Aux Compressor: Building an External Air Compressor

by Peter Fleming 1991 U300 GV 40

When I saw this thread I thought I would post what I have been working on to install in the coach this spring – for us owners of older coaches w/o 12 VDC compressors.

I rent parking indoors for our coach along with several other coaches and I want to be able to “air up” with the engine off, and then be ready to pull out soon after starting the engine to avoid filling the garage with diesel fumes.

I used the VIAIR 2.54 CFM model 40040 with a 33% duty cycle vs 100% duty cycle and a smaller CFM.

I made the air tank from 4-inch SCH 40 PVC pipe. It is 18 inches long and the pressure rating is 220 psi.

I have everything mounted on some 2X4s. My plan is to keep this portable so I can use it outside of the coach for various things – and the reason I made the small tank for it.

A few words of caution:

Use solid core PVC pipe with ASTM D1785/D2665 stamped on it – rated to 220 psi (don’t use lighter “cellular core” PVC made for drain/waste/vent use only)
Use pressure rated end caps (these have the curved dome shape vs flat shape)
Use the 2 step PVC glue with the purple primer

Here are the links for the main parts (isn’t Amazon Prime wonderful…)

Viair 40040 400C Air Compressor Kit

• Motor voltage – 12 volt

• Motor type – Permanent magnetic

• Max. duty cycle: 33% @ 100 PSI

• Max. working pressure – 150 PSI

• Max. Amp draw – 29 Amps

• Max. ambient temperature – 158°F

• Min. ambient temperature – -40°F

• CFM @ 0 PSI – 2.54

• CFM @ 100 PSI – 1.34

• Dimensions – 11.25″L x 4.00″W x 7.00″H

• Net weight – 8.0 lbs

VIAIR 90113 Pressure Switch with Relay

• Regulates air compressors between 90 and 120 PSI.

• It has a built-in relay to carry longer loads and prolong life.

• Weatherproof casing and insulation

• Pre-wired and conveniently labeled

Update 5/6/13

I thought I would post an update on my compressor adventures. I have tried the VIAIR 40400 2.54 CFM unit in my coach and it just doesn’t have enough uummph to do the job. It will reach 60 psi fairly quickly but really struggles to get to 80 psi and beyond. I have ordered a larger unit – the ExtremeAire Magnum – which has a much larger 12-volt motor (95 amp draw vs 30 amp draw), a higher 6.0 CFM capacity, and it is a continuous duty.

-1.5 HP Motor
-95 amps @ 12.5 Volts DC
-Continuous Duty @ 150 psi
-6 CFM @ 0 psi
-2.6 CFM @ 100 psi
-Weight: 20 lbs.
-Dimensions: 16″ long x 6″ wide x 9.5″ tall