The Castair D5324HC2-S is a 10HP (2×5HP) three-phase duplex air compressor built on a 240-gallon horizontal ASME tank with twin C2 cast iron pumps running at 420 RPM. If your shop runs three-phase power and you need a true backup system — so a pump failure never stops production — this is the configuration that delivers it. Two completely independent compressor units share one tank, alternating loads to extend pump life and providing automatic failover if one side goes down.
This is not a light-duty compressor dressed up in heavy-duty language. The C2 pump series runs at 420 RPM — slow by design — so heat stays low, oil carry-over stays minimal, and the pumps outlast their faster-running counterparts by a wide margin. The 240-gallon tank gives your shop serious air storage capacity to absorb peak demand without constant cycling. At 1,620 lbs., this unit is built to stay put on a concrete floor for decades.
Who Needs the D5324HC2-S
This compressor is for shops that cannot afford downtime. Auto body and paint shops, production facilities, tire service operations, and any commercial shop running three-phase power that needs a compressor to be running when they arrive in the morning and still running when they leave. The duplex design means one pump can be down for service and the shop keeps operating.
At 35 CFM delivered at 175 PSI, this unit handles multiple air tools running simultaneously — impact guns, grinders, blow guns, sand blasters, paint guns — without the pressure drop that comes from undersized equipment. If your shop regularly runs two or more technicians on air tools at the same time, a single 5HP unit is not going to cut it. This one will.
Castair C2 Pump Features
- All cast iron construction: Pump cylinders, crankcase, and valve plates are cast iron — not aluminum — for long service life and quiet operation.
- Slow 420 RPM operating speed: Lower RPM means less heat, less wear, less noise, and less oil consumption compared to pumps running at 1,000+ RPM. This is the C2 pump, the heavier of the two pump options in the duplex lineup.
- Tapered roller bearings: Both ends of the crankshaft use tapered roller bearings for superior load support and reduced friction — not cheap ball bearings.
- Precision steel connecting rods: Automotive-type rod insert bearings at the crankshaft and bearings at the wrist pin for long service life and reliability.
- Disc and spring valves: Easier to service than reed valves, higher efficiency, and more reliable under continuous duty.
- 4-ring pistons: Four rings per piston for higher compression efficiency and reduced oil carry-over into the air stream.
- Centrifugal unloader: Every pump starts unloaded — no fighting against pressure on startup, which protects the motor and extends pump life.
Tank, Motor, and Control Features
- 240-gallon horizontal ASME tank: Powder-coated with channel base for stability. ASME certification means the tank meets pressure vessel safety standards, not a gray-market import spec.
- ASME safety valves: Certified pressure relief — not aftermarket hardware.
- Fully enclosed metal belt guard: Safety compliance and pump protection.
- Copper discharge and unloader tube or stainless-steel braided flex line: No plastic fittings in the discharge path. Copper or stainless where it counts.
- Heavy-duty 1725 RPM industrial motors: Full 15% service factor or higher — built to run hard without overheating.
- Magnetic starter mounted and wired (-S models): The -S suffix means the magnetic motor starter is factory-installed and pre-wired. You connect power to the panel. This saves installation time and ensures correct wiring.
Duplex System: How It Works
A duplex compressor is two complete compressor units — two pumps, two motors — on a shared tank. The control system alternates which pump runs first on each cycle, keeping run hours balanced between the two units. If pump A fails, pump B keeps running. Your shop does not stop.
For shops in environments where downtime means lost revenue (collision repair, fleet maintenance, production), the duplex architecture is not a luxury — it is a risk management decision. One pump failure on a simplex unit shuts the shop down. On a duplex, you call the service tech and keep working.
Factory-Mounted Options Available
The D5324HC2-S can be ordered with factory-installed options (part numbers for reference):
- Low Oil Control (#6304x2M): Shuts down the unit before oil starvation damages the pump.
- Hour Meter (#HRM75x2M for 230V, #HRM460x2M for 460V): Track run hours for scheduled maintenance intervals.
- Alternator (#ALT230M or #ALT460M): Automatically alternates which pump leads each cycle to equalize wear.
- Electronic Auto Drain (#SDV03M): Automatically purges condensation from the tank on a timed cycle. If you are not draining your tank manually every day, you need this.
- Dual Control (#DC2x2M for C2 pumps): Enables start/stop or continuous unloaded operation. Eliminates excessive restarts during heavy use periods. Extends pump and motor life, reduces electrical bills.
- Intake Noise Silencers (#SA100x4M for C2): Reduces inlet noise without restricting airflow.
- Belt Tensioner (#215Dx2M for 7.5–10HP): Spring-loaded belt tensioning for consistent drive performance and longer belt life.
- Right From the Start Kit (#RFS001D for 10HP): Includes the key maintenance items you will need at first service.
- Vibration Pads (#VP1004): Isolate the compressor from the floor to reduce vibration transmission and noise.
- Belt Guard Aftercooler (#BGAC1x2M, 70 CFM for 10–20HP units): Cools compressed air before it enters the tank, reducing moisture content.
- All Options Bundle (#AOC2D): Order all asterisk options together for a 10% discount on the options package.
Available Configurations — Duplex Series
Castair builds the duplex series across three HP classes (5HP, 7.5HP, 10HP per pump) and two pump series (C1 and C2), in single-phase and three-phase, on 120-gallon or 240-gallon tanks. Here is how the 5HP-per-pump lineup fits together:
- D5112HC1-S: 2×5HP, 10HP total, single-phase, C1 pump (767 RPM), 120-gallon tank — 35 CFM@175 PSI, 1,110 lbs.
- D5124HC-S: 2×5HP, 10HP total, single-phase, C1 pump (767 RPM), 240-gallon tank — 35 CFM@175 PSI, 1,460 lbs.
- D5112HC2-S: 2×5HP, 10HP total, single-phase, C2 pump (420 RPM), 120-gallon tank — 35 CFM@175 PSI, 1,300 lbs.
- D5124HC2-S (this unit): 2×5HP, 10HP total, three-phase, C2 pump (420 RPM), 240-gallon tank — 35 CFM@175 PSI, 1,620 lbs.
C1 vs. C2 Pump — What Is the Difference?
Both pump series deliver the same CFM output at the same pressures. The difference is in how they get there. The C1 pump runs at 767 RPM on a lighter pump body. The C2 runs at 420 RPM on a heavier, larger-bore pump. The C2 runs cooler, quieter, and with less vibration. The C2 is also heavier — the 240-gallon C2 unit weighs 320 lbs. more than the C1 equivalent. If you are choosing between them, the C2 is the better long-term investment for continuous-duty applications.
When to Choose the 240-Gallon Over the 120-Gallon
The 240-gallon tank is not about producing more air — the output is identical. More tank volume means longer time between pump cycles, lower motor start frequency, and more air reserve for peak demand spikes. If your shop runs tools that draw a lot of air in short bursts (sandblasters, plasma cutters, large impact guns), the bigger tank buffers those spikes more effectively. If floor space is tight, the 120-gallon unit delivers the same working pressure and CFM — you will just cycle more frequently.
When Does a Shop Need This vs. Stepping Up or Down
- Step down (single-pump industrial unit): If downtime is manageable and your budget does not justify a duplex, the Castair I538HC2-S (5HP, 3-phase, 80-gallon) or I5312HC2-S (120-gallon) handles the same CFM without the backup pump. Less money, same air output, no redundancy.
- This unit (D5324HC2-S): Right for shops that need backup capability and run three-phase power. 35 CFM at 175 PSI handles two to three air tools running simultaneously. The 240-gallon tank keeps cycle frequency low.
- Step up (7.5HP duplex): If your shop is regularly running more than three technicians on air tools, or if you run equipment with sustained high CFM demand (spray booths, large sandblasters), move to the D7324HC2-S (2×7.5HP, 56.2 CFM@175 PSI) or D7312HC2-S (120-gallon version). More CFM headroom, same duplex reliability.
Technical Specifications
- Model: D5324HC2-S
- Configuration: Duplex (2 pumps, 2 motors)
- Motor: 2×5HP, 10HP total
- Phase: 3-phase
- Pump Series: C2 (cast iron)
- Pump RPM: 420
- CFM @ 0 PSI: 44
- CFM @ 175 PSI: 35
- Tank: 240-gallon horizontal ASME
- Tank Type: Powder-coated steel, ASME certified
- Dimensions (L×W×H): 85 × 30 × 64 inches
- Weight: 1,620 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 lineup — not just the popular units — so when you need a specific configuration, we either have it or can get it. Free shipping on all orders. Free tech support at 866-217-0063 — call before you buy if you have questions about installation, electrical requirements, or which configuration fits your shop. We sell with full manufacturer warranty and honest buying guidance. If a different model fits your situation better, we will tell you.
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