The Castair C1 is a two-stage, inline 2-cylinder air compressor bare pump rated for use with 4 to 7.5HP motors. This is a replacement pump — it ships without a motor, tank, or base. You supply the motor and mount it to your existing or new compressor frame. The C1 is the right choice when you're rebuilding a worn-out compressor that's in an otherwise serviceable frame, or when you're doing a ground-up build with a specific motor and tank combination.
Key specifications from the product listing: 16.875" flywheel OD with a 2-groove B-section (2B) pulley configuration, and a 2-quart oil capacity. The two-stage inline cylinder arrangement means the air is compressed twice — first stage brings it to an intermediate pressure, second stage takes it to full system pressure — which is why two-stage pumps deliver better efficiency and lower discharge temperatures than single-stage designs at the same pressure.
Key Features
- Two-Stage Compression: Two-stage design delivers better thermal efficiency and lower discharge air temps compared to single-stage at equivalent pressures
- Inline 2-Cylinder Configuration: Compact inline layout — both cylinders in a straight line rather than a V arrangement
- 16.875" Flywheel OD, 2B Groove: 2-groove B-section pulley accepts standard B-section V-belts for motor connection
- 4-7.5HP Motor Range: Wide HP compatibility gives you flexibility in motor selection for a rebuild or new build
- 2 Quart Oil Capacity: Splash-lubricated cast iron pump — change oil per manufacturer intervals for long service life
- Cast Iron Construction: Cast iron cylinders and components resist wear and maintain sealing surfaces over long service periods
- Bare Pump (No Motor): You choose and supply the motor — select the HP and voltage that matches your application
Technical Specifications
- Part Number: C1
- Pump Type: Two-stage, inline 2-cylinder reciprocating
- Motor Compatibility: 4 to 7.5HP
- Flywheel OD: 16.875"
- Pulley/Flywheel Grooves: 2B (2-groove, B-section V-belt)
- Oil Capacity: 2 quarts
- Lubrication: Splash-lubricated
- Cylinder Material: Cast iron
- Manufacturer: Cast Air
- CFM output, maximum working pressure, RPM range — contact us for complete specifications.
When to Choose the C1
- Pump Replacement: Your existing compressor has a seized or worn pump, but the motor, tank, and frame are in good shape — replace just the pump
- New Build, 4-7.5HP Range: Building a custom compressor with a specific motor and tank configuration — the C1 gives you the pump head to pair with your own components
- Upgrade Path: Replacing a single-stage pump with this two-stage unit for better efficiency on a high-duty-cycle application
- Commercial Shop Air: Suitable for auto shops, body shops, fleet maintenance, and light industrial applications in the 4-7.5HP motor range
Two-Stage vs. Single-Stage
Single-stage pumps compress air once and send it directly to the tank. Two-stage pumps like the C1 compress the air in two steps with intercooling between stages. The result is lower discharge temperatures, less moisture in the compressed air, and better volumetric efficiency at higher pressures. If you're running tools that need sustained 100-175 PSI or running a high duty cycle, two-stage is the right design. For lighter-duty use at lower pressures, single-stage is simpler and less expensive. The C1 is the two-stage option in this HP range.
Why Buy From OEM Diagnostic Tools?
We stock Cast Air compressor pumps and components for commercial and industrial applications. Specialist supplier since 2016. Free shipping on qualifying orders. Call us for pricing, availability, and help identifying the right pump for your motor and application — this is the kind of purchase where a 5-minute conversation saves you from ordering the wrong unit.
Call 866-217-0063 for pricing, availability, and help!
