A while back I was forced to buy a new air compressor because the tank of my old one was frightfully, dangerously, corroded and unsafe. (that's not on me; I'd bought it well-used and put years more use on it before I realized the previous owner probably never drained it.)
Since I also had a shiny new blast cabinet, and a bit of inheritance, I figured I'd better buy a big one. I didn't need a huge tank, but all compressors which have enough continuous CFM to drive my blast cabinet come with very large tanks. To be fair, a big tank extends the life of the compressor pump.
So I wound up with a 5HP / 60gal unit, delivering 21CFM @ 40PSI, 18CFM @ 90PSI, 16CFM @ 35PSI:
Since then, a lot of stuff has happened to keep me from finishing the compressor installation, including a difficult holiday period, injuries, a death in the family, recovering from planned surgeries, and so on and so forth.
Money has been tight, too. So there hasn't been a lot going on in my shop about which to blog... until now.
When I was researching which compressor to buy, a found a forum discussion concerning complaints about the lifetime of the pressure switch on Ingersoll-Rand compressors being sold at the Lowes Hardware chain stores. [note; Lowes are not longer selling them]
Notes were compared, and it seems that the switches on the units being sold in the chain store were lighter-duty units compared to the same rating and size compressor purchased through an I-R dealer. Everything else- tank, motor, pump, pulleys, was the same.
Hmmm. You wouldn't think there would be that much margin in a presure switch. But consider the target market for this size unit: small business to medium-large business. You can't buy air compressor pressure switches at most hardware stores. Ingersoll-Rand has a service rep or sales desk in every major city in America. Small Business Man will most likely just call an expert to fix it. So... kinda shitty, but it's a savage business jungle out there in the international market, it's still an American company assembling their stuff in America, and most importantly, the tank is made here.
So I bought one from Lowes anyway, and I planned to hack the switch with Quench-Arc type devices to prolong the life of the switch contacts.
When I first got the unit and tested it, I looked at the switch contacts to see how beefy they were. They're... not, especially. Considering that this compressor sports a 5HP motor, I estimate the inrush current at around 135A.
The contact bars are about 0.25" wide, and at least two distinct divots in the contacts are visible in the photo.
Call me crazy but that seems like a lot of pitting for two or five starts to date. But then, those contacts do seem a bit small for 135A of inrush (22A FLA).
I could gin up some fancy soft-start mechanism, which would incidentally reduce the amount of intereference / voltage sag this thing induces in the shop, garage and my wife's office, thus playing nicer with computers and other more refined electronics.
But that would take work. And besides, the feed to the subpanel is enormous, the wire to the compressor is, while not oversized, at least plenty adequate, and it's an excellent quality capacitor-start, capacitor-run motor.
Incidentally, it's a "U.S. Motors" brand motor, which used to be a reputable brand, but it's actually owned by Nidec Motors these days, and they are made in Mexico. That said, they are still considered to be a well-made, conservatively-rated, meets-lots-of-specs from various standards organizations, and in general should give a long service life with very little trouble.
<--- So I installed this; a pair of Quencharc supressors in a separate metal box (in case they someday explode) screwed to the switch housing.
Flying leads connect through a gromet sealed with hot glue - again, this is in case of capacitor or resistor failure, as these are connected to a 240V / 30A circuit.
I fully expect this to prevent me from having to replace the pressure switch (it's usually the swich contacts, not the pressure mechanism, that fails) in my lifetime. In general, this appears to be a rugged, well-made unit with name-brand components and naturally a corrosion-resistant, certified and tested tank.
So why the pedestrian-looking pressure switch?
The next step is to run some 10 AWG nmc through the shop / garage rafters, but as I am recovering from all sorts of accidents and injuries new and old right now, I might take it easy for the rest of today.
"Slow and steady wins the race" said the tortoise, as well as a good friend of mine on many, many occasions.
PS: the window in the box is there specifically so I can see if (when) the Quench-Arcs let go... why would I expect them to fail? Are they not reliable? Are they not good products? Oh they are, they are... but I may not have used exactly the correct units for a motor this large... I might have used some that I happened to have lying around, specified for a lower power contacts... the voltage is fine, but I am kinda curious A) how good a job they'll do and B) how long they will last in this duty.
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