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Compressor Question

YYCHM

YYCHM

(Craig)
Premium Member
I recently discovered how convenient it is to have compressed air available in the shop, so I brought my little portable compressor in from the shed and set it up between the mill and lathe. The question I have is can I leave the tank pressured up all the time or should I discharge it at the end of the day. I know you need to drain the condensation from it periodically.

Thanks
 
I drain a bit in the morning to get rid of the moisture - rest of the time it is on - I am on the ship right now...Compressor is ready to blow... LOL - provided you have your airlines leak free, the compressor will only run when you are using it. You will know if it is not leak free at about 3am when it starts up and you have to peel yourself off the ceiling.....haha
 
A compressor tank is like a battery - it stores energy. Discharging that energy without it doing any work is waste. So you will be wasting energy. Question is, how big is the tank and how high is the pressure in it == how much are you wasting. For large tanks, say 80 gal at say 150 PSI it could be up to say 10min to fill it up... so you waste like just over 0.5 kw/h ...

For a small compressor losses are still there but with tiny tank we are talking about far less wasted.

Of course you are not a green person for doing so - Greta is angry at you.

I leave my tank always under pressure. If you are afraid of leaks then you can have a cut off valve on it switched each time you leave for the day.

Also the cycle from empty to full will heat up the tank more then regular cycle == more water in your tank.
 
2 Gal 100 PSI Max LOL. It self discharges 60 PSI over the course of a week. Not sure where the leak is. Maybe the pressure cut off switch or compressor connection to the tank. Can't get to those connections to perform a leak test without taking the top cover off (which I may do yet). More curious if leaving the tank pressurized with the compressor switched off will kill the compressor seals or what ever over time for some reason.
 
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There should be a check valve at the tank inlet so there shouldn’t be any pressure on the seals.


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Personally, I shut my compressor off before I leave the shop. Torches off, heater off, compressor off, lights off, doors locked. It’s just habit.
I don’t discharge it though, the next time I turn it on I open the drain, it’s one way to remind myself to drain it
 
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I shut off my compressor when I am done with it and leave it pressurized. I don't drain it as often as I should. My hose reel has a slow leak, so if I leave the compressor on it will do exactly like Brent said. Only my garage/shop is right under my bedroom so I also get the wife after me if I don't shut it off. Only took a couple times to remember to shut off the compressor.
 
YYCHobbyMachinist said:
I recently discovered how convenient it is to have compressed air available in the shop, so I brought my little portable compressor in from the shed and set it up between the mill and lathe. The question I have is can I leave the tank pressured up all the time or should I discharge it at the end of the day. I know you need to drain the condensation from it periodically.

Thanks
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I always leave mine pressurized. A trick I leaned from a pro shop is to place an easy to operate value as close as possible to the tank—typically 2 feet, and right after your whip hose (or closest to the output connection to your tank as possible). As others have mentioned a tank will discharge itself over a week because of leaks. But because the leaks are likely to occur throughout the system, having the valve next to the tank means you only have 1 source of failure instead of 20 or 30.

I have a 60 gal tank and have been keeping it charged for almost 20 yrs. My previous tank was 26 gal and I would hear it kick in at night. That drove me nuts. A guy with a pro shop told me this trick and I put the value in right next to the compressor. Just turn it off when you are finished using air. Now your points of failure drop from however many connections in your system to just one. My 60 gal goes 7-10 days w/o kicking in when the valve is closed (compared to every night before I installed the valve).

A tip for homeshops is to mount your compressor and valve as close as possible (if you can) to the man door to your garage—especially if your garage is attached. This way if you forget to close the valve and it kicks in at 3 AM, you can just reach out through the door and turn it off to prevent further bleeds in the middle of the night and throughout the week.

This approach works for me.

Greta and I don't see eye to eye anyways.

valve.jpg
 
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In the long term (like 20 years) the stress of cycling from no to high pressure can introduce stress cracks if there is a flaw. Never a need to depressure if you have a valve like @CalgaryPT suggests. Turning the power off at night can avoid the problem of a faulty pressure switch causing a motor burnout, or far worse a tank rupture.
 
I just remembered a friend of mine left his on, and his airline blew a hole in it overnight. A million to one odds of that happening to a guy. Anyway his compressor ran all night long, without him knowing it, he said the motor and pump were so hot he couldn’t go anywhere near them for quite some time. He’s lucky there was no fire
 
Everything in my shop area except the overhead lights is on a power bar that I switch off every night or if I leave the house, so no chance of any surprises that way.
 
I have a master switch for the compressor... but I managed to break a spring in it ... The motor has overheating relay in it so if there is an accident such as huge air leak it will trip without killing the motor.

Almost everything else is on 3ph so gets turned off when I leave the shop. I have only compressor, small grinders and sander on 1ph that are plugged in.

Maybe should fix that master switch - 12h or more of it running non stop would also be a nice addition to the power bill.
 
Chicken lights said:
I just remembered a friend of mine left his on, and his airline blew a hole in it overnight. A million to one odds of that happening to a guy. Anyway his compressor ran all night long, without him knowing it, he said the motor and pump were so hot he couldn’t go anywhere near them for quite some time. He’s lucky there was no fire
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That's a valid point. We've never had a situation when no one is around the house and it is vacant for more than an hour or two in 25 years. But I take your point. I've often thought of wiring a smoke detector that I can selectively shut off/on in my garage but never found one that didn't have issues due to the dust. Perhaps a heat sensor approach might be a better idea. The combo of the valve and the power as suggested by @Dabbler seems solid.
 
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Yes you can leave pressurized, the tank killer is moisture and unless you are outdoors running constant it’s not a huge problem, accumulations in the shop setting are minimal but increases for big garage doors use in adverse weather (spring melt/rain), one quick way to tell if you Have to drain is; give a couple blasts on your hand and feel if it’s leaving moisture behind, some tools will even puff a cloud of visible moisture from the discharge port. Mostly I see this where the compressor is in a cold damp basement (the only source of power in new construction) while its hot outside the moisture from rains and nights dew gets trapped ending up in the tank resulting in up to1/4cup of typically brown coloured water per day, that’s about 2 nailers, leaky hose and compressor units only as big as 1-2man can carry.
 
I got usually milky white discharge from my port... I guess its better then rust colored one. But I am a bit puzzled why its white - does it mean some oil gets into the tank?
 
Tom Kitta said:
I got usually milky white discharge from my port... I guess its better then rust colored one. But I am a bit puzzled why its white - does it mean some oil gets into the tank?
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I’ve always thought that was a feature to prevent rust.[emoji3166]


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Tom Kitta said:
I got usually milky white discharge from my port... I guess its better then rust colored one. But I am a bit puzzled why its white - does it mean some oil gets into the tank?
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Yup, it's oil. If you've ever overfilled the crankcase on a small OHV engine like a Honda snowblower (like I have), it will puke the white frothy stuff out the value cover. What's happening is the oil is getting aerated through cavitation and it bubbles too high into the values and then comes out the valve cover in an engine. But in an air compressor it has an easier path to the tank, and thus resides there. This is especially true if the tank is new or in good shape on the inside (little rust). As it ages, you'll still get the white frothy stuff but the rust colours it brown. Your oil sump could also be contaminated with water if you are seeing excessive amounts of this froth. Changing your oil more frequently will help likely, because it should remove water contaminated in the sump.

In hydraulic systems the first sign of water contamination is milky fluid. Too much cavitation and you may see froth. The danger is that froth lacks the lubrication properties that the oil should have, and can cause damage in hydraulic or engine systems. It's less of an issue in a compressor pump, unless it is caused by aeration in the sump. Do a hot oil change after a lengthy drain. This is the first fix you should do. If you still get lots of froth you may have a pump/cylinder issue, often ring related or a weak valve can cause this too. But try swapping the oil first if you haven't done so for a while; it could be contaminated. Becuase of the nature of compressor, you'll always get some froth. But it shouldn't be cupfuls.
 
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CalgaryPT said:
Yup, it's oil. If you've ever overfilled the crankcase on a small OHV engine like a Honda snowblower (like I have), it will puke the white frothy stuff out the value cover. What's happening is the oil is getting aerated through cavitation and it bubbles too high into the values and then comes out the valve cover in an engine. But in an air compressor it has an easier path to the tank, and thus resides there. This is especially true if the tank is new or in good shape on the inside (little rust). As it ages, you'll still get the white frothy stuff but the rust colours it brown. Your oil sump could also be contaminated with water if you are seeing excessive amounts of this froth. Changing your oil more frequently will help likely, because it should remove water contaminated in the sump.

In hydraulic systems the first sign of water contamination is milky fluid. Too much cavitation and you may see froth. The danger is that froth lacks the lubrication properties that the oil should have, and can cause damage in hydraulic or engine systems. It's less of an issue in a compressor pump, unless it is caused by aeration in the sump. Do a hot oil change and a lengthy drain. Then change the oil. This is the first fix you should do. If you still get lots of froth you may have a pump/cylinder issue, often ring related or a weak valve can cause this too. But try swapping the oil first if you haven't done so for a while; it could be contaminated.
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My little loader at the shop had so much water in the gearboxes the oil froze a couple winters ago. Tried to let out the clutch and it wouldn’t move.
Pulled the drain plugs and started chipping away at the iced up oil :D
 
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