ASPE CPD LATEST EXAMS ANSWERS AND
QUESTIONS SET A+
✔✔When selecting a centrifugal pump, in addition to determining the required head at
the design capacity, it is very important to also check what? - ✔✔The system
head/capacity curve to avoid possible future problems. The pump must be able of
satisfying minimum and maximum requirements in addition to the design requirements.
✔✔For parallel operation, the pump heads must be equal, but what may vary? -
✔✔Pump capacities.
✔✔For series operation, the pump capacities must be equal, but what may have
different values? - ✔✔Pump heads.
✔✔For multiple pump system proper operation, all pumps should have what type of
curve? - ✔✔Continuously rising characteristic.
✔✔For parallel operation of two or more pumps, the combined performance curve is
obtained by adding what? - ✔✔The capacities horizontally at the same heads. (100
GPM at 30‘ + 100 GPM at 30‘ = 200 GPM at 30’)
✔✔For series operation of two or more pumps, the combined performance curve is
obtained by adding what? - ✔✔The heads vertically at the same capacities. (100 GPM
at 30‘ + 100 GPM at 30‘ = 100 GPM at 60’)
✔✔When is a good time to use two or more pumps in parallel? - ✔✔When the system
demand varies greatly.
✔✔What is the benefit of operating pumps in parallel? - ✔✔To obtain greater capacities.
✔✔What is the benefit of operating pumps in series? - ✔✔When it is not advantageous
or efficient to add additional stages to a single pump, pumps are operated in series to
obtain greater heads.
,✔✔What does NPSHr vary with? - ✔✔The speed and capacity of the pump.
✔✔Define ‚Äúvapor pressure‚Äù - ✔✔The pressure a liquid exert on its surroundings
(this varies directly with temperature)
✔✔When calculating NPSH, use which pressure, absolute or gauge? - ✔✔Absolute. To
convert psi (or psig) to feet absolute, add the barometric pressure (14.7 psi at sea level)
to the liquid psi to obtain psia, and then multiply by 2.31 to obtain feet absolute.
✔✔How does one avoid pump cavitation? - ✔✔Ensure the NPSHa (available,
determined by system) is greater than the NPSHr (required, a function of the pump).
✔✔What are some adverse effects of pump cavitation? - ✔✔In addition to impeller
damage, cavitation generally results in reduced pump capacity (due to presence of
vapor in the pump), the pump head may also be reduced and exhibit some instability,
the power consumption may become erratic, and vibration and mechanical damage
such as early bearing failure can also occur.
✔✔What are the definitions of each of the pump affinity laws in terms of IMPELLER
DIAMETER? - ✔✔1) The capacity varies with the diameter 2) The head varies with the
square of the diameter 3) The brake horsepower varies with the cube of the diameter
✔✔When altering a pump impeller, what percent decrease can be achieved without
adverse effects? - ✔✔For an average impeller, 20 percent of the original maximum
diameter.
✔✔What are the definitions of each of the pump affinity laws? - ✔✔1) The capacity for a
given point on the pump head/capacity curve varies with the speed 2) The head varies
with the square of the speed 3) The brake horsepower varies with the cube of the speed
✔✔Why are pumps with non-overloading power curves advantageous? - ✔✔The drive
is not overloaded under any operating condition.
✔✔What is the telltale sign of an overloading BHP pump curve? - ✔✔When the BHP
curve continues to increase with increased capacity
✔✔What does a non-overloading pump BHP curve look like? - ✔✔A curve that flattens
out and decreases as the capacity increases beyond the maximum efficiency point.
✔✔For a pump, describe ‚Äúflat characteristic curve‚Äù - ✔✔This is a curve where only
a slight variation in head occurs from shutoff to design capacity. The curve might also
be drooping or rising (it will still have a portion where the head is approximately constant
, over a range of capacity, called the flat portion). This curve is NOT desirable for putting
pumps in parallel.
✔✔For a pump, describe ‚Äústeep characteristic curve‚Äù - ✔✔This is a rising
head/capacity characteristic curve where a large increase in head is developed at
shutoff in relation to the head developed at design capacity. This curve is ideal for
putting pumps in parallel.
✔✔For a pump, describe ‚Äúdrooping characteristic curve‚Äù - ✔✔A curve where the
head developed at shutoff is less than developed at some other capacity and is also
called a drooping head/capacity characteristic
✔✔For a pump, describe a ‚Äúrising characteristic curve‚Äù - ✔✔A curve where the
head rises continuously as the capacity decreases, and is also called a rising
head/capacity characteristic
✔✔Vent terminals should be no smaller than what? - ✔✔The stack served (1-1/2 inches
minimum).
✔✔What is the minimum vent size to allow for frost enclosure? - ✔✔3 inches
✔✔What is usually an adequate size for sump or ejector vents? - ✔✔It has been found
in practice that except for extremely large installations, 3 inches is usually an adequate
size, but the vent should not be less than 1-1/4 inches.
✔✔When designing sump or ejector vents, what requirements are applicable? - ✔✔All
the requirements for the proper design of the sanitary system are applicable, thus, the
air must be conveyed by the vent piping at the same rate as the maximum rate at which
sewage enters or is pumped out of the receiver.
✔✔What are some considerations when designing vapor vents? - ✔✔When a vapor
vent is used, it must be isolated from the sanitary venting system and the stack must
extend through the roof. The base of the vapor vent stack should terminate in a trap to
prevent the escape of vapors and spill to a trapped, vented, and water-supplied
receptacle. An individual vapor vent drip can be connected through an air gap to the
inlet of the trap serving the fixture. The minimum stack size should be 13 inches, but
should be sized by empirical methods or the rational approach.
✔✔Where are vapor vents now applied? - ✔✔Sterilizing equipment and bedpan
washers, and this is disappearing. These used to apply to water closets and urinals, but
is no longer necessary.
✔✔Where does the suds pressure zone extend to in a vent stack connected to a suds
pressure zone? - ✔✔The suds pressure zone extends the vent stack base connection
upward to the level of the suds pressure zone in the soil or waste stack.
QUESTIONS SET A+
✔✔When selecting a centrifugal pump, in addition to determining the required head at
the design capacity, it is very important to also check what? - ✔✔The system
head/capacity curve to avoid possible future problems. The pump must be able of
satisfying minimum and maximum requirements in addition to the design requirements.
✔✔For parallel operation, the pump heads must be equal, but what may vary? -
✔✔Pump capacities.
✔✔For series operation, the pump capacities must be equal, but what may have
different values? - ✔✔Pump heads.
✔✔For multiple pump system proper operation, all pumps should have what type of
curve? - ✔✔Continuously rising characteristic.
✔✔For parallel operation of two or more pumps, the combined performance curve is
obtained by adding what? - ✔✔The capacities horizontally at the same heads. (100
GPM at 30‘ + 100 GPM at 30‘ = 200 GPM at 30’)
✔✔For series operation of two or more pumps, the combined performance curve is
obtained by adding what? - ✔✔The heads vertically at the same capacities. (100 GPM
at 30‘ + 100 GPM at 30‘ = 100 GPM at 60’)
✔✔When is a good time to use two or more pumps in parallel? - ✔✔When the system
demand varies greatly.
✔✔What is the benefit of operating pumps in parallel? - ✔✔To obtain greater capacities.
✔✔What is the benefit of operating pumps in series? - ✔✔When it is not advantageous
or efficient to add additional stages to a single pump, pumps are operated in series to
obtain greater heads.
,✔✔What does NPSHr vary with? - ✔✔The speed and capacity of the pump.
✔✔Define ‚Äúvapor pressure‚Äù - ✔✔The pressure a liquid exert on its surroundings
(this varies directly with temperature)
✔✔When calculating NPSH, use which pressure, absolute or gauge? - ✔✔Absolute. To
convert psi (or psig) to feet absolute, add the barometric pressure (14.7 psi at sea level)
to the liquid psi to obtain psia, and then multiply by 2.31 to obtain feet absolute.
✔✔How does one avoid pump cavitation? - ✔✔Ensure the NPSHa (available,
determined by system) is greater than the NPSHr (required, a function of the pump).
✔✔What are some adverse effects of pump cavitation? - ✔✔In addition to impeller
damage, cavitation generally results in reduced pump capacity (due to presence of
vapor in the pump), the pump head may also be reduced and exhibit some instability,
the power consumption may become erratic, and vibration and mechanical damage
such as early bearing failure can also occur.
✔✔What are the definitions of each of the pump affinity laws in terms of IMPELLER
DIAMETER? - ✔✔1) The capacity varies with the diameter 2) The head varies with the
square of the diameter 3) The brake horsepower varies with the cube of the diameter
✔✔When altering a pump impeller, what percent decrease can be achieved without
adverse effects? - ✔✔For an average impeller, 20 percent of the original maximum
diameter.
✔✔What are the definitions of each of the pump affinity laws? - ✔✔1) The capacity for a
given point on the pump head/capacity curve varies with the speed 2) The head varies
with the square of the speed 3) The brake horsepower varies with the cube of the speed
✔✔Why are pumps with non-overloading power curves advantageous? - ✔✔The drive
is not overloaded under any operating condition.
✔✔What is the telltale sign of an overloading BHP pump curve? - ✔✔When the BHP
curve continues to increase with increased capacity
✔✔What does a non-overloading pump BHP curve look like? - ✔✔A curve that flattens
out and decreases as the capacity increases beyond the maximum efficiency point.
✔✔For a pump, describe ‚Äúflat characteristic curve‚Äù - ✔✔This is a curve where only
a slight variation in head occurs from shutoff to design capacity. The curve might also
be drooping or rising (it will still have a portion where the head is approximately constant
, over a range of capacity, called the flat portion). This curve is NOT desirable for putting
pumps in parallel.
✔✔For a pump, describe ‚Äústeep characteristic curve‚Äù - ✔✔This is a rising
head/capacity characteristic curve where a large increase in head is developed at
shutoff in relation to the head developed at design capacity. This curve is ideal for
putting pumps in parallel.
✔✔For a pump, describe ‚Äúdrooping characteristic curve‚Äù - ✔✔A curve where the
head developed at shutoff is less than developed at some other capacity and is also
called a drooping head/capacity characteristic
✔✔For a pump, describe a ‚Äúrising characteristic curve‚Äù - ✔✔A curve where the
head rises continuously as the capacity decreases, and is also called a rising
head/capacity characteristic
✔✔Vent terminals should be no smaller than what? - ✔✔The stack served (1-1/2 inches
minimum).
✔✔What is the minimum vent size to allow for frost enclosure? - ✔✔3 inches
✔✔What is usually an adequate size for sump or ejector vents? - ✔✔It has been found
in practice that except for extremely large installations, 3 inches is usually an adequate
size, but the vent should not be less than 1-1/4 inches.
✔✔When designing sump or ejector vents, what requirements are applicable? - ✔✔All
the requirements for the proper design of the sanitary system are applicable, thus, the
air must be conveyed by the vent piping at the same rate as the maximum rate at which
sewage enters or is pumped out of the receiver.
✔✔What are some considerations when designing vapor vents? - ✔✔When a vapor
vent is used, it must be isolated from the sanitary venting system and the stack must
extend through the roof. The base of the vapor vent stack should terminate in a trap to
prevent the escape of vapors and spill to a trapped, vented, and water-supplied
receptacle. An individual vapor vent drip can be connected through an air gap to the
inlet of the trap serving the fixture. The minimum stack size should be 13 inches, but
should be sized by empirical methods or the rational approach.
✔✔Where are vapor vents now applied? - ✔✔Sterilizing equipment and bedpan
washers, and this is disappearing. These used to apply to water closets and urinals, but
is no longer necessary.
✔✔Where does the suds pressure zone extend to in a vent stack connected to a suds
pressure zone? - ✔✔The suds pressure zone extends the vent stack base connection
upward to the level of the suds pressure zone in the soil or waste stack.
