Parr Instrument 6400 - Manual (Page 70)

6400
Calorimeter Instruction Manual
10-1
TROUBLESHOOTING
Bomb Exhaust Troubleshooting
The bomb exhaust and sealing is controlled by movement 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 (bomb 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 maximum 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
systematically 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.
Confirm Correct Operation of the A1251DD Solenoid Valve
If the piston does not move, it is worthwhile at this point to confirm that both sections of
the A1251DD are working properly (Figure 15). For the location of the A1251DD
assembly, Figure 12.
Disconnect the 1/8 nylon pressure hose at the elbow connection nearest the back panel
by using a 7/16 wrench. Apply power to the unit and re-enter the I/O diagnostics. Turn
the exhaust output on. Oxygen should flow from the elbow connection on the A1251DD.
Turn the bomb exhaust output off and re-connect the nylon pressure hose. Disconnect
the 1/8 nylon pressure hose at the middle connection. Activating the bomb seal output
should produce a flow of oxygen at the elbow.
Turn off the bomb seal output and reconnect the nylon pressure hose. If neither
solenoid produces a flow of gas when activated and the O2 Fill key does not produce a
flow of gas, then, in all likelihood, the 527VB flow restrictor is plugged and should be
replaced. If only one of the solenoids sources gas when activated, then the problem
must be further diagnosed as either being electrical (I/O board, solenoid coil or external
wiring) vs. mechanical (in the valve) and dealt with in an appropriate manner.
If either solenoid sources gas when it is off (i.e. leaks) then replacement of the entire
A1251DD solenoid assembly is indicated. For reference purposes, the normal upward
thrust generated by the 966DD2 piston is 50 pounds. The downward thrust is 20
pounds. Far less than 20 pounds are required to move the piston in either direction
when the bomb is not pressurized.
Service the O-rings on the 966DD2 Piston
This process is described in the 500 test maintenance section.