Air Compressor question - hot pipes?

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Old 08-31-09, 01:40 PM
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Air Compressor question - hot pipes?

I bought a 20 gallon 5hp devilbiss air compressor used from someone in the city. It's in great condition but unfortunately it tipped over in transit on the way home after purchasing it (and it tipped over hard, from braking for a red light).

I checked the belt over for misalignment or anything else strange, changed the oil that sort of thing. Everything seems to work fine..

When I run it, however, I have noticed the pipe that runs from the little engine block looking thing to the actual air tank gets extremely hot and fast. I'm talking from being ice cold from sitting there, by the time it reaches 60 PSI it's already too hot to touch. I have included a picture of an air compressor that looks like mine and circled the pipe in question.

pic here:
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The question is, is this normal? After we get this sorted out, I've got a few other questions I might tack on. Thanks in advance to you more experienced users.
 
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Old 08-31-09, 02:11 PM
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Completely normal...when air is compressed it gets hot, real hot. If everything else is working no problem.

btw..the engine block thing IS the compressor.
 
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Old 08-31-09, 08:07 PM
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Ok good, I was worried that upon the tipping over i may have damaged the check valve thus overworking the compressor to reach the higher PSI values.

Knowing that everything is "ok" I do have some other questions regarding the compressor. It's a "200 PSI" compressor but the guy that had it before me had it set to stop at 120 PSI. It starts pumping again when it reaches 80 PSI. I believe this is all configurable.

Can anyone venture a guess as to why he would want the max PSI to be 120? It seems like I'm not really using the full capacity of the tank if I'm only going to 120. Could anyone provide any input on this?

Thanks again in advance for handling all the noobish questions.
 
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Old 08-31-09, 08:12 PM
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Most air tools don't want much over 80 PSI (if you read the manual).
Paint spray is much less.

No real point to compress air to 200 other than to waste power.
I can bet you can imagine how much harder it would be to turn that wheel when the air is exerting 400 lbs or more on the poor old piston.
 
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Old 08-31-09, 08:25 PM
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gotcha I was thinking if i worked it really hard and got some extra air in there (higher pressure) it would run "less" to fill up. But all in all it will probably even out with the bad side effect of having to press out the higher numbers like you're saying.

So i guess the rule of thumb is keep it a bit lower and let it run a higher number of times, but every time it runs it's easier for the compressor to work.

One more question (hopefully). I'm assuming each tool want's to be run at a different PSI. It is my understanding that the regulator controls this. That no matter what PSI is in the tank, the reg lets you control what psi is at the output nozzle.

Does this mean I should be modifying the regulator per tool to make sure I'm running at the suggested PSI? I think most do 90 anyway but I know some sprayers run lower around 40.

Thanks again for all the great answers! I'm so happy I didn't ruin the check valve or anything else by tipping it. It sounded like a pretty tough fall.
 
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Old 08-31-09, 08:51 PM
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You are correct. Just remember in order to adjust the outlet pressure, you need to "dead end" the air line and turn the knob. It won't adjust sitting still without air moving through it.
 
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Old 09-01-09, 04:38 AM
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"It's a "200 PSI" compressor"

Are you sure? I have a 6 hp 60 gallon air compressor, I'm not sure at what pressure it quits pumping but I'm sure it's 150psi or less. It's possible the tank is rated for 200psi.... and for safety you always want a tank stronger than the compressor.
 
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Old 09-01-09, 06:05 AM
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Originally Posted by chandler View Post
You are correct. Just remember in order to adjust the outlet pressure, you need to "dead end" the air line and turn the knob. It won't adjust sitting still without air moving through it.
I'll take a look at the manual before doing it as well, but are you saying that I need to, for instance, hook up an air blower and have it constantly releasing air while turning the knob?

I think I just got confused by the term "dead end" because then I'm not stopping anything I'm letting it go. Let me know and thanks for the advice.

As far as the 200 PSI comment, you're right - it might just be the tank, I'll have to look into it. Either way I'll probably leave it set where it's at and if I dial it up I probably won't go over 150 (if the compressor itself is rated at 200, this has got to be a safe number as far as longevity is concerned right?)
 
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Old 09-01-09, 11:12 AM
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Yes, dead ending the hose, means having air flowing through it, like with a blower, etc. Sorry for the terminology. The gauge and adjustment must see air flowing past it in order to attain a good level of air at your specified psi.
 
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Old 09-01-09, 02:48 PM
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Another thing to consider when raising the pressure setting is that the higher the pressure setting the higher the temperature the compressed air will be.
This will cause the air tank to become warmer causing less moisture to condense in the tank, giving you more grief with water in your hose.
 
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Old 09-02-09, 11:37 AM
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FIFY

Originally Posted by GregH View Post
Another thing to consider when raising the pressure setting is that the higher the pressure setting the higher the temperature the compressed air will be.
This will cause the air tank to become warmer causing *more* moisture to condense in the tank, giving you more grief with water in your hose.
At least I'm assuming you meant "more" instead of "less". Makes sense to me, perhaps I should leave well enough alone.

Perhaps a couple votes where you guys keep your max pressure rating at? Maybe tell me that max rating of your compressor and where you actually keep it?
 
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Old 09-02-09, 11:46 AM
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No...I think he meant Less. Well..wait..thats if you use it as it runs. If it stays hot in the tank (long usage, constant running) then the compressed air won't cool until it goes through the regulator and into the hose and your tools.

If you just run it and let it sit til the air cools..then it would prob mostly stay in the tank.

I have a smaller DeWalt...125 max. I normally run the output right at 100 psi since that works just fine for all my tools. Never messed with the regulator to adjust the max..never saw a need....
 
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Old 09-02-09, 03:32 PM
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Right, I did mean less.
As said you want the tank to be cool so the water ends up there.
It is the principle that makes refrigerated air dryers work.

If a compressor is properly sized to the consumption of the tool moisture becomes somewhat less of a problem.
If you buy a 10 cfm @ 100 psi compressor and then purchase a 10 cfm @ 100 psi air tool, after the reserve is depleted, it would run continuously as long as the tool runs.
No big deal with tools like impacts or air chisels but where people have problems is with continuously running tools like air sanders.
On a hot muggy day get on a sander for eight hours on a DIY auto body job and you will think you hooked the sander up to a garden hose!

Or put another way.................."Sorry dear, there is a very good reason to buy that BIGer air compressor.............Wanna hear it!"
 
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Old 09-08-09, 07:45 PM
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Originally Posted by GregH View Post
Right, I did mean less.
As said you want the tank to be cool so the water ends up there.
It is the principle that makes refrigerated air dryers work.

If a compressor is properly sized to the consumption of the tool moisture becomes somewhat less of a problem.
If you buy a 10 cfm @ 100 psi compressor and then purchase a 10 cfm @ 100 psi air tool, after the reserve is depleted, it would run continuously as long as the tool runs.
No big deal with tools like impacts or air chisels but where people have problems is with continuously running tools like air sanders.
On a hot muggy day get on a sander for eight hours on a DIY auto body job and you will think you hooked the sander up to a garden hose!

Or put another way.................."Sorry dear, there is a very good reason to buy that BIGer air compressor.............Wanna hear it!"
another thing to consider is the DUTY CYCLE of the compressor. most are 50% duty cycle.( off 1/2 the time; on 1/2 the time) 100% duty cycle(cast iron cyl.-preferrably with low pressure/high pressure (two phase)) is a better choice when buying.
 
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Old 09-15-09, 06:58 AM
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So I have another quick question that is unrelated to the original topic, but it's small and doesn't warrant another entire post. I went to the hardware store in search of "30-weight compressor oil" as specified in the manual (for an oil change).

I talked to a kid working there that told me this farm brand of detergent-less oil is what I'm looking for. Would anyone else be able to verify his claim?
 
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Old 09-15-09, 04:05 PM
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All you need for any small reciprocating compressor is 30 weight non-detergent oil.
All non-detergent oil is clearly marked as such so if his farm oil spells this out on the front of the container you will be good to go.
 
 

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