Castair I25312HC4Z-S: 25HP 3-Phase Industrial Air Compressor — 120 Gallon Horizontal with Mounted Starter
The Castair I25312HC4Z-S is a 25-horsepower, 3-phase, 120-gallon horizontal industrial air compressor built on the C4 cast iron pump with a factory-mounted magnetic motor starter. This is the 25HP configuration of the same C4 pump platform used in the 20HP models — the difference is motor size and resulting RPM. At 25HP, the C4 pump runs at 710 RPM and delivers 109 CFM free air and 90 CFM at 175 PSI, making this one of the higher-output reciprocating compressors in Castair's lineup.
For a busy production shop, body shop, or industrial facility where demand regularly runs 75-90 CFM at pressure, the I25312HC4Z-S is the right size. Below that, you are paying for horsepower you are not using. Above 90 CFM continuous demand, look at the 30HP I30324HC4Z-S.
The 120-gallon horizontal tank is appropriate when floor footprint and ceiling height are both constraints. The same pump is available with a 240-gallon tank as the I25324HC4Z-S — if your demand pattern includes high-volume spikes rather than steady consumption, the larger tank handles those peaks better.
C4 Pump — Core Engineering
Pump Specifications
- Pump designation: C4 — Two-stage, V4 cylinder configuration
- Rated HP range: 15-25HP — the 25HP application is within the designed operating range
- Pump RPM at 25HP: 710
- Cylinder arrangement: V4 — four cylinders in a V configuration for smooth, balanced operation
- Oil capacity: 1 gallon
- Construction: 100% cast iron — cylinders, heads, valve plates, crankcase
- Bearings: Tapered roller bearings at both crankshaft ends
- Connecting rods: Precision steel with automotive-type rod insert bearings at crankshaft and wrist pin
- Valves: Disc and spring design — field-replaceable
- Pistons: 4-ring configuration for efficiency and low oil carry-over
- Unloader: Centrifugal — loadless start-up on every cycle
Tank and Frame
- Tank capacity: 120 gallons, horizontal
- Tank construction: Powder-coated ASME-rated steel with channel saddle frame
- Safety valve: ASME-rated, factory installed
- Belt guard: Totally enclosed metal
- Discharge lines: Copper tubing or stainless braided flex line
Motor and Electrical
- Horsepower: 25HP
- Phase: 3-phase
- Motor speed: 1725 RPM industrial
- Service factor: 15% minimum
- Motor starter: Factory-mounted magnetic motor starter (Z designation)
- Max working pressure: 175 PSI
Performance Specifications
- Motor output: 25 HP
- Electrical: 3-phase with factory-mounted magnetic starter
- Tank capacity: 120 gallons, horizontal
- Pump: C4 (Two-stage, V4)
- Pump RPM: 710
- Free air delivery (0 PSI): 109 CFM
- Delivery at 175 PSI: 90 CFM
- Max pressure: 175 PSI
Dimensions and weight: Contact us for current shipping specs on the 120-gallon C4Z configuration. The 240-gallon version (I25324HC4Z-S) is 90x39x70 at 1,725 lbs.
What's in the Box
- Castair I25312HC4Z-S compressor — fully assembled
- 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 not included — available as factory option BGAC3M (for 20HP and up). Electrical connection to 3-phase service by licensed electrician.
Available Configurations — 25HP Industrial Series
- I25312HC4Z-S (this unit): 25HP, 3-phase, 120gal Horizontal, C4 pump, 710 RPM, 90 CFM @ 175 PSI, mounted starter
- I25324HC4Z-S: 25HP, 3-phase, 240gal Horizontal, C4 pump, 710 RPM, 90 CFM @ 175 PSI, 90x39x70, 1,725 lbs — same pump, double the storage
Comparing the 20HP and 25HP on the C4 platform:
- 20HP (I20324HC4Z-S): 519 RPM, 72 CFM @ 175 PSI
- 25HP (I25312HC4Z-S): 710 RPM, 90 CFM @ 175 PSI
- 30HP (I30324HC4Z-S): 794 RPM, 105 CFM @ 175 PSI
Moving from 20HP to 25HP adds 18 CFM at 175 PSI — a 25% increase in usable output from the same pump. If your shop is consistently running at the top end of 20HP capacity, the 25HP step-up makes a real difference in how many simultaneous users the system can support without pressure drop.
When Does a Shop Need This?
- Continuous air demand of 75-90 CFM at 175 PSI — large body shop, production facility, or multi-bay automotive service operation
- 3-phase electrical service is available and adequate for a 25HP motor load
- You need a factory-mounted starter for code compliance or simplified installation
- The 120-gallon tank footprint fits your installation space and your demand is steady enough to not require the 240-gallon buffer
Why Buy From Air Compressor Factory Direct?
Since 2016, we have helped shops and facilities size, purchase, and install industrial air compressors. At 25HP, this is a significant capital purchase. We will help you verify that your electrical service is adequate, confirm the installation footprint works, and advise on aftercooler options based on your actual processes.
- Free shipping to commercial addresses in the lower 48 states
- Free tech support at 866-217-0063
- Full Castair manufacturer warranty
- Honest sizing guidance — we will tell you if the 20HP or 30HP is more appropriate for your load
- Authorized dealer with direct Castair factory support
Call 866-217-0063 for quick answers and help!
