S

seaplaner

Member
Here's a basic question for the experienced and learned power tool users.

I have an oilless Craftsman 33 gal compressor, works great, (noisy as a buzz saw, though). My problem is that it's a pain to discharge the pressure each evening when I know I'll be using it again the next morning.

So, is there any major harm to the compressor in leaving it partially charged for, say, a weekend? (Followed by draining, etc.)

I know that high pressure condenses water that can cause corrosion if left in the tank, but does a day or two of water, here and there, make a difference?

One other thing, this unit is secure, in a garage, and the kids are grown and gone.

Thanks much - - - this is a great site
 
I have the same compressor.

Leaving it charged is fine. The water that's in there will be there whether you charge the tank or not (i.e., it's there until you drain it).

Replace the crappy drain valve with a 90 degree elbow, a 4-5" straight length of galvanized pipe, and a ball valve. It will make draining (or rather, 'blowing the water out') much easier. Costs maybe 5 bucks at HD or Lowes, plumbing section. Use teflon tape.

Blow out the water after the air in the tank has cooled (it heats up when it's compressed and the water condenses out as it cools).
 
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seaplaner said:
Here's a basic question for the experienced and learned power tool users.

I have an oilless Craftsman 33 gal compressor, works great, (noisy as a buzz saw, though). My problem is that it's a pain to discharge the pressure each evening when I know I'll be using it again the next morning.

So, is there any major harm to the compressor in leaving it partially charged for, say, a weekend? (Followed by draining, etc.)

I know that high pressure condenses water that can cause corrosion if left in the tank, but does a day or two of water, here and there, make a difference?

One other thing, this unit is secure, in a garage, and the kids are grown and gone.

Thanks much - - - this is a great site
Click to expand...
No harm in leaving it fully charged. Almost all the condensation occurs very shortly after a compression cycle, so just drain the water before you go on a trip and no worries.
I don't know of any machine shops that discharge their air tanks when they go away for the weekend.

Fatigue failure is not REALLY an issue in these but if you were counting loading cycles (goes into the fatigue life calculation) you certainly get more and larger cycles by depressurizing the tanks than by leaving them full. The static pressure on the tank is inconsequential.

-mike
 
I have the same compressor. I leave it full pressed up all the time. I think the confusion comes from the instructions supplied with the compressor. It says "Drain tank after each use". I believe the are telling you to drain the water from the tank, not to blowdown the whole tank.
 
Leave it compressed, but periodically discharge the water.
For the noise you mention (mine is oil free and noisy, too), you can make an insulated box. I built one in MDF and particle board on 2x4 frame, lined it with thick rubber mats (good sound absorber), then dense carpet pad (some absorption and reflection attentuation), then finally carpet (mainly reflected sound). Lid is very dense, and seals with two rubber seals. Access doors and vent passages were added - now the beast is tamed to a dull hum. I estimate at least 20dB attentuation, though haven't measured. It gets warm inside, and I will do temp measurements and consider a quiet fart fan as Dan Checkoway did ( http://www.rvproject.com ). But, then again, if it burns up, I will have an excuse to get an oiled quiter compressor. Some pics in my website, first entry.
Carl
http://mykitlog.com/cnpeters
 
I agree with all of the above. HOWEVER, turn the compressor off when you won't be around! No personal experience, but have heard that if a hose or fitting blows, the compressor will fire up and run until it burns your shop down.
 
I have a 26 Gal 5 HP oiled comp. (which is also very loud) and leave it on and full ALL the time. Sometimes it wakes me up in the middle of the night (its in my basement) but I just put my pillow over my head and fall back asleep.
 
drain the compressor

In a previous life, I was a National Guard company commander. My unit was an engineer company. We had the normal 2 1/2 ton trucks as well as M920 tractors that we used to pull the lowboy trailers with the D-8 Dozers. One of the biggest maintenance problems we had was getting the young soldiers to drain the tanks for the air brakes. If they did not, the brake valves would get rust particles in them and lock the brakes.

It may not be applicable to the air compressors we use, but I drain the tank after each use and leave the valve open until the next use. That procedure eliminated the brake problem on our trucks, so I suppose it will help with these tools.

I agree with the post suggesting adding a 90 degree street el with a short section of pipe to get the drain valve in a convenient location.
 
Shut off valve

I leave the compressor fully charged but have a ball valve on the outlet. When finished for the day I would close the ball valve and shut off the power at the pressure switch. Just be sure to drain the condensation once in a while...
 
If you really wanted to get anal on this, you could add a valve immediately at the tank drain, then a length of pipe to create a trap, and then another valve. The trap could be on a 90 degree angle as proposed. Leave the top valve open and the bottom valve closed. When you want to drain the tank, close the top valve and open the bottom valve. You could drain the tank without losing the compressed air in it. After draining, close the bottom valve and open the top one again. It would also keep water out of the tank itself.
 
sf3543 said:
If you really wanted to get anal on this, you could add a valve immediately at the tank drain, then a length of pipe to create a trap, and then another valve. The trap could be on a 90 degree angle as proposed. Leave the top valve open and the bottom valve closed. When you want to drain the tank, close the top valve and open the bottom valve. You could drain the tank without losing the compressed air in it. After draining, close the bottom valve and open the top one again. It would also keep water out of the tank itself.
Click to expand...
I like this idea! I have a 60 gal 7HP shop compressor with a drain valve on the bottom of the tank. If I set the tank on the shop floor there is no way to get to the very cheap drain valve. My solution has been to set the entire compressor up on cinder blocks. this has given me about 10 or 12 inches of clearance to get to the valve but my drain valve has gotten stripped so I cannot open it. I think I will drain the air and replace this valve with a setup that is described above. Having an easy way to drain the tank should definetly allow me to keep water from accumulating in the tank. Thanks for the suggestion.
 
Another idea... Harbor Freight sells pressure actuated automatic tank drains for $16 or so. Each time the compressor kicks on or off, the valve opens momentarily and water is supposedly blown out. I bought one because I often forget to drain the tank... the problem is, I keep forgetting to install the valve.
 
upright

please watch out when reaching under vetical compressors as i have often found black widows under mine :eek: i since installed a 12'' piece of pipe and a 90 deg ball valve for a drain. i still check for the widows and i often find them there.
 
N674P said:
I agree with all of the above. HOWEVER, turn the compressor off when you won't be around! No personal experience, but have heard that if a hose or fitting blows, the compressor will fire up and run until it burns your shop down.
Click to expand...

Ooh, that's bad. Does it not have some type of overheat protection? I never considered that & leave mine plugged in all the time.
 
Compressor issues

I have personally had a "charged/pressurized " compressor in my residence for 25 years and never had a bad experience. Its a good idea to have a ball valve at the discharge to shut-off airflow after working, as leaving a HOSE pressurized is a definate NO-NO. For those who enjoy silent (or at least fairly quiet) air tool use , I have these recomendations: I had a garage shop in a ranch type house in my early years, and mounted my 30 gal. craftsman compressor in the attic next to the gable vent, then ran 1" PVC down the wall to a QD for the hose. Worked pretty good, and muffled the sound greatly.In my current house, I have an attached hangar on the side, and have a basement garage in which I located an 80 gal/5hp compressor, then ran the PVC to the hangar...wala! cant even hear it! Many folks put the compressor outside in a small "outhouse" with the same results...dont worry about babying the compressor...they are workhorses that will go a lot longer than a measly RV project...
 
da di da du da di da du (tune from twilight zone)

RV7Factory said:
Another idea... Harbor Freight sells pressure actuated automatic tank drains for $16 or so. Each time the compressor kicks on or off, the valve opens momentarily and water is supposedly blown out. I bought one because I often forget to drain the tank... the problem is, I keep forgetting to install the valve.
Click to expand...
My gosh! My exact life!
I'll install it this weekend...I think.:eek:

-mike
 
The warning about the fire hazard is valid. When my IA showed up at a customer's place he found the compressor in the guy's hangar on fire as it ran with air blowing out a broken hose line. The customer was out back & had no idea his place was about to burn down. Compressor motors are designed for an intermittant duty cycle.
 
In the air tools section of Lowes, they have all the fittings needed for installing a ball valve shut-off.

On mine, where the discharge exits the pressure switch, I installed a ball valve. from there, I added a Tee. One end of the Tee goes directly to a air hose connection. the other end goes to the factory regulator. I run the air-drill, die grinder, cut-off tool, blow gun. . . from the direct connection. about the only thing I use the regulator for is the rivet gun. This saves from having to re-adjust the regulator each time I want to use a tool that is fond of high pressure. This set up might have set me back $10-15. Chump change for an airplane builder. Better yet, since you bought it at Lowes, tell the wife it is for the house and not airplane stuff.

BTW, I use two hoses of different color to keep them seperated. Word of warning: Take a walk on the $9 hose at Lowes. It is junk. Spend the extra for the industrial hose.
 
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I just leave the drain valve on mine very slightly open (you can just barely hear the hiss). When I'm done with a shop session I turn the compressor off, let it depressurize (it takes a while) and then the water drains. The valve is not open enough to cause the motor to come on very much - when I'm in the shop and not using air, it will kick on every 1.5 hours or so for a couple minutes.
 
One comment on leaving the compressor pressurized - iron + water + oxygen leads to rust. We all know that rust is created by a chemical reaction that oxidizes the iron. But, the higher the partial pressure of oxygen, the faster that chemical reaction will occur. If your compressor is pressurized to 105 psi, the rusting process will be occuring at 8 times the rate it would be if the compressor was unpressurized.

Compressor tanks to blow up. If you don't worry about what it might do to you, or your family, at least think about the potential damage to your aircraft.

Go to the RV List Archives, and search on "compressor & explosion" (without the quotes).
 
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Kevin Horton said:
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Compressor tanks to blow up. If you don't worry about what it might do to you, or your family, at least think about the potential damage to your aircraft.

Go to the RV List Archives, and search on "compressor & explosion" (without the quotes).
Click to expand...
A bit more help here please. I'm getting no hits searching on compressor & explosion.

Thanks,

-mike
 
It looks like the link I provided somehow made the RV-List Archive screw up its default selections. I have updated the link to one that works, I think. Confirm the following selections are made. If not, make them manually:

Select Archive to RV
Select one of the options for Message Order
Select one of the options for Output Method

Use compressor & explosion as the Search String.

I get 16 hits. The ones posted by Cy Galley are the most interesting ones.
 
Compressed air "do's and don'ts"

Just a few more thoughts about water in the compressed air tank...

1) I installed one of those automatic drain valves from H.F. (see the link above) and have been pleased with it. Every time the compressor comes on, a short burst of water and air comes out and scares the dog! :eek: But it does a great job of draining the water automatically. :) I was not happy with the plastic tubing they supplied for the control air and ended up replacing it with copper tubing.

2) I used to design industrial compressed air systems and will offer a few comments on the piping system...(of course if you use a hose, just skip to the end)
Imagine a rust particle or water drop travelling through the piping...and make it easy for the operator (you) to remove it. On vertical runs, install a tee at the bottom of the run with 6-12 inches of straight pipe running down beyond the tee and terminating with a ball valve. Then you can regularly blow down each vertical run with the ball valve. Also, be sure to install a filter and moisture trap close to the discharge of the compressor.

Make sure you use Schedule 40 pipe. Wall thickness of pipe is designed based on "schedules." The higher the schedule number, e.g., "80" or "160," the thicker the wall thickness. Don't use less than Schedule 40 for low pressure (<~300 psig) compressed air in 3/4" or smaller pipe. Schedule 80 and above are too expensive for our air systems but would provide adequate failure margins.

I won't get into talking about PVC pipe versus galvanized iron pipe versus copper tubing. If you do use PVC, absolutely make sure you use Schedule 40, but also be aware that many building codes do not allow any PVC for compressed gases, including air. If you're interested, check the archives of this forum or the RV-List, and you'll read a lot of reasons not to use PVC. When it fails, it produces shards as opposed to an iron pipe splitting. Some of the PVC for water piping sold at L's or The H.D. is not Schedule 40 but doesn't need to be for water. There's a lot of difference in the stored energy of air at 80 psig versus water at 80 psig. Just look at the specifications stamped on the side of the pipe; if it doesn't say "SCH 40" don't use it for air.

Somewhere years ago, I posted some photos of a ruptured compressed air tank. I don't remember now where I posted it, but if you see it or a similar one, it will get your attention.

Didn't mean for this to be so long...y'all be careful out there!
Don Hull, P.E.
 
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