I'm with junquecol on this one, if your existing compressor is still in good condition, has been reasonably well maintained, and still meets your needs then you are probably Ok. If it has lasted 30 years without a rebuild it is most likely an oilled compressor (don't forget to change the oil annually). My only concern would be the 30 year old tank -- it may be time to have it professionally hydrotested unless you know for certain it has been drained at the end of each day for all 30 years. Although most tanks fail with just pinhole leaks (never try to plug such a tank -- they are at end of life!) a small percentage fail catastrophically without warning and are equivalent to setting off a small stick of TNT in your shop -- and the larger and higher pressure the tank, the more spectacular (and occassionally lethal) the results. Hydrotesting is cheap insurance by comparison. The other option, of course, is to simply replace with a new tank and decommission the old (drill one or more large holes through it to discourage others from reusing).
If your compressor is no longer meeting your needs then you are probably looking for something along the lines of 1.5-2HP with a 20-30gal tank. Such a compressor will not be able to fulfill the needs of a typical HVLP gun continuously, but the tank capacity (coupled with pump) should be sufficient for spraying flutes and other small items. Just realize that most of the middle-of-the-road quality and above compressors are going to cost $300-400 new in this size range.
You can buy used -- a good quality cast-iron pump that has been properly maintained has a long service life. However, you must again beware that the previous owner may not have taken good care of their tank so a professional hydrotesting is suggested if the compressor is more than a few years old. Short of getting very lucky as Ben325e did, your price range pretty much limits you to used compressors in this range if you want to go larger than 1.5-2HP, 20-30gal.
The features you most want to look for:
- Cast Iron cylinders (solid cast-iron is better than aluminum with CI-sleave which is better than all aluminum)
- Cast Iron or Aluminum heads (some will say CI only, but aluminum dissipates heat more effectively)
- Oil lubricated (either splash lubricated or pressurized -- both are well suited to shop use).
- Belt driven with intact belt guard
- ASME certified tank with a functioning pressure relief valve whose pop-off pressure is equal to or less than that of the tank's certified working pressure). Especially check this if buying used.
- If you want sustained long-duration operation of HVLP and other hungry accessories you will want atleast 10 SCFM @ 90PSI (3-5HP, 220V) and a 30-80gal tank, otherwise look for something in the 4.2-6 SCFM @90PSI with a 20-30gal tank (1.5-2HP, 120V) which will allow for short duration use of hungry accessories.
- Although 2-stage compressors are nice, single-stage are more than adequate for shop use. However, all things considered, a two-stage unit (with an intercooler) with its maximum pressure dialed down to 135-150PSI will produce cooler air than a comparable single-stage unit.
For Spraying: Use either a coalescing filter coupled with dessicant filter or a long metal air line (min 20ft, more is better) to pre-cool the warm air with a coalescing filter at the end of that line. Elevate the line so that water in the line runs back towards the tank for easy single-point draining and let each location that you tap into the line for air draw off the top of this line with a 180deg loop before the tap's drop -- this keeps most of the liquid water in the main distribution line and out of your coalescing filter. If you've been using your existing compressor for spraying then water contamination is something you have likely already addressed.
If you opt for a large compressor tank, set it up so that you can easily drain it. Most come from the factory with a petcock valve located dead-center of the bottom of the tank for complete draining. Some manufacturers will add an elbow and a ball valve to extend this drain to a more convenient location. If yours does not come equipped as such, add your own elbow and ball valve to make draining easier.
For my new compressor, I will be installing a solenoid valve (with 240V coil) so that all I need to do is press a pushbutton to drain my tank since getting down to floor level/bending over is not so easy for me. I may even decide, in the future, to install a programmable timer to do this for me.
I'm sure others can expand upon this even more.
But yes, I know of it as the infamous tank drain with the melting unloader tube.
