Article: Keeping the tires inflated

Tires, shocks, sway bars, air bags... What crosswind?
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skater
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Article: Keeping the tires inflated

Post by skater »

Introduction

As you probably are aware, the rear tires in our B190s are spec'd to be inflated to 80 PSI - which happens to be the limit of the tires in question. And if you don't run that much, you can actually destroy the rear tires - trust me on this. Unfortunately most small 12 volt air compressors can't handle that load, or take a very long time to do it. This article covers my research on the problem, what I purchased to solve it, and my future plans.

Choosing A Compressor

My experience with cigarette lighter-based air compressors has not been good - they just aren't that strong. So when I realized I needed something capable of 80 PSI, I first thought of portable 120 volt air compressors. However, they tend to be heavy and bulky, even the smaller ones, and I wanted something I could take with me on the road. At the same time I didn't have a lot of money to spend on the deal. After searching around, I found this article on 4x4Wire.com that talks about the Superflow MV50 and MasterFlow MF-1050 compressors, which are essentially the same compressors with a different brand name. In that article the author bought the Superflow MV50, but I was able to find the MasterFlow MF-1050 at Pep Boys for about $50.

As mentioned in that article, the compressor includes about 25 feet of air hose with a nonstandard connection, and various needles for inflating balls or just blowing air. It also includes an intake air filter that screws on and a nice carrying bag. I think it's a pretty good buy, and it seems to work quite well.

Using The Compressor

First, let me make it clear that this compressor will do the job of keeping your camper's tires inflated without any modifications, with the following caveats:

* The compressor draws 30 amps, which means you need to connect it directly to the battery with the included clamps. I keep the engine running when I'm trying to use the pump, and I strongly recommend you do the same.
* The compressor has (barely) enough hose and wire so that you can inflate the rear tire on the side of the battery you connected it to; it will not reach to the opposite rear tire.
* The compressor will not start and will blow its fuse when I try to pump up a tire that already has 60-70 PSI in it. Get extra fuses, or find one of the 30 amp circuit breakers that will fit in standard ATC fuse position. You'll need one that has the long lugs because the circuit breaker won't fit in the holder where the fuse does. (I just bought the breaker today and haven't tried it, but my understanding is that it resets when you disconnect the power if it trips.) To avoid the overload problem in the first place, contrary to the directions, start the pump, then hook it to the tire.
* The inflation nozzle is not standard - you have to screw it on to the valve stem of the tire. The pressure gauge is on the pump, not the inflation nozzle.

Circuit breaker
Image
30 amp circuit breaker in place of fuse (click for larger shot)


As good as it is, I had a few issues, not the least of which is wanting to be able to inflate the tow dolly's tires or even the attached car's tires. So, I decided to modify it a bit.

Modifying The Compressor

The first issue was that I wanted a better tire inflation chuck. This turned out to be problematic because most chucks shut off the air flow when they aren't actually pumping up a tire, which means the air pressure in the pump and hose jump within seconds (literally) to 70 PSI or more. So, I stuck with the original constant flow chuck.

The second issue was that I wanted more hose length. Even when I'm inflating the tires on the camper, it's nice to not be stretching the hose or the wires or (worse) the valve stem. However, the quick disconnects included with the pump are non standard, so this took some work.

Image
Image of nonstandard quick disconnects.


I bought an air compressor starter kit (approximately $20) that included a tire inflation chuck, a 25' coiled hose, various male and female disconnects, and a few other things. The hose got one female disconnect and one male disconnect.

To put a standard female quick-disconnect on the pump, I pulled out the oddball one and discovered that it does not use standard threads. It was some sort of fine thread, a bit smaller than 1/4" NPT. So, I bought a 1/4" NPT tap and handle (about $20 for both) and tapped out the pump to 1/4" NPT. I used Vaseline to keep the metal shavings on the tap, then used a Shop-Vac to remove the metal shavings that fell into the pump despite my caution. Then it was a simple matter to thread in a 1/4" NPT nipple with a female quick disconnect on it, using pipe thread tape. I used a straight nipple, but I plan to change it to a 90-degree bend like they did in the 4x4Wire.com article so the disconnect doesn't stick out as far (though it still fits in the bag).

Image
Pump with new female quick disconnect.


For the original air hose, I cut off the oddball female quick disconnect, and inserted a hose barb. Note the hose is NOT 1/4", try 1/8". I was able to get it partway on to a 1/4" hose barb with MUCH work. Don't forget the hose clamp. The end of the barb had threads, on to which I installed a male quick-disconnect.

So, now, the pump and original hose work exactly as they did before - connect the hose, turn it on, and go pump. But if I need more distance, I can now easily pop in the second hose to give myself an extra 25' (or, with more hoses, even more).

Image Image

Modified hose and closeup of the two ends.

Issue - Watch Your Pressure!

One thing I realized is that the female quick-disconnects retain air. That is, if I don't have the inflation hose hooked up to it so it can release air, the pump WILL pressurize against the quick-disconnect, and as I mentioned before it happens VERY quickly, so be careful! This is probably why the original setup had a male connection on the pump instead of the usual female. The pump's maximum pressure is apparently 120 PSI, and I don't know if there's a safety switch on it (I didn't really feel like finding out the hard way).

Future Plans - Permanent Mount in the Camper

It'd be nice to have on-board air in the camper so I don't have to open the hood and start the engine every time. Hooked up correctly, the pump could be run off the converter's 12 volt power which means it'd work whether you have shore power available, the generator running, or the engine running. (It'll also work off just the camper's battery but I wouldn't use it for more than a short time that way.)

I believe the air compressor could be mounted easily under the couch between the converter and the furnace. There is enough room for it there, and the wiring from the converter would be easy.

It'd be nice to have hookups outside the camper, say behind the front and rear bumpers, so that I could just plug in the 25' hose, turn the pump on, and inflate away. The easier I make it for myself, the more likely I am to do the chore!

The 4x4Wire.com article describes using an air tank as a buffer with a pressure switch. Viair sells a 2.5 gallon tank that I believe will fit next to the frame rails on the passenger side (on mine) - it's only 6 inches in diameter and about 2 feet long. The tank runs about $67, but then you'll spend another $85 or so with hookup parts (pressure switch, hose, drain, etc.). Also, this adds weight to an already heavy vehicle. However the advantage is that you'd be able to use a good inflation chuck, even one with a gauge, without worrying about the compressor exploding.

A second option would be to go tankless and just run hoses directly to the bumper connectors. In this rig, I envision a switch near each connector that would control the pump (a couple bucks each), but this will complicate the wiring and you'd still want a pressure switch just in case ($20, plus various hardware parts to hook it up). In this case you'd still need to use the original inflation chuck to prevent the overpressure situation.

Other Options

The Viair company sells compressors that are intended for on-board use, and they sell portable models that likely could be converted to permanent mount as 4x4Wire.com did with the MV-50 they bought.
mtnmanb
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Re: Article: Keeping the tires inflated

Post by mtnmanb »

This is a ton of modding and jumping through hoops. Is there anything out there that will inflate to 80 psi without modding or doing special tricks (ie hooking staight to battery, bringing extra fuses because they will blow, extra hoses, starting pump before hooking up to tire, etc)?

B)
'90 bought 27Apr2012
Added Safe-T Stabilizer shock, port. generator, EZE RV gutters, curtains, memory foam 5.5" mattress, rebuilt bunk, Double Pancake LED light, O2 sensor, shore plug, 4655 Converter, Battery under couch, MaxxFan Fantastic Fan
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skater
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Re: Article: Keeping the tires inflated

Post by skater »

mtnmanb wrote:This is a ton of modding and jumping through hoops. Is there anything out there that will inflate to 80 psi without modding or doing special tricks (ie hooking staight to battery, bringing extra fuses because they will blow, extra hoses, starting pump before hooking up to tire, etc)?

B)
Sure: A 120 volt air compressor. That's what I use now, in fact, after I burned up the one above by letting it run too long while winterizing one time. A better 12 volt pump might be able to do it, too, but I haven't tried it.
1991 Airstream B190 - bought, 2005; sold, 2011; bought 2017
1995 Airstream Excella 30' trailer

WBCCI #13270, Washington, DC Unit
mtnmanb
Weekend Camper
Posts: 61
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Re: Article: Keeping the tires inflated

Post by mtnmanb »

Thanks, I'll probably just do that and power it with my Honda 2000 generator.

Do you keep the front inflated at 80 psi too?

B)
'90 bought 27Apr2012
Added Safe-T Stabilizer shock, port. generator, EZE RV gutters, curtains, memory foam 5.5" mattress, rebuilt bunk, Double Pancake LED light, O2 sensor, shore plug, 4655 Converter, Battery under couch, MaxxFan Fantastic Fan
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skater
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Re: Article: Keeping the tires inflated

Post by skater »

mtnmanb wrote:Thanks, I'll probably just do that and power it with my Honda 2000 generator.

Do you keep the front inflated at 80 psi too?

B)
No, the fronts were spec'd at 52 PSI or something like that. Check the sticker on the driver's door frame to be sure.

I did inflate the spare to 80 PSI though - figuring it was easier to let air out to 52 PSI than it would be to add 28 PSI to get it to 80 PSI along the road.
1991 Airstream B190 - bought, 2005; sold, 2011; bought 2017
1995 Airstream Excella 30' trailer

WBCCI #13270, Washington, DC Unit
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usachris
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Re: Article: Keeping the tires inflated

Post by usachris »

skater wrote:
Tue May 15, 2012 2:20 pm
No, the fronts were spec'd at 52 PSI or something like that. Check the sticker on the driver's door frame to be sure.

I did inflate the spare to 80 PSI though - figuring it was easier to let air out to 52 PSI than it would be to add 28 PSI to get it to 80 PSI along the road.
Smart move on the spare air pressure!
Christopher Salazar
1999 B190 #301352
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