Outdoor equipment terms: power, fluid, chain and service labels
Use these definitions to interpret equipment labels and the linked service examples. A unit or component name describes one feature; it does not establish part fit, operating permission or equipment condition. Follow the linked guide for the actual model and specific application.
Terms and applications
- Displacement
- Swept cylinder volume, commonly cc. It is not a universal power rating. Displacement details.
- Two-stroke / four-stroke
- Piston strokes per cycle. Lubrication layout still needs the actual model; some four-stroke engines use mixed fuel. Two-stroke / four-stroke details.
- Useful life, emissions
- Certification period for emissions requirements; not predicted remaining engine life. Useful life, emissions details.
- SAE viscosity
- Oil flow classification; use the engine’s temperature chart and approved grade. SAE viscosity details.
- API category
- Specified engine-oil performance category; viscosity is a separate requirement. API category details.
- Choke / purge / primer
- Different starting devices. A purge system can return fuel to the tank instead of injecting it into a float bowl. Choke / purge / primer details.
- Rated / maximum watts
- Continuous and separately limited output ratings; read the actual generator manual. Generator load sizing and connection choices.
- VA / W
- Apparent versus real power. For a single-phase load, W = V × A × power factor. VA / W details.
- Ah / Wh
- Charge versus nominal energy. Wh = nominal volts × amp-hours; usable energy depends on conditions. Compare batteries by watt-hours and compatibility.
- CCA
- Starting-current test rating under specified cold conditions; different from amp-hours. CCA details.
- Pitch / gauge / drive links
- Chain spacing, drive-link thickness and loop count; chain family and approved application also matter. Pitch / gauge / drive links details.
- Kickback
- Rapid saw reaction associated with bar-nose contact or pinching; read the applicable reaction and protection instructions. Kickback details.
- PTO
- Power take-off / blade engagement arrangement; its controls and interlocks depend on the mower. PTO details.
- PSI / GPM
- Pressure versus water flow. Their product is arithmetic, not a universal cleaning-speed test. PSI / GPM details.
- Nozzle number
- Common flow convention in GPM at 4,000 PSI; separate from spray angle. Nozzle number details.
- CFM / MPH
- Air volume per time versus air speed; compare stated nozzle and test conditions. CFM / MPH details.
- Total dynamic head
- Suction lift plus discharge rise and friction for the actual water path. Total dynamic head details.
- Duty cycle
- Permitted running proportion under stated conditions; tank volume does not establish continuous compressor delivery. Duty cycle details.
- Slope percent
- Rise divided by horizontal run, multiplied by 100; it differs from degrees. Slope percent details.
- Shear fastener
- Specified sacrificial drive part; a stronger hardware substitute can damage the machine. Shear fastener details.
Two common unit mistakes
A 2-foot rise over 10 feet of horizontal run is 20 percent slope, about 11.3 degrees. A nominal 18-volt, 5-Ah pack is 90 Wh; a 20-volt maximum marketing label would overstate that nominal-energy calculation.
Use model service for an actual part or fluid and calculators for arithmetic after identifying the right inputs.
Reference
Glossary
A short definition for every term this site uses that is not self-explanatory on first read: engine and fuel terms, electrical and generator terms, cutting and chain terms, hydraulic and airflow terms, and the standards bodies behind the safety pages. The definitions follow equipment systems.
Airflow terms such as CFM sit beside the pressure and operating conditions needed to interpret them; battery terms such as watt-hours sit beside voltage and capacity. Use the section matching the equipment, then follow its linked guide for the actual model, measurement conditions and worked examples.
Each definition links to its equipment, engine, parts or safety guide for a fuller explanation. Those guides provide the figures and reasoning that apply the term to an actual task.
Use the short definition here first, then check the linked example before carrying a specification into a purchase or repair decision.
An unfamiliar specification needs both a definition and its operating context. Use the equipment, engine, parts and safety sections to identify the term, then keep its stated units and conditions with it.
A short label can describe different measurements when the test pressure, fuel, model or operating load changes. Each entry links to the page that covers it in depth.
Nothing here states a figure for a named model: a definition of what a term means is not the same claim as a specification for a specific machine.
Engine and fuel
| Term | What it means |
|---|---|
| cc (cubic centimeters) | Engine displacement: the swept volume of the cylinder. A rough proxy for power within one engine family, not a unit you can compare fairly across brands or engine designs. |
| Two-stroke / four-stroke | How many piston strokes complete one power cycle. A two-stroke mixes oil into its fuel and has no separate oil sump; a four-stroke keeps oil in an isolated sump changed on a schedule. See two-stroke and four-stroke. |
| EPA emission class (I–V) | The federal category a small spark-ignition engine is certified under, printed on the emission control label along with displacement and model year. See reading the label. |
| SAE viscosity grade (e.g. SAE 30, 10W-30) | How an oil’s flow resistance is classified at cold and operating temperature. See oil grades. |
| API service category | The certification (shown as the “API donut” on the bottle) confirming an oil meets a defined set of engine-protection tests. See oil grades. |
| Ethanol blend (E10, E15) | Gasoline containing 10% or 15% ethanol by volume. E15 is federally prohibited in every nonroad engine regardless of manufacturer approval. See ethanol and stabilizer. |
| Phase separation | The point at which ethanol-blended gasoline that has absorbed enough water splits into a gasoline layer and a corrosive water-ethanol layer. It cannot be reversed by shaking or adding more fuel. |
| Choke vs. primer | A choke restricts air to enrich the mixture for a cold start; a primer bulb manually pushes extra fuel into the carburetor. They solve the same problem differently and are not interchangeable procedures. |
Electrical and generators
| Term | What it means |
|---|---|
| Running watts (rated/continuous) | What a generator produces hour after hour: the figure to size a load against. See Portable generator loads and transfer connections. |
| Starting watts (surge/peak) | A brief higher output available for a second or two while a motor spins up. Not sustainable, and not the number to size continuous load against. |
| kW vs. kVA | kW is real power delivered to a resistive load; kVA is apparent power before accounting for a motor load’s power factor. A generator’s continuous rating is usually the more relevant of the two for household use. |
| Automatic transfer switch (ATS) | A device on a standby generator that switches a building’s supply between utility power and the generator automatically, and prevents both sources from being connected at once. See standby generators. |
| Interlock kit | A mechanical device fitted to a breaker panel that prevents the main breaker and a generator breaker from both being switched on at the same time, used with a portable generator as a lower-cost alternative to a transfer switch. |
| Amp-hours (Ah) | A battery pack’s stored charge rating. Compares packs only within the same voltage platform. See Nominal battery energy and compatible tools. |
| Watt-hours (Wh) | Volts multiplied by amp-hours: the figure that compares battery energy storage honestly across brands and voltage platforms. |
| Cold cranking amps (CCA) | The current a starting battery can deliver at −18°C for 30 seconds. The number that predicts whether it will crank a cold engine. See starting batteries. |
| BCI group number | A starting battery’s physical case size and terminal layout code (e.g. U1, U1R). Says nothing about capacity or cranking power. |
Cutting and chain
| Term | What it means |
|---|---|
| Chain pitch | The distance between drive links, measured as half the span across three consecutive rivets. See chain, pitch and gauge. |
| Chain gauge | The thickness of the drive-link tang, which must match the bar’s groove width. |
| Drive links | A count of the tangs around the chain loop, not a measurement: it sets the chain’s overall length. |
| Low-kickback chain | Chain with raised depth gauges and shaped tie straps that limit how much wood a cutter can take during a kickback event, classified under ANSI/OPEI B175.1. See chainsaw kickback. |
| Chain brake | A band that clamps the clutch drum to stop the chain within a fraction of a second, triggered by the front hand guard or by inertia. |
| Kickback | The sudden upward-and-back rotation of a saw when the upper quadrant of the bar tip contacts material. See chainsaw kickback. |
| Mulching blade / lift | A mower blade profile with a curved, longer edge that holds a clipping in circulation under a closed deck; “lift” is how far the trailing edge turns up to move air. See mower blades. |
| Deck spindle | The bearing assembly a mower blade mounts to and spins on. Wear here produces a rumble before it produces an uneven cut. |
Pressure, hydraulics and airflow
| Term | What it means |
|---|---|
| PSI (pounds per square inch) | Pressure: the force concentrated at the nozzle. The headline number on a pressure washer box, and only half of what finishes a job. |
| GPM (gallons per minute) | Flow: how much water moves. Multiplied by PSI gives cleaning units, the figure that compares two machines. See pressure washers. |
| Unloader valve | The pressure-washer component that diverts flow back to the pump inlet when the trigger is released, preventing pressure buildup in bypass. |
| Two-stage pump (log splitter) | A hydraulic pump that delivers high flow at low pressure for a fast approach, then switches to low flow at high pressure once resistance rises. See log splitters. |
| CFM vs. MPH (blowers) | CFM (cubic feet per minute) is volume of air moved; MPH is air speed at the nozzle. Neither alone predicts how well a blower clears wet, packed leaves: the force behind the airflow does. |
| Auger vs. impeller (snow blowers) | The auger is the front spiral that gathers snow; the impeller is the fan that throws it out the chute. A two-stage machine has both; a single-stage machine’s auger does both jobs. |
| Shear pin | An intentionally weak pin connecting an auger to its shaft, designed to break before the gearbox does when the auger strikes something solid. |
| Total dynamic head (water pumps) | Suction lift plus discharge head plus friction loss in the hose and fittings: the figure a pump’s GPM rating is plotted against. The same pump moves far less water against a high head than a low one. See water pumps. |
| Centrifugal vs. positive-displacement (pumps) | A centrifugal pump spins an impeller and its output falls smoothly as head rises; most portable utility and trash pumps are this type. A positive-displacement pump moves a fixed volume per cycle regardless of head and can build damaging pressure against a closed line. |
| Solids-handling rating (trash pumps) | The largest solid particle diameter a pump’s impeller can pass without clogging. Buying on GPM alone while ignoring this is the standard mistake for water that is not clean. |
| CFM @ PSI (air compressors) | Air delivered per minute at a stated pressure: the only version of a compressor’s CFM figure that compares fairly across machines. A CFM number with no PSI attached is not comparable. See air compressors. |
| Duty cycle (air compressors) | The fraction of time a compressor motor can run before it needs to rest and cool, commonly well under 100% on a consumer-grade unit, which is why one can seem to "run out of air" under sustained use while working exactly as designed. |
| Single-stage vs. two-stage (air compressors) | A single-stage compressor reaches final pressure in one piston stroke and suits intermittent use up to roughly 150 PSI. A two-stage compressor cools air between two compression steps, reaches higher pressure more efficiently, and is built for continuous shop or trade duty. |
Standards and regulatory bodies
| Term | What it means |
|---|---|
| ANSI | The American National Standards Institute, which accredits the process behind a voluntary consensus standard without writing the technical content itself. |
| OPEI | The Outdoor Power Equipment Institute, the trade association that develops the B175 (handheld tools) and B71 (turf care equipment) standard series with ANSI accreditation. |
| UL | UL Standards & Engagement, which develops and certifies against safety standards including UL 2201 (generator carbon monoxide shutoff) and the UL 62841 series (electric and battery hand-held and lawn-and-garden tools). |
| CPSC | The U.S. Consumer Product Safety Commission, the federal agency that publishes product recalls and proposes mandatory safety rules. See checking a recall. |
| EPA (40 CFR Part 1054) | The federal regulation governing emissions and labeling for small nonroad spark-ignition engines. See the emission control label. |
Glossary: questions
Does the glossary state a specification for a specific model?
No: every entry defines what a term means, not a figure for a named machine. A definition of what "chain gauge" or "running watts" means is a different claim from a specification for a specific model, and the guide only makes the first kind.
Why are the glossary entries grouped by system rather than alphabetically?
System grouping keeps related measurements together. For airflow, compare CFM with the stated pressure or test conditions; for batteries, distinguish stored watt-hours from instantaneous output and working runtime. Once the definition is clear, the linked equipment guide supplies the surrounding calculation or service decision instead of leaving the term isolated from its application.
What is the difference between chain pitch and chain gauge?
Pitch is the distance between drive links, measured as half the span across three consecutive rivets; gauge is the thickness of the drive-link tang, which must match the bar's groove width. They are two independent measurements a replacement chain must match separately, not two names for the same thing.
Does a higher CFM or a higher MPH rating matter more when comparing two leaf blowers?
Neither alone, since CFM (volume of air moved) and MPH (the air's speed at the nozzle) describe two different properties of the same airflow, and a blower can rank higher on one while ranking lower on the other. The force behind the airflow, which depends on both figures together, is what determines how well a blower clears wet, packed leaves: see the leaf blower and trimmer equipment page for the full comparison.
Why does the glossary define both PSI and GPM for pressure washers, rather than just PSI?
Because PSI (pressure) alone is only half of what finishes a cleaning job: GPM (flow) is the other half, and PSI multiplied by GPM gives cleaning units, the figure that compares two machines fairly. A high-PSI, low-GPM machine and a lower-PSI, higher-GPM machine can produce very different real-world results despite one number looking more impressive.
What is the difference between kW and kVA for a generator?
kW is real power delivered to a resistive load; kVA is apparent power before accounting for a motor load's power factor. For household use, a generator's continuous kW rating is usually the more directly relevant of the two figures.
What is the difference between an automatic transfer switch and an interlock kit?
An automatic transfer switch, used with a standby generator, switches a building's supply between utility power and the generator automatically and prevents both sources from connecting at once. An interlock kit is a mechanical device fitted to a breaker panel that prevents a portable generator's breaker and the main breaker from being switched on simultaneously: a lower-cost, manual alternative rather than an automatic equivalent.
Why does amp-hours (Ah) compare batteries only within the same voltage platform?
Because amp-hours measures stored charge without accounting for voltage, so a higher Ah figure on a lower-voltage platform can store less energy than a lower Ah figure on a higher-voltage one. Watt-hours (volts multiplied by amp-hours) is the figure that compares battery energy storage across different brands and voltage platforms.
What is total dynamic head, and why does it matter more than a water pump's GPM rating alone?
Total dynamic head is suction lift plus discharge head plus friction loss in the hose and fittings: the figure a pump's GPM rating is plotted against, since the same pump moves far less water against a high head than a low one. A GPM number quoted without its corresponding head is only true at one specific condition, not a general performance claim.
What is the difference between a single-stage and a two-stage air compressor?
A single-stage compressor reaches final pressure in one piston stroke and suits intermittent use up to roughly 150 PSI. A two-stage compressor cools air between two compression steps, reaches higher pressure more efficiently, and is built for continuous shop or trade duty rather than occasional home use.
What is phase separation, and can it be fixed by adding more fresh fuel?
Phase separation is the point at which ethanol-blended gasoline that has absorbed enough water splits into a gasoline layer and a corrosive water-ethanol layer. It cannot be reversed by shaking the container or topping it up with fresh fuel: once separated, the affected fuel has to be removed and disposed of under local fuel-waste rules, not blended away.