|
What is Explosion Proof?
Electric Powered Industrial Equipment, used in
areas containing explosive or flammable materials,
must be designed to prevent any operation of the equipment from igniting the
atmosphere. The design and construction of Gregory Industrial Trucks permit
their classification as Explosion Proof (EX) by Underwriters Laboratories (UL)
and enable their use in explosive and hazardous atmospheres.
Auto Ignition Points
Metal surfaces, such as electric
motor housings or electrical component enclosures, may become hot and must be
kept below the auto ignition temperature of the explosive atmosphere. Gregory EX
Trucks are designed to stay well below these temperatures.
Sparks
Sparks, either as a result of an electric arc or from static discharge, cannot
be permitted in an explosive atmosphere. Gregory EX Trucks use electrical
systems in EX enclosures to eliminate electric arcs and utilize static
conductive tires to eliminate static discharge.
EX Enclosures
An EX Enclosure is a case or housing that
has been tested and approved to contain electrical components or apparatus.
Although the joints of EX enclosures will permit the entry of explosive vapors,
the strength of the enclosures must contain any internal explosion. The enclosures of Gregory EX Trucks have been
hydrostatically tested by UL for internal explosive resistance to pressures in excess
of UL requirements without failure.
The joints of
enclosures must also have a length and fit so that any flames occurring within the
enclosure are snuffed out and hot gases are cooled before reaching the outside
atmosphere.
The combustion within an Explosion Proof Enclosure is contained
by strong walls and accurately fitted joints which prevent flames and hot
gases from escaping.
Types of EX Enclosures
Two methods are commonly used and approved in the construction of these joints: Bolt Down
Enclosures and Screw Type Enclosures.
Method One: Bolt Down
Enclosure
Consists of accurately ground and fitted faces clamped together with a
multiplicity of bolts. Accurately machined flanges of suitable length and fit
prevent escape of hot gases.
Method Two: Screw Type Enclosure
Uses accurately threaded parts with UL specified screw dimensions that have at least five
full threads engaged when the joint is closed. Threaded joints provide a
labyrinth path to snuff out flames and to cool gases.
Gregory
EX Forklifts use a Bolt Down Enclosure and Screw Type Enclosures for all 36-volt systems; and the Screw
Type Enclosures for all 12-volt and 24-volt systems.
Conduits, Shafts and Switches
The conduits from one housing, junction box or enclosure to another, must be sealed at one end with a special two part
sealing compound capable of withstanding the pressures and temperatures expected
in the event of an explosion within either the conduit or the enclosure. This
prevents the passing of flames or hot gases from one enclosure to another. The
conduits must also be of sufficient strength to contain the resulting pressures.
It is also required that where shafts or other moving mechanical linkage pass
through the walls of an enclosure, the fit and length of the orifice must not permit the passage of flames or gases to the outside
atmosphere. Gregory EX Trucks meet and exceed all UL designated requirements for
explosion proof construction.
Gregory EX Trucks
All Gregory EX
Trucks are tested and Classified to U.S. and Canadian Safety Standards by UL for use in
Class I, Divisions 1 & 2, Groups C & D; Class II, Divisions 1 & 2, Group G
and Class III, Divisions 1 & 2 Hazardous Environments.
|
