The Castair D7112HC2-S is a 15HP (2×7.5HP) single-phase duplex air compressor on a 120-gallon horizontal ASME tank with twin C2 cast iron pumps running at 585 RPM. Of all the single-phase 7.5HP duplex configurations Castair builds, this is the one to buy if your shop runs the compressor hard. The C2 pump delivers more CFM than the C1 at the same horsepower — 56.2 CFM versus 49.6 CFM at 175 PSI — because the larger pump bore compensates for the slower shaft speed. You get more air output, a cooler-running pump, and a machine that tolerates high duty cycles without overheating.
Single-phase 15HP duplex systems are rare. Most compressors in this output class require three-phase. The D7112HC2-S operates on single-phase electrical service, which makes it the only practical option for facilities without three-phase infrastructure. If you are running an auto repair shop, fleet service center, or tire shop out of a building with standard single-phase power and you need 56 CFM at 175 PSI with backup redundancy, this is what you buy.
Who Needs the D7112HC2-S
This compressor is built for single-phase shops with high air demand and no tolerance for downtime. Body shops running spray equipment and air tools simultaneously. Tire shops running multiple bays. Fleet maintenance operations where three or four technicians work on air tools at the same time. Any single-phase facility where 56.2 CFM at 175 PSI keeps everyone working without pressure recovery delays.
The duplex configuration — two independent pump-and-motor assemblies on one tank — means that when one pump needs service, the other keeps the shop running. No emergency calls to a rental company. No sending technicians home. You schedule the repair on your timeline, not your compressor's failure timeline.
Castair C2 Pump Features
- All cast iron construction: Cylinders, crankcase, and valve plates are cast iron. Cast iron runs cooler and quieter than aluminum under sustained loads, and it is more dimensionally stable as it heats and cools through work cycles.
- Slow 585 RPM operating speed: The C2 pump runs at 585 RPM — deliberately slowed by using a larger pump bore instead of spinning faster. This translates directly to lower operating temperatures, less wear, and longer service intervals.
- Larger pump bore than C1: The C2 moves more air per revolution than the C1. At 585 RPM versus the C1's 895 RPM, the C2 still delivers 56.2 CFM versus 49.6 CFM at 175 PSI. More air, less stress on the pump internals.
- Tapered roller bearings: Both crankshaft ends run on tapered roller bearings — not ball bearings. Tapered rollers handle both radial and axial loads, which is important in a reciprocating compressor where crankshaft forces act in multiple directions.
- Precision steel connecting rods: Automotive-type rod insert bearings at the crankshaft journal and bearings at the wrist pin. This is how long-life industrial piston machines are built.
- Disc and spring valves: Higher efficiency and easier field service than reed valves. When a valve wears, you replace it — you do not replace the pump head.
- 4-ring pistons: Four rings per piston for better compression sealing and lower oil carry-over into the air stream. Fewer rings on a cheap pump means more oil in your air lines.
- Centrifugal unloader: Every cold start is unloaded. The pump builds speed before the load engages, protecting both motor windings and pump components at each startup cycle.
Tank, Motor, and Control Features
- 120-gallon horizontal ASME tank: Powder-coated steel with channel base. ASME certification is not a marketing claim — it means the vessel design and construction met third-party pressure vessel safety standards.
- ASME safety valves: Certified pressure relief. Not aftermarket replacements — factory-original certified components.
- Fully enclosed metal belt guard: Keeps debris out of the drive system and meets OSHA safety requirements for exposed rotating machinery.
- Copper discharge and unloader tube or stainless-steel braided flex line: The discharge path handles heat and pressure. Copper and stainless handle it. Plastic does not belong there.
- Heavy-duty 1725 RPM industrial motors: Full 15% service factor or higher. Rated for continuous industrial use.
- Magnetic starter mounted and wired (-S models): Factory-installed magnetic motor starters are pre-wired. You run power to the panel. No field wiring of the starter itself.
Duplex System: What It Actually Means
Two pump assemblies. Two motors. One shared tank. One control panel that alternates which pump leads each cycle. If pump A fails tonight, pump B runs tomorrow morning when your shop opens. You call for service at your convenience — you are not down.
For the D7112HC2-S specifically: 1,430 lbs. on a concrete pad, two independent 7.5HP single-phase motors, 56.2 CFM of working air at 175 PSI. This is not a back-up purchase — it is the primary compressor for a serious shop that has thought through what happens when a pump fails.
Factory-Mounted Options Available
- Low Oil Control (#6304x2M): Shuts down both units before oil starvation can score pump cylinder walls. Critical for shops that push their equipment hard.
- Hour Meter (#HRM75x2M for 230V): Track actual operating hours per pump unit for interval-based maintenance scheduling.
- Alternator (#ALT230M): Automatic load alternation on each cycle to equalize run hours between the two pump units. This is what prevents one pump from running 10,000 hours while the other runs 4,000.
- Electronic Auto Drain (#SDV03M): Timer-controlled condensate purge from the tank base. Tanks that are not drained regularly corrode from the inside. This eliminates that maintenance failure mode.
- Dual Control (#DC2x2M for C2 pumps): Allows the unit to run unloaded during periods of sustained demand rather than cycling off and restarting repeatedly. Motor inrush at startup is 4 to 5 times running amperage — reducing starts reduces electrical cost and motor wear simultaneously.
- Intake Noise Silencers (#SA100x4M for C2): Inlet silencers cut intake noise without flow restriction. Two silencers per duplex unit (one per pump).
- Belt Tensioner (#215Dx2M for 7.5-10HP): Spring-loaded tensioner maintains belt geometry as belts stretch over time. Prevents slippage and uneven wear.
- Vibration Pads (#VP1004): Four isolation pads. Reduces floor vibration transmission and slightly reduces operating noise in the shop.
- Belt Guard Aftercooler (#BGAC1x2M, 70 CFM for 10-20HP units): Reduces moisture content in the air system by cooling compressed air before it enters the tank.
Available Configurations — 7.5HP Single-Phase Duplex
- D7112HC1-S: 2×7.5HP, single-phase, C1 pump (895 RPM), 120-gal, 49.6 CFM@175 PSI, 1,240 lbs. — lighter, slightly lower CFM, same duplex reliability.
- D7112HC2-S (this unit): 2×7.5HP, single-phase, C2 pump (585 RPM), 120-gal, 56.2 CFM@175 PSI, 1,430 lbs. — more CFM, cooler pump operation, heavier unit.
- D7124HC1-S: 2×7.5HP, single-phase, C1 pump (895 RPM), 240-gal, 49.6 CFM@175 PSI, 2,140 lbs. — same pump output with larger air storage volume.
- D7124HC2-S: 2×7.5HP, single-phase, C2 pump (585 RPM), 240-gal, 56.2 CFM@175 PSI, 1,780 lbs. — maximum single-phase duplex output with largest tank.
C1 vs. C2 at the Same HP — The Core Decision
Same horsepower, same price tier, meaningfully different performance and longevity profile. The C1 at 895 RPM is lighter and costs slightly less. The C2 at 585 RPM delivers 14% more CFM at working pressure and runs at significantly lower temperatures under load. For a shop that runs its compressor continuously through a workday, the C2 pays back its additional cost in lower operating temperature, lower maintenance frequency, and longer pump life. The C1 is the right call for moderate demand cycles where you want to keep weight and cost down.
When Does a Shop Need This vs. Stepping Up or Down
- Step down (D7112HC1-S): If 49.6 CFM at 175 PSI is enough for your typical tool load and you want a lighter unit, the C1 version is the right call. Same frame, lighter pump, lower operating cost upfront.
- This unit (D7112HC2-S): Single-phase power, high demand, need for redundancy, and you want the maximum CFM output from a 120-gallon duplex configuration. The right size for most active auto repair and body shops running four or more air tool drops.
- Step up (three-phase): If your building has three-phase service, the D7312HC2-S delivers the same C2 pump performance at lower amperage draw on three-phase. Three-phase motors run cooler and more efficiently for the same HP rating. If you have three-phase, use it.
Technical Specifications
- Model: D7112HC2-S
- Configuration: Duplex (2 pumps, 2 motors)
- Motor: 2×7.5HP, 15HP total
- Phase: Single-phase
- Pump Series: C2 (cast iron)
- Pump RPM: 585
- CFM @ 0 PSI: 70
- CFM @ 175 PSI: 56.2
- Tank: 120-gallon horizontal ASME
- Dimensions (L×W×H): 85 × 28 × 57 inches
- Weight: 1,430 lbs.
- Magnetic Starter: Included, factory-mounted and wired
- Max Pressure: 175 PSI
Why Buy From Air Compressor Factory Direct?
We have been selling and supporting professional-grade air compressors since 2016. We stock the full Castair duplex lineup — every configuration, both pump series, all tank sizes. Free shipping on all orders. Free tech support at 866-217-0063 — call us before you buy if you want help sorting out single-phase amperage requirements, C1 versus C2 pump selection, or whether a 120-gallon or 240-gallon tank fits your shop's demand profile. Full manufacturer warranty. Honest guidance on what you actually need.
Call 866-217-0063 for quick answers and help!
