Air Compressor Questions

[alex123]

So I did that test by connecting the cutoff tool right to the compressor. It was cold in the garage and I didn't feel like pulling out a 50ft hose to do the test.

The 4 gallon compressor, per it's gauge said it was starting at just under 120psi (I should check that since it should fill to a bit higher) then kicked in at just under 90. I'm sure I could keep cutting at less than 90 but consider it was dropping about 10 psi/second. It wasn't going to run much longer. The big compressor fills to 135 on the gauge and kicks in at around 100 so the PSI drop is similar to the smaller one. At 100 psi the tank pressure is still higher than the tool's operating pressure thus no loss in performance.

I can't offer any insight into the CAT 15020 (or the Kobalt low noise 26 gallon that might be a better deal) or the Kobalt 2 stage beyond playing specs games. No doubt the 30 gallon Kobalt gives you a lot more tank and about 25% more pump. That's not insignificant on paper. I'm not sure how much it will come into real world play. Basically never for an impact. It could matter if you use a blow gun a lot.

OK, when I was helping my dad and brother out with some rebuilt compressors I created an Excel table to calculate fill times just to make sure the compressors were ball park hitting their specs. So as part of this discussion I found the video below.

The spreadsheet predicted 9:22 to fill from empty. He said it took 9:18. I had a private moment of pride

OK, so I used the same calculation to guess how much air my cutoff wheel used and how fast it would drain a compressor. An estimate of 25CFM seems right give how long it took to drain my small and large compressor. So ignoring the pump turning on, it would take about 20 seconds for the cutoff wheel to take my 20 gallon compressor from 135 psi to 90. The same calculation says the big Kobalt would take 56 second from 175psi to 90. Well, that would give you some pretty reasonable cutting time and honestly, since the pump would kick in at, probably 135 psi) you would probably get just over a minute of run time. It would then take about 4:30 to refill the tank to 175 psi. So yeah, that is a useful increase in run time before waiting vs my 20 gallon compressor. Of course, my 20 gallon with a lower peak pressure will refresh in 1:30. BTW, that semi-quiet Husky would, based on specs, match the two stake Kobalt.

So let's run that same calculation with the 15 gallon CAT and 26 gallon silent Kobalt.
CAT 1520: 150psi down to 90, 15 gallon tank, 25 cfm cutoff tool: 20 seconds, refill: 1:31, $410 (all but matches my 20 gallon compressor)
Kobalt 26gal quiet: 150psi down to 90, 26 gallon tank, 25 cfm cutoff tool: 34 seconds, refill: 3:10 $300

and the others:
Kobalt 30 gal 2 stage: 175psi down to 90, 30 gallon tank, 25 cfm cutoff tool: 56 seconds, refill: 4:33 $470
Husky 30 gal semi-quiet: 175psi down to 90, 30 gallon tank, 25 cfm cutoff tool: 56 seconds, refill: 4:33 $310
Dewalt 15gal:225 to 90, 15 gal, 25cfm tool: 44 sec, 3:30 refill, $410

Well, as much as I would like to have more shop projects these days I don't. I'm not going to wear out my compressor that fast so the universal motors (Husky and DeWalt) and oil free pumps (all but the 2 stage Kobalt) aren't drawbacks to me. Also, for the over $100 savings if I went with the 26gal or Husky would be more than enough to pay for a set of brushes and pump rebuild. If I were moving a lot the smaller size/weight of those designs would matter.

Of the lot I would probably pick the Husky because it's not too loud and noise isn't critical to me. If noise was critical I would probably pick the 26 gal because the performance hit isn't too bad vs the CAT and the cost savings is big.

Sorry, yet another long, rambling post.

I can't thank you enough for this helpful post!

So here's what I'm thinking about each of these units:

Kobalt 30 Gallon - Pro: 175 PSI, 30 Gallons, 5.3CFM, Oiled pump Con: Loud

Husky 30 Gallon - Pro: 175 PSI, 30 Gallons , Cheaper than Kobalt Con: Loud (but quiter than Kobalt), 5.1 CFM (vs 5.3 on the Kobalt), Online reviews not as good as Kobalt, Oil Free pump

Dewalt - Pro: 225 PSI, 78dB (not bad), only $349 Con: 15 Gallons, Oil Free

CAT - Pro: Very low noise level, 5.3CFM , Quick refill time Con: 15 Gallons, Oil Free

Kobalt 26 Gallon - Will no longer consider due to low CFM @90


So it looks like a toss up between the Kobalt 30 gallon and the CAT 15020C.
What I like about the Kobalt, is that its a larger tank, and a higher PSI. The CAT on the other hand wins in the low noise department. But then there's the refill issue. You mentioned above that CAT will refill in 1:31, but Kobalt will take 4:33. At that point, I'm thinking, who cares if its a shorter run time if it'll take 3 minutes less to refill each time. I really don't know...

 

[Citation]

Just to review noise levels,
Husky: 78
Kobalt 2 stage: 87
CAT 2hp: 70db
CAT 1hp: 60db. This is the one people typically rave about.

Point being the husky is closer to the CAT than the Kobalt for noise.

Keep the refill comment in context. First that was refill from 90 psi. My guess is the refill time is much less since it probably kicks in at something like 130. Second, it's not like you can't use the compressor as it's filling

Glad the long post was helpful!

 

[TRWham]

Do you care more how long the compressor runs for each refill, or how often it runs? Because, for a given net displacement, the total compressor run-time is going to be the same for a given total amount of air used. If the tank is smaller, the same capacity compressor will simply run more often to refill it, but it will refill faster each time it runs.

 

[DGersic]

Good point!

For reference, I have a 1 car garage, so not a lot of space. I’d love to have a monster compressor, but it won’t fit. So I have this



33 gallon, “6 HP” Craftsman. I have no problem running tools with this. Have 1/2” impact (HF Earthquake XT), as well as HF level die grinders, cutoff tool, ratchet, air hammer, etc. Some were from HF, others from Farm&Fleet. Nothing special.

The die grinder drains it fastest, and the high pitch whine carries, so my wife can hear it in the house. Garage is detached. I try not to run that past a reasonable hour in the evening. The other stuff is ok, with the door closed the noise of the compressor doesn’t carry far.



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[u3b3rg33k]

I had my friend get the "2HP" CAT 10 gal compressor. all he does is automotive work (tire changes, etc), and the 5CFM @90PSI is the number that matters (not the nonsense horsepower number). plenty of wishful thinking in the horsepower ratings (input vs output). he has a communal garage in a hoity-toity area and it keeps the neighbors from complaining about the noise.

unless you are running big continuous tools, the single most important factor is probably tank size. bigger = better.

 

[alex123]

Just to review noise levels,
Husky: 78
Kobalt 2 stage: 87
CAT 2hp: 70db
CAT 1hp: 60db. This is the one people typically rave about.

Point being the husky is closer to the CAT than the Kobalt for noise.

Keep the refill comment in context. First that was refill from 90 psi. My guess is the refill time is much less since it probably kicks in at something like 130. Second, it's not like you can't use the compressor as it's filling

Glad the long post was helpful!

I've actually been watching reviews on the Husky since my last post, and I have to say I am impressed. There are two different 30 gallon models though, both are advertising as quiet, and am not sure which one is the right option for me. There's this one, and then there's this one. I know there is a PSI difference..... so I'm interested in knowing run time for each with a fixed CFM tool (say 25 CFM for example, as we used in the prior example). I'm also interested in knowing refill time for each (approximately). Just overall, thoughts on each model would be greatly appreciated as well.

Many thanks!

 

[alex123]

Do you care more how long the compressor runs for each refill, or how often it runs? Because, for a given net displacement, the total compressor run-time is going to be the same for a given total amount of air used. If the tank is smaller, the same capacity compressor will simply run more often to refill it, but it will refill faster each time it runs.

That's like choosing between two unfavorable situations... LOL. My goal would be to get a longer run time, while minimizing the number of times the unit kicks it. When it does kick in, I'd like to keep it as short as possible.

 

[alex123]

For reference, I have a 1 car garage, so not a lot of space. I’d love to have a monster compressor, but it won’t fit. So I have this



33 gallon, “6 HP” Craftsman. I have no problem running tools with this. Have 1/2” impact (HF Earthquake XT), as well as HF level die grinders, cutoff tool, ratchet, air hammer, etc. Some were from HF, others from Farm&Fleet. Nothing special.

The die grinder drains it fastest, and the high pitch whine carries, so my wife can hear it in the house. Garage is detached. I try not to run that past a reasonable hour in the evening. The other stuff is ok, with the door closed the noise of the compressor doesn’t carry far.



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Is it the die grinder that makes the loud noise, or the compressor? I'm not sure I understood which you were referring to.
As well, that's 6hp so I'm assuming it's 240V? If it's 110V, please include the link, and I'd love to consider it. Unfortunately 240V is not an option for me though.

 

[alex123]

I had my friend get the "2HP" CAT 10 gal compressor. all he does is automotive work (tire changes, etc), and the 5CFM @90PSI is the number that matters (not the nonsense horsepower number). plenty of wishful thinking in the horsepower ratings (input vs output). he has a communal garage in a hoity-toity area and it keeps the neighbors from complaining about the noise.

unless you are running big continuous tools, the single most important factor is probably tank size. bigger = better.

The CAT looks like a really nice unit. The only problem is that I've read some really negative reviews. If you go to some of the YouTube videos, there are a number of complaints. Everything from the unit being dead on arrival, to parts falling malfunctioning within a week of purchase. It has me confused because everyone on the threads seem to like them.

 

[TRWham]

That's like choosing between two unfavorable situations... LOL. My goal would be to get a longer run time, while minimizing the number of times the unit kicks it. When it does kick in, I'd like to keep it as short as possible.

That’s three things, and physics says you can only have 2 of them at a time at most. You have put mutually exclusive constraints on the problem. A bigger tank gives you longer run time on the tank and fewer refills, but those refills will be longer. The small tank means less run time on the tank and more frequent refills, but those will be shorter. Higher cut-out pressure wouldn’t help the small tank because the refill time would increase.

 

[DGersic]

Is it the die grinder that makes the loud noise, or the compressor? I'm not sure I understood which you were referring to.

As well, that's 6hp so I'm assuming it's 240V? If it's 110V, please include the link, and I'd love to consider it. Unfortunately 240V is not an option for me though.

The noise that carries is the die grinder. High pitched whine, like a dentist drill on steroids. The compressor, with the door closed, is audible outside, but not loud.

Yes, 240V circuit for this one. It’s the tank size that matters more for what you’re looking at. The “6HP” rating is probably BS, for whatever that’s worth.




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[Citation]

I've actually been watching reviews on the Husky since my last post, and I have to say I am impressed. There are two different 30 gallon models though, both are advertising as quiet, and am not sure which one is the right option for me. There's this one, and then there's this one. I know there is a PSI difference..... so I'm interested in knowing run time for each with a fixed CFM tool (say 25 CFM for example, as we used in the prior example). I'm also interested in knowing refill time for each (approximately). Just overall, thoughts on each model would be greatly appreciated as well.

Many thanks!

OK, the 175 psi model: 175 to 90, 25 CFM 56 sec: 4:33 to refill from 90
155 psi model: 155 to 90, 25 cfm 43 sec: 3:21 to refill from 90.

Note that in both cases I don't know what the actual cut in pressures are. Once the pump kicks in it won't keep up with cutoff wheel but it will extend things a bit. However, assuming you run the tank down to 90 then the refill numbers are comparable.

In real world use the differences between these (and several others) are probably small and rarely would be noticed. More likely you are either demanding more air than either could supply or you are within the limits of both. The 75 vs 78 db is also not that much.

 

[Citation]

The CAT looks like a really nice unit. The only problem is that I've read some really negative reviews. If you go to some of the YouTube videos, there are a number of complaints. Everything from the unit being dead on arrival, to parts falling malfunctioning within a week of purchase. It has me confused because everyone on the threads seem to like them.

For what it's worth I bought a CAT 5510A off ebay for perhaps $60. Listed as leaking air out the regulator. It was in near new shape but was probably a returned item. The regulator was definitely bad but I wanted to understand why rather than just replace it. It turns out the factory installed a critical seal upside down. Upside down meant that pressure pushed the seal out of position. Once I recognized the problem it was a very easy fix. But that meant this thing left the factory without being properly tested. Until I got the 20 gallon compressor back in my garage I used the CAT quite a bit because it was quiet, sufficient for most of my needs (light impact, air gun, inflating tires), didn't have cold start issues like my Emglo (a big deal when I had questionable wiring going to the garage), and just wasn't that obnoxious to be around when it was on. It wasn't an example of great component quality and it wasn't going to take much load to exceed it's ability.

I'm tempted to keep it even now that I have the 20 gallon compressor back. The quiet aspect is just really nice.

 

[Citation]

That’s three things, and physics says you can only have 2 of them at a time at most. You have put mutually exclusive constraints on the problem. A bigger tank gives you longer run time on the tank and fewer refills, but those refills will be longer. The small tank means less run time on the tank and more frequent refills, but those will be shorter. Higher cut-out pressure wouldn’t help the small tank because the refill time would increase.

Yeah, when it comes down to it, bigger tank and higher pressure both try to do the same thing, give you more air reserve.

 

[DGersic]

Compressor noise is only one piece of the puzzle here. Air tools are noisy. And noise carries. If your primary concern is noise annoying the neighbors, the compressor matters, but so do the tools, and how and when you use them.

Is this something you’ll use every day? Day or evening? Weekends? Once a month? Your neighbors may be cool with a couple of Saturday afternoons a month wrenching on a project. They won’t be cool with cutoff wheels and air hammers at 3am every night.

Can you abate the noise? Closed doors help, but you may bake in the summer if there’s no a/c or ventilation. Is the structure detached? Or will your garage shop be directly under somebody’s bedroom?

A few dB of noise difference in the compressor won’t matter much. 10dB is significant, though.



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[u3b3rg33k]

The CAT looks like a really nice unit. The only problem is that I've read some really negative reviews. If you go to some of the YouTube videos, there are a number of complaints. Everything from the unit being dead on arrival, to parts falling malfunctioning within a week of purchase. It has me confused because everyone on the threads seem to like them.

It's a cheapish Chinese setup, so keep that in mind. I went over mind with a fine tooth comb, and torqued every external bolt down based on fastener size. Oil free is nice, but remember it's a hobby unit, rated for 4k hours of service life before it needs rebuilding. a good pressure lubed Quincy is rated somewhere around 50k hour life IIRC.

 

[alex123]

That’s three things, and physics says you can only have 2 of them at a time at most. You have put mutually exclusive constraints on the problem. A bigger tank gives you longer run time on the tank and fewer refills, but those refills will be longer. The small tank means less run time on the tank and more frequent refills, but those will be shorter. Higher cut-out pressure wouldn’t help the small tank because the refill time would increase.

Excellent summary. It's much more clearer to me now that I've read your post!

 

[alex123]

The noise that carries is the die grinder. High pitched whine, like a dentist drill on steroids. The compressor, with the door closed, is audible outside, but not loud.

Yes, 240V circuit for this one. It’s the tank size that matters more for what you’re looking at. The “6HP” rating is probably BS, for whatever that’s worth.




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Cool. Thanks for the info!

 

[alex123]

For what it's worth I bought a CAT 5510A off ebay for perhaps $60. Listed as leaking air out the regulator. It was in near new shape but was probably a returned item. The regulator was definitely bad but I wanted to understand why rather than just replace it. It turns out the factory installed a critical seal upside down. Upside down meant that pressure pushed the seal out of position. Once I recognized the problem it was a very easy fix. But that meant this thing left the factory without being properly tested. Until I got the 20 gallon compressor back in my garage I used the CAT quite a bit because it was quiet, sufficient for most of my needs (light impact, air gun, inflating tires), didn't have cold start issues like my Emglo (a big deal when I had questionable wiring going to the garage), and just wasn't that obnoxious to be around when it was on. It wasn't an example of great component quality and it wasn't going to take much load to exceed it's ability.

I'm tempted to keep it even now that I have the 20 gallon compressor back. The quiet aspect is just really nice.

Yes, I think those units are close to 70 dB. Your recommendation of the Husky compressors is actually a good one. They are rated at 75dB/78dB

 

[alex123]

OK, the 175 psi model: 175 to 90, 25 CFM 56 sec: 4:33 to refill from 90
155 psi model: 155 to 90, 25 cfm 43 sec: 3:21 to refill from 90.

Note that in both cases I don't know what the actual cut in pressures are. Once the pump kicks in it won't keep up with cutoff wheel but it will extend things a bit. However, assuming you run the tank down to 90 then the refill numbers are comparable.

In real world use the differences between these (and several others) are probably small and rarely would be noticed. More likely you are either demanding more air than either could supply or you are within the limits of both. The 75 vs 78 db is also not that much.

The 175 psi model is about $100 cheaper... I think that's better based on the fact that it gives me a slightly longer run time (at the cost of slightly longer refill). You're right, the 3 dB is negligible.

 

[alex123]

Compressor noise is only one piece of the puzzle here. Air tools are noisy. And noise carries. If your primary concern is noise annoying the neighbors, the compressor matters, but so do the tools, and how and when you use them.

Is this something you’ll use every day? Day or evening? Weekends? Once a month? Your neighbors may be cool with a couple of Saturday afternoons a month wrenching on a project. They won’t be cool with cutoff wheels and air hammers at 3am every night.

Can you abate the noise? Closed doors help, but you may bake in the summer if there’s no a/c or ventilation. Is the structure detached? Or will your garage shop be directly under somebody’s bedroom?

A few dB of noise difference in the compressor won’t matter much. 10dB is significant, though.



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You make an excellent point. This compressor will be used strictly for automotive repair and maintenance. So I think I'll use it once every 3 weeks to a month. Even then, it'll be during the day. So maybe I'm dwelling too much on the noise. Again, excellent point.

 

[alex123]

It's a cheapish Chinese setup, so keep that in mind. I went over mind with a fine tooth comb, and torqued every external bolt down based on fastener size. Oil free is nice, but remember it's a hobby unit, rated for 4k hours of service life before it needs rebuilding. a good pressure lubed Quincy is rated somewhere around 50k hour life IIRC.

Thank you for letting me know. Honestly, if I can get 4k hours of service, I'll be jumping for joy. I only intend on using the unit 1-2 times per month.

 

[bsaint]

Won't that setup take forever to fill the tank?

No not a real 1.5hp.

 

[alex123]

Just to review noise levels,
Husky: 78
Kobalt 2 stage: 87
CAT 2hp: 70db
CAT 1hp: 60db. This is the one people typically rave about.

Point being the husky is closer to the CAT than the Kobalt for noise.

Keep the refill comment in context. First that was refill from 90 psi. My guess is the refill time is much less since it probably kicks in at something like 130. Second, it's not like you can't use the compressor as it's filling

Glad the long post was helpful!

I was just rereading this thread, and thought about something. I noticed some people are taking their air compressors and adding an auxiliary tanks for higher capacity. As for right now, the Husky is the front runner for me. Down the road, would adding an auxiliary tank be an option for me if I go with the Husky?

 

[Citation]

Yes, you can add a second tank. The easiest way (not the best) is to make a T fitting then use a hose to connect the second tank/compressor in line with the first. It's best if the second tank's safe working pressure and blow off valve match that of the compressor. More complex if they don't.

I messed with it a while back when I happened to have a pair of 4 gallon compressors. Too bad I didn't have 2 circuits in the garage so it just gave me extra tank, but not CFM.

Here are a few videos where people did this.

This video is well done but I think his setup would be better if he included a shut off valve on the line into the pig tank. It would allow him to disconnect the pig tank without the need to drain it first and allow it to still be used as a portable tank.

 

[alex123]

Yes, you can add a second tank. The easiest way (not the best) is to make a T fitting then use a hose to connect the second tank/compressor in line with the first. It's best if the second tank's safe working pressure and blow off valve match that of the compressor. More complex if they don't.

I messed with it a while back when I happened to have a pair of 4 gallon compressors. Too bad I didn't have 2 circuits in the garage so it just gave me extra tank, but not CFM.

Here are a few videos where people did this.

This video is well done but I think his setup would be better if he included a shut off valve on the line into the pig tank. It would allow him to disconnect the pig tank without the need to drain it first and allow it to still be used as a portable tank.

Thank you for sharing this info. My understanding is the CFM stays the same, capacity increases by whatever the amount of the auxiliary tank is, PSI stays the same, tool run time increases, initial and refill fill ups take longer. It's this correct?

 

[DGersic]

Thank you for sharing this info. My understanding is the CFM stays the same, capacity increases by whatever the amount of the auxiliary tank is, PSI stays the same, tool run time increases, initial and refill fill ups take longer. It's this correct?

Yes, exactly.



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[Citation]

Thank you for sharing this info. My understanding is the CFM stays the same, capacity increases by whatever the amount of the auxiliary tank is, PSI stays the same, tool run time increases, initial and refill fill ups take longer. It's this correct?

As DG said, yes. But if you have a second circuit you can use the second pump as well.

 

[alex123]

Yes, exactly.



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Thank you. I guess they just sell empty tanks for this kinda stuff? I don't habe 2 compressors

 

[alex123]

As DG said, yes. But if you have a second circuit you can use the second pump as well.

That would be awesome... But unfortunately I don't have 2 compressors. But hey, the price of the husky makes it worthwhile to buy 2. That way I get twice the run time... And its still 110v