Guidelines for care & Use of Dry Solvent Stills [Example]

* Do not grease or oil the regulator thread of a cylinder valve. Oil on a gas cylinder thread will
soon be under very high pressure. If the gas reacts at all with organic material, this could lead to an
explosion. This is especially true for Oxygen gas cylinders. Teflon tape can be used on the outlet side of
the regulator, but not on the primary fitting connection between the regulator and the cylinder.
* Never use a cylinder without an attached regulator.
* Add flashback arresters to oxygen and hydrogen cylinders when used for torches for
glassblowing or glass working. Flashback occurs when flames actually traverse through the gas line back to
the cylinder outlet.
* Do not completely empty a cylinder before returning it to the loading dock area. Slight positive
pressure (between say 5 and 15 psi) will keep atmospheric oxygen from contaminating the cylinder
contents, so that the cylinder can be safely refilled by the gas cylinder supplier.
* Do not over-tighten a hand-valve on a gas cylinder. If hand tightening will not completely close
the valve, call the gas cylinder company for removal after taking it at once to the loading dock.
* Do not over-tighten the hand-valve on the liquid nitrogen tank in the loading dock area when
you are through dispensing liquid nitrogen. The pipe wrench attached to the wall is for opening frozen
valves, not for closing the valve. The slightest extra pressure on the valve when closing may damage it.
Over-tightening the valve will crush the Teflon seals inside the valve and when this happens, the valve has
to be rebuilt.
We have placed a pipe wrench near the liquid nitrogen tank, loading dock area, for use in
loosening frozen valves, when opening them. Some people are using the wrench for closing the valve
afterward, which naturally makes it harder for the next person to open it again. PLEASE DON’T OVER-
TIGHTEN THE VALVE WHEN CLOSING IT, or we will remove the wrench. There is no need for
anything other than hand-tightening to shut off the valve. Occasionally, this hand valve may freeze in the
open position, while you are dispensing liquid nitrogen. This happens especially when you turn it wide
open and take a great deal of liquid from the tank. Water vapor in the air, specially on a rainy day, will
actually freeze in the valve and make it hard to close. In this case, it may be justifiable to use the pipe
wrench to just “crack” or “break” the frozen hand valve, without tightening it shut, and then closing it the
rest of the way with your hand (in an absolute emergency, you could even pour hot water over the hand
valve to thaw it).
The simplest thing to do, while wearing thick insulation gloves, is to gently turn the valve back and
forth when you open it up all the way on - that way, it can’t freeze.
Sometimes, the safety valve (connected to the pressure gauge, on the opposite side of the tank from
the dispensing hand-valve) begins releasing high-pressure vapor, with a hissing sound. The safety valve
opens when too much pressure builds up above the layer of liquid gas inside the tank. This happens usually
just after the tank has been delivered since the temperature outside is a lot higher than inside the building
and movement of the tank during transportation has caused buildup of pressure from rapid evaporation.
When the pressure in the tank goes above 22 pounds per square inch (psi), the safety valve automatically
opens.
Sometimes this valve will frost over and freeze, again because of water moisture in the air freezing
upon contact with liquid nitrogen. When this happens, open the vent valve (the hand valve connected to the
safety valve with the pressure gauge attached) and bleed off a little pressure until the gauge reads about 18
psi, at which point the emergency venting from the safety valve will stop. Alternately, you could
actually pour hot water over the safety valve and thaw it. National Welders personnel occasionally do this.
You can get the water from the loading dock sink. The lab manager will leave small buckets or pans under
the sink for this purpose.
Perhaps you can pour water from one bucket while catching it as it falls from the valve into another
smaller bucket.
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