MIL-T-13291F
3.6.6.1 Cover, automatic closing. When specified (see 6.2.1), the hot-dip.
tank shall be provided with an automatic closing insulated cover hinged to the
tank body to close over the dip compartment opening. The cover shall be pro-
vided with a handle for raising and lowering and shall embody a latch to hold
The automatic closing shall be accomplished
the cover in the open position.
with a temperature-operated mechanism positioned above the compound level to
ensure closing of the cover when excessive temperature exists in the ambient
air.
The cover, if open, shall close automatically when the temperature at
the sensing element exceeds
30° F for class A tanks, and
for class
B and C tanks. The effort required to raise or close the cover and components
attached thereto shall not exceed 25 pounds force. A counterbalance mechanism
may be used when necessary to limit the effort. required to open and close the
cover to not more than the 25 pounds force.
3.6.7 Master switch. Each hot-dip tank shall be provided with a master
switch embodying a circuit breaker disconnect. The switch shall be capable of
isolating from the power source all electrical equipment except the program-
ming switch motor.
3.6.8 Programming switch. When specified (see 6.2.1), each hot-dip tank
shall be provided with a programming switch of 7 day cycle.
The programmer
shall permit 7 day preelection of variable daily duty demands of 1 to 23
hours with provision of skipping days where operation is not required.
Time
indicating scales shall be calibrated in increments not greater than 1 hour.
stat shall permit selection of any temperature between not more than 100 and
for type I, class A tanks, 100 to
for type II and type III class
A tanks, 100 to
for class B tanks, and 150 to 600° F for class C tanks.
Indirectly heated tanks shall also be provided with a thermostatic switch for
selection and automatic control of the heat transfer fluid temperature between
not more than 100 and
F for class A tanks, 100 to
F for class B
tanks , and 150 to
F for class C tanks.
Temperature indicating scales
shall be marked in increments not greater than
F and shall be accurate
within
F and capable of being recalibrated.
3.6.10 Relay. The electrical control system may utilize a relay for carry-
ing current to the heating units.
3.6.11 Thermometer. A thermometer shall indicate temperature of the dip
material.
Indirectly heated tanks shall have a thermometer to indicate tem-
perature of the heat transfer fluid. The thermometers shall have a minimum
temperature range of 50 to
F for class A tanks, 50 to
F for class B
tanks, and 100 to
F for class C tanks.
Temperature indicating scales
be marked in increments not greater than
shall
F and shall be accurate
within
F. If an indicating thermostatic switch is furnished, the thermo-
meter shall not be required.
3.6.12 Heat transfer fluid. Indirectly heated tanks (type III) shall be
furnished with a sufficient quantity of heat transfer fluid to permit tank
operation.
The fluid shall be noncarbonizing and shall have a flash point not
less than
F.
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