Owner's manual

9
MAINTENANCE & TROUBLESHOOTING
Parr Instrument Company
48
INSPECTION OF CRITICAL SEALING SURFACES
The sealing grooves and related surfaces for most of
the Parr bombs are machined to tolerances as small as
+/- 0.001” (0.03mm). As a result, any imperfection
in a sealing surface resulting from either normal use
or carelessness in handling the bomb can cause the
bomb to leak. If the damage or accumulated wear is
much less than 0.001” (0.03mm), then careful polishing
will restore the bomb sealing to an as new condition.
Imperfections that penetrate the sealing surface more
than one or two thousandths of an inch (0.03-0.06mm)
may render the seal surface unserviceable.
Any surface that comes in contact with an elastomer
seal should be carefully examined for imperfections
that would compromise its ability to seal. A freshly
sharpened pencil can be used to probe the metal sealing
surfaces for significant imperfection. If the pencil
point hangs up in the imperfection, further attention
is warranted. An attempt should be made to polish
(remove) any significant imperfections. This operation
generally requires the use of a lathe in order to
guarantee that the sealing surface to be repaired remains
concentric with the mating surface. Knowledge of the
dimensional tolerances and the ability to accurately
measure or gauge the affected area is required in order
to insure that too much polishing (metal removal)
has not taken place. We recommend that bombs with
significant imperfection of this nature be serviced at
Parr.
CAUTION!
Avoid prying elastomer seals (O-rings and
quad-rings) from seal grooves with metallic
tools.
The use of dental picks and other metallic tools to pry
the seals from their grooves is strongly discouraged.
These hard steel tools, if misused, can leave permanent
tool marks on the sealing surface, which are difficult
or impossible to remove. These blemishes are hidden
by the seal during normal use and as a result, are not
readily apparent as the cause of a leaking bomb.
Larger size seals (0.8” or 20 mm O.D.) typically used
to seal the bomb head can be extracted from its groove
using either of the following two methods:
Grasp the outer circumference of the seal with the 1.
thumb and forefinger and slide them together while
applying sufficient pressure on the seal to cause it to
pucker out of the groove. With the other hand, grab
the exposed, pinched section and pull the seal from
the groove.
Use a non-metallic object, such as the rounded 2.
corner of a plastic credit card, to simply pry the seal
from its groove.
Smaller diameter seals usually require a different
approach. A portion of the seal should be carefully
pulled, not pried, from the groove with a small pair of
pliers or a hemostat. The exposed portion of the seal
can then be cut, or pulled further to remove the seal.
The pliers or hemostat should never contact the sealing
surface, only the seal.
BOMB EXHAUST TROUBLESHOOTING
The bomb exhaust and sealing is controlled by move-
ment of the 966DD2 piston inside of the 1140DD
bomb seal/release cylinder. This assembly is mounted
on the bottom of the calorimeter air can. The piston is
driven to the up position (exhaust) by applying oxygen
at 30 atm to the 1/8 male connector (344VB). The
piston is driven down (bomb seal) by applying pressure
to the 376VB elbow. The application of the oxygen
pressure is controlled by the A1251DD three station
solenoid valves. There is a flow restrictor, part 527VB,
on the inlet side of this solenoid which limits the maxi-
mum flow rate of oxygen and in turn creates a gradual
increase in pressure at the 1140DD bomb seal/release
cylinder when the solenoid is turned on. Failure of the
bomb to exhaust in a timely fashion can have more than
one cause. Certain causes can be eliminated systemati-
cally by checking the bomb exhaust diffuser, at the end
of the bomb exhaust line, for any restrictions in the six
small cross drilled holes. This fitting should be removed
from the tubing, inspected thoroughly and cleaned as
required.
Service the O-rings on the 966DD2 Piston
This process is described in the 500 test maintenance
section.
Confirm function of the 966DD2 piston
In order to reduce the amount of time it takes to du-
plicate and troubleshoot this type of situation, the I/O
diagnostics can be used to pressurize and exhaust the
bomb without having to run lengthy combustion or pre-
tests.