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  #1  
Old 02-28-2004, 09:43 PM
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Air compressor/impact wrench question

I know this question is a little off the board, but I figured someone here would know. My wife got me an air compressor for Christmas with an impact wrench and I'm having trouble getting the wrench to work right. My first air tool...

Compressor is 20 gallon, 5 hp and 6.5 SCFM @ 40 psi and 5.1 SCFM @ 90 psi. My impact wrench specs are Avg SCFM - 5.1 @ 90 psi (20% usage), continuous SCFM - 25.4 @ 90 psi (100% usage), max rpm is 7000, max torque is 250 ft lb and working torque is 60-200 ft lb.

I am having trouble taking off lug bolts, I figure I'm only getting about 60-70 ft lbs of torque. I know that my tank is small, I understand the basics but I'm not sure what 20% usage means. If my impact is max 250 ft lb does that mean at 20% usage I'm only going to get about 50 ft lb (20% of 250)? Sorry if this is a stupid question, but I can not figure out why I'm not getting any better torque. I always understood 20% usage to refer to time - you wouldn't be able to use the tool continually or for very long at a time before the pressure would drop and you would have to wait for the tank to recover. Thanks for the help.

Ryan

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Old 02-29-2004, 02:00 AM
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do you have a pressure gauge on the line?

There is also, or on some wrenches and adjustment for torque...
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  #3  
Old 02-29-2004, 08:48 AM
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Have you put oil in the impact gun, where required?

Happy Motoring, Mark
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Old 02-29-2004, 09:45 AM
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Yes to both - I set the pressure gauge to the tool at 90 psi (per the impact wrench instructions) and I have turned the impact regulator up to the highest setting, and I have carefully followed the oiling instructions. There are two places to oil the wrench, one for the air motor and the other for the impact mechanism. I have done both. For the impact wrench you put about 1 oz of oil in the side, run the wrench for about 30 secs and then open the screw and force the excess oil out. The instructions say to do this over until the excess oil expelled is clear oil. I can't really get to that point - the oil that I continue to dump looks dirty. BTW, this is the second impact wrench - I took the first back because it was doing the same thing and the store gave me another one just like it from another air compressor kit.

Ryan
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  #5  
Old 02-29-2004, 02:29 PM
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The 20% refers to the amount of time you can run the gun every 10 minutes. so you can run the gun 2 minutes out of every 10 and expect max performance. This is the same rating that you find on home welders. Most are rated at 20-30%.

You should an oiler on the discharge side of your pressure regulator. The oiler looks like a regulator but w/o the adjusting handle. It is filled with air tool oil and is adjusted so that you can see a drop of oil in the sight glass drop every few minutes of use.

If your gun has a 250 ft/lb rating it should produce 250 lbs. at 90 psi. Because of the drop in pressure it won't hit at that rate for long but it should definately start off at that power. Check the size of your supply hose. Too small and it won't deliver the volume.

Remember that most tire shops, and esp. the ones that do truck tires, have their compressors set at 175+psi. Many of their 1" (that is a 1" anvil which is the square thing that holds the sockets) guns will deliver upwards of 1,000ft/lbs. of torque at this pressure. This means that when they put your lug nuts on with a 1/2" gun the can esily run them up over 250ft/lbs. That is a lot of torque on a nut that isn't supposed to be tightened over about 80ft/lbs.

When you go to your local tire shop ask to see the torque wrench that they use on tires. Chances are good that they can't spell torque wrench much less have one, and even if they have one I bet that not only do they not use it but they don't even know the proper torque for auto lug nuts. Walk back to the compressor and look at the pressure gauge on the tank. I bet that it is set at 150 psi or better. This pressure, even in a 1/2" gun, will kill auto lug nuts.

Rig up a quick connect with a pressure gauge between the end of your hose and your gun. This will let you check the pressure right at the gun. Run the gun for a few seconds and check to see if the pressure at the gun drops faster than at the tank. If so you need the next size larger hose, esp. if you have 50 ft. or so of hose.

Good luck.
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Old 02-29-2004, 03:16 PM
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Ok, thanks for your response. I understand that I should be able to get 200+ ft lbs of torque, but for only a short period of time. I will lose force as I lose air pressure. That's what I thought, but I couldn't get the wrench to work right, so I started to question. The hose is 25 ft and I think 3/8 ", but it could be 1/4". I'm not sure what you mean by hooking a pressure gauge up between the tool and the tank. Should I tee off right at the tool? I'm not sure how to do this - I think I understand the why, but not sure how to set it up. Thanks.

Ryan
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Old 02-29-2004, 05:59 PM
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Quote:
but I couldn't get the wrench to work right
Had to run my 1/2" impactor this afternoon to remove the flywheel fasteners at the back of the crank.

Are you using the impact to remove the lug nuts or just to break them loose. Break em loose and then use your 3/8" air ratchet to remove them the rest of the way.
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Old 02-29-2004, 06:05 PM
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I can't even break them loose - I'm not getting the necessary torque. Using my torque wrench as a measure, I can't break anything loose that is tighter than 60 ft lbs, or so, and it won't tighten down a bolt/nut tighter than 60 ft lbs.

Rysn
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Old 02-29-2004, 06:09 PM
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I guess the next question is how small a tank you got? Is the compressor having to stay running all the time. If the compressor is having to say on you probably don't have enough horse power - oh, I meant to say air.
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Old 02-29-2004, 09:30 PM
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The size of the hose is pretty important, as is the length. Probably should be at least 3/8 hose not extended beyond 8 feet. Otherwise, would need to move up to a larger hose diameter.

You might want to consider getting an impact wrench. This pulsates or pounds as it turns and is good for removing large, highly torqued nuts.
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  #11  
Old 02-29-2004, 10:20 PM
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That's what I'm using here - I can't get it to impact! Spins like crazy, but it is not impacting and per my previous posts, this is the second wrench I've tried. From what I've read, 25 ft is not that long and I'm almost positive the hose is 3/8".
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Old 02-29-2004, 11:16 PM
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Uh, I guess I did not read the post carefully-was thinking you were using an air ratchet.

Only additional thought in a weak attempt to redeem myself is to re-think the hose. I just bought an impact wrench last week from Sears and the instructions say use at least 3/8 inch hose and if extended longer than 8 feet, upgrade to a larger hose.
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1971 280SL Tunis Beige Metallic
1971 280SL Tobacco Brown (13K miles)
1970 280SL Deep Red
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  #13  
Old 03-03-2004, 08:44 PM
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`Take your impact to any local garage or tire store. Ask them to show you how to hook it up and see if they can get it to break loose a lug nut. Failing that take it to a tool repair shop. Most, if they deal in impacts, should have a torque meter. They can try the gun on it and it should tell them exactly how many ftlbs. it is putting out If you can verify that you are only getting 60 ftlbs. there is something wrong someplace. It seems odd that 2 wrenched would both not perform.

You should be able to break loose any nut/bolt associated with the average auto using a 1/2" drive by 18" long breaker bar. Any bolt that is except the crankshaft dampener bolt on a VW engine. I think they tighten to about 260 ftlbs.

Another thing that helps with an impact. If the bolt/nut is tight try turning the socket in the direction you are going-like you are trying to assist the wrench. This takes the slack out of the inpact weights and causes the wrench to hit just a bit harder.

Many impact wrenches do not 'impact' when they are free spinning. The two inpact weights only come into play when there is resistance through the socket. Impact wrenches are rated by 'ipm' impacts per minute, 'rpm' free running speed (usually about 7,000 rpm), and torque in ft. lbs.

My suggestion about connecting the pressure gauge next to the impact will tell you how much pressure drop you get between the tank and the gun. This will tell you if you need a larger hose, or if the delta P is too fast, whether you need a larger tank. To connect the gauge get a 3/8" pipe tee, a 3/8" X 150 psi gauge, and 2 male quick connect nipples, or what ever kind of connectors you use to connect the gun to the hose. Install the gauge on the side of the tee and the connectors to the other ends. You should read tank pressure at the gauge.

Pull the trigger and see what you pressure drop is. If it is really noticeable your hose is too small. If it takes a minute to bleed down then the tank is too small and the compressor is also probably too small. Couple the wrench to a bolt and try it. If you get full tank pressure at the gun and it doesn't loosen the bold at over 60 ftlbs. then there is something wrong with the gun. By doing the above you will have some numbers that you can take back to the dealer or the tool repair man.
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  #14  
Old 03-03-2004, 09:47 PM
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Thanks for the reply and the help. I have decided that the wrnech is fine and that I have an air supply problem. I took the wrench to a friend yesterday (Mechanic) and had him hook the wrench up to his air (probably around 125 psi) and it worked fine. My wrench is rated 5.1 SCFM at 90psi, which is exactly what my 20 lb, 5 hp air compressor is. But i've been doing some reading and it seems to me that if you want to run an air tool you need 1.5 times the SCFM out of your compressor than what is listed as average requirements for the tool. So in my case, since the impact wrench is 5.1 SCFM at 90 psi, I would need an average SCFM of about 7.5 at 90 psi from my compressor. I am thinking of buying a 450 ft lb ipact with an average SCFM requirement of 4.0 at 90 psi. Also, my freind suggested running the wrench at higher than 90 psi, but I'm sure I lose SCFM if I do this , right?

Needless to say, this is a little confusing.

Ryan
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  #15  
Old 03-04-2004, 01:52 PM
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Before you run off and buy another impact look at what you are going to be doing with it. No auto mechanic I know and few big truck mechanics use a 450 ftlb. impact wrench. And if they do it isn't very often. Also, how much at one time will you use the wrench? Don't spring for a compressor that will let you run your wrench at 100% capacity for 100% of the time cause you just aren't going to use the wrench that much. If you aren't on an assembly line you don't need this kind of capacity. Also remember that it cost money to run a compressor that big. If you have a big tank and just need to loosen a couple of bolts you still have to fill the entire tank. If you really need capacity you can run two tanks with an isolating valve that allows you to use one tank and keep the other in reserve.

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