The Castair D10124HC3-S is a 20 total horsepower duplex two-stage air compressor combining the largest standard tank in the single-phase 2x10HP lineup (240 gallons horizontal) with the slower-running HC3 pump (570 RPM). It delivers 70 CFM at 175 PSI combined, weighs 2,150 lbs, and measures 94" x 30" x 64". This is the top configuration in the single-phase 2x10HP family — maximum tank storage, slowest pump RPM, lowest operating temperature, and quietest operation of the four single-phase variants.
Who This Unit Is For
The D10124HC3-S is specified by shops that run the compressor hard, continuously, and need it to hold up over years of heavy use. The combination of 240-gallon storage and 570 RPM HC3 pump means:
- Fewer pump start/stop cycles per shift due to the large tank buffer
- Lower pump operating temperature due to slow RPM, extending valve and ring life
- Quieter operation than an equivalent 758 RPM HC2 unit
- Duplex redundancy — one pump keeps the shop running if the other needs service
You are paying for the largest, most durable configuration in this power class. If your shop runs spray painting, plasma cutting, sandblasting, or has multiple simultaneous air tool users, this is the appropriate specification.
Pump and Motor Specifications
- Configuration: Duplex (two pumps, two motors)
- Total HP: 20 HP (2 x 10 HP)
- Phase: Single-phase
- Pump RPM: 570 (HC3 pump)
- CFM at 0 PSI: 90 CFM combined
- CFM at 175 PSI: 70 CFM combined
- Max Pressure: 175 PSI
- Stage: Two-stage
Tank and Physical Specs
- Tank Capacity: 240 gallons, horizontal ASME
- Dimensions (LxWxH): 94" x 30" x 64"
- Weight: 2,150 lbs
- Tank Finish: Powder coated
- Safety Valve: ASME rated, installed
- Magnetic Starter: Mounted and wired (factory installed)
Cast Iron Pump Features
- All cast iron construction for long life and quiet operation
- 570 RPM HC3 pump — slowest in the 2x10HP duplex lineup, lowest heat, quietest
- Tapered roller bearings at both ends of crankshaft
- Precision steel connecting rods with automotive-type rod insert bearings
- Disc and spring valves for easy service and reliability
- 4-ring pistons for efficiency and reduced oil carry-over
- Centrifugal unloader for loadless starts
Single-Phase 2x10HP Duplex Comparison
- D10112HC2-S — 120gal, 758 RPM, 85x28x57, 1,470 lbs — entry configuration
- D10124HC2-S — 240gal, 758 RPM, 85x30x64, 1,820 lbs — larger tank, same RPM
- D10112HC3-S — 120gal, 570 RPM, 94x28x57, 1,800 lbs — slower pump, smaller tank
- D10124HC3-S — 240gal, 570 RPM, 94x30x64, 2,150 lbs — maximum configuration (this unit)
When Does a Shop Need This vs. Stepping Down
The D10124HC3-S is right for: High-utilization shops on single-phase power, long-cycle processes (collision painting, sandblasting, CNC machining), shops where noise level matters and floor space accommodates a 94" x 30" footprint, and anywhere the compressor will run 6-8+ hours per day.
Step down to D10124HC2-S if noise and pump temperature are not primary concerns — same tank, same output, 330 lbs lighter.
Step down to D10112HC3-S if your peak demand does not exhaust a 120-gallon tank — save cost and floor space.
Consider three-phase (D10324HC3-S) if three-phase service is available — three-phase at this horsepower level is more efficient and the motors run cooler.
Technical Specifications
- Model: D10124HC3-S
- Manufacturer: Castair (Cast Air, Inc.) — Spicer, Minnesota
- Total HP: 20 HP (2 x 10 HP)
- Phase: Single-phase
- Pump RPM: 570 (HC3)
- CFM @ 0 PSI: 90
- CFM @ 175 PSI: 70
- Tank: 240 gallon, horizontal, ASME, powder coated
- Dimensions (LxWxH): 94" x 30" x 64"
- Weight: 2,150 lbs
- Magnetic Starter: Included, factory mounted and wired
- Safety Valve: ASME rated, installed
Why Buy From Air Compressor Factory Direct?
We have been selling Cast Air industrial compressors since 2016. The D10124HC3-S is a $13,000+ investment and the difference between HC2 and HC3, and between 120 and 240 gallons, is real — we can help you confirm which configuration matches your duty cycle before you order. Free shipping, free technical support at 866-217-0063, full manufacturer warranty.
Call 866-217-0063 for quick answers and help!
Frequently Asked Questions
What is the advantage of a duplex compressor like the D10124HC3-S over a single-pump unit?
The D10124HC3-S runs two 10 HP cast iron pumps sharing a single 240-gallon tank, so you get 20 HP total output without the startup amp surge of a single 20 HP motor. Each pump cycles independently, which cuts heat buildup and wear per pump significantly. For shops running continuous demand, duplex units handle load spikes better and recover pressure faster than a comparably-sized single.
Can the D10124HC3-S run on just one pump if the other is down for service?
Yes — each pump on the D10124HC3-S operates independently and can run solo while the other is offline for maintenance or repair. You'll see reduced CFM output (roughly half capacity), but the unit stays operational and the 240-gallon tank helps buffer demand during that period. This is one of the main practical reasons shops spec a duplex over a single-pump machine.
Does the D10124HC3-S include an alternating start controller, and why does it matter?
The D10124HC3-S is available with an alternator option that automatically rotates which pump starts first on each cycle. This matters because it equalizes run hours across both pumps, so you're not wearing out one motor while the other sits — both reach service intervals at roughly the same time. Without an alternator, the lead pump accumulates significantly more hours and typically fails first.
What happens if one pump on the D10124HC3-S fails completely?
The surviving pump takes over and the unit keeps running at reduced capacity — your shop doesn't go down. Cast Air's all-cast-iron pump construction on the D10124HC3-S means failure is less common than on aluminum-pump units, but when it does happen, replacement pumps are available as direct swap components. If you need help sourcing parts or diagnosing the failure, call us at 866-217-0063 — we're an authorized Cast Air dealer and can get you the right part fast.
Is the maintenance schedule different on the D10124HC3-S compared to a single-pump compressor?
The service intervals per pump are the same — oil changes, belt tension, valve inspection — but on the D10124HC3-S you're performing those tasks on two pumps instead of one. The upside is that with an alternator installed and balanced run hours, both pumps hit their intervals simultaneously, so you can do both in a single service visit rather than staggered downtime. Cast Air's cast iron pump design also extends valve and ring life compared to aluminum-bore units, which reduces how often you're into the pump heads.
