ACtion Magazine - July/August 2017 - 27

Positive pressure for operator cabins
tion and pressurization systems in terms of maintenance
costs.
"Intake filters can cost several hundred dollars each,
plus you have to shut down the equipment to change them
out," Losching says. "Minimizing the amount of debris being deposited into the filter will extend its service life to
the point where a quality pre-cleaner and pressurizer can
pay for itself fairly quickly."
Keeping the cab dust-free can also prolong the life of
sensitive electronic controls, circuit boards, switches, and
displays, adds Brocx. "If you're rubbing grit into a touch
screen, you're not going to be too happy about the consequences," he says.

Under pressure
Both SAE and ISO recommend pressurization levels
for enclosed off-highway equipment cabs in a range of 50
to 200 pascals.
"For pressurization to work properly, the cab has to be
sealed really well," Brocx says. "You'll always have air
venting out but you'd like it to be controlled, or to at least
know where the leaks are. The better the seal, the easier it
is to maintain cab pressure and prevent dust from getting
in."
Because many specialty heavy-equipment OEMs source
cabs from outside suppliers, the quality of sealing can
vary. In addition to doors and windows, common leakpoints include skip-welded seams, grommets, and gaskets
for wiring, hoses, and drains. Brocx says there are several
methods for finding leaks but an ultrasonic leak detector
and a sound generator is more accurate and sensitive than
a smoke blower and leaves no residue.
More sophisticated pre-cleaner and pressurizer units
can constantly monitor air pressure in the cab and automatically vary the motor speed. They can maintain an optimal pressure level inside the cab even when a door or
window is open. Some systems have displays and controls
to enable the operator to adjust the set point or be notified
if the cab pressure falls or the system needs service. A
data-logger can record events for future reference.
"We've been making pre-cleaners for heavy equipment
since 1972 and the demand for better reporting and monitoring is just taking off," Losching says. Companies want
to be proactive about showing compliance with OSHA and
other standards, and they like having a record of it.
Mostly, though, they want happy, healthy, and productive operators. Off-highway work is tough physically and
mentally, Losching notes, and skilled people are hard to
find. For an employer, air quality can be a competitive
advantage.

Good housekeeping
While spec'ing equipment is important, good housekeeping also helps.
An enclosed cab should be routinely inspected for integrity. Holes and cracks should be sealed with silicone.
Filters should be checked at recommended intervals, ensuring that gaskets aren't cracked or torn. Instead of inspecting filter media by sight, use a dust-load indicator set
to the manufacturer's recommended change interval.
"Probably the most common source of leaks is the operator just going about his job," says Losching. "Make
sure the HVAC unit is performing properly so he isn't
tempted to open a window. Position blowers up high, since
the floor is usually the dirtiest part of the cab and fans tend
to kick up dust from boots and clothes.
"Finally, if you maintain heavy equipment, take care
to avoid dust exposure yourself, especially during a filter
change," he concludes.
"It's an advantage to have a filter that's fairly simple to
clean or swap out," Brocx says. "The contaminated filter
will be easier to handle and dispose of, and you're more
likely to do the job at regular intervals." ❆

July/August 2017 * ACTION

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Table of Contents for the Digital Edition of ACtion Magazine - July/August 2017