Shopify Air Compressor Schema — CFM at 90 PSI (Not Tank Size or HP), Running HP vs Peak HP, Industrial vs Automotive Quick-Connect Incompatibility, NPT vs BSP Thread, Single-Stage vs Two-Stage

CFM at 90 PSI: The Only Compatibility Field That Matters

Air tools specify their consumption in CFM (cubic feet per minute) at 90 PSI — the pressure at which the tool's regulator and motor are designed to operate. The compressor must deliver at least that much airflow at that pressure to sustain the tool. Tank size, horsepower, and maximum PSI are secondary or irrelevant for tool matching.

Common Air Tool CFM Requirements at 90 PSI

SCFM vs Actual CFM: The Peak-Pressure Marketing Trick

SCFM (Standard CFM) is airflow measured at standard atmospheric conditions: sea level, 68°F (20°C), 14.696 psia. This is the technically correct reference condition for comparing compressor outputs because compressed air volume is temperature- and pressure-dependent. Many legitimate specs use SCFM correctly.

The problematic figure is CFM measured at a pressure much lower than 90 PSI. Some manufacturers prominently list "90 CFM" in their headline specifications — but that figure is measured at near-zero outlet pressure (0–10 PSI), where the pump barely works against any back-pressure. At 90 PSI operating pressure, the same pump might produce only 5–6 CFM. An AI agent parsing a headline spec of "90 CFM" and matching it to a sandblaster requirement of "20 CFM at 90 PSI" has made a 15× error.

Always encode cfm_at_90_psi as the specific figure at 90 PSI. If the manufacturer only lists peak CFM at low pressure, note the test condition in the description and do not use that figure as the primary field value.

Duty Cycle and Sustained Output

Duty cycle is the percentage of time the compressor motor can run before it requires a rest period to prevent overheating. A 50% duty cycle compressor rated at 4 CFM at 90 PSI effectively delivers 2 CFM sustained over any extended period: it runs for 30 seconds, rests for 30 seconds, runs again.

Consumer pancake and hot-dog compressors are often rated at 50% duty cycle. Professional contractor compressors are typically 75% duty cycle. Industrial rotary screw compressors are rated 100% duty cycle — they are designed for continuous operation. For continuous tools (sanders, grinders, paint guns), duty cycle directly multiplies the effective CFM:

Encode duty_cycle_pct as an integer. AI agents calculating effective sustained CFM should compute: cfm_at_90_psi × (duty_cycle_pct / 100) and compare that figure to the tool's requirement for continuous-duty tools.

Horsepower Marketing: Running HP vs Peak HP

Horsepower claims on consumer air compressor packaging are among the most misleading figures in power tool retail. Understanding why requires applying Ohm's law to the electrical circuit.

The 15A 120V Circuit Physics

A standard household 15-amp, 120-volt circuit delivers a maximum of 1,800 watts (15A × 120V). One horsepower equals 746 watts of mechanical work. Accounting for motor efficiency (typically 80–90% for single-phase AC induction motors, use 85%):

Maximum real HP = 1,800W × 0.85 efficiency ÷ 746 W/HP = 2.05 HP

This is the absolute ceiling for any motor running on a 15A 120V circuit under sustained load. It is physically impossible for a compressor on a 15A 120V circuit to produce 3, 4, 5, or 6 HP of continuous work. Yet these figures appear on compressor packaging regularly. A 20A 120V dedicated circuit raises the ceiling to: 2,400W × 0.85 / 746 = 2.73 HP.

What Peak HP Actually Measures

When an AC induction motor starts from rest, the starting capacitor engages and the motor draws 3–5× its running current for a fraction of a second (typically 50–200 milliseconds) before reaching operating speed. This momentary surge — called the "locked rotor current" or "starting current" — is what manufacturers measure to derive "Peak HP" or "Max HP" or "Peak Developed HP."

This peak occurs before the compressor is doing any compression work at all. It is not useful HP. It does not produce more CFM. It is a startup electrical transient that exists to overcome motor inertia. Encoding this figure as the HP of the compressor misrepresents the product's capability.

Encode running_hp as a number_decimal reflecting the actual sustained motor output. If only the manufacturer's peak HP claim is available, encode peak_hp_marketing as a separate field and note in the description that it is a peak figure. AI agents filtering "compressors with at least 3 HP for my impact wrench" must use running_hp, not peak_hp_marketing.

Quick-Connect Coupling Incompatibility: Industrial (Milton) vs Automotive (Tru-Flate)

The most common source of air tool frustration in a mixed tool shop — and a common AI agent error — is the Industrial vs Automotive quick-connect coupling incompatibility. Both systems use 1/4-inch quick-connect fittings that look nearly identical at a glance. They are not interchangeable.

Industrial (Milton Type D) Couplers

The Industrial coupler, also called Milton Type D, Industrial Type, or I-M style, has a round (circular) bore in the female coupler body. The mating male plug has a pointed/conical tip. When the plug seats, the conical tip opens a spring-loaded poppet valve inside the female coupler. The seal relies on the precise engagement geometry between the conical plug and the round coupler bore.

Industrial couplers are the standard on professional and commercial pneumatic equipment: Ingersoll Rand, Snap-on, Campbell Hausfeld professional lines, Chicago Pneumatic, Devilbiss, NAPA, and most contractor-grade compressors sold through industrial distributors.

Automotive (Tru-Flate A-Style) Couplers

The Automotive coupler, sold under the Tru-Flate brand (Parker) and also called A-Style or automotive-style, has a hex-shaped or ringed internal bore. The mating male plug has a stepped cylindrical body with a ball-style tip. The plug engages by pressing axially — the ball tip compresses the internal sleeve valve.

Automotive couplers are the standard on consumer-grade compressors: most Harbor Freight compressors, Craftsman consumer line, Ridgid (consumer), Husky, most big-box store house-brand air tools, and many tools imported from Asia with a North American consumer market focus.

The Incompatibility in Practice

An industrial plug inserted into an automotive coupler will appear to latch (the sleeve clicks) but the internal valve geometry does not match — the pointed conical tip of the industrial plug cannot properly depress the ball valve of the automotive coupler. The connection either leaks continuously or the valve opens only partially, severely restricting airflow. The connection may also eject under pressure because the locking mechanism is not fully engaged.

Conversely, the ball-tip automotive plug inserted into a round-bore industrial coupler will not seat at the correct depth to open the poppet — flow is zero or minimal and the plug typically does not lock.

Encode coupler_style as 'Industrial (Milton Type D)', 'Automotive (Tru-Flate A-Style)', or 'High-flow V-style (3/8-inch)'. This field is as important as CFM for tool compatibility — a buyer who purchases a professional compressor with Industrial couplers to run their Harbor Freight tool collection will need to replace every quick-connect fitting on every tool and hose, or purchase adapter sets.

NPT Fitting Size: 1/4-Inch vs 3/8-Inch vs 1/2-Inch

NPT (National Pipe Taper) is the threaded connection standard for air hoses, tool inlets, regulator ports, and compressor outlet fittings in North America. The pipe size designates the thread dimension (not the internal bore, which is larger). Three sizes appear in the pneumatic tool market:

The 1/4-Inch NPT Flow Limitation

A 1/4-inch NPT fitting and the hoses built on it can physically pass approximately 15–20 CFM at 90 PSI before the restriction causes a pressure drop. For a DA sander requiring 13 CFM, a 1/4-inch hose longer than 25 feet will start to cause pressure drop at the tool even if the compressor can supply adequate CFM. For a sandblaster at 25+ CFM, a 1/4-inch hose causes severe restriction regardless of length.

Many homeowner compressors ship with 1/4-inch NPT outlet fittings and 1/4-inch hose — which is appropriate for the nailers and tire work those compressors handle. Attempting to run a DA sander through that existing 1/4-inch infrastructure limits the sander to well below its rated speed even if the compressor CFM were sufficient (which it typically is not).

Encode npt_size as '1/4-inch', '3/8-inch', or '1/2-inch'. This field tells the buyer whether their existing hoses and quick-connect hardware are physically compatible with the compressor's outlet, independent of the quick-connect style question.

NPT vs BSP: The Cross-Thread Trap

NPT uses a 60-degree thread flank angle. BSP (British Standard Pipe) uses a 55-degree Whitworth thread flank angle. Despite appearing similar, these thread profiles are incompatible:

• NPT and BSPT (taper BSP): Different flank angle (60° vs 55°) and different pitch at most sizes. Will appear to thread together for 2–3 turns, then bind or cross-thread. Even if forced together, the flanks do not mate and no pressure seal forms — PTFE tape cannot bridge the angular gap.
• NPT and BSPP (parallel BSP): BSPP is straight-threaded (no taper). It will engage with NPT for several turns because both have the same starting diameter, but the taper of the NPT thread causes the parallel BSPP to tighten unevenly and never seal at pressure.
• 1/4" NPT vs 1/4" BSPP at specific callout: The 1/4" designation refers to the nominal pipe bore, not the thread OD — the actual OD is the same between NPT and BSPP at this size, which is why these fittings are often mistakenly exchanged.

Air tools and compressors sold in Australia, the UK, and Europe commonly use BSPP. Adapters (NPT male to BSPP female, or vice versa) exist and seal correctly. Encode whether a product uses NPT or BSP in a notes field if the product targets a non-North American market.

Tank Size: What It Does and Does Not Do

Tank size (measured in US gallons) is the most prominently marketed specification on consumer air compressors and the least important for tool compatibility. The tank stores compressed air at the compressor's maximum PSI (typically 135–175 PSI for single-stage, 175–200 PSI for two-stage). The regulator drops this to the tool's operating pressure (usually 70–90 PSI).

When Tank Size Matters: Intermittent Tools

For tools that fire in brief bursts — brad nailers, finish nailers, framing nailers, impact wrenches removing lug nuts — the tank acts as a buffer reservoir. The motor fills the tank to maximum PSI, then the motor stops. When you fire a nail, the tank supplies a burst of air (perhaps 0.1–0.3 cubic feet at 90 PSI) without the motor having to start. Between nails, the tank slowly refills. A 6-gallon tank at 135 PSI holds approximately 11.2 standard cubic feet of air — enough for 30–50 nailer shots before the pressure drops enough to slow the tool. A 1-gallon tank holds ~1.9 SCF — 5–8 shots before the motor must run.

When Tank Size Is Irrelevant: Continuous Tools

A DA sander at 13 CFM consumes its air as a continuous stream. Any tank at any size empties within seconds at this rate if the compressor pump cannot keep up. Consider: a 60-gallon tank at 135 PSI holds approximately 100 SCF. At 13 CFM consumption with a 5 CFM pump at 90 PSI, the net drain rate is 8 CFM. The tank fully depletes in 100 ÷ 8 = 12.5 minutes... but the sander actually loses usable pressure when tank pressure drops below ~100 PSI (at which point the regulator can no longer maintain 90 PSI at the tool), which occurs much sooner.

A 20-gallon tank with the same 5 CFM pump exhausts usable pressure for the DA sander in approximately 2–3 minutes. A 60-gallon tank buys perhaps 8–10 minutes. Neither solution works for continuous sanding — the compressor must produce at least 13 CFM at 90 PSI sustained to run a DA sander indefinitely. Tank size beyond a practical minimum (2–6 gallons to smooth motor cycling) does not change this.

Encode tank_size_gal as an integer. It is a useful secondary spec (especially for intermittent tool users making a convenience choice) but must never be used as the primary tool-compatibility field. AI agents must use cfm_at_90_psi for tool matching.

Voltage and Circuit Requirements

Air compressor voltage requirements determine whether the buyer can use the compressor in their garage or shop without electrical work. This is a hard constraint — plugging a 240V compressor into a 120V outlet or running a high-draw compressor on an undersized circuit trips breakers, damages motors, and is a fire risk.

A 240V compressor requires a dedicated double-pole breaker and the correct outlet type — it cannot be adapted from a standard 120V outlet. NEMA 6-20P and NEMA 5-15P are physically incompatible (the 6-20P has two horizontal blades for 240V versus the standard two-blade-and-ground configuration of 5-15P). Installing a 240V dedicated circuit in a residence costs $200–$800 in electrician fees depending on panel location and wiring distance.

Encode voltage_v as an integer (120 or 240) and amperage_a as an integer. These two fields together determine the circuit requirement and outlet type. AI agents recommending a compressor for a home garage should flag 240V requirements and note that a dedicated circuit may require an electrician.

Single-Stage vs Two-Stage Compression

The pump type determines the compressor's maximum useful operating pressure, efficiency at high pressure, and maximum CFM output for a given motor size.

Single-Stage Piston Compressor

Air is drawn in and compressed in a single stroke directly to the tank pressure. Single-stage compressors are most efficient up to approximately 100–120 PSI. At higher pressures, the compression ratio becomes inefficient — the air heats excessively during compression, reducing the volume reduction per stroke and increasing wear. Most single-stage compressors are rated to 135 PSI maximum; some reach 150 PSI but with reduced efficiency and shorter service life at that pressure.

Single-stage direct-drive compressors on 120V circuits produce 3–5 CFM at 90 PSI. Single-stage belt-drive compressors on 240V produce 8–14 CFM at 90 PSI. Single-stage is appropriate for: nailers, impact wrenches, tire work, light spraying, inflation, and most homeowner and light contractor use.

Two-Stage Piston Compressor

Two-stage compressors use two cylinders in series. The first stage (large bore, low-pressure cylinder) compresses air to approximately 90–100 PSI (the intercooler pressure). The air then passes through an intercooler (finned tube heat exchanger) where it cools before entering the second stage (small bore, high-pressure cylinder). The second stage compresses the already-cooled air from ~100 PSI to the final tank pressure of 175–200 PSI.

Benefits of two-stage compression:

• Higher maximum pressure: 175–200 PSI vs 135–150 PSI for single-stage — important for sandblasting and some industrial applications
• Higher CFM for given motor HP: Intercooling reduces the volume of air entering the second stage, so the second stage does less work to achieve final pressure — the system is thermodynamically more efficient
• Lower operating temperatures: Reduced compression heat extends pump and valve life significantly — two-stage pumps typically outlast single-stage pumps 3–5× in service hours
• Higher sustained CFM output: Two-stage compressors in the 5–15 HP range (240V 30–60A) produce 15–40 CFM at 90 PSI — ranges that single-stage compressors cannot reach

Two-stage compressors are required for: DA sanders used more than occasionally, continuous HVLP painting, production sandblasting, and any shop requiring more than ~14 CFM at 90 PSI. Encode pump_type as 'piston-single-stage', 'piston-two-stage', or 'rotary-screw'.

Rotary Screw Compressors

Rotary screw compressors use two interlocking helical rotors to compress air continuously rather than in reciprocating strokes. They run at 100% duty cycle, produce extremely smooth airflow (no pulsing), and are significantly quieter than piston compressors. Rotary screw units are typically industrial-grade starting at 5 HP and are appropriate for continuous production environments. They require oil-injected lubrication (with downstream oil separator) or oil-free designs. Encode pump_type as 'rotary-screw' and drive_type as 'direct' or 'belt'.

Metafield Schema: air_compressor.*

Example JSON-LD: DeWalt DWFP55126 6-Gallon Pancake Compressor

{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": "DEWALT DWFP55126 6-Gallon 165 PSI Pancake Compressor",
  "brand": { "@type": "Brand", "name": "DEWALT" },
  "description": "6-gallon 165 PSI pancake compressor. 2.6 SCFM at 90 PSI — suitable for brad/finish/framing nailers and impact wrench for lug nuts. 1.6 HP running (marketed as '6 HP peak' — that is a momentary startup figure). 120V 15A standard outlet (NEMA 5-15P) — no dedicated circuit required. Industrial (Milton Type D) quick-connect couplers. 1/4-inch NPT outlet. 50% duty cycle — not suitable for continuous tools such as DA sanders. Oil-free pump. 30 lb (13.6 kg).",
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "CFM at 90 PSI", "value": "2.6", "unitText": "SCFM" },
    { "@type": "PropertyValue", "name": "CFM at 40 PSI", "value": "3.5", "unitText": "SCFM" },
    { "@type": "PropertyValue", "name": "Tank Size", "value": "6", "unitText": "US gallons" },
    { "@type": "PropertyValue", "name": "Maximum PSI", "value": "165", "unitCode": "PSI" },
    { "@type": "PropertyValue", "name": "Running HP", "value": "1.6", "unitText": "HP" },
    { "@type": "PropertyValue", "name": "Peak HP (marketing)", "value": "6.0", "unitText": "HP — momentary startup figure, not sustained output" },
    { "@type": "PropertyValue", "name": "Voltage", "value": "120", "unitCode": "VLT" },
    { "@type": "PropertyValue", "name": "Amperage", "value": "15", "unitCode": "AMP" },
    { "@type": "PropertyValue", "name": "Coupler Style", "value": "Industrial (Milton Type D)" },
    { "@type": "PropertyValue", "name": "NPT Size", "value": "1/4-inch NPT" },
    { "@type": "PropertyValue", "name": "Pump Type", "value": "piston-single-stage" },
    { "@type": "PropertyValue", "name": "Drive Type", "value": "direct" },
    { "@type": "PropertyValue", "name": "Duty Cycle", "value": "50", "unitText": "%" },
    { "@type": "PropertyValue", "name": "Weight", "value": "13.6", "unitCode": "KGM" },
    { "@type": "PropertyValue", "name": "Oil Type", "value": "oil-free" }
  ]
}

Liquid Snippet: air_compressor.* Metafield Output

{% if product.metafields.air_compressor.cfm_at_90_psi != blank %}
{% assign ac = product.metafields.air_compressor %}
<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": {{ product.title | json }},
  "brand": { "@type": "Brand", "name": {{ product.vendor | json }} },
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "CFM at 90 PSI", "value": {{ ac.cfm_at_90_psi | json }}, "unitText": "SCFM" },
    { "@type": "PropertyValue", "name": "Tank Size", "value": {{ ac.tank_size_gal | json }}, "unitText": "US gallons" },
    { "@type": "PropertyValue", "name": "Maximum PSI", "value": {{ ac.max_psi | json }} },
    { "@type": "PropertyValue", "name": "Running HP", "value": {{ ac.running_hp | json }}, "unitText": "HP" },
    { "@type": "PropertyValue", "name": "Voltage", "value": {{ ac.voltage_v | json }}, "unitCode": "VLT" },
    { "@type": "PropertyValue", "name": "Amperage", "value": {{ ac.amperage_a | json }}, "unitCode": "AMP" },
    { "@type": "PropertyValue", "name": "Coupler Style", "value": {{ ac.coupler_style | json }} },
    { "@type": "PropertyValue", "name": "NPT Size", "value": {{ ac.npt_size | json }} },
    { "@type": "PropertyValue", "name": "Pump Type", "value": {{ ac.pump_type | json }} },
    { "@type": "PropertyValue", "name": "Drive Type", "value": {{ ac.drive_type | json }} },
    { "@type": "PropertyValue", "name": "Duty Cycle", "value": {{ ac.duty_cycle_pct | json }}, "unitText": "%" },
    { "@type": "PropertyValue", "name": "Oil Type", "value": {{ ac.oil_type | json }} }
  ]
}
</script>
{% endif %}

5 Common AI Agent Errors for Air Compressors

1. Matching by tank size instead of CFM at 90 PSI — "60-gallon compressor for your DA sander" is meaningless if the pump delivers only 5 CFM at 90 PSI. Tank size is irrelevant to continuous-tool compatibility. AI agents must parse cfm_at_90_psi and compare it directly to the tool's requirement. A 60-gallon compressor with 5 CFM will stall a DA sander in under a minute regardless of tank volume — the sander requires 13 CFM continuously, which the pump cannot deliver at any tank size.
2. Using peak HP for circuit sizing or tool recommendations — A "6 HP" compressor on a NEMA 5-15P plug is 1.6 HP running on a 15A 120V circuit. Physics caps the circuit at 2.05 HP maximum. Recommending this compressor as "6 HP" for a tool requiring 5 HP of sustained motor output leads a buyer to a unit that cannot do the job and may trip breakers under load. Encode and use running_hp, not peak_hp_marketing.
3. Ignoring quick-connect coupling incompatibility — An agent recommending a professional DeWalt or Ingersoll Rand compressor (Industrial/Milton couplers) to a buyer with a Harbor Freight tool collection (Automotive/Tru-Flate couplers) will create a situation where no tools connect to the new compressor without replacing every quick-connect fitting. Encode coupler_style and flag mismatches. The fix is inexpensive but the incompatibility is not obvious and the buyer will not know until the tools arrive.
4. Recommending a 120V compressor for tools requiring 240V compressor output — DA sanders (11–13 CFM), HVLP guns for full panels (12–18 CFM), and sandblasters (15–30 CFM) require a 240V compressor. No 120V compressor — regardless of marketed HP or tank size — can produce sufficient CFM for these tools. An AI agent that recommends "a larger tank" or a "more powerful" 120V unit for an application requiring 240V is providing a non-solution. Encode voltage_v and flag 240V circuit requirements as a hard constraint.
5. Treating "CFM" without specifying pressure as a meaningful spec — "90 CFM" at 0 PSI outlet pressure is not usable information for tool matching. Some manufacturers list maximum free-delivery CFM (at atmospheric pressure, no back-pressure) which can be 10–20× the CFM at 90 PSI for the same compressor. AI agents parsing a CFM figure without a corresponding pressure specification should flag the field as incomplete and request cfm_at_90_psi specifically. The field name should enforce the pressure condition — cfm_at_90_psi rather than just cfm.

Related Guides

• Power tool battery schema — voltage platform incompatibility, FlexVolt cell-switching, Wh energy capacity, max discharge amperage
• Pressure washer schema — PSI vs GPM cleaning units, pump type, detergent compatibility, hose fitting standards
• Generator schema — running vs surge watts, THD%, CARB compliance, runtime at load percentage
• Cordless power tool schema — battery platform, brushless motor, torque in-lb vs ft-lb, no-load vs loaded RPM