Survive Hostile Controls Environments

Sealing boots for toggle,
pushbutton, rotary and
rocker devices
Survive Hostile
Controls
Environments
By john Arnold, APM HEXSEAL
Body Armor for Switches and Circuit Breakers
nsealed electromechanical
switches and circuit breakers
offer limited environmental
protection against harsh contamination penetration. The switches and
breakers might be on oil platforms in
the Gulf of Mexico, the Permian Basin, the Bakken Shale, petrochemical
plants, refineries in Louisiana, in the
Arctic or in the Antarctic. No matter
the location, care must be taken with
this sensitive equipment.
Constant exposure to moisture, ice, dust, dirt, fungus, lubricants, cleaning solvents and chemically corrosive atmospheres will
U
eventually reach the internal contact
mechanisms making them susceptible
to damage and shorting. External operational problems can occur, too.
For example, the exterior toggle/
pushbutton well is a prime location
for dirt collection and ice build-up,
which can interfere with the switch's
or breaker's free-movement and reliability. Contaminants can seep past
the switch/ breaker mounting hole,
exposing delicate circuitry to shorting
and corrosion, as well.
Even sealed switches/ breakers
are exposed to the same potential
environmental risks. That is because
hermetically sealed devices are designed to protect only the internal
mechanism. It does nothing to prevent clogging in the actuator well or
prevent seepage past the mounting
hole.
During World War II, the U.S.
military was made painfully aware of
this type of control reliability problem, and shortly thereafter, a seal company joined with the Department of
Defense to develop a series of seals,
based on a newly created specification
(MIL-DTL-5423), that addressed
these issues.
The result was the development
of two patented families of sealing
boots for switch and circuit breaker protection that included a special panel sealing washer for sealed
switches. They are rated to IP66/ 68
dust and water ingress protection.
For more than 60 years, these seals
have been extensively used in military,
naval, land and avionics applications
throughout the world. They are a UL
Recognized Component and RoHS
compliant.
The oil and gas industry has also
embraced this sealing technology, and
it is used on control panels in some of
the harshest environments including:
• Portable oil shale excavating equipment
• Robotics for welding and inspection of pipelines
• Drill rigging
Sealing Boots for Most
Instrumentation
Sealing boots are available for toggle,
pushbutton, rotary and rocker devices with configurations matching
most popular brands. The vast majority of boots are fabricated from highperformance silicone rubber with a
molded-in mounting-nut that replaces the original switch's exterior nut.
Other elastomeric materials are
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11
,..___ Heavy duty, armored, stainless
steel , mushroom head boot
Pushbutton style
front-of-panel mounted
switch boot
Digital Panel Meter custom cover
1-- - - Lever style back-of-panel
mounted circuit breaker boots
Toggle style
front-of-panel mounted
switch boots
Lever style front-of-panel
mounted sealing boots
1-- - -
Pushbutton style
front-of-panel mounted
switch boot
- - --=:
Lever style back-of-panel
mounted ci rcuit breaker boot
Rocker style
front-of-panel mounted
circuit breaker boots
Figure 1 . A NEMA enclosure with switch and circuit breaker boots
also available to match specific environmental chemical exposures.
(see Table 1). These UL Recognized
Component boots are precision engineered. For example, many of the
toggle boots are designed with an inner secondary seal affording additional protection should the exterior be
compromised by a puncture or tear.
High-performance
silicone
Material
Relevant
Specifications
features several important properties-including extreme elongation;
high actuation life (up to 100,000 operations and beyond); and a wide operating temperature range, from -94 F
to +400 F (-70 C to +204 C). These
boots are molded and oven agedwhich is an effective method to reduce silicone out gassing to an absolute acceptable minimum-therefore
..............,,
Servi ce Temp
Ozone
Chemicals
Oil
___
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l:t~Th'lf!HillJ.!J
rl
'
Solvents Tensile PSI Elongation Abrasion Compression
%
Resistance
Set
Silicone
Rubber
A-A-59588
CLASS 1&11
GR 30-70
-94 ·F to 4oo·F
Excellent
-7o·c to 204 ·c
Good
Good
Fair
500-1800
100-800
Fair
Excellent
Silicone
Rubber
ASTM 01418
GR 30-70
-8o·F to 4oo·F
Excellent
-62·c to 204 ·c
Good
Good
Fair
500-1800
100-800
Fair
Excellent
FluoroSilicone
Rubber
MIL-R-25988
AMS 3326
GR 60
-78•F to 15o•F
Excellent
-61 ·c to 66•c
Excellent
Excellent Excellent 2000-2200
300-400
Good
Excellent
Buna N
(NBR)
Neoprene
(EPR)
ASTM 02000-90
-65°F to 25o•F
M2BG714
-54·c to 121 ·c
GR 60
MIL-R-3065
GR 60
-65·F to 3oo·F
-54·c to 149•c
Fair
Good
Excellent
Good
1500-3000
400-600
Good
Excellent
Good
Good
Good
Fair
1500-4000
100-700
Excellent
Good
Excellent
Poor
Good
1400-1600
500-600
Excellent
Excellent
Ethylene ASTM 02000-90
-6s·F to 3oo· F
Propylene
M3BA708
Excellent
-s4·c to 149•c
(EPOM)
GR 60
.. ..
12
preventing silicone molecule migration that could coat sensitive electrical and electronic components causing circuit malfunction.
To prevent contaminant seepage
past the mounting hole cut-out, each
boot has a perimeter sealing rib that
is pressed against the panel surface
when the boot is tightened. For extremely rough handling situations in
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Upstream Pumping Solutions • Spring 2012
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Table 1. Materials chart
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Constant exposure to moisture, ice, dust, dirt, fun-
gus, lubricants, cleaning solvents and chemically
corrosive atmospheres will eventually reach the
internal contact mechanisms making them susceptible to damage and shorting.
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Behind-panel mount
which workers wear gloves, for example, several switch seals are available
that feature a stainless steel (armored)
exterior with a silicone membrane/
boot that fits over and transfers the
actuation motion to the standard toggle or pushbutton switch. This is also
an ideal solution for high-pressure
and high-temperature wash down
situations.
Circuit Breaker Boots
Circuit breaker boots present a
somewhat
different
challenge.
Environmentally protecting the
breaker externally and internally is
not enough. The operator must also
be able to view the circuit status, as
well. That is why a clear version of silicone rubber is used.
The elastomeric cover must maintain its clear visibility for an extended
period of time and not yellow or otherwise degrade from UV and other
exposure or contamination. Plus, it
must provide long actuation life and
be robust enough to absorb rough
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handling while providing the operator with sufficient tactile feel.
Besides pushbutton, rocker and
toggle styles, single and multiple lever styles are available. Some can be
mounted from the front-of-the panel,
and others are mounted from behind.
Special 0-Ring embedded stainless
steel screws can be used to secure these
boots (a front-panel-mounted version
also uses these self-sealing screws to
secure a steel mounting frame). These
same self-sealing screws are successfully being used in oil and gas field
exploration instrumentation sensors.
Sealing Boot Selection
A wide choice of sealing boots is offered for switches and circuit breakers.
A simple way to match and select the
right boot is to visit a suppliers' website and review the catalogs, which
contain dimensional information and
comprehensive cross-reference charts.
Also computer-aided design (CAD)
and PDF drawings should be available on the site so that end users can
double check the dimensions against
the controls presently in operation or
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Upstream Pumping Solutions • Spring 2012
those planned for installation. This
an important step as controls manufacturers occasionally change dimensions. Here are some guidelines to
follow:
• What size threaded bushing does
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IEC 60529
DEGREES DF ACCESS
TO HAZARDOUS PARTS ,
FIRST CHARACTERISTIC NUMERAL
First Characteristic Numeral:
With Respect to
So lid Foreign Objects
IP
IEC 60529
DEGREES OF PROTECTION
AGAINST WATER INGRESS,
SECOND CHARACTERISTIC NUMERAL
Second Characteristic Numeral:
t - - - With Respect to the Harm·
1---
IP
fullngress of Water
0
Non-protected
0
Non-protected
1
Protected against solid
foreign objects " 50 mm
diameter
1
Protected against vertically
falling water drops
2
2
Protected against solid
foreign objects" 12.5 mm
diameter
Protected against vertically
falling water drops when
enclosure tilted up to 15°
3
Protected against so!!d
4
3
4
Protected against solid
foreign objects" 1.0 mm
diameter
5
Protected against water jets
6
Protected against powerful
water jets
7
Protected against the effeels of temporary immersion in water
8
Protected against the effeels of continuous immersion in water
5
Dust-protected (Dust shall
not penetrate in quantity to
interfere with satisfactory
operation of the apparatus
or to impair safety)
6
Dust-tight (No ingress of
dust)
llllll:lettiiJIII
•
•
Protected against spraying
water
foreign objects" 2.5 mm
diameter
•-
•
•
Protected against
splashing water
•••
•
your switch use, (e.g., 15/ 32-32,
M12x1, 3/ 8-24, M6x 0.75, 1,4-40,
etc.) ?
W hat is the height of the tip of the
switch actuator above the threaded
switch bushing?
For rotary switches, what is the
diameter of the shafi: ?
If a rocker switch is used, what are
the dimensions of the bezel and actuator and the height of the rocker
above the plane of the bezel face?
I
• 1
ror ctrcmr 1oreaKers,
constaer
the number of levers, mounting
method and overall dimensions.
In all instances, specify the elastomeric material that best conforms
to the environmental challenges.
Silicone will suffice for most, but
there are exceptions (see Table 1).
T"
•
•.
AC motor controllers typically
AC motor controllers typically have
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15
Type
Intended Use and Description
1 ......... Indoor use primarily to provide a degree of protection against limited amounts of falling dirt.
2 ......... Indoor use primarily to provide a degree of protection against limited amounts of falling
water and dirt.
3 ......... Outdoor use primarily to provide a degree of protection against rain, sleet, windblown
dust and damage from external ice formation.
3R ....... Outdoor use primarily to provide a degree of protection against rain, sleet, and damage
from external ice formation .
3S ....... Outdoor use primarily to provide a degree of protection against rain, sleet, windblown
dust and to provide for operation of external mechanisms when ice laden.
4 ......... Indoor or outdoor use primarily to provide a degree of protection against windblown dust
and rain, splashing water, hose-directed water and damage from external ice formation.
4X ....... Indoor or outdoor use primarily to provide a degree of protection against corrosion,
windblown dust and rain , splashing water, hose-directed water and damage from external
ice formation.
5 ......... Indoor use primarily to provide a degree of protection against setiiing airborne dust,
falling dirt, and dripping noncorrosive liquids.
6 ......... Indoor or outdoor use primarily to provide a degree of protection against hose-directed
water, and the entry of water during occasional temporary submersion at a limited depth
and damage from external ice formation.
6P ....... Indoor or outdoor use primarily to provide a degree of protection against hose-directed
water, the entry of water during prolonged submersion at a limited depth and damage
from external ice formation .
12
12K ..... Indoor use primarily to provide a degree of protection against circulating dust, falling dirt,
and dripping noncorrosive liquids.
13 ....... Indoor use primarily to provide a degree of protection against dust, spraying of water, oil ,
and noncorrosive coolant.
these boots installed for protection
against wash down and hostile environments, as do NEMA 4X enclosures (see Table 2) and IEC type
electrical distribution and industrial
controls as described in this article.
Figure 1 shows some of the various
ways these boots can be installed to
protect both externally as well as
within the enclosure.
john Arnold is Sales &
Marketing manager at
A PM HEXSEALmanufacturer ofenvironmental switch and
circuit breaker sealing
boots and se?f-sealingfastener products
and solutions. His background spans positions in metallurgy, gasket design and
chemical transfor systems. john can be
reached atj.arnold@apmhexsealcom.
seepex.com
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511 Speedway Dr.
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[email protected]
www.seepex.com
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Spring 2012