lmh wrote:
The price of operating generators depends on whether you've got good compressed air already in the building. If you do, and it's of a sufficiently high pressure, you don't need a generator with built-in compressors, and it's the built-in compressors that fail. The rest of the generator will run with little maintenance for a long time. In fact it'll work even better if it's not attached to a hot and vibrating compressor.
If you've only got one instrument, there isn't much alternative, and all the generator manufacturers will fleece you for outrageous sums for replacement little compressors, which will fail depressingly regularly.
If you have the space, you can get a generator that uses an external compressor, and find your own compressor. If you are a larger lab or technical platform with multiple instruments and a higher demand for nitrogen, abandon the mini-generators and get a big system with a separate compressor. This is much more efficient and much less liable to failure; we're using a big generator capable of over 200L/min with a variable-speed screw compressor producing 10-bar air to feed it, and after some initial hitches that have been ironed out, it seems (looking around for wood to touch) to be pretty good. Although it looks alarming, it was also cost-effective to purchase, compared to a whole suite of little 30L/min generators. Of course when it fails, the entire lab stops...
This is what we switched to using. We have one of the Nitroflow units that run off the in house air system. We upgraded our building wide compressor to a huge dual stage one, but for just a single LCMS I would think that the smaller dual stage that can be found at Lowe's or similar hardware supplier would work well. Definitely get the dual stage, they cost a little more, but the increased capacity and pressure work well to prevent the compressor from running constantly. Dual stage will have oil in them, but that can be filtered out. We bought a system that reduces both oil and moisture in the system, it is a refrigerated condensing unit which gives us a constant supply of dry air for the building. I believe it is a Campbell Hausfeld unit, they are available at places you will find commercial grade air tools.
The biggest maintenance item it to remember to vent/drain the condensed moisture and oil from the bottom of the air compressor tank at least weekly, if not daily. This reduces the load on the initial filters and prolongs the life of the compressor. Oil changes in the compressor are usually requires twice a year. Otherwise the Nitroflow just need maintenance every few years if you keep it fed with clean air.
