Milnor 7272TG1L, Установка и обслуживание

Страница: 88 / 206

Fire Safety System Operation and Maintenance
PELLERIN MILNOR CORPORATION
2.
About the “Min Fire” and “Outlet Temperature Exceeded 220°”
Faults
These faults, described below, are preemptive; neither results in an error that requires the operator
to take immediate action. However, data about the fault is recorded in the dry cycle details
memory (see "Drycode Reports" elsewhere). These faults interfere with the intended processing
and often indicate that the goods are being overheated. Overheated goods discharged from the
dryer may have a burned smell even though they did not catch fire. If you notice such a smell,
review the dry cycle details for these loads. If the data indicates that the cycle ended with a
min
fire
or
outlet temperature exceeded 220°
fault, investigate and correct the cause, as follows:
2.1.
Min Fire (MINF)
—This condition applies only to gas- and propane-fired dryers and refers to
the valve position of the modulating gas valve when the controller commands it to go to position
000. When properly set, the gas valve remains open slightly at this commanded position. A min
fire fault occurs when the controller detects that the outlet temperature continues to rise during
min fire. This condition usually indicates that the goods overheated and are at risk of catching
fire. As soon as the fault occurs, the controller immediately attempts to counteract it by
advancing the drycode to the cooldown step. Some causes of min fire faults include:
plastering —If the basket speed called for by the drycode is too high, the goods can adhere to the
basket (plaster), rather than tumble as they lose moisture and become lighter. Once this occurs,
the goods will tend to overheat on the surface that is against the basket.
gas train malfunction —If, for example, a modulating gas valve is damaged such that it cannot
throttle down completely, it may be unable to lower the flame to the min fire position.
min fire set too high —The min fire position is adjustable and must be set in accordance with the
gas and air setting instructions in the service manual. This setting can also change as a result
of damage to components.
2.2.
Outlet Temperature Exceeded 220° (>220)
—This fault applies to all except dryers
with non-modulating steam valves. 220° F (104° C) is 5°F (3° C) below the set point of the outlet
temperature switches (Fenwals) that actuate the sprinkler. It is intended to preempt sprinkler
actuation, if possible, by successively canceling each remaining heating step in the drycode if
outlet temperature remains above 220° F (104° C) for at least five seconds at the start of the step.
As with a min fire fault, this condition may be the result of plastering or a gas train malfunction.
If the goods are not yet on fire, this function can avoid an unnecessary sprinkler actuation. But if
a fire has already started, the temperature switches should quickly actuate the sprinkler.
3.
Resolving No-fire Sprinkler Actuations
If a dryer experiences sprinkler actuations when there is no fire, this typically indicates one of
two problems:
• A temperature switch is damaged. This is the most likely cause. Typically, the ST225-2
temperature switch is at fault. The switch probe can bend if a piece of goods gets past the
basket seals, through the blower, and into the outlet duct where it hits the probe. Replace a
damaged switch and refer to “Felt Seal Inspection and Maintenance” in the service manual
for information on avoiding this type of damage.
• Drying temperatures are not within the normal range. The causes described in Section
2.1 , above, if severe enough, can result in sprinkler actuation.
Resolve no-fire sprinkler actuations by correcting the cause. Never disable the sprinkler. If a
fire should occur, the sprinkler is your first line of defense, and your best defense against a
potentially uncontrollable situation.
82