flash into vapor or steam bubbles. Once these bubbles flow past the
low-pressure zone into normal pressure area downstream, these bubbles collapse. As
the bubbles collapse, they literally tear the metal off the pump casing, causing a pitted
facia.
,✔✔What can cause cavitation to occur in piping? - ✔✔When the direction of flow is
sharply changed and the velocity of flow is high, fluids flowing around a short bend
radius at a high velocity.
✔✔The pressure loss of flowing fluid due to friction varies approximately with the square
of _______, and is directly related to _________? - ✔✔The Velocity, the roughness of
the pipe wall.
✔✔What kind of valve should always be installed in the discharge line of pumps and
why? - ✔✔Spring-loaded check valves because they are designed to close at the exact
moment water flow comes to a rest. The velocity of flow does not change when the
check closes, thus no hydraulic shock is produced.
✔✔What kind of valves should never be used in the discharge line of pumps and why? -
✔✔Swing check valves, because when the pump stops, a reversal of flow occurs, and
the check slams closed, causing a sudden change in velocity.
✔✔What is one device that was used as a means of controlling hydraulic shock until it
was deemed ineffective? - ✔✔Air chambers. They often were improperly sized and
almost always lost their air charge.
✔✔What is a simplified expression for the increase in pressure caused by hydraulic
shock? - ✔✔The Jacowsky Formula
✔✔What are the most common causes of hydraulic shock? - ✔✔The starting and
stopping of pumps, improper check valves, rapid closure of valves; particularly the last
15 percent of movement.
✔✔What are some effects of hydraulic shock? - ✔✔Expand and burst pipe, weakened
joints, leaks, vibration, broken hangers, valve and faucet wear, ruptured tanks and
heaters, damage to meters, gauges, and temperature regulators, and accelerated
deterioration of the entire piping system. Hydraulic shock can occur without water
hammer, destroying a system before danger is recognized.
✔✔What is water hammer? - ✔✔The noise created by pipes moving as a result of
hydraulic shock.
✔✔What is hydraulic shock? - ✔✔Hydraulic shock occurs when fluid flowing through
pipe is subjected to a sudden and rapid change in velocity, such as may be caused by a
quick closing valve. The kinetic energy of the fluid is converted into a dynamic pressure
wave (which may travel at rates as high as 3,000 miles/hr). The longer the pipe and the
faster the velocity, the greater the pressure wave (surge). This pressure wave produces
, an impact, travelling back and forth until it is dissipated. When pipe is not adequately
supported, this wave causes the pipe to vibrate or hit against building structure.
✔✔Name some adverse effects of high velocity flow in piping: - ✔✔Noise, cavitation,
increase danger of hydraulic shock and water hammer, increase erosion and corrosion.
✔✔What maximum velocity should never be exceeded? - ✔✔10 fps
✔✔What should always be of prime importance to the plumbing designer? - ✔✔The
maximum velocity of water flow in the piping during periods of peak demand.
✔✔What other factor has an effect on pressure drop through a fitting? - ✔✔Velocity
✔✔What is the rule of thumb for determining equivalent length of piping in design
phase? - ✔✔Assume 50 percent of the developed length as an allowance for fittings
and valves.
✔✔What are the average values for the coefficient of friction for brass and copper and
for steel? - ✔✔0.02 for brass and copper, and 0.04 for steel
✔✔What equation is used to determine friction head loss? - ✔✔The Darcy Equation
✔✔How does friction head loss relate to velocity? - ✔✔Friction head loss varies
approximately with the square of the velocity.
✔✔Friction head loss is directly proportional to...? - ✔✔The roughness and length of the
pipe.
✔✔Friction head loss is inversely proportional to...? - ✔✔The diameter of the pipe.
✔✔Name the four things that affect head loss due to friction - ✔✔"1. The density and
temperature of the fluid 2. The roughness of the pipe 3. The length of the run 4. The
velocity of the fluid"
✔✔What is flow (or residual) pressure? - ✔✔The pressure measured at any point while
water is flowing (this is the pressure read on a pressure gauge installed in the piping.)
Flow pressure can be ignored in plumbing calcs.
✔✔What is friction head and which equation do you use to find it? - ✔✔Friction head is
the pressure loss along the line of flow caused by the friction produced by flowing water.
You use Bernoulli’s equation to solve for it.
✔✔Define velocity head. - ✔✔Velocity head (V^2 over 2g) is a measure of the decrease
in static pressure head experienced in feet of water column.
QUESTIONS SET A+
✔✔Name and describe the two methods of determining peak demand for domestic
water systems in the US. - ✔✔Empirical method and Method of Probability. EM: Based
on arbitrary decisions arrived at from experience and judgement and is useful for only
small groups of fixtures. MP: Based upon the theory of probabilities and is most
accurate for large groups of fixtures. (Never use for a small number of fixtures.)
Remember to add FU values and not GPM values. Add all FUs first, then convert to
GPM.
✔✔Give examples of continuous demand outlets and intermittent demand outlets. -
✔✔Continuous: hose bibbs, lawn irrigation, air-conditioning make up, water cooling, etc.
Intermittent: plumbing fixtures.
✔✔Define Maximum Flow, Average Flow, and Maximum Probable Flow: - ✔✔The flow
that will occur if the outlets on all of the fixtures are opened simultaneously (maximum
possible flow). The flow that is likely to occur in the piping under normal conditions. The
maximum flow that will occur in the piping under peak conditions (peak demand or peak
flow).
✔✔What is an easy way to eliminate noise problems in plumbing? - ✔✔Maintain a flow
velocity under 8 FPS in all parts of the pipe.
✔✔Describe the phenomenon of cavitation. - ✔✔The centrifugal force developed
around a short bend radius at high velocity causes an increase of pressure at the outer
bend with a resultant lowering of pressure at the throat. This low-pressure zone can
drop below atmospheric pressure to a pressure that corresponds to the boiling point of
the flowing fluid. Under this condition, the cavity that forms at the inside of the bend
permits the fluid to flash into vapor or steam bubbles. Once these bubbles flow past the
low-pressure zone into normal pressure area downstream, these bubbles collapse. As
the bubbles collapse, they literally tear the metal off the pump casing, causing a pitted
facia.
,✔✔What can cause cavitation to occur in piping? - ✔✔When the direction of flow is
sharply changed and the velocity of flow is high, fluids flowing around a short bend
radius at a high velocity.
✔✔The pressure loss of flowing fluid due to friction varies approximately with the square
of _______, and is directly related to _________? - ✔✔The Velocity, the roughness of
the pipe wall.
✔✔What kind of valve should always be installed in the discharge line of pumps and
why? - ✔✔Spring-loaded check valves because they are designed to close at the exact
moment water flow comes to a rest. The velocity of flow does not change when the
check closes, thus no hydraulic shock is produced.
✔✔What kind of valves should never be used in the discharge line of pumps and why? -
✔✔Swing check valves, because when the pump stops, a reversal of flow occurs, and
the check slams closed, causing a sudden change in velocity.
✔✔What is one device that was used as a means of controlling hydraulic shock until it
was deemed ineffective? - ✔✔Air chambers. They often were improperly sized and
almost always lost their air charge.
✔✔What is a simplified expression for the increase in pressure caused by hydraulic
shock? - ✔✔The Jacowsky Formula
✔✔What are the most common causes of hydraulic shock? - ✔✔The starting and
stopping of pumps, improper check valves, rapid closure of valves; particularly the last
15 percent of movement.
✔✔What are some effects of hydraulic shock? - ✔✔Expand and burst pipe, weakened
joints, leaks, vibration, broken hangers, valve and faucet wear, ruptured tanks and
heaters, damage to meters, gauges, and temperature regulators, and accelerated
deterioration of the entire piping system. Hydraulic shock can occur without water
hammer, destroying a system before danger is recognized.
✔✔What is water hammer? - ✔✔The noise created by pipes moving as a result of
hydraulic shock.
✔✔What is hydraulic shock? - ✔✔Hydraulic shock occurs when fluid flowing through
pipe is subjected to a sudden and rapid change in velocity, such as may be caused by a
quick closing valve. The kinetic energy of the fluid is converted into a dynamic pressure
wave (which may travel at rates as high as 3,000 miles/hr). The longer the pipe and the
faster the velocity, the greater the pressure wave (surge). This pressure wave produces
, an impact, travelling back and forth until it is dissipated. When pipe is not adequately
supported, this wave causes the pipe to vibrate or hit against building structure.
✔✔Name some adverse effects of high velocity flow in piping: - ✔✔Noise, cavitation,
increase danger of hydraulic shock and water hammer, increase erosion and corrosion.
✔✔What maximum velocity should never be exceeded? - ✔✔10 fps
✔✔What should always be of prime importance to the plumbing designer? - ✔✔The
maximum velocity of water flow in the piping during periods of peak demand.
✔✔What other factor has an effect on pressure drop through a fitting? - ✔✔Velocity
✔✔What is the rule of thumb for determining equivalent length of piping in design
phase? - ✔✔Assume 50 percent of the developed length as an allowance for fittings
and valves.
✔✔What are the average values for the coefficient of friction for brass and copper and
for steel? - ✔✔0.02 for brass and copper, and 0.04 for steel
✔✔What equation is used to determine friction head loss? - ✔✔The Darcy Equation
✔✔How does friction head loss relate to velocity? - ✔✔Friction head loss varies
approximately with the square of the velocity.
✔✔Friction head loss is directly proportional to...? - ✔✔The roughness and length of the
pipe.
✔✔Friction head loss is inversely proportional to...? - ✔✔The diameter of the pipe.
✔✔Name the four things that affect head loss due to friction - ✔✔"1. The density and
temperature of the fluid 2. The roughness of the pipe 3. The length of the run 4. The
velocity of the fluid"
✔✔What is flow (or residual) pressure? - ✔✔The pressure measured at any point while
water is flowing (this is the pressure read on a pressure gauge installed in the piping.)
Flow pressure can be ignored in plumbing calcs.
✔✔What is friction head and which equation do you use to find it? - ✔✔Friction head is
the pressure loss along the line of flow caused by the friction produced by flowing water.
You use Bernoulli’s equation to solve for it.
✔✔Define velocity head. - ✔✔Velocity head (V^2 over 2g) is a measure of the decrease
in static pressure head experienced in feet of water column.
