Thanks very much, Hanno. Ours is a Cryomech system as well and it has
been performing smoothly in every other respect. But, we exactly did
encounter this kind of disruptions a few times in the two plus years of
operation. Last Friday evening, I got the automated call from the BMPC of
my pumped 800 magnet due to the lower pressure downstream and fortunately
one of my colleagues was nearby to make sure that the compressor was shut
off on time.
We were suspecting originally the reflective piece on the wall but we are
currently talking about replacing the lower laser sensor. Thank you for
your timely tip about the setting for shutoff pressure, in the meantime.
Best regards
Rajan
On Tue, Aug 15, 2023 at 8:37 AM <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
>
>
>
--
____________________________________
Rajan K Paranji, Ph.D.NMR Facility Manager
*Department of Chemistry**Room 65, Bagley Hall*
University of WashingtonSeattle, WA 98195
phone : 206 685 2581 fax: 206 685 8665email: rajanp_at_uw.edu
____________________________________________________________________
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Received on Tue Aug 15 2023 - 11:21:40 MST