A portable air compressor can provide a source of pressurized air when you’re traveling.
By Peter D. DuPre
One of the “must have” pieces of equipment for a motorhome is an air compressor. Some coaches are equipped with an on-board air compressor that supplies the air brakes and suspension system, and also can be utilized for other air needs. But for those whose motorhomes do not have an on-board air system, there’s always the option of carrying along a portable air compressor.
Portable air compressors have many uses, such as inflating rubber rafts, powering air wrenches, blowing dust off the exterior, and removing moisture from water lines when winterizing the motorhome. But perhaps the most important use for the average motorhomer is to inflate the tires.
Tire inflation levels need to be checked when the tires are cold, which means the vehicle “” motorhome, towed vehicle, or both “” should not have been driven or towed for at least three hours before the measurement is taken. If you have to drive to an air station, it should be no farther than a mile. The problem is that fuel stops with reliable air pumps are often few and far between, particularly if you like driving on the roads less traveled. If you drive longer than a mile, the tires heat up and the increased pressure does not allow for an accurate reading. Adding cold air from the air station’s compressor tank will just complicate measuring matters. However, if you have a portable air compressor on board, checking tire pressures on your motorhome can be done at your convenience, and the resulting extension of tire tread life expectancy means that the compressor could pay for itself in short order.
When choosing a portable air compressor, it is important to understand the difference between an inflator and a compressor. A tire inflator is generally a small, 12-volt-DC unit that plugs into the vehicle’s DC accessory socket and is very useful for inflating beach balls, air mattresses, small car tires, and so on. Generally, these small units sell for less than $30 and often come with a built-in flashlight. They are great for light-duty inflation needs, but most cannot produce enough compressed air to inflate the average motorhome tire. For larger tires you’ll need a portable air compressor capable of producing a minimum of 125 pounds per square inch (psi) of air. These units are available in 12-volt-DC and 110/120-volt-AC versions, and both types are fine for inflating the average motorhome tire. If you intend to also use the compressor to power an air wrench, you probably should consider the 110/120-volt variety.
How an air compressor works
The air compressor is a pump that sucks in air (air pressure at sea level is 14.7 psi) through an intake port and uses a mechanical means (usually a piston) to push, or compress, the air through a one-way valve into the storage area or tank. As the air continues to be packed into the receiver area, it is continually compressed, so as the tank “fills,” the pressure inside the tank increases. In theory, a strong compressor could continue to compress the air in the tank until the tank ruptured. To prevent this from happening, a preset pressure switch monitors the air pressure inside the receiving area or tank. When the air pressure in the tank reaches the preset high-pressure level, the compressor automatically shuts off.
When the air in the tank is released “” such as when the tires are being filled “” the pressure inside the tank decreases. When the pressure drops low enough, the low-pressure setting on the switch automatically activates the compressor to begin operating again, pumping air back into the tank until the high-pressure set point is reached.
How air compressors are rated
Although the air put into the tires is rated in psi, the rate at which the compressor delivers the air is measured in cubic feet per minute (cfm). The problem is that cfm will vary with atmospheric pressure, temperature, and even humidity, so rating a compressor can be complicated. So that compressors are all measured by the same standard, air compressor manufacturers rate their units in standard cubic feet per minute (scfm). Both cfm and scfm determine how fast the unit will fill the intended target or supply air for power tool use. The higher the number, the faster it will work. But remember, it’s important to compare the same rating of either cfm or scfm with the same pressure.
This measurement standard use for scfm, determined by the International Organization for Standardization (ISO), is taken as cfm (sea level) at 68 degrees Fahrenheit and with a relative humidity of 36 percent. The ratings are given at a specific air pressure. For example, the Sears Craftsman 6-gallon pancake compressor (#15216) is rated at 2.6 scfm @ 90 psi. However, as the pressure decreases, the scfm rating will increase, so at 40 psi, the same unit has a scfm of 3.5.
What to buy
Here are a few pointers when deciding which compressor to purchase. When comparing air compressors, note the scfm, cfm, and psi ratings and compare similar ratings to one another. By doing this, you will get a good idea of what the compressor can do. Also, do not use horsepower ratings to determine the power of an air compressor. Horsepower ratings in this instance can be misleading.
When choosing an air compressor for motorhome use, it’s important to make sure it can supply the amount of air needed to inflate large tires, which means you’ll need one that can deliver 125 psi. If you also plan to use the unit to power air tools, make sure it is equipped with an adjustable regulator so you can turn down the maximum setting when using air wrenches. For air tool usage, an air storage tank is required; 1-gallon tank is the minimum size, while a 3-gallon tank is preferred. Another consideration is the duty cycle of the air compressor. This typically is expressed in a percent and measures how much time the compressor motor can safely run within a set time period before it is given a rest. Usually duty cycle is expressed as a percentage of a certain time frame, often in 10-minute segments. Running the compressor in excess of the duty cycle percentage without giving it a rest can damage the motor.
A number of different brands and models of portable air compressors are on the market, and there is no one “right” unit for RV use. Much depends upon what you see as its main uses and what type of motorhome you own. A large Type A coach with significant basement storage space may provide plenty of room for a larger compressor. On the other hand, in smaller Type B or Type C units with limited storage area, a smaller hand-carried, 2-gallon air compressor may be more practical. The bottom line when choosing a portable air compressor is to consider your overall needs, storage space, and, of course, your budget.
As for sources, large home improvement stores such as Lowe’s and Home Depot sell air compressors, as do Sears, Camping World, Harbor Freight Tools, and automotive parts stores such as NAPA. Plus, you can always look online for good buys. To give you an idea of what’s currently available to consumers, here is a small assortment of air compressor models.
Campbell Hausfeld Model FP209499
This 3-gallon, 120-volt-AC air compressor, with its tank-mounted compressor, is rated with a maximum of 100 psi and is designed for light-duty use. It is suitable for adjusting air pressure by a few pounds but is not really powerful enough for timely tire inflation. But with its 2-cubic-foot size and 22.3-pound weight, this unit may be suitable for smaller RVs where stowage space it at a premium.
The 3-gallon tank for air storage means that pump pulsations are eliminated, producing a smooth flow of air. The tank-mounted compressor has a built-in scoop-type handle, which reduces the height of the unit and makes the top-mounted gauges with adjustable air pressure valve easy to see and use. The duty cycle is 25 percent, and it provides 0.36 scfm @ 90 psi. Included with the unit is an accessory kit featuring a 25-foot recoil hose; a blow gun; a female coupler; two inflation needles; two male plugs; an air chuck; an inflation adapter; a tapered inflation nozzle; and a roll of PTFE tape. The unit comes with a one-year limited warranty. It has a suggested manufacturer’s retail price of $62.30.
Campbell Hausfeld; (800) 543-6400; http://www.chpower.com/
Craftsman Model 15312
This 2-gallon, 120-volt-AC horizontal air compressor features a lightweight, compact design and a 17-piece accessory kit that includes a dual tire chuck; sealing tape; a tapered nozzle; a threaded adapter; two inflation needles: a safety nozzle; a blow gun; two female quick-connect couplers; two male quick-connect plugs; a female quick-connect plug; two male adapters; an NPT female adapter; a tire gauge; and a 25-foot coil air hose. It has a built-in carrying handle, weighs 26 pounds, and measures 17 inches by 17 inches by 13 inches. The 120-volt compressor is rated at 3.7 scfm @ 40 psi and 2.4 scfm @ 90 psi and delivers a maximum 125 psi.
Additional features include dual quick-connect outlets for two hoses and operation of multiple tools; an integrated control panel; a cast-iron cylinder for better heat dissipation; and an oil-lubed pump for longer life and quiet operation. The manufacturer’s suggested retail price is $129.99.
Craftsman Model 15310
This 3-gallon, direct-drive, 120-volt-AC oil-lubricated compressor provides a lightweight, portable source of air power for many do-it-yourself projects. It features a horizontal tank with a cast-iron cylinder and aluminum-finned copper outlet and delivers 2.4 scfm at 90 psi. It weighs 38 pounds and measures 19 inches by 9 inches by 19 inches. Other features include universal quick-connects for tools and air hoses; twin gauges and an air regulator; an oil-level sight glass with automotive-style air filter; large rubber feet for stability; a cushioned carrying handle; a dual tire chuck; sports inflation needles; a tire gauge and adapters; plus a a 25-foot coiled nylon air hose, a blow gun, and spare quick-connects. The manufacturer’s suggested retail price is $139.99.
Craftsman Model 15216
This 6-gallon, 120-volt-AC pancake compressor features an oil-free universal motor atop a pancake-style air tank and is capable of delivering up to a maximum 150 psi and 2.6 scfm at 90 psi. Features of this 42-pound compressor include universal quick-connects, dual regulated air couplers, a 25-foot PVC air hose, and a nine-piece accessory kit. The manufacturer’s suggested retail price is $169.99.
Sears; (800) 349-4358; http://www.sears.com/
Firestone Inflation Station
Available in two models, the Firestone Inflation Station, from Firestone Industrial Products, is designed to instantly supply up to 150 psi to inflate air springs, tires, air mattresses, swimming rafts, basketballs, or whatever else needs air.
Both Inflation Station kits (models 9289 and 9290) include a 150-psi air compressor, an 8-foot power cable with brass alligator clips to attach directly to a 12-volt battery, a 25-foot coiled air hose, a tire inflator tool with gauge, two blower nozzles, and a needle valve tool “” all packed in a heavy-duty canvas carrier.
Inflation Station model 9289 has a 35 percent duty cycle with a 1.69 cfm rating at 60 psi and weighs 9 pounds, while model 9290 has a 20 percent duty cycle and a 1.02 cfm rating at 60 psi and weighs 7.25 pounds.
Inflation Stations are available from any Firestone Ride-Rite air helper spring dealer. The suggested manufacturer’s retail price for model 9289 is $362.15, while model 9290 is $249.27. Both come with a two-year limited warranty.
Firestone Industrial Products; (800) 888-0650; http://www.ride-rite.com/
This 1-gallon portable 120-volt-AC compressor weighs just 21 pounds but can provide up to a maximum of 125 psi. The unit provides 0.66 cfm at 90 psi and has a 50 percent duty cycle. It is powered by a 1/2-horsepower induction motor and includes an oil-free pump for reduced maintenance. The compressor comes with a quick connector.
The manufacturer’s suggested retail price for the EX1001 is $149 and it comes with a five-year limited warranty.
Maxus, (888) 629-8748; http://www.maxustools.com/
This portable 12-volt-DC compressor is a gearless, direct-drive unit that is sealed for moisture and dust resistance. Designed specifically for inflating RV tires, the 8.75-pound 400P-RV has a 33 percent duty cycle (at 100 psi), provides 1.62 cfm at 60 psi, and has true 150 psi capability for inflating higher psi RV tires.
The compressor includes a 33-foot coil quick-connect hose with a multifunction inline gauge that eliminates the need to go back and forth from tire chuck to tire gauge. In addition, a 25-foot extension hose comes with the unit. Both hoses are equipped with heat-shielded quick-connect fittings for ease of use and protection.
Other features include an anodized aluminum alloy cylinder; an automatic reset thermal overload protector; permanently sealed and lubricated bearings; stainless-steel valves; heavy-duty battery clamps with a 40-amp insulated heavy-duty fuse holder; a 45-degree two-way quick-connect open-ended air chuck; a 90-degree twist-on open-ended inflator/deflator; a three-piece inflation tips kit; an aluminum sand tray for stabilization; and a sturdy canvas stowage bag with side pockets for tools. The 400P-RV has a manufacturer’s suggested retail price of $279 and comes with a one-year warranty.
Viair Corporation; (949) 585-0011; http://www.viaircorp.com/