Castair I15312VC3-S: 15HP 3-Phase Industrial Air Compressor — 120 Gallon Vertical with Aftercooler
The Castair I15312VC3-S is a 15-horsepower, 3-phase, 120-gallon vertical industrial air compressor built around Castair's heavy-duty C3 cast iron pump. This is not a consumer or commercial unit dressed up in industrial clothing — it is a purpose-built shop compressor engineered for continuous-duty applications where downtime is not acceptable. At 795 RPM, this machine runs quieter and cooler than high-speed competitors, which translates directly into longer pump life and lower maintenance costs over the years.
The -S suffix means this unit ships with an aftercooler mounted to the belt guard, which reduces discharge air temperature before it enters the tank. Cooler compressed air means less moisture carryover, which matters if you are running air-powered tools, spray guns, or any process that is sensitive to water contamination. If you are in a shop environment where air quality affects your work — body work, painting, sandblasting, precision air tools — the aftercooler pays for itself quickly.
This is the heavy-duty 15HP vertical option in Castair's Industrial Series lineup. The vertical tank configuration saves floor space compared to the horizontal equivalent, making it a practical choice for shops where square footage is at a premium. The 120-gallon ASME tank provides adequate storage for most multi-technician shop environments running air ratchets, impact guns, air chisels, and other pneumatic tools simultaneously.
Pump Design and Construction
All Cast Iron Pump — Why It Matters
- Pump designation: C3 — Two-stage, W3 cylinder configuration
- Pump RPM: 795 — significantly slower than typical industrial compressors running 1,100-1,200 RPM, reducing heat and wear
- Cylinder material: 100% cast iron throughout — cylinders, heads, valve plates, crankcase
- Tapered roller bearings at both ends of the crankshaft for superior support and reduced friction compared to standard ball bearings
- Precision steel connecting rods with automotive-type rod insert bearings at crankshaft and bearings at wrist pin — same engineering approach used in long-life diesel engines
- Disc and spring valves for easy service, higher efficiency, and long-term reliability — replaceable without specialized tools
- 4-ring pistons for higher efficiency and reduced oil carry-over into the air stream
- Centrifugal unloader provides loadless start-up every time — the pump starts under no load, then comes up to pressure; this eliminates the torque spike that kills motors and belts on cheap compressors
- Oil capacity: 1 gallon (C3 pump)
Tank and Frame
- Tank capacity: 120 gallons, vertical configuration
- Tank construction: Powder-coated ASME-rated steel with 4 legs for stability on vertical models
- ASME safety valve: Factory installed, sized for this compressor
- Belt guard: Totally enclosed metal — not plastic, not mesh — keeps debris out and provides a mounting surface for the included aftercooler
- Discharge and unloader lines: Copper tubing or stainless-steel braided flex line depending on configuration
Motor and Electrical
- Horsepower: 15HP
- Phase: 3-phase (requires 3-phase power supply — this is not a single-phase unit)
- Motor rating: Heavy-duty 1725 RPM industrial motor with full 15% service factor or higher
- Pressure switch: Standard industrial pressure switch with unloader
- Max operating pressure: 175 PSI
Aftercooler (Included with -S Models)
- Aftercooler part number: BGAC2M (50 CFM, belt guard mounted) — rated for 15HP applications
- Function: Cools compressed air after the pump and before the tank, condensing moisture before it enters the system
- Benefit: Significantly reduces water carryover to air tools and downstream equipment — particularly important for painting, sandblasting, and precision pneumatics
Performance Specifications
- Motor output: 15 HP
- Electrical requirement: 3-phase
- Tank capacity: 120 gallons, vertical
- Pump RPM: 795
- Free air delivery (0 PSI): 61.7 CFM
- Delivery at 175 PSI: 50.2 CFM
- Max pressure: 175 PSI
- Dimensions (LxWxH): 44 x 30 x 82 inches
- Weight: 1,185 lbs
- Aftercooler: Included (BGAC2M belt guard mounted)
What's in the Box
- Castair I15312VC3-S compressor — fully assembled
- BGAC2M belt guard mounted aftercooler (50 CFM rated)
- ASME safety valve (factory installed)
- Pressure switch with unloader
- Metal belt guard (totally enclosed)
- Copper discharge and unloader tubing (or stainless braided flex line)
- Owner's documentation
Note: Magnetic motor starter is NOT included unless you select the -S with mounted starter option. Verify electrical requirements with your electrician before ordering — 3-phase service is required.
Available Configurations in the 15HP Industrial Series
- I15312VC2-S: 15HP, 3-phase, 120gal Vertical, 898 RPM, 55.0 CFM / 45.3 CFM @ 175 PSI, 44x30x75, 980 lbs — lighter, faster pump, smaller C2 configuration
- I15312HC2-S: 15HP, 3-phase, 120gal Horizontal, 898 RPM, 55.0 CFM / 45.3 CFM @ 175 PSI, 69x24x50, 980 lbs — horizontal version of the C2
- I15312VC3-S (this unit): 15HP, 3-phase, 120gal Vertical, 795 RPM, 61.7 CFM / 50.2 CFM @ 175 PSI, 44x30x82, 1,185 lbs — larger C3 pump, more CFM, slower RPM
- I15312HC3-S: 15HP, 3-phase, 120gal Horizontal, 795 RPM, 61.7 CFM / 50.2 CFM @ 175 PSI, 69x24x62, 1,185 lbs — horizontal version of the C3
The VC3 vs. HC2 choice comes down to CFM needs and floor space. The C3 pump gives you 50.2 CFM at 175 PSI versus 45.3 CFM from the C2 — roughly 11% more usable air. If your shop runs multiple high-CFM tools simultaneously (plasma cutters, large sanders, spray booths), the C3 pump is worth the extra weight and cost. If you are running standard shop tools and have a smaller footprint, the C2 handles most two-to-three technician shops comfortably.
When Does a Shop Need This vs. Stepping Up or Down?
This unit (I15312VC3-S) is right for you if:
- You are running 3 to 5 technicians simultaneously on air tools (impacts, ratchets, air chisels)
- You have 3-phase electrical service available in your shop
- Floor space is limited — the vertical tank has a smaller footprint than the 240-gallon horizontal models
- You need aftercooler-treated air for painting or sensitive pneumatic processes
- Your required CFM at pressure is in the 40-55 CFM range
Step down to a 10HP unit if:
- You are running 1-2 technicians and standard shop tools — the 10HP series (I10312VC2-S or I10312VC3-S) delivers 35 CFM at 175 PSI, which handles most 2-tech shops without the 15HP power requirements
Step up to the 20HP or 25HP if:
- You are running 5 or more technicians, heavy spray booth work, or sandblasting — the I20324HC4Z-S at 72 CFM and 240-gallon tank handles large multi-bay operations
- Your peak demand exceeds 50 CFM continuously
3-phase consideration:
- All 15HP+ units require 3-phase electrical service. If you only have single-phase power, the maximum practical option in the Industrial Series is the 10HP single-phase units. Do not attempt to run a 15HP compressor on single-phase power.
Why Buy From Air Compressor Factory Direct?
We have been selling industrial air compressors and shop equipment since 2016, and we specialize in exactly this type of equipment. When you call us, you talk to someone who understands the difference between a C3 and C4 pump, knows what CFM your spray booth actually needs, and can tell you whether you need the aftercooler option or not based on your application.
- Free shipping on this unit to commercial addresses in the lower 48 states
- Free tech support — call us at 866-217-0063 before and after your purchase
- Full manufacturer warranty through Castair
- Honest configuration advice — we will tell you if you need a bigger or smaller unit rather than just taking your order
- Authorized dealer with direct access to Castair factory support
Call 866-217-0063 for quick answers and help!
