Having trouble choosing which air compressor best suits your fossil preparation requirements? This guide makes it simple for you to make a choice tailored to your needs. There is an awful lot of specific terminology in the world of air compressors, and not just any one will do (no, really, it could be dangerous if you get the wrong one).
We stock a variety of different air compressors in our shop; a selection we have curated to suit the varying needs of the fossil preparator from amateur to professional. We are stockists for NuAir, Draper, Bambi and Scheppach. Whilst we have access to the full ranges of these companies, we have carefully curated a selection of compressors best for fossil cleaning and preparation. We can give you all the advice you need prior to purchase and as much help as we can give you once you receive your shiny new compressor!
Terms like PSI and CFM are banded about, along with so many other abbreviations, so we’re here to help you make sense of it all. Especially if you’re buying in the UK where we use some strange hybrid of imperial and metric measurements depending on what we’re talking about.
What will you be using your air compressor with?
First, you must assess all tools that you will be using the air compressor with. For some this is just one air scribe (when starting out with a set up), and for others it is a small fleet of air scribes and an air abrasive unit. In essence, buy the compressor for the tool(s) that you have or are planning on getting. Think about the tools you might buy in the future, and whether this would mean replacing your compressor with a more advanced one.
All tools require different amounts of air, and so you need to know the intake in CFM (cubic feet per minute) or LPM (litres per minute) and the minimum pressure required for the tool to work or the PSI (pounds per square inch) or in Bar (100 PSI = 6.9 Bar).
|All tools require different amounts of air, and so you need to know the intake in CFM (cubic feet per minute) or LPM (litres per minute) and the minimum pressure required for the tool to work or the PSI (pounds per square inch) or in Bar (100 PSI = 6.9 Bar). ||This is an Air Abrasive Unit, the Vaniman Mobile Problast. Air abrasive units typically consume the most air in the world of fossil preparation (unless using stonemasonry chisels or air powered angle grinders). Therefore, if you have or are considering purchasing an air abrasive unit - work to that air consumption as it is likely to be the highest you encounter.|
It’s worth considering the recommended requirements of the tool so that it works at its best. For instance, Impact Driven air pens use a great deal less air and work at much lower pressures than Pusher Plate Driven air pens (see here for a breakdown of the differences!), and therefore the impact-driven models are able to run from a smaller air compressor. Which types of tools you have will depend on the types of fossils you are preparing. Air abrasives and pneumatic grinders typically use a great deal more compressed air than air pens.
Then you must establish how many tools will be working at any given time. If it’s just you, unless you have some sort of superpower, you will only be using one tool at a time and so you will choose your compressor based upon your maximum requirements. If it’s you and your partner or colleague, you’ll need to add together the air intake and the pressure requirements of each tools you will be using at one time.
How do air compressors work?
For once we have named something pretty well in the English Language, air compressors do what they say on the tin. They intake air and compress it until it reaches a certain pressure within the tank, which is then used by your tool. When the air in the tank drops below a lower limit, it ‘kicks in’ (this is the noisy bit) and repressurises the reservoir allowing for a constant stream of compressed air.
Below is a list of factors to consider when choosing an air compressor. These are decided by the minimum requirements of the tool(s) you have; although you can probably be more flexible with the tank size and running time if you have a larger budget.
Check out the PSI or Bars of the compressor you’re looking at buying. Does it exceed your maximum requirements? Then you’re on the right track. Most compressors have a working pressure of 8 bar/115 PSI but some like to be up at 120PSI. An air compressor that operates up to 8 Bars is suitable for the majority of pneumatic fossil preparation tools.
The maximum pressure setting will be set by the factory and you won’t be able to adjust this, but you can adjust the cut-in pressure. You can also add a pressure regulator or pressure-reducing valve which maintains a constant output pressure without fluctuations.
You’ll come across two terms - displacement and free-air delivery. These are really important for establishing the CFM or LPM that will reach you tools.
- CFM or LPM DISPLACEMENT is the measurement of the amount of air drawn into the compressor’s pump, and so is only a theoretical measure of the displacement of air assuming 100% efficiency. Therefore, it is not the best indication of how your tool will run and therefore should be taken with a pinch of salt.
- CFM or LPM FAD (Free-Air Delivery) is the measure of air actually displaced and therefore a measure of the compressed airflow that will actually be delivered to your tool. The air delivered to the tool is typically a third less than the air displaced by the compressor for direct drive compressors, and a quarter less for belt-driven compressors. The FAD gives you a better idea of air output than displacement, but bear in mind these measures are calculated in a laboratory at a set temperature. If you see a FAD listed that is too good to be true as compared to the displacement, it probably is and that compressor is best avoided.
For example, a direct drive compressor that is advertised with a displacement of 10CFM, then the free air delivery is probably around 6.6CFM.You should always consider the FAD when thinking about the minimum air flow that your tool will require.
Another point to consider with flow rate is how many tools you will be running. If you have a lot of tools and various splitters or other peripherals, or you have a longer air hose (if you’ve isolated your compressor from your workspace or your electrical outlet is far away) you will need to account for these pressure drops and buy a compressor with higher CFM/LPM than you think you’ll need.
A good rule of thumb is to go for a Free Air Delivery that is at least 4 times that of your most demanding air powered tool (the finger is pointing at you air abrasives!).
You’ll see compressors listed in terms of power consumption (either in kilowatts or horsepower). For the majority of compressors used in fossil preparation, you’ll see gradations of 1.5 HP (1.1kW), 2 HP (1.5kW) or 3 HP (2.2kW). The more power the compressor consumes, the more air in can compress in a given time. Therefore, a 1HP 50l compressor might displace and deliver less air than a 3HP 25l compressor.
Higher powered compressors are important in terms of duty cycle (see below) as they can ‘kick in’ less and you might be able to get away with a smaller model, but this comes at a trade off that they consume more electricity.
Most compressors can compress approximately 4 CFM to100 PSI per unit of horsepower. If you’re looking at some silenced compressors, you’ll see much lower power consumption. Don’t let this throw you - just look at the air displacement or free air delivery to get an idea of if that suitable for your task.
Duty Cycles & Running Time
You’ll come across the term duty cycle quite a lot, which is usually written as a percentage. This is a critical factor in choosing an air compressor. Fossil preparation can be a demanding activity in the sense that even somebody who can only squeeze in an hour at a time is putting more strain on their air compressor than somebody using an air powered stapler in short, sharp bursts.
If a compressor has a duty cycle of 50%, this means it can only run for 5 out of 10 minutes before it needs to stop taking in air and chill out a bit whilst it cools down. Otherwise, you’ll end up tripping the thermostat and have to wait until its cool again.
Typically, the more expensive the air compressor, the higher the duty cycle (with the exception of silenced compressors which usually are more expensive with a lower duty cycle). 100% duty cycle compressors do exist, but they’re extortionate and not necessary for the average preparator. A cheap air compressor may have a 25% duty cycle, and a maximum running time of 15 minutes. This means that for every 15 minutes it’s running, you’ll have to stop it kicking in for 45 minutes (i.e. by putting your tools down).
Air Compressor Tank Sizes
The tank on an air compressor doesn’t produce air, it stores it. The amount/volume of compressed air a compressor will hold impacts how well certain tools will work. Additionally once the tank is filled, a larger tank compressor will not have to run as much to maintain the airflow provided the compressor pump can produce more compressed air than you are using.
Air compressors suitable for fossil preparation typically come with tanks (reservoirs) of 24/25l, 50l,100l and 150l. The more air that can be stored in the tank, the more time the compressor will have to cool down between kicking in. This means that if you have a larger tank, you might be able to afford to go for one with a lower duty cycle or a lower power consumption. If you have a tool that requires a high flow rate (higher CFM/LPM) then you will need a compressor with a larger capacity so that it won’t overheat.
In fossil preparation, we typically use a constant flow of air, and so if the tank is not big enough the compressor will overheat and you’ll need to take frequent breaks. Most Pusher Plate Driven tools would be inadvisable with a 25l direct drive compressor, but work brilliantly with a 50l tank fitted with the same motor. The ZOIC Impact Driven air scribes require less pressure and a lower airflow and so the would be suitable with a 25l compressor.
These next points are more matters of personal preference and budget. Whilst it is vital to match the working pressure, air delivery, duty cycle and therefore tank size to the requirements of your tools - things like maintenance levels and noise made are up to you (within the realms of reason).
Oiled or Oil Free?
Oiled compressors require compressor oil (often specific to the compressor) for lubrication, whereas oil-free compressors have Teflon to keep their pistons running smoothly which means they are lower maintenance. Aha! Surely this is a no-brainer? Why would I get something which requires more effort if there’s something else available? Sadly, as with many things in life, there’s a catch.
This is an important consideration for many people as nobody wants the neighbours out with their pitchforks. The noise an air compressor emits is measured in decibels. Modern compressors (non-silenced - more on this later) usually range from 60-100db, and only make this noise whilst they are taking in air. Therefore if you have a larger capacity tank, and a tool that uses lower pressures, you won’t be having to listen to it for as long.
However, numbers don’t really help you decide how noisy something is. You must bear in mind not only how annoying the noise could be. For instance, a direct driven compressor runs at a much more grating frequency than a belt-driven compressor.
Also think about potential damage it could do to your hearing with prolonged exposure and the steps that you could take to prevent this.
- 100db - a jackhammer (serious damage possible in 8 hour exposure)
- 88db - Food Blender (likely damage in 8 hour exposure)
- 80db - Dishwasher (possible damage in 8 hour exposure)
- 70db - Television/radio
- 60db - Conversation in a restaurant
Bear in mind that decibels are measured on a logarithmic scale, not a linear one. This means that 80db is twice as loud as 70db, and 90db would be four times as loud. 110db is the threshold for genuine pain to the human ear and is 16 times as loud as 70db.
This brings us onto….
‘Silent’ or ‘Quiet’ Compressors
Some compressors are marketed as silent (or ultra-quiet) when they are between 30-70db. As we discussed, this could still be as loud as a conversation or your television in the evenings (but much less pleasant).
- 50db - light traffic, refrigerator
- 40db - a quiet library
- 30db - a whisper
This type of compressor usually costs more (especially the genuinely super-quiet ones). They are typically higher maintenance as oiled compressors are often quieter than oil-free ones. Whilst it is possible to get an oil-free compressor that runs at 30-40db, you’ll certainly be paying for the pleasure.
There are some cheaper models out there, but these are considerably underpowered for most tasks and are only for light use. Have a look at the displacement or FAD, as well as the duty cycle before making your decision. A 50l budget silenced air compressor will have about the same functionality and a shorter lifespan than a 24l direct drive compressor.
BUDGET SILENT COMPRESSORS FOR HOBBY USE ONLY
These silenced air compressors are fantastic for quietly running very low air consumption air pens such as the ZOIC PalaeoTech range (air consumption on all tools is below 8l/min (0.3 CFM). Ideally, with many of these compressors, you'll want to be using tools that use less than 15 l/min (0.5CFM). Not all air pens are compatible - we know of some that use 55l/min (2 CFM). Budget silent compressors should not be used heavily and will not have as long a lifespan as noisy or more expensive counterparts.
PROFESSIONAL SILENCED COMPRESSOR
A quality silenced air compressor comes with more of a price tag but will have a comparable power level and durability to the noisy air compressors. We stock two types, Bambi and NuAir.
We stock the most suitable of the Bambi Budget range of air compressors. These UK made compressors have 'cult status' within many industries for excellent manufacturing quality, durability and air output. We have a 24l one that has been going for 25+ years!
The NuAir AIRSIL 100l Compressor is a normal belt driven air compressor (more efficient than direct drive counterparts), but the motor is contained in a noise muffling cabinet (with suitable ventilation). The AIRSIL compressor will comfortably run air scribes and air abrasives, without the noise. This model is the most powerful in the range that will run off a standard single-phase household electricity supply.
Reducing Noise Levels
Bear in mind that there might be other steps you can take to reduce the noise level of your compressor depending upon how DIY-minded you are; and of course all methods come with added expense. Many people chose to instead keep their compressor in a different room and feed the air hoses through the wall!
You could use sound dampeners, mufflers, an intake silencer or isolate the compressor from your workspace or from wherever it is an annoyance. The only inadvisable method is creating a soundproof box, as this could be a serious fire risk if not ventilated correctly. This would require more skill to dampen the noise from the ventilation holes.
What are the minimum requirements for the fossil preparation tools I am using?
Low air consumption air pens can be used with relatively small air compressors. The whole range of ZOIC air pens or air scribes are extremely low air consumption within their respective categories (all under 10l/min or 0.3CFM). Other brands vary widely, please check with the manufacturer (the highest we are aware of is nearly 10x the air consumption of our range).
Minimum of 24l air compressor such as the 24l Draper (best for a tight budget where noise isn't an issue - also available as part of our fossil prep starter kit), the Oil-free 24l NuAir Super Silent, the durable and powerful 24l Bambi or the Quiet 50l Scheppach (for those on a tighter budget who need silent). For a slightly quieter time of it, the 50l Draper 1.5kW has the same motor as the 24l, but has the capactiy to hold twice as much air and so will therefore kick in less often.
Noisy Air Compressors
|Draper 24l (1.5kW) Air Compressor (£)|
Noisy, oiled, powerful for its size. Direct Drive compressor perfect for most beginners.
|Draper 50l (1.5kW) Air Compressor (£)|
Noisy, oiled, direct drive. Will run some other brands of air pen better than the 24l Draper. Will kick in less often than the 24l with the ZOIC range. Not suitable for air abrasives.
Quiet/Silent Air Compressors
|QUIET Scheppach 50l Oiless Air Compressor (££)|
Not as powerful but the larger air reservoir makes up for it.
|SILENT Bambi 24l Oiled Air Compressor (£££)|
As powerful as its noisy counterparts. Genuinely silent and very durable.
|QUIET NuAir 24l Air Compressor (££)|
Oiless and powerful for its size, durable. Excellent value.
This air compressor runs the entire range of ZOIC PalaeoTech air pens as well as the Vaniman Mobile Problasts. It is the minimum requirement for most air abrasives. It will also run pretty much all air pens from all brands. Some air abrasives have a higher air consumption than the Vaniman, so please check before purchasing. If in doubt and you have the space, we recommend upgrading to a 100l air compressor as the price jump isn't huge.
The most important feature of the compressor listed here (the 50l Draper 2.2kW) is that it has a more powerful motor than some others (2.2kW or 3HP as opposed to 1.5kW).
A lower power 50l compressor might be tempting to the untrained eye because the tank size is the same but the compressor is cheaper. However, a 1.5kW motor would not be powerful enough to run air pens as well as air abrasives! It's worth paying a little extra to get a compressor that can cope.
|Draper 50l 2.2kW Air Compressor (££)|
|100l 2.2kW 3HP Belt-Driven Draper Air Compressor (£)||150l 2.2kW 3HP Belt Driven Draper Air Compressor (££)||SILENT 100l Belt Driven Silenced Air Compressor (£££)|
All the power of a standard belt-driven compressor, but with an inbuilt silencing cabinet, with carefully engineered safety precautions.