The Castair D7112HC1-S is a 15HP (2×7.5HP) single-phase duplex air compressor on a 120-gallon horizontal ASME tank with twin C1 cast iron pumps running at 895 RPM. This is Castair's answer for single-phase shops that need genuine redundancy: two complete compressor units sharing one tank, alternating duty cycles, with automatic failover if either pump goes down.
If your facility only has single-phase power but you cannot afford to shut down when a compressor fails, the D7112HC1-S solves that problem. Most 15HP compressors require three-phase. This one does not. You get 49.6 CFM at 175 PSI from a duplex system on standard single-phase electrical service — that is a real differentiator for smaller facilities, farms, and older buildings without three-phase infrastructure.
Who Needs the D7112HC1-S
Auto repair shops, body shops, fleet maintenance operations, tire shops, and manufacturing facilities on single-phase power that run multiple air tools simultaneously. At 49.6 CFM delivered at 175 PSI, this unit supports three to four technicians working on air tools at the same time without meaningful pressure drop. The 120-gallon tank provides solid air storage for peak demand without requiring a 240-gallon footprint.
The duplex configuration makes this the right choice when compressor downtime directly costs you money. If a pump or motor needs service, the second unit keeps your shop running while you schedule the repair. For a collision shop or production floor, that capability pays for itself the first time it prevents a half-day shutdown.
Castair C1 Pump Features
- All cast iron construction: Cylinders, crankcase, and valve plates are cast iron. Not aluminum, not composite — cast iron, which runs cooler and lasts longer under sustained duty cycles.
- 895 RPM operating speed: The C1 pump runs at 895 RPM — half the speed of many imported pumps — for reduced heat, less noise, and longer service intervals.
- Tapered roller bearings: Both ends of the crankshaft use tapered roller bearings for superior load support and reduced friction compared to ball bearings.
- Precision steel connecting rods: Automotive-type rod insert bearings at the crankshaft and bearings at the wrist pin. This is the same engineering approach used in industrial piston engines.
- Disc and spring valves: More reliable and easier to service than reed valves. Higher efficiency across the pressure range.
- 4-ring pistons: Four compression rings per piston for better sealing efficiency and lower oil carry-over into the compressed air stream.
- Centrifugal unloader: Every start is unloaded — the pump does not fight against system pressure at startup, which dramatically reduces motor stress and extends both pump and motor life.
Tank, Motor, and Control Features
- 120-gallon horizontal ASME tank: Powder-coated steel with channel base for stability. ASME certified — meets pressure vessel safety standards.
- ASME safety valves: Certified pressure relief — not aftermarket hardware.
- Fully enclosed metal belt guard: Safety compliance and pump protection from debris.
- Copper discharge and unloader tube or stainless-steel braided flex line: No plastic in the discharge path. Copper or stainless where heat and pressure demand it.
- Heavy-duty 1725 RPM industrial motors: Full 15% service factor or higher. These motors are rated for continuous industrial use, not intermittent residential loads.
- Magnetic starter mounted and wired (-S models): The -S suffix means factory-installed and pre-wired. Connect your power supply to the panel — no additional electrical work on the compressor itself.
Duplex Operation: Reliability by Design
A duplex compressor runs two completely independent pump-and-motor assemblies on a shared tank. On each startup cycle, the control system alternates which pump leads, keeping run hours balanced across both units. When pump A is serviced, pump B carries the shop. When pump B is serviced, pump A carries the shop. Neither event shuts you down.
Compare this to a simplex unit: one pump, one motor, one point of failure. When it goes down, your shop stops. The duplex architecture eliminates that single point of failure. For a shop with four technicians and a full schedule, that is not a minor feature — it is the reason you buy a duplex.
Factory-Mounted Options Available
- Low Oil Control (#6304x2M): Automatic shutdown before oil starvation can damage the pump internals.
- Hour Meter (#HRM75x2M for 230V): Track actual run hours on each pump for scheduled maintenance intervals. Essential for shops that run the compressor hard.
- Alternator (#ALT230M): Automatic load alternation between the two pumps on every cycle to equalize wear over time.
- Electronic Auto Drain (#SDV03M): Timed automatic condensate purge from the tank. If you are not manually draining your tank daily, moisture accumulates and corrodes from the inside out. This option eliminates that failure mode.
- Dual Control (#DC1x2M for C1 pumps): Enables start/stop or continuous unloaded operation. Cuts excessive restarts during high-demand periods. Motor starts at full amperage draw — reducing restart frequency reduces electrical costs and extends motor life significantly.
- Intake Noise Silencers (#SA100x2M for C1): Reduces inlet noise without restricting airflow.
- Belt Tensioner (#215Dx2M for 7.5-10HP): Spring-loaded belt tensioner maintains consistent drive geometry and belt tension for longer belt life.
- Right From the Start Kit (#RFS001D for 10HP): The maintenance items you will need at first service interval, in one package.
- Vibration Pads (#VP1004): Four pads that isolate the compressor from the floor, reducing vibration transmission and noise in the shop.
- Belt Guard Aftercooler (#BGAC1x2M, 70 CFM for 10-20HP units): Cools compressed air before tank entry, reducing moisture content in the air system.
- All Options Bundle (#AOC1D for C1 units): Order all asterisk options together for a 10% discount on the total options package.
Available Configurations — 7.5HP Duplex, Single-Phase
- D7112HC1-S (this unit): 2×7.5HP, single-phase, C1 pump (895 RPM), 120-gal, 49.6 CFM@175 PSI, 1,240 lbs. — starter included.
- D7112HC2-S: 2×7.5HP, single-phase, C2 pump (585 RPM), 120-gal, 56.2 CFM@175 PSI, 1,430 lbs. — heavier pump, more CFM, runs cooler.
- 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 reserve.
- 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 on the largest tank.
C1 vs. C2 Pump — Which Is Right for You?
The C1 pump runs at 895 RPM on a smaller pump body. The C2 runs at 585 RPM on a heavier, larger-bore pump. Both produce air efficiently; the C2 produces more CFM (56.2 vs. 49.6 at 175 PSI) and runs cooler because of the lower RPM. The C2 unit weighs 190 lbs. more on the same 120-gallon tank. If you are running the compressor at or near capacity regularly, the C2 is the better long-term choice. If your demand is moderate and floor space matters, the C1 delivers real performance at a lower price and weight.
When Does a Shop Need This vs. Stepping Up or Down
- Step down (5HP duplex — D5112HC1-S): If your shop runs one to two air tools at a time and single-phase 5HP delivers enough CFM (35 at 175 PSI), the 5HP duplex is less money with the same redundancy architecture. Right for smaller shops with lower sustained demand.
- This unit (D7112HC1-S): Single-phase facility, three to four air tools running simultaneously, need for backup capability. 49.6 CFM at 175 PSI on a 120-gallon tank. This is the right size for most serious single-phase auto repair and body shops.
- Step up (three-phase or larger HP): If your facility has three-phase power and wants the same 7.5HP duplex performance, the D7312HC1-S does it on three-phase at lower amp draw. If you need more CFM than 56 at 175 PSI from a duplex, you are into the 10HP duplex territory (D10112HC2-S or D10112HC3-S).
Technical Specifications
- Model: D7112HC1-S
- Configuration: Duplex (2 pumps, 2 motors)
- Motor: 2×7.5HP, 15HP total
- Phase: Single-phase
- Pump Series: C1 (cast iron)
- Pump RPM: 895
- CFM @ 0 PSI: 64.8
- CFM @ 175 PSI: 49.6
- Tank: 120-gallon horizontal ASME
- Dimensions (L×W×H): 85 × 28 × 57 inches
- Weight: 1,240 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 in every configuration — not just the units that move fastest. Free shipping on all orders. Free tech support at 866-217-0063. Call before you buy if you have questions about single-phase amperage requirements, which pump series fits your duty cycle, or how duplex control systems work. Full manufacturer warranty. Honest buying guidance — if a different model fits your situation better, we will tell you that too.
Call 866-217-0063 for quick answers and help!
