Topping off 22.5 tires.

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Thanks for the replies.  Two more questions.

Can anyone confirm Sarges comment regarding hose length?  Thought I read something about it but don't recall where.

Doc, Hitachi makes a bunch of Air compressors.  Couldn't find one that indicated 4CFM.  What model do you have? 
 
Sarge is correct but only if there is any air flow. As the flow approaches zero so does the pressure drop.

Tom
 
Tom, I think there's enough pressure.  But I'm wondering if maybe the chuck does not fit right.  In any event, I've been able to add 4 or 5 lbs which is all I wanted to do so will not worry about the compressor unless I need to replace for other reasons.  I'll just make sure the next one has a high CFM.  Love the Forum.  Learn stuff every day. 
 
garyb1st said:
Doc, Hitachi makes a bunch of Air compressors.  Couldn't find one that indicated 4CFM.  What model do you have?
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My compressor is truly ancient and is no longer in production.  It's a EC119SA
 
Gary RV_Wizard said:
Before that happens, the air chuck will probably slip off the valve and lose some pressure,
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I'm currently using an air chuck with a screw-on fitting.  It's a lot more reliable than the "clamp on" ones I've had previously.
 
garyb1st said:
Thanks for the replies.  Two more questions.

Can anyone confirm Sarges comment regarding hose length?  Thought I read something about it but don't recall where.
Click to expand...

I don't doubt added hose slows flow from friction.
Just my experience. Our compressor is piped from one building to another, maybe 200 ft away, then we have a 100' air hose which we use on our unit. Have had no problems filling to 100 psi.
 
The onboard air compressor on my motorhome, a factory installed compressor, fills the air tank to 90 PSI and shuts off. It will easily, in a couple of minutes, top off my tires from 75 PSI to 80 PSI. The air hose that fills my tires comes directly from the air tank.
 
garyb1st said:
Tom, I think there's enough pressure.  But I'm wondering if maybe the chuck does not fit right.  In any event, I've been able to add 4 or 5 lbs which is all I wanted to do so will not worry about the compressor unless I need to replace for other reasons.  I'll just make sure the next one has a high CFM.  Love the Forum.  Learn stuff every day.
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Get the one I linked to and you won't have any problems. It works as good as my 165 psi pancake.
Bill
 
Gary RV_Wizard said:
Lifting the tire off the ground won't change things one iota. The psi is the same either way, as is the amount of air needed to fill it.  Whomever told you that should be ignored if you need tire tech advice in the future.
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Heli_av8tor said:
Sarge is correct but only if there is any air flow. As the flow approaches zero so does the pressure drop.

Tom
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I just wanted to chime in on these two spot-on replies.  A lot of misinformation can be shared unwittingly and these two statements above are correct.  Pressure is primarily a function of volume and amount of matter (in this case air) placed inside of the volume, and temperature too of course.  Pressure drop is indeed a function of velocity (and other factors) but does go to zero as velocity does.  It is always good to see the number of folks on this forum who have an appropriate understanding of these things (not true on many forums!).
 
why would you not use the onboard compressor if you are in a motorhome?


dee
 
I've been thinking to just source a suitably sized 120V compressor and just shed the tank for space savings.  It'd be one thing if I needed the air capacity to run a nail gun or regulation to spray paint but for filling tires I'm not sure the tank matters.  12V tire inflators don't come with tanks, so why not 120V?  Haven't seen too many portable tankless compressors for sale (they're either 12V or big commercial grade) but I guess you could buy a basic one with a tank and split them up.

Mark B.
Albuquerque, NM
 
Mark_K5LXP said:
I've been thinking to just source a suitably sized 120V compressor and just shed the tank for space savings.  It'd be one thing if I needed the air capacity to run a nail gun or regulation to spray paint but for filling tires I'm not sure the tank matters.  12V tire inflators don't come with tanks, so why not 120V?  Haven't seen too many portable tankless compressors for sale (they're either 12V or big commercial grade) but I guess you could buy a basic one with a tank and split them up.

Mark B.
Albuquerque, NM
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I think you'd be eliminating the high limit pressure cutout switch so you'd have to be careful about over pressurizing something.  You may still be able to incorporate that switch in the discharge line.  Other than that, I don't see why it would not work. Keep us informed as to what you end up doing. You may be starting a new trend.
 
Gary B1st, our Class C motorhome has a 12 volt onboard air compressor and air tank because the slide has a pneumatic air seal. Some other Class C motorhomes have an onboard air compressor due to air bladder helper springs. I have no idea if they have enough pressure to air up tires. Our compressor airs the tank to 90 PSI which is adequate to air up our tires to 80 PSI. 
 
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