A university lab called today with a very similar question to one received earlier in the week. Again, they have a cryogenic liquid nitrogen cylinder that is set up for liquid only. This means that the only valve connections are “Liquid” and “Vent.” As was the case with a previous caller, they needed more pressure to push liquid out faster. Their proposed solution was to feed high pressure gas into the vent side forcing a high liquid discharge flow.
Did I have a problem with this? Yes.
And what was the problem? The problem is the fact that the high pressure gas cylinder was starting out with 1000psi or so of pressure and they were going to depend on manual control of a valve to regulate how much pressure they were putting into a DOT 4L-100 liquid cylinder fitted with a 150-175 psi burst disk and 22 psi relief. Granted, the relief should open if pressure gets too high and if the flow is not high enough from the relief then the burst disk would blow. The problem is that the combined outlet flow from both could possibly be too low to fully relieve the pressure coming in from the gas cylinder. This could ultimately result in the vessel exploding.
It was strongly suggested that they avoid this non-standard operation and instead secure a VGL with a pressure building circuit so that the vessel could be operated as designed. There is just no justification for generating a risk and possibly hurting someone by jury-rigging a container.
Did I have a problem with this? Yes.
And what was the problem? The problem is the fact that the high pressure gas cylinder was starting out with 1000psi or so of pressure and they were going to depend on manual control of a valve to regulate how much pressure they were putting into a DOT 4L-100 liquid cylinder fitted with a 150-175 psi burst disk and 22 psi relief. Granted, the relief should open if pressure gets too high and if the flow is not high enough from the relief then the burst disk would blow. The problem is that the combined outlet flow from both could possibly be too low to fully relieve the pressure coming in from the gas cylinder. This could ultimately result in the vessel exploding.
It was strongly suggested that they avoid this non-standard operation and instead secure a VGL with a pressure building circuit so that the vessel could be operated as designed. There is just no justification for generating a risk and possibly hurting someone by jury-rigging a container.
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