The tires on my 29′ Class A are 245/70R19.5 and need to be inflated to 100 to 110 PSI, depending on the load, so this is significantly more difficult than a normal 35 psi car tire. Many coin operated compressors at gas stations aren’t up to the task and we plan to camp in remote areas. If a tire had a leak, I might not find out until I’m already stranded. My RV does not carry a spare tire.
I understand that this compressor is quite expensive ( available from Amazon here for about $232 ), but I wanted something smaller than a 120V compressor to save on basement storage and 12V so I can use it to re-inflate my Jeep tires after a beach drive. Finally, I liked having the option of standing well away from the tire while filling them. Exploding tires may be really rare, but they make me nervous and it’s worth some of my money to not be there. As they say, your mileage may vary.
I also own a Bon-Aire BA121L 120V compressor with a claimed 2/3 HP I can run with the RV generator, but in testing it on an RV tire ( taking it from 40 to 100 PSI ) I had to quit after 25 minutes ( including 10 minutes of cool down time in the middle, per the manual – 10 minutes rest after every 15min ) at just 90 PSI when the compressor started to smoke. I terminated the test early and decided to look for a new compressor.
I replaced it with the Viair 400P-RV. I looked at the 450P, liking the continuous duty, but the 400P puts out more CFM, so the higher fill rate of the 400P seemed like a good idea. Also, it comes with all the parts you need to remotely fill a high pressure, high volume tire which, if it explodes while you’re squatting next to it, can easily kill you. If you doubt this, do a search on youtube for “tire explosion” and you’ll be convinced.
First impression: It’s solidly built and comes with a nice selection of accessories, including two extra air filters, toy and needle attachments, 60 feet of coiled hose in two 30 foot segments and a hand held valve so you can stand well away from the tire while filling. It has an air filler wand and a screw-on filler. All of the fittings look to be standard 1/4in, so connecting the compressor to other lines would be easy. The bag it comes in could be little more rugged, but it’s not too bad.
It’s also pretty big, with a bulge on the front of the bag for one of the coiled hoses and another on the back for the other hose. In the bag it’s actually not that much smaller than some of the smallest 120V compressors that I’ve seen, but it’s significantly lighter.
But this is smaller and lighter and runs on 12V, so I can use in my towed Jeep, too.
It has about a 8′ long heavy-duty fused power cord with battery clamps. I appreciated this, since I’ve burned out a cigarette outlet running a lesser compressor in the past. No compressor with any power at all should be using cigarette outlet plugs. According to Viair, the 400P starts out at 2.54 CFM but drops to 1.27 CFM by 100 PSI, at which point it’s drawing 26A, far more than you can pull out of a lighter socket.
The compressor has a pressure switch on the back by the on/off switch that turns the motor off when it gets to about 150PSI, so you can leave the compressor on without worrying about damaging it or the hoses by over-pressurizing them if it’s not connected to a tire. Nice touch. Additionally, there is a motor protection circuit that will shut off the motor if it gets too hot. If this happens, disconnect the power and let the compressor cool. Once cool, it will operate again.
Viair suggests idling the motor of your vehicle while running the compressor, not only to prevent draining your battery, but to keep the voltage up, making the compressor operate more easily. I ran my tests on my fully charged house battery pack of four 6V batteries, with my RV plugged into shore power.
To test the Viair, I dropped the pressure in one tire from 100 PSI to 40 PSI and connected the compressor. The inline gauge read the same as my regular gauge when it wasn’t filling, but it read very high while the air is going in. Just pause the filling to get an accurate reading. The compressor seemed to be filling the tire pretty quickly which was good because you have to hold the “trigger” on the valve open to fill the tire. At least it’s easy to hold open, so it’s not too difficult.
I would release the “trigger” to check the pressure every couple of minutes and in the few seconds it would take for the pressure in the gauge to equalize with the tire, the pressure switch on the compressor would shut it off. It would kick right back on as soon as I continued to flow air into the tire. Nice feature.
About 7 minutes after I started ( probably about 6:30 in actual compressor run time, with several pressure checks on the tire ) the tire was at 100 PSI and I stopped the test. This is significantly less than the listed duty cycle, which means it could have run longer if it needed to.
I lost a little pressure taking the filler off the tire and putting my pressure sensor back on, but when I turned my tire pressure monitor system on it said the tire was at 98 PSI. That’s pretty close to what the gauge read.
The cylinder head on the compressor and the air line were hot to the touch, but the motor exterior was just moderately warm. I had to let it sit for about 10 minutes before I was comfortable putting it in the bag.
I’m pleased that it can fill a large tire to a high pressure with some reserve capability left over. It’s not cheap, but it’s a good compressor and includes everything you need to fill an RV tire, or all 4 tires on your 4×4 if you use it in the sand. The Bon-Aire is going in the yard sale, this is going in the tool compartment on the RV.
Overall, I’m very pleased with my purchase and the quality of this unit. Since writing the above article, I’ve had a chance to use it to air up the tires in my Jeep after a sandy excursion in the Everglades and to add about 15 PSI to all 6 tires on an RV that had sat for several months. After the second task, the compressor was pretty warm, but it took it all in stride and did the job.
The Viair website is here – VIAIR Corporation – 12-Volt & 24-Volt Air Compressors and Pneumatic Systems. They have a wide range of portable and built in compressors for various applications at various price ranges and capacities.
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We’ve had our Viair compressor for nearly four years now, including over two years of RVing and regular off-road travel. We now carry the Viair in our Jeep, so it’s available for airing up after going off-road. We’ve had to top off our RV tires several times since going full-time and have used the Viair several times to air up an RV tire after a problem. Twice we’ve had slow leaks, once from a screw in a tire and once from a faulty valve stem, both times we were able to air up the tires without going to a service station or calling road service. Our valve stem problem happened to the RV when we were farther off the paved roads than many road service trucks will go.
Off road, we’ve upgraded to 245/75R15 A/T tires on our Jeep Liberty. When we’re driving in soft sand or on rocks we’ll air them down from their normal 37 psi to about 15-20 psi. When we’re about to get back on pavement, we need to air back up. It takes our 400P-RV less than 15 minutes, from the time we pull it out until it’s back in it’s bag and we’re driving away with full full tires. It’s done this dozens of times and it’s still working like new.
The compressor has worked great for us and we’re very happy we purchased it.