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Idea: How to Search for an Air Compressor

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WarthogARJ

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Hi there,
My first post, and I hope it will be of use.
I needed to buy an air compressor for an upcoming project: nothing hard, just needed a mid range DIY type.
So do I buy what I need, pay a bit more and get what i need NEXT project, or rent?
Sigh.

There are a LOT to look at.

I decide the Abbac range is of reasonable quality, and has a big range.
VERY big, so big it's easy to get lost.

Comment:
Based on excellent feedback below, I've modified this a bit.
The assumptions here are:
(1) Buying a NEW machine.
Obviously a good deal on a used machine won't be an exact match for price
(2) Don't need to run it 24/7/365, as in this is home use, not industrial/commercial
(3) You only look at machines where you know they are of reasonably quality
(4) Noise is not considered because you quickly see that getting a quieter machine is pretty well impossible unless you can live with very low rates, or very high price
THEREFORE, as I mention in replies to comments, if you want LESS noise, then move the machine AWAY from you.
Use a long pipe, of the right OD, and put it where your NEIGHBOURS can hear it, but not YOU...:-}
(5) Yes, I know FAD is better to use than theoretical CFM, but you will struggle to get FAD values on the machines sold for the non-industry use

I made an Excel spreadsheet of abut 20-30 of the Abbac models.
To get an idea on how the specs changed.
Then, based on basic physics, it's obvious how to rank therm, to see the trends of the "power/size/oomph" of what you can get versus price.
OK, "oomph" doesn't really have SI recognised units, but here's what i did.

In an air compressor, you want some combination of PRESSURE x SUPPLY RATE.
They generally have some link/correlation, so let's make life simpler: we'll multiply the PRESSURE (in Bar) x Supply Rate (in lpm).
Let's call THAT combo the "Oomph Factor".....:-}

Note: the value does have some physics justification, it's actually WORK (Watts), but let's keep it in units of Bar-lpm for now, and call it "Oomph" for fun.

Next factor is VOLUME of receiver tank.
Bigger is Better, in general (as my English ladyfriends say of Canadians...:-}
Assuming you don't have a space issue.

And next, well, PRICE is a big factor.

So what you do, is make a graph as follows:
(1) Break up the compressors into "Families" of Receiver Volume size: 6, 24, 50, 90, 150 litres.
(2) In each FAMILY, you plot Oomph vs Price.

See attached.
The point is, that the BEST area in this graph is Bottom Right corner.
As in, you want the BIGGEST "Oomph" you can get, at LEAST PRICE.
That's where the Arrow points.

That is, if you want a general purpose, do-all machine.
And THEN, in the same general range of "Ooomph", you would like to get as big a Volume receiver as you can.
As long as you can still afford it.
And you can still fit it in (really, no pun intended).

So the BEST region, in terms of "Oomph" vs Price is circled in Blue.
And if you pay a little bit more, you get a 50 litre unit, rather than 24 litre.

I bought that: Montecarlo 30P

If you have more $$$, and want more Oomph, go higher up.
But go UP, and to the RIGHT.
That's the best direction.
But you pay more.

However, as far as value for $$$, the Abbac Montecarlo 30P is the best pick.
If you can afford the $$$.

Otherwise, for LESS $$, move DOWN a bit, but keep RIGHT.
The best for low $$$, and Max Oomph is the Pole Position L20.

I am at present in the Land of Brexxit.....sigh.
So it's all in Pounds (Pounds in a METRIC Country? Ah, but guys still weigh themselves here in STONE. And the highway is in MILES....and on wrong side of road too...).

I say sigh, because I ENTERED it with a EUROPEAN Passport (courtesy of my English Father).
And after Brexxit.....it has decayed to UK only.
So I'm stuck.

You can use your own data if you live in TrumpLand.

Or in the Land of the Free, North of there (without all the gun deaths), you can put in whatever Canadian Tire sells...:-}

But regardless, the concept holds true.

Viva Ooomph!!

Alan
King of Ooomph
P.S. I posted the Excel spreadsheet if anyone wants it.
 

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TFrench

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If you want ultimate ooooomph and quiet, get a hydrovane. I got one at work, it's quiet enough that you can hold a conversation next to it. Cost me £350 and all I had to do was service it.
 

baldkev

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Just work out what the most power hungry tool will be and buy a compressor that will more than cooe with it. I.e a 14cfm tool will need a good capacity of storage plus a high recharge rate so the machine isnt always struggling
 

sometimewoodworker

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While @WarthogARJ s approach is certainly an excellent start, and much thanks for the work, it leaves out 3 important factors and looks to be a bit of a been counters one.
The first missed point is as has been mentioned sound level.
The second is expected lifespan. Probably not the easiest to discover, though duty cycle may help.
The third is avalablety of spare parts.
all 3 of those assuming you want 1) lowish 2) good 3) good will move you way above the the lowest prices.
 

Fergie 307

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Most important thing you don't appear to have considered is free air delivery. This is not the same as the rated cfm, it's always lower. FAD is a much more accurate representation of what will actually be delivered to the tool. Problem is most manufacturers highlight the theoretical cfm figure, based on displacement etc but a compressor that has 15cfm on this basis might only have a FAD of 10cfm. So if your most hungry tool needs 15 cfm then you need to make sure that the fad is higher than that. Then noise. As T French says a vane type is much quieter, but also more expensive.
 

WarthogARJ

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Just work out what the most power hungry tool will be and buy a compressor that will more than cooe with it. I.e a 14cfm tool will need a good capacity of storage plus a high recharge rate so the machine isnt always struggling
Yeah, I started out doing that. But then as I said, I wasn't sure what I'd end up needing it for.
So this approach is more for trying to get as much as you can, and try not to spend too much $$$.

In any case, this way helps you organise a lot of different machines.
 

WarthogARJ

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Most important thing you don't appear to have considered is free air delivery. This is not the same as the rated cfm, it's always lower. FAD is a much more accurate representation of what will actually be delivered to the tool. Problem is most manufacturers highlight the theoretical cfm figure, based on displacement etc but a compressor that has 15cfm on this basis might only have a FAD of 10cfm. So if your most hungry tool needs 15 cfm then you need to make sure that the fad is higher than that. Then noise. As T French says a vane type is much quieter, but also more expensive.
Yeah, good point.
Correct me if I'm wrong, but it seems hard to get a reliable/consistent value for FAD.

And my feeling is that for a given TYPE (as in direct drive), especiallly for a given manufacturer, then the ratio of CFM/FAD will be pretty constant.

Do you have values for FAD for a large number of compressors?
If you do, point me to them, and I'll add it to the analysis.
I couldn't find many machines that provide FAD data though.
 

WarthogARJ

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While @WarthogARJ s approach is certainly an excellent start, and much thanks for the work, it leaves out 3 important factors and looks to be a bit of a been counters one.
The first missed point is as has been mentioned sound level.
The second is expected lifespan. Probably not the easiest to discover, though duty cycle may help.
The third is avalablety of spare parts.
all 3 of those assuming you want 1) lowish 2) good 3) good will move you way above the the lowest prices.
Thanks.
Yes indeed, I don't really intend it to find the PERFECT machine.

I DID consider noise level, and to be honest, I myself would prefer a quiet machine, and would pay extra.
But, for a general purpose/home-DIY machine you seem to need to accept what you are given.

In any case, I would grab the sound level issue by the horns, and AVOID it.
As in, if it's a noisy pipper, why put it in the same room as YOU are?
Just add in larger bore pipe/tube to it, and put it where your NEIGHBOURS can hear it, but you cannot...:-}
Heh heh...or, in a more soundproofed area.

That's how it's done in industry, in any case. You put in a BIG air compressor and then pipe its output around as you need it.

Lifespan: yes, sure. But that's as you say a fuzzy concept, and I have addressed it to some extent by only graphing the Abbac range, which seems reasonable quality.

As far as duty cycle, that's not a relevant fact here, because all these things are going to be roughly the same range. If you DO want a given duty cycle, then PRICE begins to be much less important.

And in fact, the way to avoid THAT issue is also to AVOID it.
Most people don't understand this point, but the air they get is NOT from the PUMP.
It's from the RECEIVOR.
You use the PUMP to pressurise the receiver, and then once it's at set point, it turns off.
Then you draw down on the stored air.

Physics again: the PUMP has a SMALL piston, as in a fraction of a litre.
And its RPM is not very high: say +/- 3k I think I've seen.
So you cannot get your piston to supply the CFM (or FAD if you like) at the PRESSURE you need.
Not for any length of time.

So you store it up.

And if you need MORE "oomph", what do you do?
Well, the brute force way is to buy a bigger pump.
Expensive.
But I think you're better off getting a bigger RECEIVOR: a second one.

And if you want a REALLY nice system, designed properly, I'd do as follows:
- Standard pump feeding a standard sized receivor (start off with this)
- High pressure pump, feeding....a high pressure receivor
You then link them up.
And have them feed a big bore line, and put them where you don't hear them.

The high pressure pump doesn't need to be very big, it just needs to get to say 300 Bar.
Get a used (but still safe) nitrogen or argon cylinder, or better, get two.
Not so easy to find, but they do come up for sale.

This is not an off-the-shelf machine: you need to be able to design for the pressure, and do it safely.
Adding in pressure relief valves where needed.
And I'd get the used bottles retested to be safe: but that's not expensive.

As for spare parts, well, again, you only add in brands where you CAN get spare parts.
But to be honest, I don't see it as a big deal. These are SIMPLE systems, you don't NEED to buy a spare part from the dealer in most cases.

And you should modify your machine so it runs better.
Add in better cooling: if it stays cooler, it will last a LOT longer.

Is easy to add in another fan, and run it on PWM control, off a temperature sensor.
For the pump side, if it gets pretty hot during its work, improve the cooling on that too.
Add fins and a fan as well.
 

WarthogARJ

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If you want ultimate ooooomph and quiet, get a hydrovane. I got one at work, it's quiet enough that you can hold a conversation next to it. Cost me £350 and all I had to do was service it.
Yeah, I think the majority of what's sold are pretty crude machines.
But £350 is a lot more, and I suspect that was 2nd hand price too, right?

And as I said, if less noise is a factor, why not move the MACHINE away from where you WORK?
If you do the calcs, you can soon see that you don't need to use incredibly big piping to reduce line pressure drop to very low.

Pressure Drop Calculator

There are lots available, but this is easy to use.
Put in however many meters of pipe you'd need to put it next to your neighbour's bedroom window.
And adjust the OD to get the pressure drop you can live with.

It's a bit quirky, the UNITS on the flow rate change themselves, and gives you an error.
You need to keep changing them back to what you want every calculation.

For the air properties, you can get values from engineersedge, or else use:
Air Temperature: 25 C
Density (kg/m^3) = 1.184
Kinetic Viscosity (10^-6 m^2/sec) = 15.62

For a bit fancier, specify it at 15 Bar, and inlet at 25C, outlet at 20C (to show some cooling as it flowx through a long supply pipe).

The intent is not a NASA grade calc, but rather to see that 6mm ID is MUCH too small, and 8mm, or 10mm is needed at the least for anything very long.

In fact in a REALLY long supply line, it itself begins to act as part of your receiver/storeage system.
And you might choose to keep it at a higher pressure than you need for your tools, and add a secondary pressure valve at the end.
 

WarthogARJ

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Once you own a compressor you will rework the chart by plotting oomph against appalling cacophony. If you can hear yourself think, that is.
Aha, but there's an easy solution. Just buy bigger loudspeakers for your stereo!

Is same as if you have a car with annoying grinding or sqealing sounds: turn your radio up.
Voila, all that goes away.
If leaking oil begins to blur the windscreen, you can add a better degreaser in your wiper fluid to deal with that.
If the smoke from the engine starts to obscure your vision, that's harder to address.
Usually the best solution to that is to increase insurance, and leave car parked with keys in it.
That solves everything.

But surely, I don't need to suggest this to a Russian/Greek, do I?
 

Trainee neophyte

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Aha, but there's an easy solution. Just buy bigger loudspeakers for your stereo!

Is same as if you have a car with annoying grinding or sqealing sounds: turn your radio up.
Voila, all that goes away.
If leaking oil begins to blur the windscreen, you can add a better degreaser in your wiper fluid to deal with that.
If the smoke from the engine starts to obscure your vision, that's harder to address.
Usually the best solution to that is to increase insurance, and leave car parked with keys in it.
That solves everything.

But surely, I don't need to suggest this to a Russian/Greek, do I?
I am followed mercilessly by by a troop of jibbering monkeys. Every time I buy a car, there is blissful silence and tranquility, until the monkeys work out I have changed vehicles and take up residence in the new one. It takes a week to ten days before the jabbering and screeching begins - subtly at first, as they don't like to admit to their presence, but I can hear them. After a few years you have to shout to have a conversation so eventually I give in and swap my monkey-demon possessed car for a new one, and all is peace and happiness for about a week.



...and the nature of Monkey was irrepressible.
 

sometimewoodworker

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Get a used (but still safe) nitrogen or argon cylinder, or better, get two.
Not so easy to find, but they do come up for sale.
I would look at diving cylinders as, if you can buddy up with a testing shop they will tell you when they have cylinders that fail the inspection & if you guarantee that they will only ever be used at 150bar or under you may be able to buy them. You will be limited to 11 litre tanks but maybe able to get them at a reasonable price.

In fact there are a couple of 15 litre tanks on eBay that are out of test selling for £20 & £22. Ideally you would get them tested, that would give you a 5 year, in test, lifetime with the likelihood of them retesting again.
 
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clogs

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looking for a compressor.....
for general use and want it to last
1, pump needs to be cast iron if poss, twin cylinder...better cooling if a V twin....
2, always a belt drive, much quieter and if the motor or the pump goes easy to replace the item.....small direct drives are just so noisey....gotta think of the neighbours....like it or not....
3, biggish tank but thats a personal choice depending on room and mobility....
4, costing, but I would be thinking of around £400 plus.....unless u go used....
5, there are some excellent used comp out there, mostly because people buy to SMALL.....remember the big ones wont like working on an extension lead...

I was lucky to buy this monster for not much more than a new 14 cu/ft comp....but it's 3 phase.....Atlas-CopCo....very quiet .....check out the size.... compare the chair....put it on caster as once a year I totally empty my workshop and sweep n wash the floors....not for everybody tho....hence cost...
IMG_0793.JPG
 

Sandyn

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There is a comparison method called multicriteria decision analysis which is really good technique for finding the most suitable choice based on your personal requirements. You first identify the parameters which are important to you and allocate a weighting factor and for each compressor, a score. Each machine gets a rating, which is the weighting factor multiplied by the score. Many levels can be nested if a parameter has sub-parameters. It's a lot simpler than my explanation, lol. You put in all the figures and the 'best' option gets the highest score.
 

Fergie 307

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Yeah, good point.
Correct me if I'm wrong, but it seems hard to get a reliable/consistent value for FAD.

And my feeling is that for a given TYPE (as in direct drive), especiallly for a given manufacturer, then the ratio of CFM/FAD will be pretty constant.

Do you have values for FAD for a large number of compressors?
If you do, point me to them, and I'll add it to the analysis.
I couldn't find many machines that provide FAD data though.
They really should quite it as part of the spec, but often you have to ask. Generally I would say places that specialise in compressors will give that information in their listings, places like Machine Matt maybe not.
 

Pineapple

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Thanks.
Yes indeed, I don't really intend it to find the PERFECT machine.

I DID consider noise level, and to be honest, I myself would prefer a quiet machine, and would pay extra.
But, for a general purpose/home-DIY machine you seem to need to accept what you are given.

In any case, I would grab the sound level issue by the horns, and AVOID it.
As in, if it's a noisy pipper, why put it in the same room as YOU are?
Just add in larger bore pipe/tube to it, and put it where your NEIGHBOURS can hear it, but you cannot...:-}
Heh heh...or, in a more soundproofed area.

That's how it's done in industry, in any case. You put in a BIG air compressor and then pipe its output around as you need it.

Lifespan: yes, sure. But that's as you say a fuzzy concept, and I have addressed it to some extent by only graphing the Abbac range, which seems reasonable quality.

As far as duty cycle, that's not a relevant fact here, because all these things are going to be roughly the same range. If you DO want a given duty cycle, then PRICE begins to be much less important.

And in fact, the way to avoid THAT issue is also to AVOID it.
Most people don't understand this point, but the air they get is NOT from the PUMP.
It's from the RECEIVOR.
You use the PUMP to pressurise the receiver, and then once it's at set point, it turns off.
Then you draw down on the stored air.

Physics again: the PUMP has a SMALL piston, as in a fraction of a litre.
And its RPM is not very high: say +/- 3k I think I've seen.
So you cannot get your piston to supply the CFM (or FAD if you like) at the PRESSURE you need.
Not for any length of time.

So you store it up.

And if you need MORE "oomph", what do you do?
Well, the brute force way is to buy a bigger pump.
Expensive.
But I think you're better off getting a bigger RECEIVOR: a second one.

And if you want a REALLY nice system, designed properly, I'd do as follows:
- Standard pump feeding a standard sized receivor (start off with this)
- High pressure pump, feeding....a high pressure receivor
You then link them up.
And have them feed a big bore line, and put them where you don't hear them.

The high pressure pump doesn't need to be very big, it just needs to get to say 300 Bar.
Get a used (but still safe) nitrogen or argon cylinder, or better, get two.
Not so easy to find, but they do come up for sale.

This is not an off-the-shelf machine: you need to be able to design for the pressure, and do it safely.
Adding in pressure relief valves where needed.
And I'd get the used bottles retested to be safe: but that's not expensive.

As for spare parts, well, again, you only add in brands where you CAN get spare parts.
But to be honest, I don't see it as a big deal. These are SIMPLE systems, you don't NEED to buy a spare part from the dealer in most cases.

And you should modify your machine so it runs better.
Add in better cooling: if it stays cooler, it will last a LOT longer.

Is easy to add in another fan, and run it on PWM control, off a temperature sensor.
For the pump side, if it gets pretty hot during its work, improve the cooling on that too.
Add fins and a fan as well.
Thanks for your apparently sound advice. By way of helping other members to understand you:->>
 
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