compressed air

[fishnjim]

If you run a compressor for your car work, I just went through 6 weeks of repair issues with mine.   It all started when I noticed it was running too much and tried to address that but ended being another issue, cracked tank. 
If yours is using more juice than normal, check the tank and all the connections.   I suspect its been bad for a while I just didn't notice.   I was a design/weld fault.  Of course they don't make them like that any more and mine was just a few months out of warranty.
It's very quiet now and rarely kicks on when it not in use, plus I have it timed to shut off at night.
I rely on it so much when I was trying to figure out how I was going to change out the tank by myself, I realized I couldn't use my air tools...Of course, I had low tires too during the down time.

[signart]

Could you not weld up the crack?

I had a head gasket failure on my 80 gal. compressor after almost 20 years. Well, it may have been failing for the last couple years, but I discovered where my pressure loss was and repaired it with a homemade gasket after 20 yrs. of ownership. Works good now.

[TJ Hopland]

You don't want to repair the tank itself.  A crack in the tank is some sort of a flaw and welding it usually isn't addressing the flaw that caused the crack.  Lots of videos on YT of 'regular' diy sized tanks exploding and causing lots of collateral damage in the process.  Hacking things on the pump doesn't have the same safety risks because its not a pressure vessel.

I usually remember to turn mine off when I'm not using it but recently noticed it was often empty when I did want to use it.  Being an 80 gallon it takes some time to fill from empty just to pump up a tire.  I found 2 issues.  The biggest one was my drain valve had crap in it and was apparently leaking.  I didn't like it anyway so I replaced it with a ball valve and some pipe nipples.  That helped a lot but it would still leak down after a week or so so I started turning off the valve on the outlet.  I must have a slow leak in a hose fitting.   

[bcroe]

Air systems are practically never leak proof, leaving
them on 24/7 means a lot of run time replacing leaked
air.  I turn mine off, but filling a big tank takes
quite a while when I need it.  About the time my 20
gallon tank rusted through, I realized there was no
need for a big tank here.  I rebuilt it onto a new 8
gallon tank, charges pretty fast.  Bruce Roe

[fishnjim]

I've had a 80 gallon compressor running since the '90s, 24/7.  My old one 5 HP, lasted well over 20 years.  Even had one motor rebuild.  It was vertical.  Very loud.  I moved three times with it.
When I got the replacement it was sized for my bigger blast cabinet.  The old one you could only blast so long then had to stop & wait on the compressor to build back up.   This one is a 10HP compressor run by a 7.5 HP slow speed motor.   It draws less startup amps, so I didn't have to replace all my 5 HP electrical feed., <50A.  Also, nice and quiet.
A regular 7.5 HP recip compressor makes too much noise to run inside. The so called quiets ones or the same noisy ones under a noise absorbing cover and cost more. This was an early model and they buy the catalog tanks from general tank manufacturers.   They don't make centrifugals this small.
I opted for a horizontal, it's not top heavy, so easy for me to install and fits under the stairwell.
I'm a Chem E, so I've been doing code pressure vessels in all services for decades, and why I didn't try repairs.  It's a code tank, 250psig.   A crack from fatigue, has a leading edge you can't see without x-ray or destructive microscopic analysis.  Almost impossible to fix a crack like that.  You can patch over it and hermetic seal, but has to be recertified and up to the inspector's discretion if it passes, and cost associated.  These tanks are under $1000, cost that much to recertify.  Manufacturer changed the design from welded feet to saddles, which distributes the stresses better even with isolation pads.  I don't expect many issues and it's running a lot less since the new tank is up.
My point was if your compress runs a lot, check the tank too, don't assume it's good. 
I'm putting the replacement filter in now.  The old one leaked after removing.
But good point: do not weld on a pressure vessel unless you're code certified and have the tank retested before returning to service.  Not really cost effective on this scale.