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Old 10-29-2020, 07:20 AM   #15
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Quote:
Originally Posted by Mr_D View Post
I have air suspension but I carry a Viair 450 RV anyway as the onboard air is too slow.
That's surprising, as the smallest engine compressors I'm familiar with are more than 10 cfm, and usually more like 15-16 cfm at speed. That's waaaay more than any small portable can deliver, even with the coach engine idling.
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Old 10-29-2020, 07:47 AM   #16
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Originally Posted by KanzKran View Post
That's surprising, as the smallest engine compressors I'm familiar with are more than 10 cfm, and usually more like 15-16 cfm at speed. That's waaaay more than any small portable can deliver, even with the coach engine idling.
Its not just CFM. Pressure differential makes a big difference.

If your using 120 +/- PSI to push 110 PSI air thru the restrictions of a tire valve, its going to be a slow prosses.

A small portable compressor, with a 150 PSI, increases that differential pushing the sir in faster.
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Old 10-29-2020, 07:54 AM   #17
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This what I purchased from HD. They periodically have it on sale for $99.

https://www.homedepot.com/p/RIDGID-6...50HB/303379052

I then went to HF and purchased the following which I put on a slip mount near the compressor. Cost @$60

https://www.harborfreight.com/38-in-...eel-62344.html

After adding the necessary fittings, it works great. Don't have to run the motorhome to air up the tanks and when not on shore power, I just run the generator.
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Old 10-29-2020, 08:08 AM   #18
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….lots of options, 120v are better for "big jobs," 12v have more flexible uses-- like "Jeeping," inflators [no tank] vs compressors [w/tank]--both work, careful--many small compressors are designed for air tools so they don't cut back in until pressure drops below 90 PSI--a pain to use if your target tire pressure is above 90 PSI....
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Old 10-29-2020, 08:22 AM   #19
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I carry a Porter Cable CMB515 150psi compressor that works great. It only weighs 20lbs and adds air to the tires pretty fast. Others carry 12v Viair compressors but I found them slower than the PC.
I have the same one, bought when we still had our Class C. It's fairly quiet & easy to carry. I installed an air chuck to make using it easier. Works great!
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Old 10-29-2020, 10:09 AM   #20
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I have air suspension but I carry a Viair 450 RV anyway as the onboard air is too slow.
After owning several Class A's with onboard air i can say it looks like your compressor might be on its way out. you should at least have it looked at. You should have No problem filling tires up to 120 psi. Truckers have been doing this since the beginning of time.
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Old 10-30-2020, 05:48 AM   #21
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Originally Posted by Lt Dan View Post
I carry a Porter Cable CMB515 150psi compressor that works great. It only weighs 20lbs and adds air to the tires pretty fast. Others carry 12v Viair compressors but I found them slower than the PC.
That looks exactly like my compressor with the Craftsman name.
I will test this weekend.
Lt Dan, What pressure do you set the cut out at?
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Old 10-30-2020, 07:17 AM   #22
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That looks exactly like my compressor with the Craftsman name.
I will test this weekend.
Lt Dan, What pressure do you set the cut out at?
Set the press to the max to decrease the time it takes to fill tires. The closer the pressure is to tire press the longer the time it will take.
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Old 10-30-2020, 07:28 AM   #23
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Another vote for the Porter Cable CMB515 150psi compressor. It's ideal for routine tire pressure adjustments, but I can also tell you that it will inflate a flat tire. It's not a speed demon, but it will do the job in a reasonable time. As per instructions, you do want to monitor continual run time and shut it down if necessary to let it cool down. But when just adjusting tire pressures for inflated tires, you won't need to be concerned with overheating.
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Old 10-30-2020, 07:35 AM   #24
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I too carry the Porter Cable unit, except mine is red and branded Craftsman. I've had it at least 10 years.
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Old 11-19-2020, 05:38 PM   #25
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Viair-Rv 400. Here......
Fantastic customer service.
Able to pump up class a tires from 0 psi---to 85psi pretty quick.
With double hose setup, work all tires, with toad tires with ease.
Reliable, quiet, efficient, pricey.
Glad to have it on board with us.
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Old 11-19-2020, 10:05 PM   #26
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I use VIair 400 as well. If you get the accessory kit you get everything needed including double hose, storage bag, adapters, etc.... The 400 does not have the run time of the 450 but it does move a little more air volume. Both are great compressors.

The unit is fairly small. It comes in handy for bike tires as well.

I have to air my front tires to 115 psi so using my onboard air compressor takes forever to even move my tires up a pound or two.

I would either go with a compressor that will push 150 psi or add an air doubler to my coach air system. I like to keep my tire pressure just right and I don’t like to have to leave my diesel motor idling in campgrounds so I went with the VIair.

Another lesson learned is to air up in the morning before moving with no sun hitting the tires. And be sure you have a good high quality truck style air pressure gage.

Good Luck.
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Old 11-20-2020, 03:43 PM   #27
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I carry 50' of hose and connect it up front to the on board air.
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Old 11-20-2020, 05:30 PM   #28
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For me, the problem of using the engine driven air compressor isn't so much a function of the compressor operation as it is an air governor problem.

The air governor has a user adjustable (within limits) cut-out pressure. That is the high pressure limit of air pressure in the air tank. When that limit is reached, the air compressor stops pressurizing the tank. On my coach, that was set at the factory at 125 psi. At that point, the air governor does not start replenishing any air use which decreases the tank pressure until the pressure drops to about 90 - 105 psi (the cut-in pressure).

Trying to inflate a tire to 125 psi presents a challenge because that may be at, or below, the cut-out pressure of the air governor.

As I understand the air system, when you shut your engine down and the engine driven compressor stops, the air governor sees pressure drop below the cut-in limit (90 - 105 psi) and opens to allow the compressor to recharge the air tank. However, since the compressor has stopped, no air passes to the tank. A check valve prevents air loss from the tank and pressure in the tank remains at whatever pressure (somewhere between cut-out and cut-in) it was when you shut down. If you have any leakage or otherwise release air from the tank (brake application, as an example), the pressure in the tank will be below the cut-out pressure.

When you start the engine, the compressor again begins pushing air and the air governor has opened (it sensed below cut-in pressure at shutdown) and the pressure in the tank will increase to the air governor cut-out pressure.

So, if at that point you hook up your air hose and attempt to inflate your tire that's below the air governor cut-out pressure, air will start flowing into your tire.

However, for sake of discussion, lets assume that you want your tire inflated to 125 psi and it's currently inflated to 118 psi. Further, lets assume that your air governor cut-out is set to 125 psi and your cut-in is 105 psi. So, your tank pressure is 125 psi (you just started, the compressor ran, the air governor was open to allow air to pass to the tank until pressure reached the cut-out pressure of 125 psi, you heard the air dryer "chuff"). At that point, you connect your hose to the tire and air starts flowing from the 125 psi tank to your 118 psi tire. Eventually, equilibrium will be reached where the tank pressure and the tire pressure are equal and, importantly, somewhere between 118 psi and 125 psi. Still below your 125 psi target, but, above the 105 psi cut-in. And, there you sit. The engine running, the compressor spinning, the pressure still well above the air governor cut-in pressure.

Until the tank pressure drops below the cut-in limit, the air governor will not open and the tank will not re-pressurize to the cut-out limit (125 psi).

My drive and tag tires require 85 psi; no problem with those. My steer tires require 120 psi. Although that's "doable", it's a bit of a tug of war between the cut-in and cut-out.

Here's a link to the service data for a commonly used air governor: http://www.plazafleetparts.com/uploa...aintenance.pdf

Take care,
Stu
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