Castair C3G Cast Iron Air Compressor Pump — Two-Stage W3 Cylinder (15HP)
The Castair C3G is a heavy-duty two-stage cast iron bare pump built for 15HP compressor applications. It uses a W3 cylinder configuration with a 14-3B flywheel and holds 1.75 gallons of oil — distinguishing it from the standard C3 pump (which uses a 20.7-3B flywheel and 1-gallon oil capacity). The C3G is a replacement pump or a build-your-own compressor component, sold as a bare pump with flywheel. If you're replacing a worn pump in an existing 15HP compressor or building a custom unit on an existing tank, this is a Castair factory-direct component.
C3G vs. C3 — What's the Difference?
Both the C3 and C3G are 15HP two-stage cast iron pumps in a W3 (3-cylinder configuration). The key differences:
- Flywheel: C3G uses a 14-3B flywheel; the standard C3 uses a 20.7-3B flywheel
- Oil capacity: C3G holds 1.75 gallons; C3 holds 1 gallon
- Weight: Both weigh 485 lbs
- Application: The C3G is suited for configurations where the smaller flywheel diameter is required for the motor base geometry or belt drive layout
If you're replacing a C3G pump, match the flywheel spec carefully — a 14-3B versus 20.7-3B is a significant size difference that affects belt length, pulley alignment, and motor base positioning.
Pump Specifications — From Castair's Published Data
- Part Number: C3G
- Horsepower Rating: 15HP
- Weight: 485 lbs
- Compression Stages: Two-stage
- Cylinder Configuration: W3 (three-cylinder)
- Flywheel OD: 14-3B
- Oil Capacity: 1.75 gallons
- Warranty: 1 year parts only, when properly installed and maintained
Cast Iron Pump Construction
Castair designs all of their C-series pumps for the same core principles: slow RPM operation for long life, all cast iron for thermal stability and durability, and disc-and-spring valves for reliable service access. The C3G is part of the same lineage as the C3 and C4 pumps used across Castair's industrial and commercial compressor lineup.
- All cast iron: Cylinders, heads, crankcase
- Two-stage compression: W3 cylinder layout handles both low-pressure and high-pressure stages
- Tapered roller bearings: Both ends of the crankshaft — superior crankshaft support and lower friction than ball bearings
- Precision steel connecting rods: Automotive-type rod insert bearings at crankshaft, needle bearings at wrist pin
- Disc and spring valves: Easy service access, high efficiency, good durability under high cycle counts
- 4-ring pistons: Improved sealing, less oil carry-over
- Mechanical centrifugal unloader: Load-less start-up — standard on all Castair two-stage pumps
Who Needs This Pump
The C3G is a component sale — it's the right purchase for:
- Pump replacement: Your existing 15HP compressor uses a C3G pump and it needs rebuilding or replacement. At 485 lbs, this is a serious pump — plan for a hoist or engine crane for installation.
- Custom compressor builds: You have an existing ASME tank and motor and want to build or restore a compressor around a Castair pump
- Compressor rebuilders: Commercial shops that rebuild industrial compressors and need factory-fresh pump components
If you're not replacing an existing C3G pump and you need a complete compressor, you likely want one of Castair's assembled industrial units instead — the I15312VC3-S or I15312HC3-S are complete 15HP industrial compressors.
Installation Notes
- This is a bare pump with flywheel — does not include motor, tank, belt guard, pressure switch, or controls
- Oil must be added before operation — use Castair CAST-LUBE or equivalent compressor oil rated for piston compressors
- Change break-in oil within the first 8 hours of operation
- Requires compatible motor base, belt, and pulleys for your specific HP and RPM configuration
- Centrifugal unloader requires a compatible pressure switch and unloader valve — confirm compatibility before installation
- Right From the Start Kit #RFS002 includes break-in oil (GA30W), vibration pads (VP100 x4), ball valve, flex hose, and air filter element for C3 pump installations
Related Castair Pump Models
| Part # | HP | Stage | Cylinder | Flywheel OD | Oil Capacity | Weight |
|---|---|---|---|---|---|---|
| C2 | 7.5-10 | Two | V4 | 19.0-2B | 2 qt | 320 lbs |
| C3 | 15 | Two | W3 | 20.7-3B | 1 gal | 485 lbs |
| C3G | 15 | Two | W3 | 14-3B | 1.75 gal | 485 lbs |
| C4 | 15-25 | Two | V4 | 13-3B | 1 gal | 800 lbs |
Why Buy From Air Compressor Factory Direct?
We stock Castair pumps, compressors, and components and have been supplying commercial and industrial air equipment since 2016. We can help you confirm the right pump for your application, match belt and pulley specs, and select correct oil and accessories 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!
