Today we took a major step in improving patient care, in that we filled our new 900-gallon bulk tank for the first time. This poor tank had been neglected for several years for several years before we spotted it on the web; it had even been exposed to the elements since before our purchase in July, 2003. When we finally rescued it in November, 2005, it had rust spots, broken valves, and a large layer of dust.
Betty cost $12k when newly-used and can hold 900 gallons. She cost more than $3k for shipping and off-loading, and $2500 for repair and restoration. When new, these tanks go for $45k, not including shipping/off-loading. We like the price, and we like the added comfort of additional nitrogen on-site.
Hugh Hixon has been working hard to restore it to operational status. He changed the vacuum valve and modified the tank to accommodate nitrogen (originally configured for oxygen); and though we’re still working on plumbing the patient care bay for the patients, we decided it was time to partially fill the tank. I won’t comment on how we watched the wrong gauge, and filled nearly-full as opposed to part-way. …
We were only certain she was ready to fill, because Hugh had been testing — and fixing — the vacuum for many weeks. The first thing he did when it landed on the doorstep was apply a vacuum gauge and pump. Checking the vacuum pressure and the quality of the insulation were the quickest way to establish how much the refurbish would cost us.
At first, the vacuum gauge read more than we would have liked. We measured over 40 microns of gas pressure. Using a vacuum pump, we tested the insulation. That +40 micron measurement was not sustained as we continued to pump. Once the reading was below 1 micron, we stopped the pump and checked to see how the pressure responded. It rose, but with ever smaller slopes. If the vacuum has risen with consistent slope, we would have known that it was a leak, even if it was a slow leak. That this slope declined in steepness indicated a different problem.
The “getter”, a chemically-reactive lining in the vacuum that resembles kitty litter, has collected too much gas over the years and was releasing those bubbles into the vacuum. With each declining slope, we were seeing improvement in the filter these tanks have. Isolating the problem to this saturated filter was a good thing. It got better.
We waited to order a fill until the getter seemed appropriately out-gassed. And we decided to test fill.
Today’s fill was not without incident. Hugh and the nitrogen-supplier technician (an all-around useful cryotech guy) were both on hand to supervise the fill. One valve needed immediate replacing. That was accomplished with supplies on-hand. We also discovered a minor problem with a threaded valve. Replacing this valve requires we drain the tank, and we’ll be filling our portable dewars for some time to come. All nitrogen level maintenance will be done off the new tank until it’s low enough to replace the damaged valve.
Before people panic, this bulk storage tank has already been measured at better-than-industry standards of holding a vacuum of 4 microns for more than 24 hours. We’ll fix the valve, and more nitrogen will be available to the patients on demand.
All told, this project has cost us $12k, +$3k for shipping and off-loading, and $2500 for repair and restoration. Restoration is still on-going, insofar as it needs a fresh coat of paint. This will be done soon, and the patients will be moved in a week; bulk tank ready or not.