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Old 08-06-2006, 09:56 PM
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stress fatigue on a compressor

Hi Folks I am wondering about stress on a compressor. Now I know yall say don't completely drain the compressor every time you use it, but I work on the water and Im gone a month at a time. Now My question is should I leave air in it all the time,or drain it and pump it back up when I get back in.Thanks in advance...Randy

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Old 08-06-2006, 11:07 PM
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In my opinion and it is only my opinion it wouldn't matter one way or another as far as stress on your tank is conserned. If you are working with a compressor every day it is constanly being drained until it is recharged - often many many times a day. When you drain it you are draining it to remove the condensed water in it. If you drain it before you leave unless you have a lot of temperature variation the water vapor in the air in tank will not condense. If you drain the tank completely and leave the valve open until you return that should not pose a problem either. When you return and fill the tank again just drain off the condensed water and you should be good to go. Maybe I no not have all the info right and others will jump in and correct me.
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Old 08-07-2006, 06:06 PM
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DO NOT completely drain the pressure Draining the tank of WATER is necessary however draining the PRESSURE completely, if done frequently, will cause premature tank failure due to metal fatigue from excess expansion and contraction. While it is true that a tank will expand and contract slightly during normal charge/discharge cycles this is no where near the range of expansion/contraction that will occur from total discharge and recharge, it will take many total discharge cycles to cause a problem but it will eventually happen. Why do this? It only causes unnecessary wear on the pump and tank, wasted power and is of no real benefit.
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Old 08-13-2006, 07:39 AM
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i drain the water from mine everytime i walk by it. i also clean my tank out several times a year by flushing it with hot water and dawn soap.
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Old 08-13-2006, 11:52 PM
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Quote:
Originally Posted by oldred
DO NOT completely drain the pressure Draining the tank of WATER is necessary however draining the PRESSURE completely, if done frequently, will cause premature tank failure due to metal fatigue from excess expansion and contraction. While it is true that a tank will expand and contract slightly during normal charge/discharge cycles this is no where near the range of expansion/contraction that will occur from total discharge and recharge, it will take many total discharge cycles to cause a problem but it will eventually happen. Why do this? It only causes unnecessary wear on the pump and tank, wasted power and is of no real benefit.
I always wondered about this... metal has some elasticity (think springs, or a really really stiff balloon), so oldred's statement makes A LOT of sense here.
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Old 08-15-2006, 10:27 AM
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If a tank was a perfect sphere it probably would not matter much about drastic pressure changes since the stress would be spread evenly over the entire surface. On a small tank (30 -40 gal or so) or a very heavy walled tank it probably will not matter much but on the relatively light thin walled cylindrical tanks that are so commonly used the center tends to bulge quite a bit more than the ends creating highly stressed areas. These areas tend to weaken from metal fatigue caused by the flexing of this uneven expansion and contraction with the eventual cracking usually showing up at welded areas such as motor/pump mounting plates or the tank mounting feet, this seems to occur more often on horizontal tanks than on vertical because the mounting plates are welded on the thin side walls of the tank. Whenever the tank is completely drained it will contract a good deal more than it will when it just drops to the normal cut-on pressure leading to increased flex when it is repressurized. I am not saying you will destroy your tank if you let the pressure bleed off occasionally but to do it on a frequent basis will almost certainly lead to a shorter tank life so it should be limited to as few times as possible.
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