Parr Instrument 1356 - Manual (Page 11)

11
Spiking Calculations
[{EE x T(temp rise)}-e1-e2-e3-[mass(oil) x Heat Combustion(oil)]/sample m grams
2. 1108 Oxygen Bomb Maintenance and Safety Instructions
Oxygen Bomb Maintenance
Under normal usage Parr oxygen bombs will give long service if handled with reasonable
care. However, the user must remember that these bombs are continually subjected to
high temperatures and pressures which apply heavy stresses to the sealing mechanism.
The mechanical condition of the bomb must therefore be watched carefully and any parts
that show signs of weakness or deterioration should be replaced before they fail.
Otherwise, a serious accident may occur.
Do not fire the bomb if gas bubbles are observed anywhere indicating a possible gas
leak. Disassemble the parts and install new seals immediately.
Keep the 397A compression nut on the valve needle tightened firmly at all times.
Frequent tightening is important. This nut, if slightly loose, may allow a leak to develop
during the rapid pressure rise upon ignition. This type of leak may not be detectable
before firing; but if it develops, the hot gases can ignite the 20VB valve seat and burn
through the head.
Do not use extreme force when closing the needle valve. A moderate but firm turn on
the valve knob should be sufficient to stop all gas flow. Excessive needle pressure will
deform and possibly close the gas passage. If this happens, unscrew the valve body and
replace the 20VB valve seat. Accumulated salt deposits may also clog the gas passage,
making it difficult to release pressure at the end of a run. To avoid this, clean the passage
through the valve needle and deflector nut with a small drill.
Firings 500
All O-rings and 20VB valve seats should be replaced after 500 firings for the standard
1108 Oxygen Bomb and 250 firings for the 1108CL Oxygen Bomb for chlorine content
of samples is 25% or greater.
A Parr 475A service clamp offers a convenient means for clamping the bomb head firmly
in a vise without damaging the head when replacing any of the bomb head parts.
When replacing the 230A head gasket, stretch the new O-ring and let it snap into place to
be sure that it moves freely in its groove and is not twisted.
To replace the valve seat, unscrew the 397A compression nut; remove the valve stem and
the old seat, and disassemble all of the parts. Drop a new 20VB valve seat into the body
and push it down into place. Slide a 7VBCM Monel washer, two 238A O-rings and
the 378A packing cup onto the valve needle with the needle pointed upward; then adjust
the parts on the needle so that the tip of the needle is flush with or slightly recessed into
the bottom of the packing cup. Insert this assembly into the 369A outlet valve body and
press it firmly against the valve seat by tightening and 397A compression nut to 100
inch-pounds of torque.
The 238A sealing ring in the insulated electrode should be replaced with the same
frequency as the 20VB valve seat. Also keep the 411A terminal nut tight at all times. As