Custom high-performance 100% duty cycle on demand, on-board air system

[taylor.coyote]

  I thought some of you may have an interest in our on-board, on demand compressor air system. 

A little background:

It was taking a long time to air-up 8 tires with a small portable compressor. Besides filling the tires slow, the compressor maxed out its duty time in about 20-25 minutes. This caused an additional waiting period for the compressor to cool before we could complete airing up all 8 tires. When the compressor taped out, I always had some fear the compressor was cooked for good. all considered, airing up was taking the better part of an hour.  This process was laborious. We would reluctantly air down only if we were going to be off road for a full day or more.

A friend that owns a tire shop showed me a custom on board, on demand air system he had made for his truck. With his help and some fabrication time from another friend we came up with a high performance system for our truck.

Below are some images and some initial performance results of the on board sir system for our F250, 4x4 ,short bed, crew cab. Some may think this is overkill but I love being able to increase the PSI by 20 LBS for 8 tires in what should be in the range of 12-15 minutes. Most importantly, my wife is supportive and likes the new tool. 

The system mounts with a pair of "frame hangers" employing existing truck frame bolts on the passenger's sided, behind and parallel to the running board. The design compromise made with our system to have a larger tank was to give up 1" of ground clearance (bottom of tank hangs 1" below the lowest point of the running boards). We could have opted for a smaller tank without giving up any ground clearance by using 4" x 5" tubing vs. the 5" x 5" tubing used for the tank. 

Crew Cab pickup trucks generally have under body space to mount a robust system. Auto drop down running boards greatly reduce your tank size options. Most onboard systems have 2-5 gallon tanks with a single constant duty compressor.  These are less robust but still are considered to be high-performance systems. Some systems have the air tank located in a separate location than the compressor. Each rig takes your imagination to come up with a system that can work for you.

Material cost for our system was $970 for everything. Please note, a typical system will have a lower cost due to having one compressor and a smaller tank.

• 5"x 5" x 92" steel tubing
• 7 weld-in bungs
• Drain valve and pipe plugs
• Steel flat bar (frame mounts, compressor mounts, tabs for electronics)
• Paint
• Air hose and fittings
• Dual Pack Viair 450c compressor kit plus wiring kit

I purchased the compressor from Horn Blasters. They are knowledgeable about onboard air systems and provided a no questions asked replacement for some damaged components.

https://hornblasters.com/collections/air-compressors

 

Specs and initial performance

• Two Viair 450c compressors (constant duty - 150 psi  / 3.28 CFM)
• Pressure switch --100psi on / 150 psi off
• 5x5"x92" air tank = 10 +/- gallons 
• Half inch ID air delivery system
• Female quick coupler at truck hitch for air hose attachment

The system is newly installed as of this morning. I have yet to field test airing up all 8 tires to know the true air up time. I did a quick bench test by filling one tire from 50psi to 70psi and filling the 10 gallon tank form zero to 150psi.

 

Tire size                                    Fill rate

265/70/18.                               50 psi to 70 psi took 1.1 minutes

 

Ten gallon tank.                     Zero PSi to 150 PSI  took 3.3 minutes

 

on board compressors and air tank system.jpg.pdf

 

on board compressors and air tank. 2jpg.pdf

 

QUICK COUPLER AT HITCH pdf.pdftank behind running board.jpg.pdf

 

 

 

 

 

[taylor.coyote]

 

 

[John E Davies]

That is ingenious, I hope it works well for you. I am concerned about a high pressure tank hanging so low in the center of the truck, it will most likely get damaged when you go off pavement, hopefully it will just bend its brackets... 😳. How do you plan to keep mud off the compressor cooling fins? Where did you mount the remote air filters?

For $1000 I would probably look into installing an engine driven pump using a repurposed AC compressor, or just buy an off the shelf CO2 system like Powertank…. Is there some reason you chose this under frame method instead? Thanks.

John Davies

Spokane WA

 

[taylor.coyote]

Good questions. The tank is designed after my friend's that owns the auto shop. He has an older F250 with the system installed for over 5 years. No trouble so to date. We do spend a lot of time off road but seldom end up dealing with hard core 4x4 conditions. Let's face it, an F250 is not a nimble off road rig. I have yet to be in the position to be dragging the bottom of the running boards. We were thoughtful to design the "tank "frame hanger arms" to be the weak point and should give before damaging the tank.

The system is also designed for easy access to the working parts. Simply unbolt 4 bolts in the frame hanger arms and the whole systems easily can be dropped down.

For cleaning the fins, they are accessible for a hosing off through the gap between the truck and the running boards. 

Yes , a bit spendy but it takes zero storage space and does way with futzing with a portable kit. I just need to pug in the air hose and it's ready to go. The filters are inside the truck under back seat. This is mandatory to draw dry air and easy access. This is based on the five years of experience  of my friends systems and by taking with the folks at Horn Blasters for the compressors holding up under the truck. Time will tell the truth regarding our wisdom on the systems location.