Exam (elaborations)
NAPE Third Grade Engineering Review Test
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- 3rd Grade Engineer.
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- 3rd Grade Engineer.
NAPE Third Grade Engineering Review Test
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NAPE Third Grade Engineering ReviewTest
. Why is a pump primed? How is it primed? - ANS-The air must be evacuated from the
pump suction before water will fill the pump. It cannot pump air. It can be primed with
water from another source if the foot valve is tight, by using an ejector or with a vacuum
pump. Always with the pump off.
2 boilers are made of the same grade steel, same thickness of plate and same type of
joints. One is 30" diameter and the other is 60" diameter. Which will withstand the
greatest working pressure and demonstrate your answer. - ANS-The 30" diameter boiler
will withstand more working pressure because it has less total pressure on the shell.
30x30x.7854x120psi= 84,823 lbs. total pressure. 60x60x.7854x120psi= 339,292 lbs.
total pressure
A boiler designed to operate at 125 psi is now operating at 12 psi what changes will be
made to the safety valve? - ANS-If the change is permanent, a safety valve with a larger
disk and lower pressure rating will need to be installed.
A safety valve is limited to how many square feet of heating surface? - ANS-Any boiler
with more than 500 square feet of heating surface must have 2 or more safety valves.
At what pressure is the use of Cast iron fittings permitted? - ANS-15 psi or 250 degrees
Farenheit, not to exceed either one.
At what temperature does a safety valve on a superheater have to be protected with
heat resisting materials? - ANS-450 degrees F
Convert 122 degrees F. to Centigrade and show your work. - ANS-F-32 x.555=C
122-32x.555=50 degrees C
Could too much secondary air have a bad effect on the efficiency of a boiler? -
ANS-Yes. Excess secondary air will not enter into the reaction and will pass through the
furnace wasting heat out the stack.
Define BTU. - ANS-The quantity of heat required to raise the temperature of one pound
of water one degree F.
,Define combustion. - ANS-Combustion is a chemical reaction between oxygen and
combustibles. It is the process of rapid oxidation by which heat stored in fuel is
liberated.
Define flash point, ignition point, and pour point. - ANS-Flash point is the lowest
temperature at which vapors of a substance will make a flash of flame, but not continue
to burn when exposed to open flame. Ignition point is the lowest temperature at which
vapors of a substance will ignite and burn continuously when exposed to open flame.
Pour point is the lowest temperature at which liquid will flow.
Define N.P.S.H. - ANS-Net positive suction head. The amount of positive pressure on
the inlet of the pump when the pump is on.
Define Ohms Law. - ANS-Current is directly proportional to a voltage change and
indirectly proportional to a resistance change.
Define perfect, complete, and incomplete combustion. - ANS-Perfect combustion-
burning all the fuel using on the theoretical amount of air. Complete combustion-
burning all the fuel using more than the theoretical amount of air. Incomplete
combustion- when a portion of the fuel remains unburned because of insufficient
amounts of air.
Define power. Define work. - ANS-Power is the rate work is done. Work is force exerted
through a distance.
Define primary air, secondary air, and excess air. Is secondary air necessary in
hand-fired boiler and why? - ANS-Primary air enters the furnace with the fuel and
determines the rate of combustion. Secondary air creates turbulence around the fuel to
complete the burning process. Excess air is more than what is theoretically needed for
complete combustion. Yes. Secondary air is introduced above the fuel bed to burn
combustible gasses.
Define PSI, PSIG and PSIA. - ANS-Pounds per square inch- pressure exerted on a
surface. Pounds per square inch gauge- pressure that is read on a gauge. Pounds per
square inch absolute- gauge reading plus atmospheric pressure.
Define purging and two types? - ANS-Purging is the forced removal of combustibles
gases from the firebox. Pre-purge is before the pilot is lit. Post-purge is after the
combustion cycle.
,Define volt? Define ampere? - ANS-A force or pressure which causes an electron flow
of one ampere through a resistance of one ohm. One ampere of current is said to flow
when one coulomb of electricity passes a given point in a conductor in one second.
Describe a balanced (double seated) feedwater valve and why it is used? - ANS-A valve
with 2 disks and 2 seats. One disk opens with the pressure and one against. With the
forces balanced, it opens easily.
Describe a diagonal and gusset stay. Where would each be used? - ANS-A diagonal
stay is made of flat material similar to the boiler shell and is attached directly to the
boiler shell and head or tube sheet. A gusset stay consists of boilerplate riveted to the
shell and head or tube sheet by means of angle iron. They are more rigid. Both are
used to brace right angle surfaces.
Describe a metering pump (power pump) list its 3 features and what are its uses in a
power plant? - ANS-They are either diaphragm, piston or plunger operated positive
displacement pumps used for low flow applications. 3 features are accuracy of
adjustment, capable of pumping wide variety chemicals and high head service. They
are used for injecting cooling tower treatment, internal boiler treatment or external boiler
treatment.
Describe a rotary pump and does a rotary pump work on the same principle as a
centrifugal pump? - ANS-A rotary pump is a positive displacement pump consisting of a
shaft with gears, vanes, screws, lobes and cams operating in a close fitting casing.
They do not use valves in their design, permitting the pump to operate efficiently on
both low and high viscosity liquids with a low net positive suction head requirement. The
rotary pump is a positive displacement pump and does not work the same as the
centrifugal pump.
Describe a Scotch Marine boiler and how is it fired? - ANS-A Scotch marine boiler is an
internally fired, self-contained H.R.T. fire tube boiler. It has a cylindrical shell containing
the combustion chamber and tubes that are surrounded by water.
Describe a section boiler? - ANS-The sectional headers are built up of vertical sections
or units. A sufficient number of sections are clamped together to form the desired size
boiler. These boilers can be erected in an existing building by carrying them in piece by
piece.
Describe a through stay. Why are hollow stay bolts used on water legs? - ANS-A
through stay runs from one tube sheet to the other or from one flat surface to another. A
, rod threaded on both ends is held in place with nuts on the inside tightened against nuts
on the outside of the plates. A small hole is drilled into the stay bolt so if it failed a leak
will develop and be detected at once.
Describe a transformer? - ANS-It is an iron core surrounded by coils of insulated wire.
The voltage is changed in exact proportion to the number of turns connected in series in
each winding. It is used to step up or step down voltage in an A.C. circuit.
Describe how to pipe a water column on a H.R.T. boiler? - ANS-The top of the column is
connected to the top of the steam shell. The bottom is connected to a point 6" below the
center of the drum. The bottom of the sight glass is 3" above the top row of tubes, and
at least 2" above the fusible plug. The gauge glass must be ½ in diameter and the
blow-off not less than 3/4. Crosses and tees are used instead of elbows for cleaning
and inspection.
Describe how you determine if a centrifugal pump is running. - ANS-Check the delta
pressure, discharge pressure, flow switch, differential switch or sight.
Describe how you would align a motor to a pump. - ANS-The driver and the driven shaft
can be aligned by using a straight-edge the length of the coupling halves, a feeler
gauge between the coupling halves, a dial indicator or laser alignment. Always measure
the same place as the shafts rotate together. Proper alignment would be within .005
inch.
Describe the circulation of water within the Sterling boiler. - ANS-Feed water enters the
top rear drum and passes down the rear tubes to the mud drum. Steam and boiler water
go up the front banks and center drums. Circulator tubes allow the boiler water to pass
between the drums. What does not go out as steam drain via the rear tubes.
Describe three types of steam traps. - ANS-Inverted bucket: The steam and condensate
enter at the bottom and flow upward into the inverted bucket. As condensate enters the
trap it displaces the steam in the bucket, which sinks causing the valve to open. The
condensate is blown out the valve, the bucket again floats and the valve closes. Any air
caught in the trap passes through a small orifice in the bucket preventing the trap from
becoming air bound. Float and thermostatic: As the float rides up on the condensate it
will open the valve. The valve closes as the level falls. Air will cool the trap as it cools,
the thermostatic valve will open, passing the air though. Thermostatic trap contains a
bellows expanding when exposed to the heat of live steam forcing a plug into an orifice
closing the valve. As condensate cools the trap the bellows contracts opening the valve
discharging the condensate.
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