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 t
o 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
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Received on Tue Aug 15 2023 - 08:37:06 MST