The Castair D7124HC1-S is a 15HP (2×7.5HP) single-phase duplex air compressor on a 240-gallon horizontal ASME tank with twin C1 cast iron pumps running at 895 RPM. This configuration is for single-phase shops that need both substantial air storage and full backup redundancy in one machine. The jump from a 120-gallon tank to a 240-gallon tank does not change the output — you still get 49.6 CFM at 175 PSI — but it changes how often your pumps cycle and how well the system handles peak demand spikes.
At 2,140 lbs., the D7124HC1-S is a substantial piece of equipment. Plan accordingly: floor load capacity, permanent mounting position, and a nearby electrical panel capable of supplying two 7.5HP single-phase motors. This is a machine you install once and run for 20 years. It earns its floor space by keeping your shop operational even when one pump is out for service.
Who Needs the D7124HC1-S
Auto body shops, commercial service centers, and production facilities on single-phase power that need both large tank volume and duplex reliability. If your shop runs sustained air tool demand — multiple body technicians, spray booths, automated equipment — the 240-gallon tank means your pumps cycle less frequently, stay cooler, and last longer. The C1 pump at 895 RPM delivers 49.6 CFM at 175 PSI, which supports three to four simultaneous air tool operators without meaningful pressure drop.
Shops that use air-intensive intermittent equipment (sandblasters, plasma cutters, automated spray systems) especially benefit from the 240-gallon reserve. When that equipment hits peak draw, the larger tank absorbs the surge without immediately cycling the pumps back on.
Castair C1 Pump Features
- All cast iron construction: Cylinders, crankcase, and valve plates are cast iron throughout. Cast iron runs cooler, quieter, and longer than aluminum under sustained industrial loads.
- 895 RPM operating speed: The C1 pump runs at 895 RPM — roughly half the speed of many commodity compressor pumps — for reduced heat generation and longer service life.
- Tapered roller bearings: Both ends of the crankshaft use tapered roller bearings for superior crankshaft support under the radial and axial loads of reciprocating operation.
- Precision steel connecting rods: Automotive-type rod insert bearings at the crankshaft and bearings at the wrist pin. This is the engineering approach that separates long-life industrial pumps from short-life commodity pumps.
- Disc and spring valves: More reliable than reed valves under continuous duty, and easier to service in the field. When valves wear, you replace the valves — not the pump head.
- 4-ring pistons: Four rings per piston for higher compression efficiency and lower oil carry-over into the air supply. Two-ring pistons are common in budget pumps; four rings are not.
- Centrifugal unloader: Loadless start on every cycle. The pump reaches operating speed before the compression load engages, reducing motor stress and extending motor life significantly in high-cycle applications.
Tank, Motor, and Control Features
- 240-gallon horizontal ASME tank: Powder-coated steel with channel base for stability. ASME certified pressure vessel — the certification covers design, construction, and materials, not just a stamp applied after the fact.
- ASME safety valves: Certified pressure relief. Factory-original certified components — not field replacements.
- Fully enclosed metal belt guard: Meets OSHA safety requirements and keeps debris out of the drive system.
- Copper discharge and unloader tube or stainless-steel braided flex line: Heat and pressure path components are copper or stainless. No plastic in the discharge circuit.
- Heavy-duty 1725 RPM industrial motors: Full 15% service factor or higher. Built for continuous commercial use, not residential or light commercial cycles.
- Magnetic starter mounted and wired (-S models): Factory-installed, factory-wired magnetic motor starters. You run your electrical supply to the panel connection — the internal wiring is done.
240-Gallon vs. 120-Gallon: Why the Bigger Tank Matters
Both the 120-gallon (D7112HC1-S) and 240-gallon (D7124HC1-S) deliver the same 49.6 CFM at 175 PSI. The difference is cycle frequency and peak demand buffering. A 240-gallon tank takes twice as long to drop from cut-out pressure to cut-in pressure under the same air draw, which means the pumps cycle less often. Fewer cycles per hour means lower operating temperatures, less wear, and lower electrical costs from reduced motor starting frequency. If your shop runs air tools continuously for hours at a stretch, the 240-gallon tank will noticeably extend pump and motor life compared to the 120-gallon version.
Factory-Mounted Options Available
- Low Oil Control (#6304x2M): Automatic shutdown before pump oil starvation can cause internal damage.
- Hour Meter (#HRM75x2M for 230V): Track actual operating hours for both pump units. Essential for maintenance interval scheduling.
- Alternator (#ALT230M): Automatically rotates which pump leads each cycle to equalize run hours between units over time.
- Electronic Auto Drain (#SDV03M): Timer-controlled condensate drain. Tanks that are not drained daily accumulate moisture and corrode internally. This prevents that maintenance failure.
- Dual Control (#DC1x2M for C1 pumps): Enables unloaded continuous operation during high-demand periods to eliminate excessive motor starts. Motor inrush current at startup is 4 to 5 times running current — reducing starts directly reduces electrical costs and motor wear.
- Intake Noise Silencers (#SA100x2M for C1): Inlet noise reduction without airflow restriction.
- Belt Tensioner (#215Dx2M for 7.5-10HP): Spring-loaded belt tensioner prevents belt slippage and uneven wear as belts stretch over time.
- Right From the Start Kit (#RFS001D for 10HP): Consolidated maintenance kit for first-service interval.
- Vibration Pads (#VP1004): Isolation pads to reduce floor vibration transmission from the unit.
- Belt Guard Aftercooler (#BGAC1x2M, 70 CFM for 10-20HP units): Reduces moisture in the air system by cooling compressed air before tank entry.
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. — same CFM, smaller tank, lower weight.
- D7112HC2-S: 2×7.5HP, single-phase, C2 pump (585 RPM), 120-gal, 56.2 CFM@175 PSI, 1,430 lbs. — more CFM, slower pump, 120-gal tank.
- D7124HC1-S (this unit): 2×7.5HP, single-phase, C1 pump (895 RPM), 240-gal, 49.6 CFM@175 PSI, 2,140 lbs. — same pump output with maximum air storage.
- D7124HC2-S: 2×7.5HP, single-phase, C2 pump (585 RPM), 240-gal, 56.2 CFM@175 PSI, 1,780 lbs. — maximum output with maximum storage.
When Does a Shop Need This vs. Stepping Up or Down
- Step down (D7112HC1-S, 120-gallon): If floor space is constrained or your air demand does not justify 240 gallons of storage, the 120-gallon version saves floor space and 900 lbs. Same pumps, same output, more frequent cycling.
- This unit (D7124HC1-S): Single-phase power, need for backup redundancy, shop runs sustained air demand through the workday, and floor space allows a 240-gallon footprint. The right machine for a serious single-phase shop that wants low cycle frequency and long pump life.
- Step up (C2 pump or three-phase): If you need 56 CFM instead of 49.6 at 175 PSI, the D7124HC2-S uses the same 240-gallon tank with the C2 pump upgrade. If your facility has three-phase power, the D7324HC1-S (3-phase, C1, 240-gallon) delivers the same output at lower amp draw.
Technical Specifications
- Model: D7124HC1-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: 240-gallon horizontal ASME
- Dimensions (L×W×H): 85 × 30 × 64 inches
- Weight: 2,140 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 — every HP class, both pump series, all tank sizes, in single-phase and three-phase. Free shipping on all orders. Free tech support at 866-217-0063 — call if you want help comparing tank sizes, calculating whether your electrical service supports this unit, or deciding between C1 and C2 pump configurations for your workload. Full manufacturer warranty and honest guidance.
Call 866-217-0063 for quick answers and help!
