Problems 



Two minor problems occurred in our tests. An ice block in one probe limited the 

 flow of C0 2 through that row of probes instead of at the valve. A blocked probe can be 

 detected in two ways. The relief valve next to the throttle will open and start blow- 

 ing dry ice, or frost will melt from the probe caps ahead of the restriction. The flow 

 of C0 2 to the blocked row of probes was turned off and the probes emptied of C0 2 by 

 holding the relief valves open. The cap was removed from the suspected probe and the 

 ice blockage removed. The cap was then replaced and the flow of C0 2 restarted. 



The second problem was an apparent restriction in the C0 2 supply hose indicating 

 empty supply tanks. This was easily checked by observing the pressure gage at both 

 ends of the hose. Both should register about the same pressure with the gage closest 

 to the sample recording a slightly lower temperature. The C0 2 pressure during the 

 test ranged from 500 to 700 psig (0.689 MPa) depending on ambient air temperature. 



Shut Down Procedure 



Six hundred pounds (272 kg) of C0 2 liquid provided 70 to 80 minutes of operation. 

 When the C0 2 tanks became empty, there was a drop in pressure at both line gages. The 

 substrate temperature at the probes began to slowly increase regardless of throttle 

 valve setting. The system was then shut down and the various hoses and tubing dis- 

 connected and removed. The water shield was removed, a chain sling connected to the 

 four ice anchors, and the sample lifted (fig. 12). It required 4,000 to 5,000 lb 

 (1 814 to 2 268 kg) of lift force to break the sample loose. The sample was lifted 

 high enough to get the boat under it and then it was lowered into the boat for trans- 

 port to the shore (fig. 13). Tank valves were closed and the main valve opened to 

 drain the lines prior to disassembling the equipment. 



Figure 12. --Frozen sample 

 being lifted. 



The sample can be kept frozen by placing dry ice on top and around the sample. 

 We had difficulties getting our egg pocket from the boat to the transporting trailer. 

 Therefore, the top of the redd became unfrozen prior to transport. We transported 

 the sample 145 miles to the lab and without the addition of ice, most of the redd 

 remained frozen in the insulated carrying box upon arrival and even until the next 

 morning when it was dissected. Dry ice would need to be added upon lifting the sample 

 to get it to the place of analysis in its original condition. 



15 



