Exam (elaborations)
upStationary Grade 3 Engineering License (1).
- Module
- 3rd Grade Engineer.
- Institution
- 3rd Grade Engineer.
upStationary Grade 3 Engineering License (1).
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upStationary Grade 3 Engineering Licensea boiler designed to operate at 125 psi is now operating at 15 psi, what changes will be
made to the safety valve? - ANS-if change is permanent, install a safety valve with:
1) a larger disk
2) lower pressure rating
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*F. 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*F
convert 122*F to centigrade and show your work - ANS-F-32x5/9=C (5/9=.555)
122-32x.555=50*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 (British Thermal Unit) - ANS-the quantity of heat energy required to raise
the temperature of one pound of water one degree F
define combustion - ANS-a CHEMICAL REACTION between oxygen and combustibles.
it is the process of rapid OXIDATION by which the heat stored in fuel is released
define flash point
-----
define ignition point
-----
define pour point - ANS-FLASH POINT = 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 = the lowest temperature at which vapors of a substance will ignite
and burn continuously when exposed to open flame
-----
POUR POINT = the lowest temperature at which liquid will flow
define Net Positive Suction Head (N.P.S.H.) - ANS-the amount of positive pressure on
the inlet of the pump when the pump is on
define Ohm's Law - ANS-current is directly proportional to a voltage change and
inversely proportional to a resistance change
define perfect combustion
-----
define complete combustion
-----
define incomplete combustion - ANS-PERFECT COMBUSTION - burning all the fuel
using only 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 = rate at which work is done
----
WORK = force exerted through a distance
define primary air
-----
define secondary air
-----
define excess air
-----
is secondary air necessary in a 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
-----
define PSIG
-----
define 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 readings plus atmospheric
pressure
define purging
-----
name two types - ANS-purging = the forced removal of combustibles from the firebox.
-----
1) pre-purge = before the pilot is lit
2) post-purge = 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 3 types of steam traps - ANS-1) INVERTED BUCKET: the steam and
condensate enter at the bottom and flow upward into the inverted bucket. as
condensate enter 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.
, 2) FLOAT: 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 through
3) THERMOSTATIC: 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 and discharging the condensate.
describe a balanced (double seated) feed water valve?
----
why is it used? - ANS-a valve with two disks and two seats. one disk opens with the
pressure and one against
----
with forces balanced, it opens easily
describe a diagonal stay
-----
describe a gusset stay
-----
where would each be used? - ANS-DIAGONAL STAY = made of flat materials similar to
the boiler shell and is attached directly to the boiler shell and head or tube sheet
-----
GUSSET STAY = made of boilerplate riveted to the shell and head or tube sheet by
means of angle iron. MORE RIGID
-----
both are used to brace right angle surfaces
describe a gate valve
-----
where it is used most often? - ANS-a valve with a wedge shaped gate which is raised or
lowered into a passageway. the wedge-shape tightens against the sides of the slot
when closed. it offers little resistance to flow when fully open and should not be used to
throttle.
-----
for isolating devices for repair or to shut off the flow to the boiler
describe a glove valve and where is it used most often?
-----
how do you pipe a globe valve?
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