Castair I20324HC4Z-S: 20HP 3-Phase Industrial Reciprocating Air Compressor — 240 Gallon Horizontal with Mounted Starter
The Castair I20324HC4Z-S is a 20-horsepower, 3-phase, 240-gallon horizontal industrial reciprocating air compressor. Built around the C4 cast iron pump and priced at 2,542, this is a serious production compressor for multi-bay shops, body shops with active spray booths, or any industrial operation where consistent high-volume air supply is not optional.
The 240-gallon horizontal tank is the defining feature of this configuration. At 92.8 CFM free air delivery and 72 CFM at 175 PSI, the 20HP C4 pump can supply 5-7 simultaneous tool workstations. The 240-gallon tank provides the storage buffer that makes this practical in real-world shop conditions — where 3 technicians might all reach for their air guns at the same moment, or where a spray booth cycles through heavy demand periods. More tank means fewer compressor cycles per hour, which means less heat cycling of the pump and motor, which means longer service life.
The Z suffix indicates a factory-mounted magnetic motor starter. For a 3-phase unit at this power level, having the starter factory-mounted saves installation time, ensures proper electrical assembly, and simplifies the job for your electrician — they connect to a single panel rather than sourcing and mounting a separate starter enclosure.
C4 Pump — Engineering Details
Why the C4 Pump Matters
- Pump designation: C4 — Two-stage, V4 cylinder configuration
- Rated HP range: 15-25HP — this pump is built for the 20HP application, not working at its upper limit
- Pump RPM: 519 — extremely slow for a reciprocating compressor; most comparable units run 800-1,200 RPM
- Cylinder arrangement: V4 — four cylinders in a V configuration for better balance and smooth operation
- Oil capacity: 1 gallon
- All cast iron construction: Cylinders, heads, valve plates, crankcase — no aluminum in the compression path
- Tapered roller bearings at both crankshaft ends for superior load handling and reduced friction wear
- Precision steel connecting rods with automotive-type rod insert bearings — engineered for continuous-duty operation
- Disc and spring valves for high efficiency and field serviceability — replaceable without specialized tools
- 4-ring pistons for maximum efficiency and minimal oil carry-over
- Centrifugal unloader — ensures the pump starts unloaded every time, protecting the motor from startup torque overload
Tank and Frame
- Tank capacity: 240 gallons, horizontal configuration
- Tank dimensions: 90 x 39 x 70 inches
- Tank construction: Powder-coated ASME-rated steel with channel saddle frame
- Safety valve: ASME-rated, factory installed and sized for this unit
- Belt guard: Totally enclosed metal construction
- Discharge lines: Copper tubing or stainless-steel braided flex line
Motor and Electrical
- Horsepower: 20HP
- Phase: 3-phase — requires proper 3-phase electrical service
- Motor speed: 1725 RPM industrial
- Service factor: 15% minimum
- Motor starter: Factory-mounted magnetic motor starter (Z designation) — properly sized for the motor
- Max working pressure: 175 PSI
Performance Specifications
- Motor output: 20 HP
- Electrical: 3-phase with factory-mounted magnetic starter
- Tank capacity: 240 gallons, horizontal
- Pump: C4 (Two-stage, V4)
- Pump RPM: 519
- Free air delivery (0 PSI): 92.8 CFM
- Delivery at 175 PSI: 72 CFM
- Max pressure: 175 PSI
- Dimensions (LxWxH): 90 x 39 x 70 inches
- Weight: 1,700 lbs
- Price: 2,542
What's in the Box
- Castair I20324HC4Z-S compressor — fully assembled on 240-gallon horizontal tank
- Factory-mounted magnetic motor starter (Z designation)
- ASME safety valve (factory installed)
- Pressure switch with unloader
- Totally enclosed metal belt guard
- Copper discharge and unloader tubing (or stainless braided flex line)
- Owner's documentation
Aftercooler is available as factory option (BGAC3M — for 20HP and up). Electrical connection to 3-phase service is performed by the customer's licensed electrician.
Available Configurations — 20HP Industrial Series
- I20312HC4Z-S: 20HP, 3-phase, 120gal Horizontal, C4 pump, 519 RPM, 72 CFM @ 175 PSI — same pump, smaller tank
- I20324HC4Z-S (this unit): 20HP, 3-phase, 240gal Horizontal, C4 pump, 519 RPM, 72 CFM @ 175 PSI, 90x39x70, 1,700 lbs — double the tank storage
The pump, motor, and CFM output are identical between the 120-gallon and 240-gallon versions. You are buying more air storage. In a shop with consistent demand from multiple simultaneous users, the 240-gallon tank reduces compressor cycling frequency, which extends pump and motor life. It also means faster pressure recovery after a heavy draw-down — important when you are running back-to-back vehicles through a spray booth.
When Does a Shop Need This vs. Stepping Up or Down?
This unit is right if:
- You are running 5-7 simultaneous technician workstations on pneumatic tools
- You have an active spray booth consuming 30-50 CFM plus additional shop air demand
- You have 3-phase electrical service available
- You need the 240-gallon tank to buffer high-demand spikes or back-to-back heavy use
- A factory-mounted starter simplifies your installation or code requirements
Step down to the 120-gallon (I20312HC4Z-S) if:
- Your shop footprint cannot accommodate the 90-inch length of the 240-gallon tank, and your demand profile is steady enough that the smaller tank storage is adequate
Step up to the 25HP (I25324HC4Z-S) if:
- Your continuous demand exceeds 72 CFM at 175 PSI — the 25HP delivers 90 CFM from the same C4 pump platform
- You are running sandblasting equipment, large plasma systems, or other continuous-high-CFM processes alongside general shop air
Consider the 15HP if:
- Your operation is 3-4 technicians on standard shop tools without spray booth demands — the I15312HC3-S at 50.2 CFM handles that at lower operating cost
Why Buy From Air Compressor Factory Direct?
We have been selling industrial air compressors and shop equipment since 2016. At this price and weight class, you want to talk to someone before you order. We can help you verify your electrical service is adequate, confirm the footprint fits your installation space, and advise on the aftercooler option based on your application. A compressor this size is a long-term capital equipment decision — we take that seriously.
- Free shipping to commercial addresses in the lower 48 states (freight delivery — requires loading dock or forklift)
- Free tech support at 866-217-0063 before and after your purchase
- Full Castair manufacturer warranty
- Honest buying guidance — we will tell you if this is sized correctly for your application
- Authorized dealer with direct Castair factory access
Call 866-217-0063 for quick answers and help!
Frequently Asked Questions
What is the duty cycle on the I20324HC4Z-S, and can it run continuously in a production environment?
The Cast Air I20324HC4Z-S is rated for 100% duty cycle at full load — this is a direct result of the all-cast-iron construction on the pump cylinders, heads, and crankcase. Cast iron dissipates heat far better than aluminum, so the pump doesn't need mandatory cool-down cycles the way lighter-duty compressors do. For continuous-demand shops like auto body, sandblasting, or manufacturing lines, this is the right spec.
What oil does the I20324HC4Z-S take, and how often does it need to be changed?
Cast Air specifies a non-detergent 30-weight compressor oil (SAE 30) — do not use motor oil, as the detergent additives break down ring seals over time. Oil change interval is every 500 hours under normal conditions, or annually if hours are lower. Check the sight glass daily at startup; the all-cast-iron pump runs tighter tolerances than aluminum units, so keeping clean oil in it is the single biggest factor in pump longevity.
Why does this 20 HP model require 3-phase power instead of single-phase?
At 20 HP, the starting amperage draw on single-phase would exceed 100 amps, which trips breakers and stresses wiring in most shop electrical systems. Three-phase power distributes the load across three legs, drops the starting current significantly, and runs the motor cooler and more efficiently under sustained load. If your shop only has single-phase service, you'd need a phase converter — call us at 866-217-0063 and we can walk through whether that setup makes sense for your application versus bringing in 3-phase, which is the cleaner solution at this HP rating.
Is a 240-gallon horizontal tank enough for a busy production shop, or will the compressor short-cycle?
At 20 HP, the I20324HC4Z-S typically produces in the range of 80–85 CFM at 175 PSI — the 240-gallon tank gives you substantial reserve to handle burst demand from multiple tools without the pump cycling on every trigger pull. For most shops running 3–5 air tools simultaneously (impact wrenches, DA sanders, air ratchets), the 240-gallon tank is well-matched to this pump output. If you're running continuous high-CFM equipment like large spray booths or multiple plasma cutters simultaneously, total demand calculation against rated CFM is the deciding factor, not tank size alone.
What size shop or operation is the I20324HC4Z-S designed for?
This unit is sized for mid-to-large commercial shops — think 8-to-15-bay automotive service centers, body shops running two or more spray guns simultaneously, fabrication shops with welding and grinding demand, or light manufacturing lines. The 20 HP motor and 240-gallon horizontal tank handle the kind of multi-shift, multi-tool environments where a 5–10 HP compressor would be running non-stop. Cast Air has been building these all-cast-iron units in Spicer, MN since 1991, and the I20324HC4Z-S is their workhorse spec for exactly this class of shop.
