There are few products that are ‘must haves’ in the world of 4x4ing, camping and the great outdoors, but an air compressor is definitely one item that should be carried, as it can have so many handy and convenient uses – aside from tyre inflation.
Depending on your needs, there are a few things to consider when purchasing an air compressor: maximum pressure, air-flow rate, duty cycle, portability, accessories and of course price. Let’s expand on a few of these points.
If you want to pump up your tyres to 40-50psi, there’s no point purchasing a compressor that can only inflate low-pressure toys like soccer balls, air beds and kids toys. For low-pressure pumping that requires a large volume of air, all you need is a lower (maximum) pressure pump that has a flow rate as high as possible. Remember all those soccer balls, air beds and toys may have different openings, so be sure to look for varied fitments on the hose outlet.
Without knowing compressors’ internal specifications, there is no way of guessing the flow rates. That will depend on the bore, stroke, rpm, and internal design, as well as other restricting factors such as chuck type, air filter material, wiring gauge and length, and the temperatures reached while running. Just because one compressor seems identical to another, that doesn’t mean it’s the same inside – just like all car engines are not created equal, even though many are rated at the same cubic size!
IN THE world of unregulated aircompressor advertising, we checked suggested air flows with an air-flow meter and found our figures often differed from those printed on the packaging or instructions. Many air compressors achieved half of what was quoted, with some up to 100L/ min less than quoted.
What is happening with some compressors is the stated air flow is actually FAD (Free Air Delivery) – that is, when the compressor hose is not attached to a tyre and, in some cases, not even attached to the air compressor. As soon as you add the air hose and the chuck, down goes the flow rate. Add in an air valve, and down she goes again. Add in resistance in the way of air pressure inside the tyre – yep, you guessed it, the air flow rate drops dramatically.
It’s just like when manufacturers advertise horsepower or torque at the flywheel instead of at the driven wheel – there’s a huge difference because of all the resistance along the way.
It’s important to have a good duty cycle in a compressor. Roughly, the duty cycle is the amount of time the pump is actually working when it’s turned on, compared to the amount of time it’s not working when it needs to cool down. For example, two minutes on followed by two minutes off is not very good when you’re trying to pump something up quickly.
Similarly, a (claimed) 50 per cent dutycycle pump may run for 30 minutes, followed by a long 30-minute wait. Perhaps that’s okay to re-inflate your four tyres after leaving the beach – but will that pump actually do the job within 30 minutes? I’d hate to be waiting another 30 minutes while the compressor cools down before you can finish that last tyre!
Officially, duty cycle should be measured with the compressor pumping at 100psi at an ambient temperature of 22°C. It is calculated by taking the run time and dividing it by the run time plus the off time, then multiplying the result by 100; the final figure is expressed as percentage.
For example: if a compressor is rated at a 25 per cent duty cycle, it means it can only (theoretically) run for 10 minutes followed by 30 minutes turned off. So, 10 ÷ (10 + 30) × 100 = 25 per cent duty cycle – not 33 per cent as you might presume (10 ÷ 30 × 100 = 33).
Here are a few ratings so you don’t have to hit the calculator, but do keep in mind that these technical figures are at 100psi and 22°C. Pumping at less pressure and varying temperatures will change the whole show:
10% duty cycle 20% duty cycle 30% duty cycle 100% duty cycle
3 min ON / 27 min OFF 8 min ON / 32 min OFF 13 min ON / 30 min OFF Continuous duty @ 100psi and 22°C An internal thermal cut-out switch is designed primarily to protect the air compressor’s motor from burning out or overheating. You’ll have no control over this thermal cut off; when the unit heats to a preset temperature, it (in theory) stops, leaving you twiddling your thumbs waiting for it to switch itself back on.
A 100 per cent duty-cycle compressor, on the other hand, is great for our 4WD tyres, as well as those of all your mates who line up to use your pump – ’cause theirs keep cutting out!
This is the tough one. We all want to spend as little as possible, but we also want the best out of our gear. We’ve managed to round up a number of compressors that are suitable for 4WD tyre inflation as well as general use around the camp site. We’ve drawn a line at the units being portable; that is, they must be able to be carried and used from one vehicle to another – not engine-mounted or enginedriven.
Of course, most of the compressors you see here can indeed be mounted in your engine bay, under your seats or in your cargo area, but they are all initially portable units.
The CKMTP12 is a twin motor/twin cylinder unit with a four-litre air tank, and has a 100 per cent claimed duty cycle. It comes in a waterproof, impact-resistant hard case.
The high-quality, heat-resistant air line is easy to unravel, and the quick-clip chuck can be removed for higher air flow and features a stop valve so air will not flow until connected to a tyre valve. The claimed flow rate is 174.4L/min at no load and 0psi; 131.8L/min at 29psi.
This unit can be left on when the air line is removed from the tyre, preventing damage from the free-revving motor, while the twin sinteredbronze air cleaners are rated for fine bulldust, and are easily removed and cleaned. You can also operate air tools with the air tank.
It also comes with an in-line fuse and alligator clips, extra air line nozzles, and a 180psi pressure cut-off switch. Thermal protection is rated up to 115°C.
The CKMTP12 is Australian-made and comes with a two-year warranty.
Twin sintered-bronze air cleaner
The CKMP12 is similar to the CKMTP12, except that it comes with just the single motor instead of the CKMTP’s twin system. Housed in a hard case, this unit has a 50 per cent claimed duty cycle.
It comes with many of the features of the twin system, including a high-quality, heat-resistant, easy-to-unravel air line; a quick-clip chuck that can be removed for higher air flow; a stop valve so air will not flow until connected to a tyre valve; an in-line fuse and alligator clips; and extra airline nozzles.
Like the twin system, this unit can be left on when the air line is removed from the tyre, preventing damage from the free-revving motor, and has a sintered-bronze air cleaner rated for fine bulldust, which can be easily removed and cleaned. An on-off switch in the case is deactivated when the lid is closed – a good safety feature – and it also has a 105psi pressure cut-off switch and thermal protection.
It’s made in Australia and has a two-year warranty.
Sintered-bronze air cleaner
The Bushranger Max Air III has a maximum pressure of 150psi, a 72L/min air flow and a claimed maximum duty cycle of 40 minutes at 22°C and 30psi. It features a coiled highpressure hose with rubber heat protection at the disconnect end; battery-powered digital pressure gauge; trigger air release and quick-snap chuck and deflator mechanism; plus two sets of spare air-cleaner elements. The pressure switch (off at 150psi) means it can be used with an air tank.
The unit is rubber-mounted on a base plate and is stored in a soft bag. The air cleaner is mounted low to help protect it in the bag. Also comes with an in-line fuse with alligator clips; thermal-overload switch; on-off switch on body; a hard-mounting kit; and a five-year warranty.
External, 2-stage foam
Housed in a soft bag, this unit has 150psi maximum pressure, 66L/min air flow, and a maximum duty cycle of 30 minutes at 24°C and 40psi. It features a coiled, 200psi-rated hose with in-built deflator mechanism and rubber heat protection at the disconnect end; in-line pressure gauge; thermal-overload switch; hardmounting kit; two sets of spare air-cleaner elements; and an in-line fuse with alligator clips.
The low-mounted air cleaner helps protect it in the bag, and the unit is rubber-mounted on a base plate. It comes with a five-year warranty.
External, 2-stage foam
The Off-Road Pro Flow 75 from Piranha features a coiled hose with in-built deflator; screw-on chuck and in-line pressure gauge; in-line fuse and alligator clips; extra inflation nozzles; and a thermal-overload switch. The in-built air cleaner offers protection, and the unit is rubber-mounted on a base plate. It has a max pressure of 150psi; a claimed duty cycle of 30 minutes at 24°C and 40psi; and a 75L/min air flow. It has a five-year warranty.
The Vortex has a claimed maximum pressure of 150psi, and 160L/min air flow. Features include a straight rubber hose with quick clip-on chuck, deflator and in-line pressure gauge; alligator clips with in-line fuse; reset button for thermal overload; and extra inflation nozzles.
The built-in two-stage foam filter offers good protection from breakage, and the unit is mounted on rubber feet to a sand tray. On-off switch is on the body. One-year warranty.
Built-in, 2-stage foam filter
Available from leading automotive and 4x4 outlets (eg Piranha)
Housed in a soft bag, the Ironman Flomax has a claimed 72L/min air flow, and max pressure of 150psi. It features a coiled hose with screw-on chuck and deflator plus in-line pressure gauge; alligator clips with in-line fuse; extra inflation nozzles; thermal overload switch; and an on-body on-off switch. The single-stage foam filter sits high in the bag and may get damaged. Rubber feet mount the unit to a sand tray. Three-year warranty.
With a claimed 150psi max pressure and 160L/ min air flow, the Flomax Pro also comes with a three-year warranty.
Features include a coiled high-pressure hose with rubber heat protection at the disconnect end; screw-on chuck, alligator clips and in-line pressure gauge; thermal-overload switch; on-body on-off switch; and a manual pressurerelief valve. The built-in foam air cleaner offers excellent protection from breakage. Additional air outlets for toys are included, and the unit can be hard-mounted.
Built-in foam filter
This Opposite Lock unit has a claimed max pressure rating of 150psi, 72L/min air flow, and 40-minute duty cycle at 22°C and 40psi.
It comes with a soft bag; a coiled hose with screw-on chuck and deflator plus in-line pressure gauge; alligator clips with in-line fuse; extra inflation nozzles; and an on-off switch on its body.
The single-stage foam filter sits high in the bag and may get damaged.
External foam filter
The TJM unit has a claimed air flow of 72L/min.
Stored in a soft bag, it features a straight rubber hose with a screw-on chuck, brass deflator and in-line pressure gauge; alligator clips with in-line fuse; and extra inflation nozzles. The twostage foam filter sits high in the bag and could get damaged. The unit is mounted on rubber feet fitted to a sand tray. Five-year warranty.
External, 2-stage foam
The AOBCM500 is best suited for permanent mounting in a vehicle, and it comes with wiring, switches and relay for installation. It has a claimed max pressure of 200psi and 100 per cent duty cycle at 22°C and 100psi. No case or air lines are included. The pressure switch is activated at 150psi, with a safety relief valve at 188psi. Its claimed airflow is 72L/min.
While this unit is an attractive option with its included nine-litre air tank, without the additional air lines and hard wiring we were unable to test it. It has a one-year warranty.
Supplied with a soft bag, the Adventurer II has a 45min duty cycle at 40psi, claimed 160L/min air flow at 0psi, and a 150psi max pressure rating. It has a straight rubber hose with screw-on chuck, clip-on chuck and deflator, plus an in-line pressure gauge.
Other features include: alligator clips with in-line fuse; extra inflation nozzles; a circuit breaker; a spare filter set; and a thermal cutout at 105°C.
The built-in, two-stage foam filter offers excellent protection from breakage. The unit is mounted to a sand tray via rubber feet, and comes with a five-year warranty.
In-built, 2-stage foam
The Maxi 4X4 has a duty cycle of 55min at 40psi, a claimed 110L/min air flow at 0psi, and a 150psi max pressure. It comes with a straight rubber hose with screw-on chuck, clip-on chuck and deflator plus in-line pressure gauge; multiple configuration hose; alligator clips with in-line fuse; circuit breaker; thermal cutout at 105°C; on-body on-off switch; and extra inflation valves.
It breathes through its body, so there is no filter. The unit comes with a soft bag and a fiveyear warranty.
Through-body air flow
The Off-Road Pro Flow 150 has a 55min claimed duty cycle at 40psi, a 150L/min air flow at 0psi, and a max pressure rating of 150psi.
Features include: soft bag for storage; straight rubber inflation hose with screw on chuck, deflator and inline pressure gauge; alligator clips with inline fuse; circuit breaker; extra inflation nozzles; thermal cut-out; and on-body on-off switch.
The built-in two-stage foam filter offers excellent protection from breakage, and the unit is mounted to a sand tray via rubber feet.
The Off-Road Pro Flow 150 comes with a five-year warranty.
Built-in, 2-stage foam
The Lion was purchased online; the same product is available with different names.
With a claimed 28L/min air flow, this unit can inflate tyres, but it was very slow. Also, the wiring and air line aren’t long enough to reach all four tyres unless they’re passed through the cabin. Still, it did the job without cutting out or melting. There’s a warning on the box to cool the compressor after 10 minutes.
Included are battery-test and alternator-test functions and a built-in LED light; a screw-on brass chuck; and a cigarette-lighter plug.
Search the online sales sites
It’s a horses-for-courses situation here; there is no one outright winner. If you’re looking for the most compact unit on the block, you can’t go past the el cheapo Lion compressor sold online. It’d fit in to most glove boxes; just don’t expect to inflate a large tyre quickly. To our amazement, it chugged away for almost three quarters of an hour nonstop to inflate our four tyres. While I’d never advocate buying and relying on such a small pump, it could, if nothing else, be used as a back-up compressor to get you out of trouble.
If all you want is maximum blow regardless of price, weight and size, the almighty ARB twin in its sealed carry case is simply amazing and should be top of your list; it’ll out-blow all and sundry, and have a mile-long line of your mates wanting to ‘give it a go’, plus it’ll drive a multitude of air tools given its four-litre tank.
The ARB (single) compressor, while physically small, is of high quality in its body, its accessory material and its construction, plus it’s the only other unit that comes standard with a hard case – something I’d like others to emulate. It’s obvious it’s been manufactured to suit Australian use, with its unique lab-tested, sintered-bronze air-filter element (which is washable) that will keep out the finest dust particles. The complete body is watertight (it can run underwater with the air filter extended). With reasonably impressive results, this unit is a hard one to pass up, but it’s certainly nowhere near the fastest unit on test, and there are others that blow harder for less outlay.
While each of the tested units slightly differ, for my money, I’d be looking at compressors with the size and flow rates of the AC Pro Vortex, the Mean Mother Adventurer II, the Dr Air Off-Road Pro Flow 150, the Bushranger Max Air III and the Ironman Flomax Pro. All offer excellent performance figures, are affordable and (except for the Bushranger) have an internally fitted and therefore protected air filter, meaning it won’t be vulnerable when stuffed inside a soft carry bag. Personally, I’d like to see this range of pumps fitted into a hard case; it won’t enhance performance, but it’d offer protection.
As for the Air On Board unit, on paper it should be a ripper and be capable of matching the ARB twin compressor at a much lower price. Unfortunately, it’s more of a hardmounted- style kit and comes with no air line or easy plug-in wiring system, so we couldn’t give it a run.
While we can’t test long-term reliability, having seen the internals of some cheaperpriced units alongside the quality options, I’m not sure I’d trust the el cheapo to get me out of trouble – even if it were only a once-a-yearuse compressor.
Once you’ve chosen your air compressor, don’t forget to use it. It’s no good not adjusting your tyre pressures to suit the occasion, or pulling out that air bed and sending yourself dizzy by giving it mouth-to-mouth, and there’s definitely no point in having a you-beaut air compressor if you leave it at home. Take it with you every trip away and you’ll be amazed at how often it gets used.
We must also extend our thanks to all manufacturers and suppliers for sending their air compressors in for testing. A special thanks to Mean Mother (www.meanmother.com.au) for supplying the pressure gauges, and to Dynamic Wheel Co (www.dynamicwheelco. com.au) for the Dynamic steel rim and Pro Comp tyre. Without all your help, our readers wouldn’t benefit from the hours we put into each of our comparison tests.
I’VE dismantled a few air compressors and made some astonishing findings.
How about plastic pistons in a compressor that generates a lot of heat – enough heat to actually melt the piston? Not good!
Thermal cut-outs – yeah right! One el cheapo unit had no sign of any electrical or mechanical cut-out circuitry.
Did they mean it cuts out when it disintegrates?
Using cardboard from the packaging boxes to act as a gasket between the head and body of the motor – you’re kidding, aren’t you? Afraid not.
The foreign instructions on the cardboard ‘gasket’ could be clearly read – provided you were multi-lingual.
Have a close look at a few of the air cleaners; some do an excellent job at keeping giant clods of mud out of the mechanicals, but would fail dismally at keeping out dust, let alone bulldust. Only one filter is lab-tested to 30 microns to ensure bulldust stays out – that’s the sintered ARB unit.
At the end of the day, it’s a gamble for most, but sticking with reputable brands will go a long way to seeing you purchase quality gear.
AS KEEN as we were to do a few technical tests, we figured they had to be done in conjunction with real-life use. So while we made use of pumping up a common 4x4-sized Pro Comp Extreme A/T 285/70R17 tyre, we also made a few modifications to the rim. We did this so we could use an air-flow meter to record flow rates at predetermined pressures. Remembering flow rates decrease as pressure increases, we were able to make recordings without hindering compressor operation. We also had the ability to check air pressure ‘on the fly’ without having to stop pumping, disconnect the air-compressor hose from the valve, or make continuous individual pressure checks (which releases air each time a check is made).
This allowed uninterrupted and more accurate inflation timing to 0.1psi. We also took into account that all air pressure readings from the in-line pressure gauges on the air compressors (regardless of brand) are totally inaccurate while pumping air.
To ensure more ‘real-life use’ we connected each compressor exactly as you would in real use – direct to the vehicle’s battery terminal, and then left the engine running above idle.
While there was no real need to measure current draw (your engine should be running and all compressors should not draw more than your alternator can handle), we did anyway and found a common factor – in general, the higher the amperage draw, the faster the air compressor pumped air. We also ran a noncontact thermometer over the compressor motor (at the head), the handle and the compressor hose where it disconnects – this is the point you’re most likely to touch and burn your hands on after the job is done. Wear gloves! You’ve been warned!
We’ve timed each unit at performing two basic inflation tests: First, pumping one tyre from 0psi to 40psi (simulating pumping up a flat tyre) and second, inflating four tyres from 20psi to 40psi (simulating re-inflating tyres after a beach run).
We’ve also taken dB readings of each compressor to see (or hear) how noisy each unit is.
Perhaps keeping your campneighbours happy with less noise might be high on your list of needs!
The above tyre inflation times were all measured by us. Each compressor was attached to a Toyota Land Cruiser battery and the engine was left running just above idle. We used a stopwatch and figured on all times to be within applicable tolerances.
While pressure times may change slightly due to differing weather conditions and vehicle electrical systems, essentially it’s the difference from one compressor to another you should be studying, as well as the outright times measured on this test.
This should give you an idea of which unit suits your needs and pockets.
FAD means Free Air Delivery – in other words when the air compressor is not connected to anything.