MIL-HDBK-1038
The two essential determinants, both of which are considered decisive
characteristics of a diesel engine, are (a) horsepower (hp) and (b) revolutions
per minute (rpm). Brake mean effective pressure (bmep) and piston speed are no
longer considered to be essential determinants. Formerly, the following values
had been accepted as the norm for each of the determinants: (a) an intermittent
rating not more than the actual horsepower requirements of the crane and (b) 514
to 720 rpm. Bmep was previously limited to not more than 85-psi (g) and piston
speed to not more than 1300 fpm. Now the following determinants are required to
be used: (a) horsepower required to accelerate the largest drive with two others
operating at rated load plus ancillary power requirements and (b) 1800 rpm. The
number of cylinders has little significance because the engines normally operate
at all times at full governed speed. Preference in competition should not be
given to the number of strokes per cycle (2 or 4) because modern engines have been
designed to overcome the disadvantages of each. Diesel engine-generator sets are
required to be sized so that the crane drive with the largest motor(s) can be
accelerated to its rated speed while the two drives with the next largest motors
are operating at rated load/rated speed and the normal complement of ancillary
equipment is functioning. The diesel engine of a portal crane is required to be
selected, based on its prime rating, utilizing the following formula:
EQUATION
D = (1.5)(T) + (H) + (M) + (1.675) (A)
(13)
Where
D
=
Diesel engine prime rating in horsepower
T
=
minimum calculated running travel drive horsepower
H
=
minimum calculated running main hoist horsepower
M
=
minimum calculated running horsepower for the third largest drive
A
=
ancillary loads (transformer rating in kVA)
An engine mounted thermal circulation tank-type immersion water heater,
incorporating an adjustable thermostatic switch, is required to be installed. In
colder climates, an external unit for heating of engine cooling fluid and
lubricating oil when the engine is not operating is required to be used instead.
All heaters are required to be fed from a separate panel dedicated to equipment
heater and battery charger circuits. The fuel tank should be an independent,
removable component of the crane; it should be bolted to the supporting structure.
The interior of the tank should be accessible for inspection and cleaning. Its
capacity should be at least 1100-gallons. Provisions are required to be made for
filling the tank from ground level.
Depending on the type of power needed for the drives on the crane, the
generator driven by the diesel engine is either an AC or DC unit. On some cranes
with DC motors in the drives, an AC generator is used with the AC power being
electronically converted to DC power. Generators are required to be oversized to
take advantage of the "flywheel effect" to ride through short term overloadings of
the diesel engine. Generators are required to be selected based upon the power
required to simultaneously accelerate the three largest drives operating at rated
load plus ancillary power requirements. The generator of a portal crane is
required to be selected, based on its continuous rating, utilizing the following
formula:
EQUATION
G = (1.12)(T + H + M) + (1.25)(A)
(14)
189
Previous Page
