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Choosing an Air Compressor for your Fossil Prep Workshop

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. 


NuAir, Fini, Draper, Bambi and ClarkeWe 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, Fini, Draper, Bambi and Clarke. 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 tools 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).


As a general rule, air pens or air scribes require a LOT less air than air abrasives or air grinders.


It’s worth considering the recommended requirements of the tool so that it works at its best. 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 and therefore require larger and more powerful compressors. Our PRO Range of air pens have the lowest air consumption of any range in the world, and uniquely are able to run off a really tiny compressor. Our T-Rex model can even run off a battery powered airbrush compressor (see here). 


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.


The Essentials (Airflow and Pressure)

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. Well discuss noise levels and maintenance requirements later as these are more personal preferences. 


You may be tempted to think that tank size is the be all and end all. This is not the case, especially when looking at cheaper silent compressors, so a more in depth knowledge of what spec you need is required. 

Pressure

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 tools require higher pressures than this. An air compressor that operates up to 8 Bars is suitable for the majority of pneumatic fossil preparation tools. If you require more, you will need to look at 'industrial' air compressors. 


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.

Flow Rate

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. If this is the only spec listed, divide it by 4 and if that number is greater than your tools air consumption at its max. working pressure, you're probably OK.


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. Divide the FAD by 2 or 3, and if that number is greater than your tools air consumption at its max. working pressure, you're probably OK.


Another point to consider with flow rate is how many toolsaccount for these pressure drops 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.

Power

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.


Also be aware that your electrics will need to be configured to cope with your air compressor without tripping. You may wish to get an electrician in to double check if you're purchasing a compressor that requires 2.2kW (3HP) or more in power.

Duty Cycles and 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 (or equivalents in gallons in the USA). 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. The entire range of ZOIC PalaeoTech air pens will run comfortably off a 24l air compressor (even if it is not very powerful). Other brands may require significantly more air, with most needing a minimum of a 50l air compressor (especially if silent). 

Personal Preference and Budget Considerations (e.g. Noise levels)

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).


Noise Levels

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, e.g. ear defenders or locating the compressor separate from your workspace.


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.


Budget silent compressors are typically low powered for their size and some of the cheaper mass produced ones have clearly posed some danger to their users over the years with poor quality control practices. 


Budget silent compressors should not be used heavily and will not have as long a lifespan as noisy or more expensive silent counterparts.


Our rule of thumb with cheap, silent air compressors is always go up a tank size. If you would buy a 24l noisy direct drive, buy a 50l budget silent. 

Quality Silent Compressors


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 Bambi and NuAir, and Fini compressors.


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!


You can get larger air compressors with high outputs which are silenced. The Bambi PT90 is powerful, quiet and puts out a good amount of air. 


On the other end of the spectrum, you can also purchase normal belt-driven air compressors with built-in silencing cabinets like the NuAir AIRSIL 100l air compressor. 

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.

Oiled

  • Higher Maintenance. You'll be topping up and changing the oil periodically. If you don't do this, you will cause irreversible damage to your compressor and possibly invalidate its warranty. 

  • Usually more expensive

  • More durable and hard-wearing

Oil-Free

  • Lower Maintenance. You'll still need to look after your compressor in other ways, but you won't have to worry about lubrication.

  • Usually cheaper.

  • Less durable. The Teflon wears out after some use, and the pistons get dry and don't run as effectively. Only suitable for light-moderate use. 

What are the minimum requirements for the ZOIC PalaeoTech tools?

Air Pens or Air Scribes

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 (with the PRO Range all under 10l/min or 0.3CFM). Other brands vary widely, please check with the manufacturer. Some other fossil preparation tools use 10x or more the air consumption of our PRO range which is a considerable difference and must be accounted for in your compressor choice.


For our PRO Range, you can get away with the miniscule 6l Silent Fini air compressor. This is great for small spaces where quiet is essential. Generally speaking, we would normally recommend a 24l air compressor for running our air pens in a normal workspace. 


Minimum requirements for the ZOIC PalaeoTech Range

These are just suggestions for the minimum requirements. You can always go for a larger or more powerful compressor within the same range, which will kick in or cycle less often when using the same tools. These are just some examples. Check the specs if you live internationally, and try to find something with comparable specifications.
  • Draper 24l Direct Driver Air Compressor (1.5kW or 2.0HP). Great for those on a tighter budget where noise isn't an issue. These are loud, but can be kept in a separate room or ear defenders can be worn. 

  • NuAir 24l Quiet Air Compressor. Durable and powerful for its size. Not completely silent, but not an uncomfortable level of noise. Excellent value for money. 

  • Bambi 24l Silent Air Compressor. Bambi Air is one of the market leaders in genuinely silent air compressors. They have a 5 year warranty on the internal lining of their tanks, are powerful and durable. 

  • Fini Siltec 6l Air Compressor. This tiny air compressor will run our PRO Range of tools, and is suited to small spaces where noise is an issue. However, if you have the space we would recommend a larger air compressor.

Air Abrasives & Air Grinders

Air abrasives vary considerably in air consumption. It depends on the unit you've got and the powders you're using. Air grinders have famously high air consumption just because of the way that they work. 


The handheld entry-level Paasche Air Eraser will run off a 24l Draper or NuAir Compressor (as in our Budget Starter Kit), but most units will require a much larger and more powerful compressor. The Vaniman Mobile Problasts fitted with a 50-100 micron tank consume only 30lpm or 1 CFM and so can, with rest breaks, be run off a reasonably powerful 50l air compressor (although not a budget silent one). 


For the majority of air abrasives you will want a larger air compressor, usually 100l. You can often get away with a 50l direct drive compressor as long as the motor is powerful enough (2.2kW or 3HP rather than 1.5kW 2HP), but we find that the additional cost of getting a large air compressor is worth it. 


These are just some examples. Check the specs if you live internationally, and try to find something with comparable specifications.

  • Draper 100l Direct Driver Air Compressor. Great for those on a tighter budget where noise isn't an issue. These are loud, but can be kept in a separate room or ear defenders can be worn. 

  • Draper 150l Direct Driver Air Compressor. Great for those on a tighter budget where noise isn't an issue. These are loud, but can be kept in a separate room or ear defenders can be worn. 

  • NuAir 100l Belt-Driven Air Compressor with inbuilt silencing cabinet. All of the power of a standard belt-driven air compressor with an inbuilt silencing cabinet, with carefully engineered safety precautions. It is quiet, not silent, but makes an enormous difference. 

  • Bambi 90l Oil-Free Quiet Air Compressor. We love this 90l air compressor. It's quiet, not silent, but fantastically powerful for its size. It also has a duty cycle of 65% which is impressive. The air output really is exceptional. 

How to reduce noise levels on a loud air compressor

The cost of silent air compressors goes up considerably the larger and more industrial they get, and cheaper versions have all the size but none of the air output. This means that for the home workshop they are not always viable, and it is necessary to purchase a loud air compressor. There are a few things you can do to reduce the noise output of your compressor to keep yourself sane or your neighbours happy. It depends on how DIY-minded you are; and how much space you have. 


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, soundproofing insulation in your workshop, mufflers, or an intake silencer. The only inadvisable method is creating a soundproof box, as this could be a serious fire risk if not ventilated correctly. Air compressor motors can get very hot.