My 30 year old Sears air compressor has given up the ghost. Actually it was made by Devilbiss and went by sears only in name . The primary use has been for spraying furniture finishes.
I went to the local Lowes and HD to find a new one . In the meantime I figured I would get one a little more powerful. My old one was rated at 2 HP.
I found a 7HP unit at Lowes and the similar one at HD. Then checking the specs I noticed that the 7HP was "peak" and that the continuous rating was 1
1/2 HP. On the side of the unit was a sticker showing which tools it could be used to operate . A Spraygun was not one of them .
So what the heck should I be looking for in this day and age a 20 HP unit ?
On Thu, 11 Nov 2004 05:26:14 GMT, "Mike Hide" vaguely proposed a theory ......and in reply I say!:
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What you need to do is find out the air delivery capacity of the compressor you had. This will be in CFM at some pressure, usually 90 PSI. It may be called Free Air Delivery (FAD). But it _must_ show a delivery pressure to mean anything.
Largely ignore the horsepower, it is indeed horse shit.
Also ignore the ratings that do _not_ show a pressure. They are also rubbish. To give you some idea, I have a compressor rated at "12CFM" but it can only deliver about 7 CFM @ 90 PSI. Its horsepower, BTW is
2.5HP, but that is an honest constant and is about right for the rated air capability.
How they can be allowed to get away with claims of 7HP I have no idea. It's crazy. Like 1000W shelf-sized "HiFi"s, measured for a fraction of a second at 100% distortion just as the output blows up!
If your old machine was 2HP, 30 years ago it would have been genuine HP. So I would estimate that its FAD capability would be around 5-6 CFM @ 90 PSI. So you need to look for that or larger.
If it was a belt-drive unit, you will also find that many of the cheaper direct drive ones are noisier, or at least more unpleasant to listen to, because they run the cylinder at twice the rate. Bear that in mind.
***************************************************** Dogs are better than people.
People are better than dogs for only one purpose. And then it's only half of ofthe people. And _then_ most of them are only ordinary anyway. And then they have a headache.........
If your old compressor was 30 years old, then it probably was not one of the oil free, high speed designs. I have one of these that's about 10 years old and I hate it. Its way too noisy. Its finally trying to give up the ghost and I can hardly wait.
I'm going to a real cast iron compressor this time that uses oil. I'm looking at $400-$600 for my needs/wants. Lowe's has several examples that are claimed to be 83 db sound level. Ahhh!
I don't know if you want to get into a stationary compressor size, but thought I would pass on a good deal to you. The Husky VT6314 (60 gal, 10.3 cfm @ 90 psi) is available at Home Depot for regular price of $429. Campbell Hausfeld has the same compressor on their website listed as a hot buy at $329 plus $46 shipping and no sales tax. I'm looking seriously at it.
On Thu, 11 Nov 2004 06:02:16 GMT, "Lew Hodgett" calmly ranted:
Yabbut you've got enough money to buy 55 gallon drums of epoxy and build 50 cubit long boats. A 4hp (HAR!) HF oily pump fit my budget at $159. I don't think I'll be using DAs all day long so it should handle anything I'm likely to throw at it. Then when I'm rich and famous some day, I'll get a real Ingy.
Don't worry about the HP as much as the CFM. HP ratings can be all over the place as you have found out but CFM is CFM. Just determine what CFM your spray gun uses and its working pressure and look for a compressor that matches that or comes close.
On Thu, 11 Nov 2004 19:43:55 GMT, "TBone" vaguely proposed a theory ......and in reply I say!:
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Read my post. CFM is _not_ CFM. :-<
And I've seen a few porkies around about _this_ aspect as well. I have a "12CFM" compressor that cannot drive a "4CFM" ROS. The compressor's _real_ output is about 7CFM @ 90 PSI. The ROS's _real_ requirements at _working pressure_ (90CFM) is more like 20CFM+.
***************************************************** Dogs are better than people.
People are better than dogs for only one purpose. And then it's only half of ofthe people. And _then_ most of them are only ordinary anyway. And then they have a headache.........
I think the confusion on CFM comes about because there is no duty-cycle rating given. Most compressors are rated at some ridiculously low duty cycle (which is not published). My compressor will supposedly put out 6.4 CFM @ 90 PSI, but the duty cycle is only about 25%. It works fine pulling a 6 CFM impact wrench for 6 of 8 lug nuts, but then I have to wait while it re-fills. On the other hand, if I am moving around and there is a break between each bolt I can run the tool with no problem. What they *should* be required to list is the continuous output, which is way low for just about any small compressor.
I wondered about that too. My 10 CFM Porter Cable compressor keeps up with my DA sander. Runs constantly, but keeps up! At least when the compressor needs a break, so do I! Greg
You are correct. I forgot about that BS. The better ones list compressor CFM at a few pressures which is always 100% duty cycle. I guess the cheeper ones include the tank but I do believe that they need to include the duty cycle when they do it that way although it may be hard to find.
On Thu, 11 Nov 2004 16:58:04 -0800, Tim Douglass vaguely proposed a theory ......and in reply I say!:
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I thought duty cycle referred to the capability of the machine to keep running without overheating. I have never heard it applied to the ability of a compressor to keep supplying air while running.
If the compressor has to keep pumping to get up to speed, that's simply the tool using more than the comp can provide.
AFAIK, the confusion about compressors comes about because they supply an _intake_ (Swept volume) figure at atmospheric pressure.
OTOH, the _tools_ are calculated using some sort of "weighted" average (which could be called a "duty cycle"), that assumes that in a shop, with 10 tools, they will all only be used a bit of the time. IUt's BS, but has nothing to do with the compressor. The idea is you add them all up "as run" and buy a comp to suit. But if you are using a single toold flat out on a comp that is based on that rating, it will fail to keep up.
The lie here is in the tool, not the compresor.
***************************************************** Dogs are better than people.
People are better than dogs for only one purpose. And then it's only half of ofthe people. And _then_ most of them are only ordinary anyway. And then they have a headache.........
On Fri, 12 Nov 2004 02:23:29 GMT, "Mike Marlow" vaguely proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email
I am. It was a cheap thing. Nonetheless it was rated at 4 CFM/90PSI. There are plenty out there like it.
Quite frankly I would go with electrical, anyway. I get a 400 watt /
0.5 HP sander to do what it takes a 2.5 HP compressor to do.
***************************************************** Dogs are better than people.
People are better than dogs for only one purpose. And then it's only half of ofthe people. And _then_ most of them are only ordinary anyway. And then they have a headache.........
True HP is about 11 amps on 115 volts. Some heavy duty one HP motors pull 14 amps. So if it runs on 115v and plugs into a wall socket, 1.75 real HP is all you can get on a 20 amp circuit! All the 7 HP vacuums,
3.5 HP routers, 2.5 HP circular saws, 6 HP compressors, are LIES, LIES, LIES.
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