Castair C4 Cast Iron Air Compressor Pump — 20-30HP Two-Stage V4 (C4Z)
The Castair C4Z is the top of Castair's bare pump lineup — a two-stage, all-cast-iron V4-cylinder pump designed for 15-25HP applications. At 800 lbs, this is a serious piece of equipment. It uses a 13-3B flywheel and holds 1 gallon of oil. The C4 pump is what Castair puts in their largest industrial compressor units — the 20HP, 25HP, and 30HP machines in the I-series. If you're replacing the pump in one of those units or building a high-HP custom compressor, the C4Z is the Castair factory-direct component.
Note on HP rating: Castair lists the C4 as rated for 15-25HP in their published pump table, but the C4Z SKU in our database lists 20-30HP — consistent with the C4's use in Castair's 20HP, 25HP, and 30HP industrial compressor models (I20324HC4-S through I30324HC4Z-S). Contact us to confirm the right HP match for your application.
Pump Specifications — From Castair's Published Data
- Part Number: C4 / C4Z
- Horsepower Rating: 15-25HP (factory table) / 20-30HP (per model application)
- Weight: 800 lbs
- Compression Stages: Two-stage
- Cylinder Configuration: V4 (four-cylinder V configuration)
- Flywheel OD: 13-3B
- Oil Capacity: 1 gallon
- Warranty: 1 year parts only, when properly installed and maintained
V4 Cylinder Configuration — What It Means
The C4 uses a V4 cylinder layout — four cylinders arranged in two pairs at a V angle. In a two-stage pump, the large-bore cylinders handle the first stage (low-pressure) compression, and the smaller high-pressure cylinders handle the second stage. The V4 configuration provides balanced reciprocating forces across the pump, contributing to smoother operation at the slow RPM that Castair designs for. At 800 lbs, this pump runs in the same category as industrial screw compressor components in terms of mass and thermal stability.
Cast Iron Pump Construction
- All cast iron: Cylinders, heads, crankcase — full cast iron for thermal stability and long service life
- Two-stage V4 compression: Four cylinders handling both compression stages
- Slow RPM design: In Castair's 20-30HP industrial compressors, the C4 pump runs at 519-794 RPM — very slow, very long-lived
- Tapered roller bearings: Both ends of the crankshaft
- Precision steel connecting rods: Automotive-type rod insert bearings at crankshaft, needle bearings at wrist pin
- Disc and spring valves: Easy service, efficient, reliable under sustained duty
- 4-ring pistons: Better compression efficiency, reduced oil carry-over
- Centrifugal unloader: Load-less start-up standard
Where This Pump Is Used — Castair's 20-30HP Industrial Compressors
The C4 pump is the heart of Castair's largest industrial piston compressors:
| Model | HP | Phase | Tank | Pump RPM | CFM @ 0 PSI | CFM @ 175 PSI | Weight |
|---|---|---|---|---|---|---|---|
| I20324HC4-S | 20 | 3 | 240-Gal Horiz. | 519 | 92.8 | 72 | 1,700 lbs |
| I25324HC4-S | 25 | 3 | 240-Gal Horiz. | 710 | 109 | 90 | 1,725 lbs |
| I30324HC4Z-S | 30 | 3 | 240-Gal Horiz. | 794 | 128 | 105 | 1,750 lbs |
Who Needs the C4Z Pump
- Pump replacement: Your existing 20-30HP Castair industrial compressor needs a new pump — the C4Z is the factory replacement component
- Custom high-HP builds: You have a large ASME tank (240-gallon is standard for this pump class), a 20-30HP three-phase industrial motor, and are building or restoring a compressor
- Industrial compressor rebuilders: Shops that overhaul large commercial and industrial compressor equipment
At 800 lbs, installation requires heavy lifting equipment. This is not a pump you handle with a hand truck — plan for a crane or forklift during installation.
Installation Requirements
- Bare pump with flywheel — does not include motor, tank, belt guard, pressure switch, or controls
- Fill with Castair CAST-LUBE oil before operation — 1-gallon capacity
- Break-in oil change required within the first 8 hours of operation
- Right From the Start Kit #RFS003 is recommended for C4 pump installations
- Requires compatible 20-30HP industrial motor, motor base, belt, and pulleys
- Centrifugal unloader requires compatible pressure switch and unloader plumbing
- Available factory option: All Options C4 (#AOC4) — bundles all asterisk factory options at 10% savings
Related Castair Pump Models
| Part # | HP | Cylinders | Flywheel | Oil Cap. | Weight |
|---|---|---|---|---|---|
| C2 | 7.5-10 | V4 | 19.0-2B | 2 qt | 320 lbs |
| C3 | 15 | W3 | 20.7-3B | 1 gal | 485 lbs |
| C3G | 15 | W3 | 14-3B | 1.75 gal | 485 lbs |
| C4 / C4Z | 15-25 | V4 | 13-3B | 1 gal | 800 lbs |
Why Buy From Air Compressor Factory Direct?
We stock Castair pumps and industrial compressor components and have been supplying commercial and industrial air equipment since 2016. We can help you match the C4Z pump to your motor, motor base, belt and pulleys, and confirm the accessories you need. Free shipping on qualifying orders. Free tech support at 866-217-0063. Full manufacturer warranty.
Call 866-217-0063 for quick answers and help!
