I have purchased a new PC air compressor, Mod CPFC2TV3525VP, in anticipation of getting Joe Woodworkers vacume setup. My old Craftsman compressor just didn’t have the umph to get er done anymore and had to be retired. What a sweet compressor this PC is, very high tech and quiet too (for a compressor anyway). I would highly recommend this machine.
My question is this. I know you’re supposed to depressurize the tank and drain the moisture after each use, but I prefer to leave the tank pressurized. What harm, if any, is there with not depressurizing the tank after each use? This way I don’t have to pump it up for each use, rather only when pressure drops below a usable threshold. This compressor pressurizes until it hits 175 PSI where the factory set cutout switch activiates, so it can be used for quite some time (< 40-50 PSI) before having to turn on the motor to pump itself back up. Comments??
Replies
The reason you'd drain the tank at the end of the day isn't for depressurization, per se, but to drain the water from it, helping prevent rust. Over the years, the rust can deteriorate the interior of the tank to the point that it weakens and at some point explodes. That being said, there seem to be more people who don't drain the tank than those that do. Having read one first-hand report of an exploding compressor and the damage it did to the shop, I tend to drain mine more often than not.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
FG is right.
Condensation is the enemy, but it's generally a pretty benign enemy.
That is, I have a shop compressor (which is about 20 years old) that I drain maybe once a month in the winter, more often in the summer.
My job site compressor gets drained every day after I use it -- but that's mainly because it goes from an unheated truck to a warm space inside.
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"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
I knew condensation is the problem. Let me reword my question to be more specific. IF...you keep pressure in the tank, AND...minimize how often the compressor motor runs, how much of a problem is the condensation build? Even more specific, what causes the condensation to begin with? I know that as you compress a gas, heat energy is created as a byproduct, and then cold is created as pressure is released. I sat in a compression chamber once and was compressed to a couple of atmosphere's, it got real hot while the compression what happening, then fog formed as the pressure was released, it was pretty cool... er, cold actually. I'm assuming that it's on the compression release that the condensation is formed? Right? But unless I'm spray painting something e.g. releasing air over an extended period of time, how bad can the condensation buildup be?Thanks, Jeff
I don't know my science well enough to answer your question.I would guess that compressed air is colder than the ambient temp, thus the condensation. I do know that during the warmer months of the year, a surprising amount of condensation accumulates.Maybe someone who knows what they're talking about will come along here to answer your specific questions.********************************************************
"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
Jeff,
". IF...you keep pressure in the tank, AND...minimize how often the compressor motor runs, how much of a problem is the condensation build?"
It lessens the rate at which condensate builds up, because the compressor goes through fewer pressure cycles.Each cycle produces water.
"Even more specific, what causes the condensation to begin with?"---Increasing the air pressure in the tank by compressing it heats it up, which enables it to hold more moisture. When you take air out, i.e lower the pressure the air becomes colder and loses moisture via condensation.
If you do not drain the water from the tank and use the compressor every day i.e regualarly water will accumulate and there will be less space available for air since water is not compressible. Eventually you will be spraying water vapour.
Local climatic conditions affect the amount of water which can be held in the air, so on a hot moist day operating your compressor will release more condensate per cycle than on a cold day.Philip Marcou
Air holds more moisture as the temperature rises and less as the pressure rises. As the air is compressed in the compressor, the temperature rises faster than the pressure, therefore, the air exiting the compressor is still dry. But as the air sits in the tank, the relationship of P1*V1/T1 = P2*V2/T2 holds (no work being done), so it cools down below the dewpoint temperature and drops out in the tank.
I'm one of those that leaves the compressor on all the time. Mine is 28 years old now. I've had to replace the valves a few times, but everything else is original. Even if you drain the tank each day, unless you purge the tank with dry air each time, you will still have water and water vapor in the tank. If you use the compressor everyday, I don't think you are doing your compressor any favors by depressurizing it every day. And unless you have a lot of leaks, I'm sure you are using more power to repressure the system each day.
I've done a lot with my compressor to make it easy to maintain and hopefully last longer. First, I moved it into a shed next to my shop so I wouldn't have to hear it (or at least it's not as loud). I elevated it, removed the drain petcock in the tank and added a small home-made knockout pot below it to collect condensate before it enters the shop air header. I drain the pot about once a week.
The knockout pot is made out of 1 1/2 inch PVC pipe (about 12 inches tall) mounted vertically. The air enters the side (a tee) and exist the top. The drain valve is obviously in the bottom of the pot. I have another one of these pots at each point in the shop header where I have connectors. I've heard others question the use of PVC for this, but I've used this system for over 20 years. I mount everything to assure the pots are protected against bother impact and pipe strain.
I have no idea if this has made any difference in the life of my tank, but I get very little rust with the condensate now. Before the pot was installed, the condensate looked like redwood stain.
Jacob, maybe after 28 years you may feel the urge to retire that one or pass it on....
I have used the same one for 22 years now- it is a Hydrovane, which is a rotary vane turbine rather than piston type. Very efficient and little noise, few moving parts.It stays in that "cabinet" with ingoing air being pre filtered.There is an auto drain on the bottom of the tank at the end which is slightly down hill-and a hose which goes under the building. I also like to have moisture traps in the lines.
PVC piping is quite adequate provided it is suitably heavy wall and preferably ultraviolet protected.Philip Marcou
Edited 2/18/2007 2:19 am by philip
Jeff, if a hose fitting or a hose for that matter were to fail. I'm not talking pin hole. 175 psi will open a pin hole up considerably.
I had a 10 hp Curtis with a 80 gal. tank, One time an employee disconnected a tool and dropped the hose to the floor, The nipple to the quick disconnect snapped off. The hose flew up like in a cartoon and hit the employee hard on the cheek, left a red mark for a week. It could have just as easily been an eye. The dust created with was substantial. It only took a minute to shut the hose off, I doubt you could have caught it. I ran 120 psi at the regulators. What if a hose failed. You weren't there to stop it how long would the compressor run before you got back from a long weekend. If we all went to lunch the compressor was shut off, as well as every evening. The tank, separators and regulators were drained daily.You don't have to fill a tank with water to get moisture into your air supply. A few gallons could give you problems. My compressor and tank was new in 1955. The state inspector dropped by every few years to check it for deterioration or signs of corrosion. I sold it in 2001, when I changed professions. Still runs every day but not as hard as it did for me. 6-8 employees.I hope this helps Ron
All...I'm running 70 psi at the hose, 175 at the tank. It takes quite a bit of use in my one man shop to drain the pressure thru use, this is why I don't want to depressurize the tank every day. Seems a waste of electricity and unnecessarily hard on the compressor. I'll crack the valve at the bottom of the (vertical) tank for a few seconds every other day or three and monitor the moisture buildup. I'll see for myself what the reality is on this. I checked the automated valve's, that would be great, possibly one day I'll go to that, especially if I determine the moisture buildup is indeed a problem. Lastly, I don't leave the compressor electricity 'ON' when I'm not in the shop. Given the tank is up to 175 psi, I don't leave the electricity on most of the time when in use. As I said, it takes quite a while to bleed down air pressure with use, and I monitor the tank pressure and turn on the electricity long enough to pump it back up, then shut off for several days again till it needs pumped up again. I spend a heck of a lot more time cutting, fitting, scraping, gluing, clamping, measuring, etc. than I do using air. If I'm using heavy air usage tools like a die grinder, then yeah, I leave the compressor on, but that's a rarity.When I worked as a machinist, I too have seen hoses break, turning into flailing demons that can't be caught. That'll get ya movin out fast...I've also gotten face full's of water in systems that DID have problems with water buildup. That crap stinks too and sure doesn't do the air tools any good. As a machinist, I've spent hundreds of hours on the wrong end of a die grinder beburring metal parts "payin my dues"...that was decades ago, but I still remember...Many thanks to all who've responded. You've been a great help to me and I appreciate ALL your comments...Jeff
Edited 2/18/2007 4:36 pm by jeff100
That's interesting. I am familiar with rotary vane blowers, but was not aware of any in this size range. They aren't typically used for the pressure ratios that are appropriate for shop air compressors.
I googled Hydrovane and see that they are a British company. They didn't show any North American distribution. Where did you get your's?
Forget my comment about North American sources... I didn't click enough buttons on the web page...
Jeff,
Drain a small amount of air every day (5-10 seconds)when you finish and then close the petcock. You will remove most of the moisture at the end of the day by doing this. You will also keep the majority of the air inside the tank. The condensation comes from the actual compressing of the air. when the air cools, it condenses. The air left in your tank overnight will not produce condensation, because it has likely already cooled down.
Lee
Lee, what I've noticed with my small PC pancake compressor is that quite a bit (percentage-wise) of the water comes out at the end of the air-drain process. Not quite sure why this is, but that's what happens. Might be different for "real" (larger) tanks?forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Jeff,
"What harm, if any, is there with not depressurizing the tank after each use?"-----None. You also save electricty and wear and tear on the machine. There is also a marginal reduction of overall amount of moisture. But it is good to switch off the electrics-if there is a slow leak in the system you will notice it quicker-the tank will be empty in the morning/next time you use the compressor.
"This compressor pressurizes until it hits 175 PSI "---- that seems quite high to me-the usual maximum pressure in my experience is 10bars or 150 psi- why don't you shut it down to 150 psi- save wear and reduce heat which will in turn reduce moisture condensing in the tank.
There is no escaping condensation moisture in the tank- it is physics, so eventually there will be rust.Draining the tank merely prevents water building up to unacceptable levels-it does not prevent rust . At every cycle the interior of the tank will be wet enough for rust conditions.
I believe the average piston type compressor if used hard every day only needs draining once weekly at most.
The clever thing to do is to fit an AUTOMATIC DRAIN VALVE to the tank- water will drain automatically, without the need to drain all the air out too.
People can be obsessive about this kind of thing -mainly because they don't understand the basic facts- should you reach this stage I suggest you get a stainless steel tank (;)and sand bag the surrounding area...
I have heard more that once that you should drain the tank to reduce rusting and I always thought, "wait a minute. It is the air mixed with the water that causes the rust. If you have just water and the oxygen is driven out, it will never rust. I don't think you get the tank dry by just draining the water out - hence leaving it the most susceptible to rusting. As a young man I used to drain the tank to make more room for compressed air, and on a hot summer day, the petcock would freeze up for a while then thaw and drain some more. Good example of PV/T = PV/T. I don't know about stainless steel. It tends to be quite brittle. Maybe a steel lined plastic tank to work like an inner tube inside a tire would do it. Actually a good steel tank will last many years. The 175 PSI would indicate that it is a two stage compressor, made to operate for pressures of Apr. 150 to 175 PSI. The start up pressure must have been set lower by the operator. You need the higher pressures for pumping truck tires. In fact some of these big trucks use pressures of more that 200 PSI.
Yes, it is a two stage compressor. The pump cutoff switch is set at the factory to 175 PSI and is not adjustable by the user.Since the tank is pressurized this high, and the compressor is used heavily but very sporadically, I hate to depressurize it just to drain out any moisture buildup that is trivial to begin with. My previous compressor I outfitted with a good ball valve and shut the air hoses off after every use to maintain pressure in the tank. I never drained the tank on the old compressor, except in the beginning when I first got it. Given the moderate climate in the western side of Washington state, (over many years of usage) I never experienced problematic moisture buildup.I will be outfitting this new air compressor with a ball valve as well (those babys are expensive!), and using this compressor the same way. The answers I'm seeing are just what I was hoping to see, yes, it's a problem, no, it's not a serious problem. Perhaps in the beginning, to evaluate the potential for water buildup, I will crack the drain valve to drain whatever moisture is in the tank, without fully releasing the pressure in the tank, except for what escapes during the tank draining. The drain valve in on the bottom of the (vertical) tank, so this should work fine. If I find that considerable moisture is building up (and spraying me in the face)...I'll reconsider depressurizing it to drain it. Thanks to all.....
With the drain on the bottom of the tank there should be no reason to fully depressurize the tank. Just open the valve long enough to blow out the water. The tank drain on my 80 gal. 2 stage is set for 10 seconds, 5 would probably be plenty. 175lb. air pushes the water out mighty fast. I'm in the same geographic area and I get a cup a day sometimes.------------------------------------
"The West won the world not by the superiority of its ideas or values or religion but rather by its superiority in applying organized violence. Westerners often forget this fact, non-Westerners never do."---------------Samuel P. Huntington
...The tank drain on my 80 gal. 2 stage is set for 10 seconds...Where can I get an automated valve that I can retrofit into my tank? Did your tank come with this valve???Thanks...Jeff
Unfortunately it did not come with it. The one I got is made by MotorGuard. It works very well and I am very happy with it. You can set it for interval between drains and for the duration of the drain. It threads right into the drain at the bottom of the tank. I ran a hose out the wall of the shop since a cup of water with 175lbs. of air behind it makes an impressive mess. It's scared the bejeezus out of a few of the folks walking down the alley! I put a 90 degree fitting on the end of the hose so it does'nt soak anybody.------------------------------------
"The West won the world not by the superiority of its ideas or values or religion but rather by its superiority in applying organized violence. Westerners often forget this fact, non-Westerners never do."---------------Samuel P. Huntington
Jeff:
Here is one that I know to be good. I work as a Dental equipment service Tech. and this is the type that used to be used on Dental air compressors before they all became high tech with built in air dryers so that moisture isn't present in the tank.
http://www.grainger.com
Oops. After checking the link that I first posted, it won't open. This will get you to the main page . Type in "auto drain" in their search window and look at the second item on the page.
This company is a wholesaler but they will do small cash sales and seem to be present in every major city.
Bill
Edited 2/17/2007 11:59 am ET by melonhead
You don't need to bleed off the pressure to drain the water. The petcock is at the bottom and you just need to open it so the water comes out, then close it again. If you're getting sprayed in the face, move back. I use a small plastic container to catch the water and to keep it from spraying all over, I just don't open it very far. The moisture condenses out the same way clouds form when they pass a jet wing or go over a mountain top- The air density decreases rapidly enough for the principle of air being able to hold a certain amount of moisture at a given temperature and/or air pressure to manifest itself. Trying to use a blow gun or spray paint on a hot day with a small compressor is a prime example of this problem.
"I cut this piece four times and it's still too short."
Jeff,
How often you drain depends on the ambient humidity in your shop. On my shop compressor I have an automatic drain that runs daily and I can't remeber the last time I noticed any water in the sink in drains into. However I have a dehumidifier in my shop and that keep the moisture level low. That said, when I'm at a job site and running my smaller Bostitch twin tank compressor I am astounded at the amount of water that collects in the tank during the course of a warm damp summer day. THAT compressor gets drained EVERY day. If it's raining out we drain it at lunch as well.
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