Air compressor size recommendation

[drummerdimitri]

So I currently have a 24L air compressor with a 2 HP electric engine for home use (air dusting, tyre pumping, spray painting etc...)

that I feel needs to be upgraded to a 50L or maybe even a 100 L compressor since the one I own is constantly working to replenish the air

in the tank and doeskin have enough air to get most jobs done.

I've owned a 50L air compressor in the past and it was more adequate for my needs but can anyone give me a reason to go for the 100L

model? I'd like to future proof it so maybe even consider running air tools with it but will the 50L one be enough is do I NEED the 100L

model to be able to run anything off of it?

[GreyWoolfe]

It's not just the size of the tank.  The amount of air it moves at a given PSI is important.  That said, I have basically the same compressor you have.  I not only wish I had gotten one with a bigger tank but also a bigger engine and the ability to move more air.  I have hand sander that runs the tank out amazingly fast so it is useless to me.  Go for the 100L tank but make sure it can move enough air for any tool you think you might want to buy in the future.

[drummerdimitri]

Are your referring to the CFM specification?

I don't what what tool I will be using eventually but just wanted to know if a 2 HP 50L air compressor would be enough for a spray gun and maybe even an air ratchet.

Not many compressors have that specification given and even if they did they wouldn't specify at what PSI it holds true...

Also, an Italian branded 50L would cost me 200$ whereas the 100L model runs for 400$ which is a bit on the expensive side for hobby use.

[eKretz]

CFM is definitely the most important thing to get right. Tank size really doesn't make a huge difference as long as you're within reason of where you need to be. If the pump can't keep up with the air tools you're using, the tank size will make no difference. I have an 18 CFM compressor and still sometimes run out of air. Of course it will depend on what type of tools you're using. If you have a tiny little CFM requirement then the larger tank size might be nice but then it will take a lot longer to pump it up as well - so you trade off running less often for running longer or vice versa.

[rx8pilot]

The way you use the system is the first thing to sort out.

If you plan to use tools that will run for a while consuming more CFM than the pump can deliver - you need a bigger compressor.
If you plan to run tools that need higher CFM than the compressor can deliver, but only briefly, you need a bigger tank.

The latter dominated my last air system design ($25k system). We needed a LOT of CFM but only in short bursts. The average CFM was rather modest. So I figured out how big the tank needed to be to deliver the burst at the specified PSI, CFM and time while the compressor was running. When the burst demand was done, the compressor was able to re-fill the tank before being needed again. I ran the tank at 175PSI with a 100PSI regulator for the system pressure. This allowed me to get a much smaller compressor and still run some big tools, but with a time limit as a compromise.

If you are running a paint system, sanders, or any other tool that pulls a constant CFM from the system that is above the capacity of the pump - you will lose pressure and have to stop work while the system recovers.

[Mechatrommer]

If you want to be a pro full body car painter, certainly go for 100l. I have 50l comp 3hp motor (upper and lower repumping psi limit adjustable currently at 60-90psi, 180psi max red line limit)  i've done personal painting for doors, house, big closet etc just fine,the key is better quality paint gun and err proper place to do the job. Above all, the most important part is you need a regulator, its 3 fold purpose, to regulate pressure hence constant pressure everytime, 2nd is you save motor pumping from excessive air usage (unregulated) and to trap moisture out of your gun...for electronic use, i think 50l is overkill to ok already..yours 25l should be ok imho, esp little work like airbrushing but ymmv...remember... the regulator something like this cheap one can make a better day, you can get more expensive and better than this.. https://www.ebay.com/p/Air-Filter-Pressure-Regulator-Airbrush-Compressor-W-Water-Trap-Gauge-Bracket/691365316?iid=261494054661

[drummerdimitri]

Lots of good information here thanks.

So here's the thing, I do not need to run tools for too long and I'm fine not using the air compressor while it is pumping air into the tank.

If I only used the the compressor while the motor is not pumping then the CFM specification is rendered useless correct?

CFM is how much air the engine can put out without a tank under constant use am I right?

HP will dictate how fast it recovers pressure and fills the tank and a higher maximum PSI would be better since I could get "more air"

with a pressure regulator valve if my tool does not need 145 PSI which is what the one I'm looking to get is rated at.

Should I get on of those silent versions (70dB) instead of the standard 95dB models? Are there any downsides to them?

[rx8pilot]

At my home lab, I use the California Air Compressors which are really quiet. It cycles about 10-15 times per day 7 days/week for the most part. As far as I can tell - it puts out about the same CFM per horsepower as the more typical loud compressors and doesn't really cost that much. The lower speed they run at is also cooler which is better for condensation. It still gets water in the tank, but not nearly as much as other low-cost home units.

[Mechatrommer]

So here's the thing, I do not need to run tools for too long

if you can live with that. with smaller tank, you need to run/operate slower in order for the compressor to catch up with your cfm need.

and I'm fine not using the air compressor while it is pumping air into the tank.

yes. you also fine to use during pump or not pump... you also fine to not use during pump or not pump.

If I only used the the compressor while the motor is not pumping then the CFM specification is rendered useless correct?

CFM is air volume cubic feet per minute... its related to tank pressure, low psi = low cfm, high psi = hi cfm, from spray gun point of view. what is your need? usually i dont care mine as long as its working. but unregulated pressure will make things harder for example you want a uniform layer of paint. its difficult to maintain paint hand speed if pressure (hence cfm) is keep changing, thats why you need a regulated pressure. the best is you set the regulated pressure to equal or lower than the compressor lower limit psi setting (ie when motor start pumping again to reach higher psi limit)

CFM is how much air the engine can put out without a tank under constant use am I right?

from motor/engine point of view, the larger/faster the motor, the higher CFM of air it can put into the tank, but it also a function/differential of atmospheric and tank pressure. simple rule = larger motor (and number of pistons) = higher cfm.

HP will dictate how fast it recovers pressure and fills the tank and a higher maximum PSI would be better since I could get "more air"

as said, higher HP = higher CFM hence you get your tank filled quicker to the set pressure. maximum pressure will depend on piston capability and its torque curve capability or efficiency, its mechanical thing, electrically, motor only provides the torque to the piston.

It cycles about 10-15 times per day 7 days/week for the most part.

this is a function of leakage, more leakage = more pump cycles everyday... with good seal, a tank can maintain pressure in weeks without re cycling. but this only if you remove hose and everything from the tank's outlet, given the tank itself and everything fixed to it is in good seal, its hard to maintain seal on older equipments except if you can spend time to do replacements on o rings etc. remember to drain liquid/water out of the tank at regular basis. there usually a drain valve below the tank for the purpose, accumulated liquid in the tank may rust and shorten the life of it.. fwiw...

[BradC]

I have a generic 2.5HP V-twin low pressure (115PSI) compressor with a 50L tank. I run the output of that through a water separator and into a pair of 20M 3'8" hoses which are buried in the garden to get air to my garage. From there it dumps into a 200L vertical receiver. Out of the top of that it goes into another water separator/regulator. So I have about 250L of reserve air capacity.

That is enough to run a small HVLP spray gun, plasma cutter (within its own duty cycle) or tiny sand-blasting cabinet. Any bigger users (like 1/4" die grinder or large air ratchet) relatively quickly run into the air delivery limitation of the compressor. The bigger reserve capacity allows the compressor to run in longer stints and the buried hoses work really well for dropping extra moisture out of the air.

Certainly enough for weekend mechanic rattle gun or cleaning up stuff in the blasting cabinet.

It recently developed a leaky seal on one of the water traps, so it's cycling about once every 2 days at the moment. When it's sealed up properly I can leave it on and it'll cycle once every other week or so, but you have to be pretty fastidious with the leak detection bubble fluid to get those sort of hold up times under pressure. Having ball valves to isolate each quick-connector helps too as they can leak a bit and are hard to dismantle to clean.

I had a little 2HP 24L direct drive screamer for a few years and it did an OK job, but they're not designed to work as hard as I was working it and if I forgot to turn it off I was alerted to it running in the middle of the night by one of the neighbours banging on my front door at 2am. The belt drive is quiet enough that it's no biggie if I forget to turn it off.

[rx8pilot]

It cycles about 10-15 times per day 7 days/week for the most part.

this is a function of leakage, more leakage = more pump cycles everyday... with good seal, a tank can maintain pressure in weeks without re cycling. but this only if you remove hose and everything from the tank's outlet, given the tank itself and everything fixed to it is in good seal, its hard to maintain seal on older equipments except if you can spend time to do replacements on o rings etc. remember to drain liquid/water out of the tank at regular basis. there usually a drain valve below the tank for the purpose, accumulated liquid in the tank may rust and shorten the life of it.. fwiw...

It gets used quite a bit and the distribution system has a few dozen outlets and quick connects, blow-off guns, etc that keep a constant small leak in the system. I have not tried to test the compressor itself for leaks. With all the stuff connected to it, normal use is a lot more than any other factor. When I am not using anything at all - it probably cycles about every 2 hrs or so with a tiny 6gal (22l) tank. Not horrible I guess.

[Mechatrommer]

you have few dozens outlet from 22l tank? man thats ironic.

[rx8pilot]

its all very low use stuff like solder despensers, low cfm blow guns that rarely get used, etc. The number of outlets is mainly about having what I need where I need it. The total system consumption is still quite low.

Sent from my SAMSUNG-SM-G890A using Tapatalk

[tautech]

Your air compressor choice and rating is ultimately determined by only 3 things:
Peak CFM usage
Budget
Single or three phase power availability.

The hungriest (CFM) appliances IME are:
Sand blasting rigs.
Die grinders
Big nozzle dusters
Air Drills
Air grinders
Large (1/2"+) ratchet guns.

I've built a few compressor setups for my own use over the years and the best was 2 cyl 2 stage ~25 CFM 3 phase monster that could run a duster with a 1.5mm nozzle continuously @ ~90 psi and that still wasn't enough to run a die grinder without giving it a break to catch up. Lost it in a fire. 

Currently I have a 3 cyl homemade job for general light workshop duties that supplies ~12-15 CFM that is just large enough to handle most duties if you're not in a hurry to get things done.
If you go down a DIY path, factor in ~6 CFM for each HP of motor required with a single phase supply, you can allow a little less HP if 3 phase motors are used.

[nctnico]

It's not just the size of the tank.  The amount of air it moves at a given PSI is important.  That said, I have basically the same compressor you have.  I not only wish I had gotten one with a bigger tank but also a bigger engine and the ability to move more air.  I have hand sander that runs the tank out amazingly fast so it is useless to me.  Go for the 100L tank but make sure it can move enough air for any tool you think you might want to buy in the future.

For things like drills, sanders, etc it is better to get an electric one. Compressed air is very inefficient.

[Kjelt]

You can always add a second bigger tank if you need one.
I have an airpress 2500W 230VAC compressor with a 100l tank at 12 bar , price was around $700 IIRC, but I can not use a sander or a wretchet for a longer period of time.
My supplier told me that the motor should not run for a long period of time or it will shorten its life (overtemperature).
It should run about 4-6x an hour max so it could cool down sufficiently.
So if you want to work continuously for an hour or so you should buy a professional compressor that is designed to run continuously or at least for a longer stretch of time, probably better aircooled and much more expensive or goto huge tanks.

[nctnico]

Bigger tanks just take longer to fill. Basically the size of the tank governs the interval at which the compressor will run (given a constant use of air). But if you need more air than the pump can deliver you'll always run out of air. I'd go for a small tank because it will be quicker to fill.

[Mechatrommer]

but small tank will usually come with small motor and only can fit single piston. unless you want to custom made your own compressor...

[MacMeter]

Funny I just began researching air compressors, but the small type, 2 gallon tank, 1 HP motor, for air blowing mostly. The rule of thumb from what I've read is keeping the HP requirement below 2 HP if plugging into US 120 V. mains, so I'm limited to outlet power.

I think this is the model I'm going to buy:
http://www.californiaairtools.com/ultra-quiet-series-of-air-compressors/1-0-hp-air-compressors/cat-2010a/

I like the idea of an aluminum air tank that won't get rusty, and using an inline water filter I hope to get fairly clean air for blowing out computer and other air blow gun tasks. For in home use, the sound output rating of 60 db is what makes this brand of oil less compressors so popular.

Here is a site PDF page, that lists CFM for various air tools:
http://webtest.appletoncompressor.com/wp-content/uploads/2011/04/Air-Tool-or-Equipment-CFM-Requirement.pdf

[SeanB]

Remember that steel tanks need to be pressure tested every few years ( depends on what your local regs are, here it is every 3 years) for safety, and that aluminium tanks, while not being as subject to corrosion, are however very subject to fatigue, and also need the same pressure test regime.  If you get a largish compressor, also get an auto drain valve, preferably an electrically timed one, and use it to drain the tank automatically periodically. That way the moisture is removed from the tank, and it does not build up at all.

Get an oil coalescing filter ( preferably 0.2micron or better) and place on the air outlet, it does a good job of getting the oil mist out and getting a bit more of the water out. However for really dry air you will need some form of air drier, either a refrigerant unit that condenses the water out, or a PSa drier that uses a zeolite and regenerates the substrate to recycle it. A larger tank as well also cools the stored air, and this also reduces the amount of water in the compressed air, as it gets to 100% RH at a cool temperature, instead of having hotter air which can hold more vapour.

[MacMeter]

Remember that steel tanks need to be pressure tested every few years ( depends on what your local regs are, here it is every 3 years) for safety, and that aluminium tanks, while not being as subject to corrosion, are however very subject to fatigue, and also need the same pressure test regime.  If you get a largish compressor, also get an auto drain valve, preferably an electrically timed one, and use it to drain the tank automatically periodically. That way the moisture is removed from the tank, and it does not build up at all.

Get an oil coalescing filter ( preferably 0.2micron or better) and place on the air outlet, it does a good job of getting the oil mist out and getting a bit more of the water out. However for really dry air you will need some form of air drier, either a refrigerant unit that condenses the water out, or a PSa drier that uses a zeolite and regenerates the substrate to recycle it. A larger tank as well also cools the stored air, and this also reduces the amount of water in the compressed air, as it gets to 100% RH at a cool temperature, instead of having hotter air which can hold more vapour.

Hopefully, a SMALL 2 gallon aluminum tank will last the the 3000 hour life of the dual pump motor, and I'm not too concerned about fatigue, if it's designed properly. Sure steel is strong material if the potential rusty air is not a factor.

Auto drain devices are too large for small compressors this size, but its super easy to manually drain the tank after use. I don't expect too get completely DRY air on a simple setup, but on an oil less unit, I'm not concerned with that element. The "air" in those expensive throw away cans is full of chemicals and depending on the angle of use can freeze up both can and object in front.

[rx8pilot]

I had auto drains on my 20hp and 10hp systems at my CNC shop. At home, I just have a line connected to a manual valve at the end to periodically drain it. I put the compressor in kind of a hard to reach area and it is elevated just because it was the easiest spot for it and right next to the power source. In southern California it is not nearly as bad as when I lived in Houston, Texas. Compressors fill up like a bath tub there.

For the really small and occasional use - manual drains certainly work as long as you actually do it. The auto-drains can save you from yourself if you tend to forget about those things. A ruptured tank can be a problem, but at 130-ish PSI they generally don't catastrophically explode. More than likely (if anything) you end up with a leak that is very easy to hear. It does happen. My 10HP system operated at 175PSI, which had me worried enough to play it totally by the book with safety valves, auto drains, and inspections.

[Kjelt]

In southern California it is not nearly as bad as when I lived in Houston, Texas. Compressors fill up like a bath tub there.

I only do manually every three months or so and get 3cc of water max.
Depends ofcourse on usage and climate.
I never ever saw something like this though 
https://youtu.be/ElQH4FrhDvY

[MacMeter]

In southern California it is not nearly as bad as when I lived in Houston, Texas. Compressors fill up like a bath tub there.

I only do manually every three months or so and get 3cc of water max.
Depends ofcourse on usage and climate.
I never ever saw something like this though 
https://youtu.be/ElQH4FrhDvY

I'll take my chances with an aluminum 2 gallon tank just to avoid rusty air!

[rx8pilot]

In southern California it is not nearly as bad as when I lived in Houston, Texas. Compressors fill up like a bath tub there.

I only do manually every three months or so and get 3cc of water max.
Depends ofcourse on usage and climate.
I never ever saw something like this though 
https://youtu.be/ElQH4FrhDvY

Wow - never seen anything quite like that before.