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Thread: Air Compressor Draining

  1. #1
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    Air Compressor Draining

    In another thread, I asked what might happen when an air compressor tank rusts from condensation. The potential for serious injury/death/catastrophic facility damage moved me into purchasing a new compressor. Now that I have been properly educated, I will be much more attentive to this one. This leads me to ask the following question....

    I have seen some electronic compressor drains, many of which work by opening the drain valve for 2 or 3 seconds every 45 - 60 minutes. Assuming that this is sufficient to purge water from the tank, this tells me that totally emptying the tank of air is not a requirement to adequate removal of condensate. I power down my compressor at the end of each day but if I open the drain valve for (let's say) 10 seconds each time, the tank will still be filled with mostly compressed air. So...and here is my question....should I totally deplete the air every day or can I leave what's left overnight for use tomorrow?
    Last edited by Glen Blanchard; 02-03-2016 at 12:38 PM. Reason: Typo
    Regards,

    Glen

    Woodworking: It's a joinery.

  2. #2
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    As long as you drain the condensate, I see no reason to dump all of the air. Wasteful IMO. I have a 20 gallon Craftsman, probably 30 years old and I have rarely dumped all of the air. That being said, small leaks in my distribution system will leave it at zero psi on occasion.
    NOW you tell me...

  3. #3
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    I have an Ingersoll Rand ADV installed that cycles on for 4-5 seconds every 45 minutes. I power up the compressor & ADV only when I'm actually using air. I do not drain the tank. Any moisture coming out of the tank is still pretty clear after 10 years of using this system.
    Search eBay for Automatic Drain Valve, there are several to choose from. I paid $63.50 delivered in '05.
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  4. #4
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    I open the drain on my 60 gal upright compressor once a week, maybe, if I happen to remember it when I walk by. Have never let all the air out in the 3 years it's been in service; it's got power all the time so stays at around 100-125psi. Hope it doesn't explode while I'm in the shop...

  5. #5
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    Moisture condenses out of air as it cools, thus you will get more water out of a cold tank than a warm one.

    Wilkerson makes an automatic compressor tank drain valve that opens due to pressure differential in the tank. It works well (I've had one on my shop compressor for 7 years w/o problems). Horror Freight sells a clone of the Wilkerson valve for a fraction of the cost.
    Last edited by Scott T Smith; 02-04-2016 at 4:43 PM.

  6. #6
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    I went through two of the Harbor Freight automatic drain valves in three years. They stick part way open and leak air pressure.
    I have now piped the tank drain to a ball valve that's easy to reach. It only takes seconds to drain and since the valve is easy to reach I do it often, especially in the warmer humid Summers that we have here in NC.

    Charley

  7. #7
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    To pigtail on Scott's comment- warm air holds more moisture than cold air, so air loses moisture as it cools... and air cools as pressure is released. This is the principle at work behind refrigerators. A compressor creates pressure, then releases it, which creates cooling.

    This is why, when you use one of those cans of compressed air to clean electronics/keyboards/etc, the can gets super cold.

    My point is, the condensation in your tank is primarily caused when you use the compressor (release pressure). So theoretically, you really only need to drain it after you've been using it. As long as the compressor isn't losing pressure when not in use, I wouldn't expect meaningful condensation.

    That said, if your shop has big temperature swings (i.e., it's not insulated, or you live in a climate where temperatures vary a lot), I guess condensation could also be produced inside the tank.

    I have an 80 gallon 2 stage compressor. My solution was to add a street elbow to the drain, a length of pipe, a quarter turn ball valve, and a garden hose fitting on the end. That way I can stick the hose out of a window or the door to the shop to drain the tank rather than blowing water all over the shop.

  8. #8
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    Quote Originally Posted by Glen Blanchard View Post
    In another thread, I asked what might happen when an air compressor tank rusts from condensation. The potential for serious injury/death/catastrophic facility damage moved me into purchasing a new compressor. Now that I have been properly educated, I will be much more attentive to this one. This leads me to ask the following question....

    I have seen some electronic compressor drains, many of which work by opening the drain valve for 2 or 3 seconds every 45 - 60 minutes. Assuming that this is sufficient to purge water from the tank, this tells me that totally emptying the tank of air is not a requirement to adequate removal of condensate. I power down my compressor at the end of each day but if I open the drain valve for (let's say) 10 seconds each time, the tank will still be filled with mostly compressed air. So...and here is my question....should I totally deplete the air every day or can I leave what's left overnight for use tomorrow?
    Glen

    If you're using your compressor on a daily basis, then no, I see no reason to blow it down, and drain it, every nite.
    Me personally, I'd just do it manually until I saw no evidence of moisture. I do like that auto drain system though.
    We blow down our drying towers about every 5 minutes for 15-20 seconds, but this is a very, very, large system.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  9. #9
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    Just for fun, I ordered an automatic drain valve through Amazon.com just now - it ships from China so will take a while to get here. But if it works, the price is pretty much unbeatable. This is the 220V version; I intend to wire it in series with the contacts on my compressor so it's only energized when the compressor runs and should open the valve once each time the compressor starts. They have a 110V version also if you search for "Seaboltd"

    http://www.amazon.com/gp/product/B018NCVSQQ

  10. #10
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    Peter - Great explanation. Thanks everyone for educating me.

    Marty - That's a great price. The one I was looking at was just shy of a $100! I guess I need to decide if I want to automate this process. It's kind of nice doing it manually and seeing if there was any condensation in the tank. That requires remembering to do it, though. I attached an elbow with extension to my new compressor to get the valve in an easily accessible spot. It's so easy to do now that I am doing it daily. I might wind up automating it if I get lazy about it as the compressor and DC are in a closet that is only accessible if I walk out of the shop.
    Regards,

    Glen

    Woodworking: It's a joinery.

  11. #11
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    The ones from Harbor Freight are actuated by a connection to the compressor bleed down line that has pressure each time the compressor runs, but loses the pressure when the compressor shuts off.

    You don't want to connect that 220 volt unit in series with your compressor. You want to connect it to the two power leads that run to the compressor motor, after the pressure control switch. If you connect it in series, neither the auto drain nor the compressor will run.

    Your choice is also a 220 volt 50 ~ unit. Our electric power is 240 volts at 60 ~. The valve electronics and coil may not last long and the timer will not likely operate correctly, since most timing circuits depend on the power line frequency for stability. Good luck.

    They shouldn't be trying to sell that here. Please let us know how you do with it.

    Charley

  12. #12
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    Quote Originally Posted by Charles Lent View Post
    You don't want to connect that 220 volt unit in series with your compressor. You want to connect it to the two power leads that run to the compressor motor, after the pressure control switch. If you connect it in series, neither the auto drain nor the compressor will run.
    That's what I intend to do - used the wrong words maybe. The drain valve will have power when the compressor motor has power.

    Your choice is also a 220 volt 50 ~ unit. Our electric power is 240 volts at 60 ~. The valve electronics and coil may not last long and the timer will not likely operate correctly, since most timing circuits depend on the power line frequency for stability. Good luck.
    I don't expect any issues - worst case, the timer runs a little slow. The valve is run by a simple solenoid and I doubt it cares whether it's getting 50 cycle or 60 cycle AC. It's the same as this item http://www.amazon.com/Generic-Automa.../dp/B00N30G2J2 which claims it works with 24-220V, 50-60hz and has a few positive reviews.

    It also looks like similar items are sold on eBay with stickers that indicate they work on 50 or 60 - eBay item# 161320356249
    Last edited by Bruce Page; 02-05-2016 at 3:00 PM. Reason: Removed eBay link per TOS

  13. #13
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    What's the point in leaving the air for tomorrow beyond convenience? Is your tank massive? Our tank take less than 10 minutes to fill each day at the shop, so we let the air out and open the drain every night religiously.

    Quote Originally Posted by Glen Blanchard View Post
    In another thread, I asked what might happen when an air compressor tank rusts from condensation. The potential for serious injury/death/catastrophic facility damage moved me into purchasing a new compressor. Now that I have been properly educated, I will be much more attentive to this one. This leads me to ask the following question....

    I have seen some electronic compressor drains, many of which work by opening the drain valve for 2 or 3 seconds every 45 - 60 minutes. Assuming that this is sufficient to purge water from the tank, this tells me that totally emptying the tank of air is not a requirement to adequate removal of condensate. I power down my compressor at the end of each day but if I open the drain valve for (let's say) 10 seconds each time, the tank will still be filled with mostly compressed air. So...and here is my question....should I totally deplete the air every day or can I leave what's left overnight for use tomorrow?
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  14. #14
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    Quote Originally Posted by Keith Winter View Post
    What's the point in leaving the air for tomorrow beyond convenience? Is your tank massive? Our tank take less than 10 minutes to fill each day at the shop, so we let the air out and open the drain every night religiously.

    The point, Keith, is not about conserving the air for the next day. If all I have to do is open the valve for 4 or 5 seconds, I can do so and then close the valve - leaving the tank partially under pressure. If it is important to drain the tank totally, I'll have to stand and wait for it to totally drain the air. Why not merely open it up and walk away and then close the valve the next morning? I have automated the powering up of the compressor. It powers up each morning at 7:30 so that it is pressurized by the time I walk into the shop each morning. Obviously leaving the valve open overnight would defeat the purpose of this convenience.
    Regards,

    Glen

    Woodworking: It's a joinery.

  15. #15
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    Now that's pretty nice auto power up, you hadn't mentioned that. I suppose in your case I'd install an auto drain. But then you're back to an air compressor in a closet that isn't regularly inspected. Which goes back to your original concern. Maybe hook up the auto drain then set a monthly maintenance check?
    Last edited by Keith Winter; 02-05-2016 at 8:52 PM.
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