Bypass
A flow path that recirculates pump output instead of delivering it through the spray nozzle. Cat Pumps describes arrangements returning water to the pump inlet or an external tank; the actual layout matters.
CU — cleaning units
The arithmetic product of PSI and GPM, as defined in the cited SIMPSON manual. Use it to understand a specification, not as proof of surface safety or a guaranteed cleaning result.
Dilution
Reducing a concentrate's strength according to its product directions. Simple Green's cited instructions distinguish application methods and dilution choices; one product's proportions do not define another cleaner's use.
Dwell time
The period a cleaner stays on the surface before the specified next step. Follow the actual directions: the cited Simple Green cleaner must not dry before rinsing. There is no universal dwell time.
GFCI — ground-fault circuit interrupter
An electrical protective device that helps guard against shock from a ground fault. The SIMPSON manual identifies GFCI protection alongside other electrical precautions; it does not make unsafe use around water acceptable.
GPM — gallons per minute
A flow-rate unit: how much water moves in a minute. State US GPM explicitly when comparing international specifications, and keep flow distinct from pressure.
Nozzle orifice
The nozzle's opening. Cat Pumps' selection chart relates orifice size and nozzle number to flow at a stated pressure. Opening size and spray angle answer different questions.
PSI — pounds per square inch
A pressure unit expressing force per unit area. It describes a different quantity from GPM; a pressure figure alone does not specify how much water a machine delivers.
SDS — safety data sheet
A document describing a product's hazards and safety precautions. In its Canadian WHMIS guidance, CCOHS explains that an SDS provides detailed hazard information but may not contain every site-specific work procedure. Read it alongside the applicable product directions.
Spray angle
The angle of a nozzle's spray pattern, expressed in degrees. Cat Pumps treats angle selection separately from nozzle-number selection; the angle is not the orifice size.
Thermal relief valve
A temperature-responsive valve that releases hot water in relevant pump systems so cooler water can enter. It addresses heat during recirculation; it is different from a pressure-relief device.
Unloader
A pressure-control device commonly paired with a trigger gun. Cat Pumps describes it as setting system pressure and relieving pump pressure when the gun closes. This does not mean every downstream component is depressurized.
Sources & references
- CM60976 Use and Care Manual, part 7111613, English Rev. 8, June 2022 — SIMPSON. Checked October 27, 2026.
- FAQs: pressure controls, bypass, thermal valves and nozzle identification — Cat Pumps. Checked October 27, 2026.
- WHMIS — Safety Data Sheet (SDS), revised May 28, 2026 — Canadian Centre for Occupational Health and Safety. Checked October 27, 2026.
- House & Siding Cleaner — Pressure Washer Concentrate: U.S. directions — Simple Green. Checked October 27, 2026.