The Castair D7312HC2-S is a 15HP (2×7.5HP) three-phase duplex air compressor on a 120-gallon horizontal ASME tank with twin C2 cast iron pumps running at 585 RPM. This is the high-output three-phase duplex configuration in the 7.5HP-per-pump class: the C2 pump delivers 56.2 CFM at 175 PSI by using a larger bore at a slower shaft speed than the C1 pump, and three-phase motors keep amperage draw low while running cooler and more efficiently than single-phase equivalents.
If your shop has three-phase service and you need maximum CFM output with duplex redundancy on a 120-gallon horizontal tank, the D7312HC2-S is the configuration that delivers it. At 1,400 lbs. on a 120-gallon platform, it is a substantial machine — and it is designed to run hard for a long time without generating excessive heat or requiring frequent service intervals.
Who Needs the D7312HC2-S
Three-phase shops with sustained high air demand across multiple bays or production stations. Body shops running spray booths and air tools simultaneously. Fleet maintenance operations with four or more technicians on air tools. Any three-phase facility where 56 CFM at 175 PSI keeps everyone working at full capacity without waiting on pressure recovery.
The C2 pump is the right choice when your compressor runs at or near capacity for extended periods each day. The larger bore, slower RPM design runs cooler under sustained loads than the C1. Lower operating temperature means longer seal life, longer valve life, and longer bearing life. Over a compressor's lifespan, that translates to fewer rebuilds and lower total cost of ownership.
Castair C2 Pump Features
- All cast iron construction: Cylinders, crankcase, and valve plates are cast iron throughout. Cast iron handles sustained heat better than aluminum, runs quieter, and maintains tighter dimensional tolerances as it expands and contracts through work cycles.
- Slow 585 RPM operating speed: The C2 runs at 585 RPM — slower than the C1's 895 RPM — because its larger bore moves more air per revolution. Lower speed equals lower heat generation and longer service intervals for all moving components.
- Larger bore than C1: At the same 7.5HP input, the C2 delivers 56.2 CFM versus the C1's 49.6 CFM at 175 PSI. The efficiency comes from the bore-to-RPM ratio — more volume per stroke at fewer strokes per minute.
- Tapered roller bearings: Both crankshaft ends use tapered roller bearings for superior load support under reciprocating operation forces.
- Precision steel connecting rods: Automotive-type rod insert bearings at the crankshaft journal and at the wrist pin. The engineering standard used in long-life industrial reciprocating machines.
- Disc and spring valves: Higher efficiency and better durability under continuous duty than reed valves. Field-serviceable without pump head replacement.
- 4-ring pistons: Four compression rings per piston for tight sealing efficiency and minimal oil carry-over into the compressed air stream.
- Centrifugal unloader: Loadless starts every cycle — the pump reaches operating speed before compression load engages, protecting both motor and pump internals.
Tank, Motor, and Control Features
- 120-gallon horizontal ASME tank: Powder-coated steel with channel base. ASME certified pressure vessel construction and testing.
- ASME safety valves: Certified pressure relief — factory-original components.
- Fully enclosed metal belt guard: Safety compliance for exposed rotating machinery, protection from shop debris.
- Copper discharge and unloader tube or stainless-steel braided flex line: Copper or stainless in all discharge circuit paths — no plastic where heat and pressure combine.
- Heavy-duty 1725 RPM three-phase industrial motors: Full 15% service factor or higher. Three-phase motors start cleanly without capacitors or centrifugal switches, draw lower amperage for the same HP output, and run cooler than single-phase equivalents under sustained duty.
- Magnetic starter mounted and wired (-S models): Factory-installed and pre-wired magnetic motor starters. Connect your three-phase supply to the panel — the internal wiring is complete.
Duplex Architecture: Two Pumps, One Problem Solved
Two complete compressor assemblies. One shared tank. One control panel that alternates the lead pump on each cycle. If pump A goes down — a valve, a belt, a motor winding — pump B runs the shop while you arrange service. Downtime is scheduled maintenance, not emergency failure response.
For the D7312HC2-S specifically: 1,400 lbs. on a 120-gallon platform, three-phase motors, C2 pumps at 585 RPM, delivering 56.2 CFM at 175 PSI in a duplex configuration. This is the right machine for a three-phase shop that has decided the cost of downtime exceeds the cost of redundancy.
Factory-Mounted Options Available
- Low Oil Control (#6304x2M): Automatic shutdown on low oil — prevents damage before oil starvation can cause internal wear.
- Hour Meter (#HRM75x2M for 230V, #HRM460x2M for 460V): Track actual operating hours for scheduled maintenance intervals.
- Alternator (#ALT230M or #ALT460M): Automatic cycle-by-cycle lead pump alternation to equalize long-term wear between the two pump units.
- Electronic Auto Drain (#SDV03M): Timed condensate purge prevents moisture accumulation and internal tank corrosion over time.
- Dual Control (#DC2x2M for C2 duplex): Start/stop or continuous unloaded operation mode. During sustained demand above 50% duty cycle, the unit runs unloaded rather than cycling off and restarting — which reduces motor start count, electrical cost, and motor heat stress significantly.
- Intake Noise Silencers (#SA100x4M for C2 duplex): Inlet silencers on each of the two pump heads reduce intake noise without restricting airflow.
- Belt Tensioner (#215Dx2M for 7.5-10HP): Spring-loaded belt tensioner maintains consistent drive geometry as belts stretch.
- Vibration Pads (#VP1004): Four isolation pads to reduce floor vibration from the unit.
- Belt Guard Aftercooler (#BGAC1x2M, 70 CFM for 10-20HP units): Cools compressed air before tank entry to reduce moisture content in the air system.
- All Options Bundle (#AOC2D for C2): Order all asterisk options together for 10% off the options total.
Available Configurations — 7.5HP Three-Phase Duplex
- D7312HC1-S: 2×7.5HP, three-phase, C1 pump (895 RPM), 120-gal, 49.6 CFM@175 PSI, 1,210 lbs. — lighter, slightly lower CFM, same tank.
- D7312HC2-S (this unit): 2×7.5HP, three-phase, C2 pump (585 RPM), 120-gal, 56.2 CFM@175 PSI, 1,400 lbs. — maximum CFM on 120-gallon in three-phase.
- D7324HC1-S: 2×7.5HP, three-phase, C1 pump (895 RPM), 240-gal, 49.6 CFM@175 PSI, 1,560 lbs. — C1 pump with larger air storage.
- D7324HC2-S: 2×7.5HP, three-phase, C2 pump (585 RPM), 240-gal, 56.2 CFM@175 PSI, 1,750 lbs. — maximum output and storage in three-phase 7.5HP duplex.
When Does a Shop Need This vs. Stepping Up or Down
- Step down (D7312HC1-S, C1 pump): If 49.6 CFM at 175 PSI covers your demand and you want a lighter unit at lower cost, the C1 version on the same 120-gallon tank saves 190 lbs. and some money. Same tank, same redundancy, less CFM, lighter pump.
- This unit (D7312HC2-S): Three-phase power, sustained high demand, need for backup redundancy, and you want maximum CFM from a 120-gallon duplex footprint. The right call for active three-phase shops running four or more air tool drops simultaneously.
- Step up (240-gallon tank): If your demand cycle is sustained enough that a 120-gallon tank cycles too frequently, the D7324HC2-S delivers the same C2 pump performance on a 240-gallon tank. Same CFM, less frequent cycling, longer pump life in high-use environments.
Technical Specifications
- Model: D7312HC2-S
- Configuration: Duplex (2 pumps, 2 motors)
- Motor: 2×7.5HP, 15HP total
- Phase: Three-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: 1,400 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 carry the full Castair duplex lineup — both pump series, all tank sizes, single-phase and three-phase, with and without starters. Free shipping on all orders. Free tech support at 866-217-0063 — call before you order if you want to compare C1 versus C2 pump performance for your specific duty cycle, or work out actual three-phase amperage requirements for your electrical service. Full manufacturer warranty. Honest guidance on which configuration fits your shop.
Call 866-217-0063 for quick answers and help!
