Parr Instrument 4575/76 HP/HT - Manual (Page 14)

P a r r I n s t r u m e n t C o m p a n y
4575/76 HP/HT Pressure Reactors
14
Explosion Proof Operation
If the local safety code requires that equipment
installed in the user’s laboratory must be explosion
proof, there are four possible ignition hazards to be
considered:
1. The Motor
The standard adjustable speed motor is not
explosion proof, yet these motors are not un-
duly hazardous if operated in a well ventilated
location where care is taken to prevent the
accumulation of explosive gases or vapors. To
eliminate any possible spark hazard originat-
ing at the motor, Parr can furnish an air mo-
tor as described previously, or the reactor can
be equipped with a variable speed, explosion
proof motor that is approved for use in Class
1, Groups C & D, and Class 2, Groups E, F, & G
atmospheres. Explosion proof motors are fur-
nished with a temporary power cord and plug
which are not explosion proof. The user should
remove this temporary wiring and replace
it with an explosion proof switch and wiring
which will comply with the local electrical code.
2. The Reactor Controller
The Series 4848 Reactor Controllers furnished
with these reactors contain switches and other
elements that are not explosion proof. The
minimal spark hazard associated with these
units can be resolved by installing the control-
ler in a remote location outside of the hazard-
ous area or by enclosing it in an approved
explosion proof housing. If enclosed within a
positive pressure, clean air housing, the dis-
charge from the housing must be directed into
a safe area. If requested, Parr will furnish the
long lead wires needed to mount the control-
ler in a remote location. If the controller is to
be installed in an explosion proof housing, the
user must provide the necessary housing and
installation.
3. The Heater
The elements in the heater could be dangerous
in an explosive atmosphere if the surface tem-
perature of the element becomes high enough
to ignite flammable vapors. This hazard must
be evaluated for each individual installation
since major modifications are required if the
heater must be isolated from the surrounding
atmosphere. Users who consider this a sig-
nificant hazard are urged to contact the Parr
Instrument Company for further discussion and
suggestions that might be helpful.
4. The Wiring
The wiring provided with the standard reactor
systems does not meet the standards pre-
scribed for explosion proof operation. Optional,
intrinsically safe barriers are available.
Periodic Pressure Tests
Each cylinder used in a Parr stirred reactor is
tested under hydrostatic pressure to 1.3 times its
maximum rating before it is released from the fac-
tory. Micrometer caliper measurements are taken
during this test to check the deflection of the walls
and bottom of the cylinder under pressure. Exces-
sive deflection or failure of the metal to resume
its original dimensions after pressure is released
indicates that a cylinder is potentially unsafe and
it will be rejected. Similar tests should be made
at regular intervals during the life of each cylinder,
and particularly whenever the user suspects that
the equipment has been over-stressed or damaged.
Some laboratories maintain hydraulic test facilities
and make it a rule that all pressure vessels must
be tested at regular intervals. Records are kept of
deflections at specific test pressures so that any
increase in deflection becomes a warning that the
metal has lost strength. Any cylinder which fails to
return to its original dimensions after application of
the prescribed hydrostatic test should be discarded
as unsafe for further use.
Users who do not have pressure test facilities can
return any Parr pressure vessel to the factory for
hydrostatic testing and overhaul. This should be
done whenever the metal shows excessive dam-
age from corrosion or whenever an over-pressure
or other unusual occurrence raises any safety
questions. To return a vessel for repair contact Parr
Instrument Company for a return authorization
number. Apparatus returned for testing and over-
haul should be shipped prepaid to Parr Instrument
Company, 211-53rd Street, Moline, Illinois 61265.
An order or letter of instructions should be mailed
to the same address, as no repair work will be
started without specific instructions and a Health &
Safety Assurance Certification form (F0042) signed
by a responsible user.