View Full Version : Helium

Mike Hopkins
13-12-2001, 03:26 AM
I had the pleasure some time back to work on a system that chilled water to cool the condenser and compressor on a helium refrigeration system. Basic layout was a Neslab water bath chiller that had a heat exchanger from the helium unit in the chilled water tank. The helium unit had a pump that circulated water through it's condenser and water jacket around the compressor.
Compressor was special breed DC winding. The compressor served the refrigeration system that cooled something in a magnetic resonance imaging machine. Not sure if it cooled the chamber or electronics associated with the MRI. I do know that the helium charge was a static charge much like what you would do with low stage on a cascade. My guess is they used helium due to possibility of a leak with a human being in the chamber.
They would maybe just talk funny for a while! But the helium line did wear a hole and lost the charge one time. Cost around 6K US
for the GE tech to come out and repair. We never fooled much with the helium unit, just the Neslab cooler. When the MRI was powered up though you had to watch your toolbag cause it would tend to be attracted to the magnetic force. Also steel toe boots make for interesting experience!
Mike Hopkins

750 Valve
13-12-2001, 09:31 AM
It's amazing how diverse our industry is, I love jobs like that, something different. That is why I wouldn't do any other job for quids!

13-12-2001, 10:43 PM
I couldn't agree more 750.

A few years back one of our guys had great fun working out why a unit only leaked refrigerant at certain times. The equipment was a reclaim machine.

Problem was the refrigerant was R13 and the machine was used for reclaiming Halon from fire extinguishers. It turned out that there was a leak between the two sides and depending on the pressures, temperatures and if it was runnng or a weekend the pressure could go up or down.

Although you acknowledge that there is going to be a pressure change with temperature it can be a bit confusing when the pressue goes up with a fall in temperature.

But he enjoyed the challenge.

26-04-2002, 01:40 AM
I have also been performing maintenance on these Magnetic Resonance Imaging Machines mounted on trailers. They seem to be three stage machines. The onboard A/C system chills glycol to approximately 17 C. This in turn cools a condenser in the chiller unit under the trailer, which I have never opened. It has a small scroll compressor which is visible through the vent openings in the cabinet. I believe that this system cools the helium condenser which has a slow speed, one cylinder compressor that makes a distinctive "chirping" sound which is audible in the scanning area. Have you worked on this chiller? If the systems shut down, the helium continues to evaporate and is lost. The MRI continues to function, but the helium gets used up. It is very costly to refill. Most of the repairs I have performed have been due to the trailer pounding over rough roads. I have worked on four different trailers that rotate to different hospitals in the area and they are all of completely different designs.