Cryocooler power failure due to stepping on the power cord

written by Eric Dufresne
MHATT-CAT
June 1, 2004
(www.mhatt.aps.anl.gov/Sectors/Sector7/Operations/FY04/run3/Power-cord)

A beamline failure occured on 5/24 following a cryocooler failure. One of our 
staff member stepped on the cryocooler power cord and the cord came loose. The 
crycooler stopped, the liquid N2 after some time boiled off and the closed loop
vented because the burst disk broke.  On Monday night, ED established that the 
cryocooler burst disk was broken, and planned the repair for Tuesday morning.
Dan Burke and Glen Moonier replaced the burst disk in the morning and several
upgrades were performed to the cryocooler set up to prevent this from happening
again:

1) cable rerouting to prevent someone from stepping on the power cable. This 
was the root cause of the problem. This was the second time this happened. The
first time ED was able to catch the system before the LN2 boiled off. After 
the first incident, the power cord clamp was bent and one of the two forks did
not hold the cord properly anymore. It was thus probably easier to loosen it.

2) Proper anchoring and repair of the power cable connector forks. Cable ties 
now secure the forks from releasing the cord.

3)A new 50 PSI relief valve that should vent the closed loop if the pressure
goes too high. This will prevent the burst disk to break.

4) We would like the O2 monitor to be displaced so that no access to the 
back of the cryocooler is required by people other than S7 staff.

On Tuesday night, the system was returned to operation and Wednesday morning the
crystal was cooled to LN2 temperature. The beamline lost 4 shifts due to this 
incident.

• 
  The back of the cryocooler power supply. Note the black power cable. This cable is held to the crycocooler by a clamp which freed itself up when someone stepped on the cable. To prevent this from happening, we have rerouted the cables behind the unit and strained reliefed them. The clamp securing the power cord to the unit was also repaired to ensure both forks were attached to the power receptacle.


• 
  Without power, the crycooler pump warmed up, the liquid nitrogen boiled and the burst disk exploded to release the N2 gas. This picture shows the busted burst disk.


• 
  To prevent this from happening again, a new 50 PSI relief valve was added to the V6 HP vent valve before the ball valve. In this fashion, whether V6 is opened or closed, the 50 PSI valve should open before the burst disk explodes at 150 PSI.


• 
  Note that with the new O2 monitor next to 7ID-A, several people may need access to the area behind the cryocooler. This is how the cable clamp was broken in the first place: someone tripped on it. I've asked Lisa Gades to request the O2 monitor to be moved away from the corner to the area written on the wall.


• 
  The O2 monitor to be moved away from the corner to the area written on the wall in June.