The Castair D15324HC3-S is the top-of-the-line duplex compressor in the Castair lineup — a 30 HP total (2x15 HP) two-stage system running on 3-phase power with a 240-gallon ASME horizontal tank. If your shop runs high sustained CFM demand with significant peak spikes — spray booths running simultaneously, high-volume pneumatic tools, or multiple bays all pulling air at once — the extra 120 gallons of storage over the D15312HC3-S (120-gallon model) means longer recovery intervals and more consistent line pressure during peak loads.
The core system is identical to the D15312HC3-S: two 15 HP two-stage cast iron pumps, C3 pump configuration at 795 RPM, 100.4 CFM at 175 PSI, magnetic starter mounted and wired, duplex alternator standard. The difference is the tank: 240 gallons stores roughly twice the compressed air volume, which translates directly to more usable air between compressor cycles and better pressure stability when demand spikes.
Castair has been building these in Spicer, Minnesota since 1991. These are purpose-built commercial systems, not rebranded import machines.
Key Features
Pump Construction — C3 Configuration
- All Cast Iron Construction: Cast iron cylinders, heads, and crankcase — long service life and quiet operation at 795 RPM
- C3 Pump at 795 RPM: Slowest-running, longest-life pump configuration in the Castair duplex lineup — less heat, less wear, lower noise floor
- Tapered Roller Bearings: Both ends of the crankshaft — superior load support and lower friction than ball bearings
- Precision Steel Connecting Rods: Automotive-type rod insert bearings at crankshaft and wrist pin — serviceable at standard maintenance intervals
- Disc and Spring Valves: Higher efficiency and easier service than reed valves; straightforward replacement when maintenance is due
- 4-Ring Pistons: Better sealing efficiency, reduced oil carry-over into discharge air
- Centrifugal Unloader: Loadless start every time — eliminates the heavy inrush current of loaded starts and reduces motor stress
Two-Stage Compression
- Two-Stage Design: First stage to intermediate pressure, second stage to 175 PSI — more thermally efficient than single-stage at this pressure level
- 175 PSI Maximum Operating Pressure: Covers all standard pneumatic tool and equipment requirements
- Copper Discharge and Unloader Tube or Stainless Steel Braided Flex Line: Factory-selected based on configuration; both handle the discharge temperatures and pressures involved
Tank, Controls, and Electrical
- 240-Gallon ASME Horizontal Tank: Powder-coated steel with channel base supports; ASME certified for pressure vessel safety
- Dimensions: 94" L x 30" W x 68" H — plan your floor space and doorway clearances before ordering; this is a significant installation
- ASME Safety Valves: Factory installed on both pump discharge lines
- Magnetic Starter — Mounted and Wired: Factory-installed for the 3-phase motors; includes overload protection and low-voltage release
- Duplex Alternator Control (Standard on C3): Automatically rotates which pump leads each cycle — equalizes run hours and wear between the two units
- Metal Belt Guard — Totally Enclosed: OSHA-compliant drive belt and pulley guarding
- Heavy Duty 1725 RPM Industrial Motors: Full 15% service factor or higher — rated for continuous shop duty cycles
240-Gallon Tank Advantage
- Twice the Air Storage vs. 120-Gallon: Longer run time between pump cycles when demand is intermittent; better pressure stability when multiple tools spike simultaneously
- Lower Duty Cycle on Pumps: More tank volume means the pumps run fewer total hours per unit of air delivered — extends service intervals and pump life in high-demand environments
- Better Pressure Recovery: After a high-demand event, the larger tank provides more buffer while the pumps bring pressure back up
What's in the Box
- Castair D15324HC3-S duplex compressor (two 15 HP pump-motor assemblies, 240-gallon ASME tank, common skid)
- Magnetic starter — factory mounted and wired
- Duplex alternator control (standard on C3)
- ASME safety valves (factory installed)
- Pressure gauges and controls
- Belt guards (factory installed)
- Owner's manual and service documentation
Ships on freight. This system weighs 2,355 lbs shipped — confirm site access, forklift or crane availability, and floor load capacity before delivery. Call us to coordinate.
Available Factory-Mounted Options
- Low Oil Control (#6304x2M): Shuts down the affected pump on low oil — prevents running dry
- Hour Meters (#HRM75x2M / #HRM460x2M): Individual runtime tracking per pump for accurate service intervals
- Electronic Auto Drain (#SDV03M): Timed automatic tank drain — critical for moisture management in a 240-gallon tank
- Aftercooler (#BGAC2x2M — 100 CFM rated): Cools compressed air before it reaches your distribution system, dramatically reducing moisture
- Belt Tensioner (#254Dx2M — 15 HP): Simplifies belt maintenance
- Vibration Pads (#VP1004 — set of 4): Reduces floor vibration transmission
- Right From The Start Kit (#RFS003D — 25 and 30 HP): Initial startup service items
- All Options C3 Package (#AOC3D): All available options bundled
Available Configurations — 30 HP Duplex Options
- D15312HC3-S — 30 HP (2x15), 3-Phase, 120 gal, 100.4 CFM @ 175 PSI — $13,098.85: Same pump system, smaller tank — right choice if floor space is limited or peak demand spikes are short
- D15324HC3-S (this unit) — 30 HP (2x15), 3-Phase, 240 gal, 100.4 CFM @ 175 PSI — $14,509.00: Maximum storage for highest-demand environments
For lower CFM requirements, step down to the 20 HP (D10312/D10324) or 15 HP (D7312/D7324) duplex units — they cover 70 CFM and 49.6 CFM respectively at significantly lower cost.
When Does a Shop Need the 240-Gallon vs. the 120-Gallon?
Both models deliver identical CFM output — the pumps are the same. The question is whether your shop's demand pattern benefits from more storage:
- Choose 240-gallon (D15324HC3-S) when: Multiple spray booths or high-CFM tools run simultaneously and cause pressure drops; you have the floor space; your budget accommodates the ~$1,400 difference; or pump longevity under heavy duty cycles is a priority
- Choose 120-gallon (D15312HC3-S) when: Floor space is tight; your peak demand events are short and spaced far apart; or you want to minimize upfront cost and your usage pattern supports it
Technical Specifications
- Model Number: D15324HC3-S
- Series: Duplex Series
- Horsepower (each / total): 2x15 HP / 30 HP total
- Electrical: 3-Phase
- Pump Configuration: C3
- Pump RPM: 795
- CFM @ 0 PSI: 123.4
- CFM @ 175 PSI: 100.4
- Maximum Pressure: 175 PSI
- Tank Capacity: 240 gallons
- Tank Style: ASME horizontal with channel base
- Dimensions (L x W x H): 94" x 30" x 68"
- Shipped Weight: 2,355 lbs
- Magnetic Starter: Included, factory mounted and wired
- Alternator Control: Standard on C3 configuration
- Price: $14,509.00
Why Buy From Air Compressor Factory Direct?
We have specialized in professional-grade shop compressors since 2016. At $14,509, this is a capital equipment decision — not something to click-and-ship without talking through your shop's actual requirements. Call us and we will review your CFM demand, electrical service, floor space, and usage pattern. If the 240-gallon tank is overkill for your shop, we will tell you. If you need it, we will explain exactly why.
- Free Shipping on qualifying orders (freight delivery; site requirements must be confirmed)
- Free Technical Support — 866-217-0063
- Full Manufacturer Warranty — Castair stands behind this equipment
- Honest Configuration Guidance — 120 vs. 240 gallon, option packages, electrical requirements
Call 866-217-0063 for quick answers and help!
Frequently Asked Questions
What is the advantage of a duplex compressor like the D15324HC3-S over a single-pump unit?
A duplex setup gives you built-in redundancy and continuous-duty capability that a single pump can't match. The D15324HC3-S runs two 15 HP pumps sharing a 240-gallon tank, so each pump carries half the load — meaning lower operating temperatures, less wear per pump, and longer service intervals than a single 30 HP unit pushing the same CFM. For shops that can't afford downtime, that load-sharing arrangement is the practical reason to spec a duplex.
Can one pump on the D15324HC3-S run independently if the other is down for service?
Yes. Each pump on the D15324HC3-S has its own motor, pressure switch, and check valve, so either pump can carry the system on its own while the other is being serviced or repaired. Output will drop to roughly half rated CFM on a single pump, but the 240-gallon tank helps buffer demand during that period. This is one of the core reasons duplex units get spec'd for production environments where maintenance can't mean a full shop shutdown.
Does the D15324HC3-S include an alternating control, and why does it matter?
The D15324HC3-S includes an alternator control that rotates lead/lag pump duty automatically, so both pumps accumulate equal run hours over time. Without alternation, the lead pump takes the bulk of starts and hours, wearing out significantly faster than the lag pump. Equal hour distribution on a unit like this — two cast iron single-stage pumps at 15 HP each — directly extends the interval before your first major rebuild on either side.
What happens to the D15324HC3-S system if one pump fails completely?
A failed pump on the D15324HC3-S doesn't kill your air supply — the working pump continues to maintain tank pressure and the system stays online at reduced capacity. Most pressure switch configurations will flag the failed side, but the operational pump keeps cycling normally. This is the real-world failure mode that makes duplex units the right choice for critical applications; a single-pump failure on a comparable unit means zero air until it's fixed. If you're troubleshooting a pump failure on this model, our techs can walk you through diagnostics at 866-217-0063.
How does a preventive maintenance schedule differ on the D15324HC3-S compared to a single-pump 30 HP unit?
With two pumps sharing the workload on the D15324HC3-S, each cast iron pump runs cooler and accumulates hours more slowly than a single pump carrying the full system load — so oil change intervals and valve inspection intervals per pump are effectively extended relative to run time on that individual pump. That said, you're now maintaining two pump assemblies, two sets of intake filters, two belt drives, and two motor bearings, so total PM touchpoints are higher even if each individual interval is more forgiving. The practical approach is to schedule PM on both pumps simultaneously to keep the alternator cycle balanced and avoid having one side in significantly better condition than the other.
