Hi Hanno,
This has also happened to me. I caught it quickly, but it was scary. All
my systems, except for my pumped 800, have back-pressure regulators, so
hopefully they'd be safe. Anyway, in my case, the cause of the problem
was that the power cable of the lasers was loose. It connects to the
recovery compressor on the front where it says "laser sensor". The
connector screws on and it had become loose. The lasers just stopped
working - the first indication I had was that the bag was completely
deflated, which I had never seen.
Thanks a lot for the tip about the switch that controls the shutoff
pressure! I'm going to try it.
-Robert
On 8/15/23 08:32, jl167_at_gatech.edu wrote:
> Dear All,
> We recently observed a very dangerous vulnerability with our Cryomech
> (now Bluefors) Helium recovery system, which I feel is important to
> share here. This is the recovery system with a bag and the 350 PSI
> compressor.
> The fill level of the bag is controlled via two laser-switches. If the
> bag is near fully inflated the upper switch will start the compressor,
> which pumps the bag down to a lower level. Once the bag is almost
> empty the second (lower) laser-switch triggers a stop of the compressor.
> A failure in the lower laser switch (in our case the switch just had
> gone out of alignment) will not stop the compressor, the bag will
> completely deflate and the compressor will create a vacuum in the
> recovery line leading to the magnets. Obviously, this can cause a
> drastic increase in Helium-boiloff in a worse case scenario it can
> quench all magnets connected to the recovery system (let's just say we
> were lucky, all of our magnets are ok).
>
> In order to protect oneself from this vulnerability one should make
> sure that
> (1)
> backpressure regulators are installed and properly set at all magnets
>
> (2)
> the Cryomech compressor has a switch, which controls a shutoff
> pressure. For our system this switch was set to a negative pressure.
> This switch can be adjusted to 0 PSI. With the 0 PSI, the compressor
> will shut down prior to pulling a vacuum. We tested this by hooking a
> He-tank to our recovery line (magnets were disconnected).
> In order to reach the switch, the side panels of the compressor have
> to be removed and the switch has to be unbolted from the bottom-plate
> of the compressor, which is a bit of a hassle.
>
> Thank you to Davis and Abner from Cryomech for helping us to address
> this problem; they have no objections that I share this issue here.
> I suggested that they publish a service-bulletin describing the fix.
> In the meantime, I am happy to create a more detailed set of
> instructions to check and potentially change the setting of this switch.
>
> Kind Regards,
>
> Hanno
>
--
-----------------------------------------------
Robert Peterson, Ph.D.
Facility Manager - NMR Technology Center
UCLA-DOE Institute for Genomics and Proteomics
UCLA Dept. of Chemistry and Biochemistry
phone: (310)825-1816
fax: (310)825-0982
peterson_at_mbi.ucla.edu
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Received on Tue Aug 15 2023 - 11:46:19 MST