UC Irvine N2 filling procedure (Oxford 800 MHz)

From NMR Wiki

Jump to: navigation, search
Liquid N2 transfer line.
Liquid N2 transfer line.
Fig. 2 Liquid N2 port. Normal view.
Fig. 2 Liquid N2 port. Normal view.
Fig. 3 Liquid N2 port prepared for connecting the transfer line.
Fig. 3 Liquid N2 port prepared for connecting the transfer line.
Liquid N2 fill in progress. In this picture transfer line nozzle is not wrapped (with a towel) as it should have been. Covering up cold metal parts prevents formation of ice plug over the securing nut and saves thaw time.
Liquid N2 fill in progress. In this picture transfer line nozzle is not wrapped (with a towel) as it should have been. Covering up cold metal parts prevents formation of ice plug over the securing nut and saves thaw time.
filling magnet with liquid N2 and liquid He simultaneously
filling magnet with liquid N2 and liquid He simultaneously

Duration: ~1.5-2 hrs (starting at 25 % level) + 0.5-1 hr to thaw-off and remove the transfer line.

Equipment

  • full 200 L liquid nitrogen tank on wheels, non-magnetic, 22psi
  • liquid nitrogen transfer line (Fig. 1)
  • non-magnetic wrench to connect transfer line
  • two plastic tubings to fit exhaust ports
  • aluminum stair-case ladder on wheels

Procedure

  • write down level of liquid nitrogen, nitrogen and He boil-off rates
  • lower the magnet on the antivibration legs by letting out commressed air supporting the magnet
  • prepare N2 port on the magnet as shown on figure 3
  • bring the tank (22 psi, 200L on wheels) within ~3-4 m of the magnet
  • connect transfer line to the tank (using non-magnetic wrench)
  • open output valve on the tank to cool the transfer line.
  • as output nozzle of the liquid N2 line cools, continuously keep wiping off any condensation/frost with towel or thick glove
  • once liquid nitrogen starts sprouting from the nozzle, close the valve
  • remove remaining frost from outer surface of the nozzle
  • insert nozzle into the magnet N2 inlet port; note the depth of insertion, do not let the nozzle reach maximum depth; if you feel transfer line cannot be driven any lower - pull it upwards an inch or so.
  • hand-tighten the nut securing transfer line to the magnet N2 inlet port, while not attempting to support the weight of the transfer line; the latter measure helps prevent leaks of liquid N2 during the fill
  • open the output valve on tank, open pressure builder valve
  • wrap open metal parts of the transfer line with cloth towels - especially the nozzle as it helps prevent accumulation of frost and speeds up thaw-off in the end
  • watch the increase of liquid nitrogen level on the monitor screen - it should be 0.5-1.0 %/min
  • close tank outlet valve once liquid starts sprouting from the exhaust tubings
  • let the nozzle thaw, then remove it, re-attach N2 exhaust pipe and emergency release valve
  • restore pressure in the antivibration legs
Personal tools