Castair 15 HP 2 Stage Iron Bare Pump With Flywheel Cylinder W3 C3

Castair C3 Cast Iron Air Compressor Pump — 15HP Two-Stage W3 with Flywheel

The Castair C3 is a two-stage cast iron bare pump designed for 15HP applications. It uses a W3 (three-cylinder) configuration with a 20.7-3B flywheel and holds 1 gallon of oil. At 485 lbs, this is a heavy-duty industrial pump — it's the foundation for Castair's 15HP industrial compressor units and is sold as a replacement pump or component for custom compressor builds. The price point ($3,715.25) reflects what you're getting: a full cast iron industrial pump, not a light-duty commercial unit.

Pump Specifications — From Castair's Published Data

• Part Number: C3
• Horsepower Rating: 15HP
• Weight: 485 lbs
• Compression Stages: Two-stage
• Cylinder Configuration: W3 (three-cylinder)
• Flywheel OD: 20.7-3B
• Oil Capacity: 1 gallon
• Warranty: 1 year parts only, when properly installed and maintained

C3 vs. C3G — Choosing the Right 15HP Pump

Castair offers two 15HP W3 pumps. The key difference is flywheel size and oil capacity:

• C3: 20.7-3B flywheel, 1-gallon oil capacity, 485 lbs — larger flywheel diameter for standard motor base configurations
• C3G: 14-3B flywheel, 1.75-gallon oil capacity, 485 lbs — smaller flywheel for configurations where the larger diameter won't fit the belt drive geometry

If you're replacing an existing pump, match the flywheel specification exactly. The flywheel OD determines belt length and pulley alignment. A wrong flywheel spec means re-engineering the entire drive system.

Cast Iron Pump Construction

Castair's C-series pumps share a common design philosophy: all cast iron, slow RPM, and precision machined internal components. The C3 is the same pump used in Castair's 15HP industrial compressor units (I15312VC3-S, I15312HC3-S).

• All cast iron: Cylinders, heads, crankcase — full cast iron throughout
• W3 three-cylinder layout: Three cylinders in a W configuration — two low-pressure, one high-pressure — handling both compression stages
• Tapered roller bearings: Both ends of the crankshaft for superior support and reduced friction
• Precision steel connecting rods: Automotive-type rod insert bearings at crankshaft, needle bearings at wrist pin
• Disc and spring valves: Service-friendly design, high efficiency, reliable under sustained cycling
• 4-ring pistons: Better sealing efficiency, reduced oil carry-over into compressed air
• Mechanical centrifugal unloader: Load-less start — the motor starts unloaded and compression begins as RPM builds
• Slow RPM design: Castair's C3 runs at 795-898 RPM in their assembled compressor lineup — this slow speed is what gives the pump its long service life and quiet operation

Who Needs This Pump

• Pump replacement: Your existing 15HP industrial compressor uses a C3 pump — the pump needs replacement or overhaul and you want a factory-new unit versus a rebuild
• Custom compressor builds: You have an existing ASME tank (120-gallon or larger is typical for 15HP industrial use) and a 15HP industrial motor and are building or restoring a compressor
• Equipment dealers and rebuilders: Shops that service and rebuild commercial and industrial compressors

If you need a complete assembled 15HP compressor, the Castair I15312VC3-S (vertical, 120-gallon, 61.7 CFM @ 0 PSI, 50.2 CFM @ 175 PSI, 1,185 lbs) or I15312HC3-S (horizontal equivalent) are complete factory-built units.

Installation Requirements

• Bare pump with flywheel — does not include motor, tank, belt guard, pressure switch, or controls
• Fill with Castair CAST-LUBE compressor oil before first operation — break-in oil change required within the first 8 hours
• Right From the Start Kit #RFS002 is recommended — includes break-in oil (2x GA30W gallon), vibration pads, ball valve, flex hose, and air filter elements
• Requires compatible motor, motor base, belt, and pulleys for your specific RPM and drive configuration
• Centrifugal unloader requires a compatible pressure switch and unloader plumbing
• At 485 lbs, you need a hoist, engine crane, or forklift for installation

Related Castair Pump Models

Why Buy From Air Compressor Factory Direct?

We stock Castair pumps and have been supplying commercial and industrial air equipment since 2016. We can help you match this pump to your motor, motor base, belt and pulleys, and confirm the oil and accessories you'll need for installation. Free shipping on qualifying orders. Free tech support at 866-217-0063. Full manufacturer warranty.

Call 866-217-0063 for quick answers and help!