The Castair I73CUC1-S is a 7.5 HP, 3-phase industrial air compressor in a "cube" configuration — the pump and motor are mounted on a compact base without a receiver tank. This is a specialty configuration for shops or industrial applications that have a remote or central receiver tank already installed, or where a separate ASME tank is being sized and specified independently. The C1 pump runs at 895 RPM and delivers 32.4 CFM at 0 PSI (24.8 CFM at 175 PSI) — the same output as the I738VC1-S and I738HC1-S, just without the tank assembly.
The cube configuration is less common in general shop installations but standard in industrial settings where a central receiver feeds multiple branch lines across a large facility, or where replacement of a pump/motor unit on an existing tank is needed. If you're replacing an existing compressor pump and motor while retaining your tank, this is worth a call to confirm compatibility before ordering.
When a Cube Pump Configuration Makes Sense
- Central plant / remote receiver: Your facility has a large central air receiver (100+ gallons) already plumbed to your shop — you need the pump and motor unit but the tank is staying put
- Replacement pump installation: The existing compressor tank is in good condition but the pump or motor has failed — a cube unit lets you mount a new pump and motor on the existing base or a new saddle
- Custom installations: Your installer or integrator is handling the full system design including tank sizing, after-coolers, and piping — they want the pump/motor unit only
- Limited ceiling height: A vertical tank may not fit and you want to design a low-profile installation with a separate horizontal tank mounted elsewhere
Pump Features — Cast Iron C1 Two-Stage
- All cast iron construction: Cylinders, heads, and crankcase — no aluminum components in the compression path
- Slow 895 RPM operation: Belt-driven from the 1,725 RPM industrial motor, keeping heat and wear low across a long service life
- Tapered roller bearings at both crankshaft ends: Superior support for the two-stage pump loads and belt-drive side loads
- Precision steel connecting rods: Automotive-type rod insert bearings at crankshaft, needle bearings at wrist pin
- Disc and spring valves: Easy to service in the field, reliable under sustained pressure cycling
- 4-ring pistons: Reduced oil carry-over into the discharge air
- Centrifugal unloader: Every start is a no-load start — head pressure releases before the motor torques up
Motor and Electrical
- 1,725 RPM heavy-duty industrial motor: Full 15% service factor or higher — continuous duty rated
- Factory-mounted magnetic motor starter (-S): 3-phase overload protection installed at the factory and wired to the unit
- 3-phase operation: Smooth starts, lower peak current draw, longer motor life vs. single-phase
What's in the Box
- Castair I73CUC1-S cube compressor assembly (C1 pump, motor, base/cube frame, belt drive, belt guard)
- Factory-mounted magnetic motor starter (3-phase, sized for 7.5HP)
- Copper discharge and unloader tube (installed)
- Pressure switch (installed)
- Tank not included — this is a tankless cube pump unit
Available Configurations
- I73CUC1-S (this unit): 7.5HP, 3-phase, cube (tankless), C1 pump, 895 RPM, 32.4 CFM@0PSI / 24.8 CFM@175PSI, magnetic starter included
- I73CUC2-S: 7.5HP, 3-phase, cube (tankless), C2 pump, 585 RPM, 35.0 CFM@0PSI / 28.1 CFM@175PSI, magnetic starter included
- I738HC1-S: Same C1 pump, motor, plus 80-gal horizontal ASME tank — 64x20x48 in., 625 lbs, full compressor unit
- I738VC1-S: Same C1 pump, motor, plus 80-gal vertical ASME tank — 32x24x74 in., 625 lbs, full compressor unit
When Does a Shop Need This vs. a Full Unit
Buy the I73CUC1-S when you already have an ASME-rated receiver tank in your installation and need the pump and motor assembly only. This saves the cost of a tank you don't need and may simplify your installation if the tank is being custom-fabricated or is already in place.
Buy the I738HC1-S or I738VC1-S instead if you need a complete, ready-to-operate compressor including the tank. Those units ship as a complete assembly with the ASME tank already mounted and the pump/motor ready to go.
Choose I73CUC2-S if you need the higher CFM output of the C2 pump (28.1 vs. 24.8 CFM at 175 PSI) in the cube configuration.
Technical Specifications
- Model: I73CUC1-S
- Horsepower: 7.5 HP
- Phase: 3-phase
- Configuration: Cube / Tankless
- Tank: Not included
- Pump Model: C1 (two-stage, cast iron, inline-2)
- Pump RPM: 895
- CFM @ 0 PSI: 32.4
- CFM @ 175 PSI: 24.8
- Max Working Pressure: 175 PSI
- Motor Speed: 1,725 RPM
- Starter: Factory-mounted magnetic motor starter included
- Discharge Tube: Copper
- Belt Guard: Metal, fully enclosed
Why Buy From Air Compressor Factory Direct?
We specialize in industrial and commercial air compressors and have been matching shops to the right equipment since 2016. When you call us, you're talking to someone who knows the Castair lineup — pump models, tank options, starter requirements, CFM calculations for your tool mix. Free shipping, free technical support at 866-217-0063, and the full Castair manufacturer warranty. If you're comparing cube pump configurations or deciding between the C1 and C2, call us.
Call 866-217-0063 for quick answers and help!
