Engineering:Pressure washing

Short description: Use of high-pressure water jet for cleaning hard surfaces

A pressure washer is used to remove old paint from a boat.

File:Kärcher K3.550 pressure washing using a Dirtblaster wand attachment.webm Pressure washing or power washing is the use of high-pressure water spray to remove loose paint, mold, grime, dust, mud, and dirt from surfaces and objects such as buildings, vehicles and concrete surfaces. The volume of a mechanical pressure washer is expressed in gallons or liters per minute, often designed into the pump and not variable. The pressure, expressed in pounds per square inch, pascals, or bar, is designed into the pump but can be varied by adjusting the unloader valve or using specialized nozzle tips. Machines that produce pressures from 750 to 30,000 psi (5 to 200 MPa) or more are available.

The terms pressure washing and power washing are used interchangeably in many scenarios, and there is some debate as to whether they are actually different processes.

A pressure washing surface cleaner is a tool consisting of two to four high-pressure jets on a rotating bar that swivels when water is flowing. This action creates a uniformed cleaning pattern that can clean flat surfaces at a rapid rate.

Hydro-jet cleaning is a more powerful form of power washing, employed to remove buildup and debris in tanks and lines.

Areas of Use

Pressure washing is employed by businesses and homeowners to reduce allergies, minimize hazards, and improve aesthetics. A pressure washer is used to clean residential surfaces such as gutters, roofs, decks, paved areas, siding, cladding, and windows. They are also used to clean commercial surfaces such as office buildings, churches, schools, hospitals, and other large buildings.

Equipment

Commercial pressure washing trucks. Set up with 2 hot water machines each and a window cleaning trailer.

Concrete cleaning with a surface cleaner.

There are 2 main types of pressure washers. Hot water pressure washers and cold water pressure washers. Each have their own purpose. Hot water pressure washers are best for washing flatwork (concrete driveways, walkways, etc) that can have grease or oil residue. They are best to use when cleaning parking garages, drive thru's, and gas stations. Hot water is achieved with the use of a burner unit. Hot water helps emulsify grease and oil on surfaces and helping to remove it quicker. Cold water machines are most commonly used to wash residential areas. Siding, gutters, roofs, decks, and windows can all be cleaned effectively with the use of a cold water pressure washer.

Surface cleaners are a pressure wash tool that allows the cleaning of larger surface areas. There are many models. A surface cleaner is made of a disc shaped housing, a rotating swivel, and a set of bars attached to the swivel with nozzles at the end of the bar. The water enters the surface cleaner through a trigger gun at the top of the handle bar, travels through a hose, the swivel, and the bar ending up passing through specifically sized nozzles to spray the surface and remove dirt and grime.

Nozzles

Pressure washer nozzles alter the direction of flow and velocity of the water. Nozzles allow users to reach a greater distance or apply more pressure to a difficult-to-clean surface. Nozzles are color-coded for easy identification, with black nozzles covering the widest degree (65°) and red nozzles covering the least (0°). Great care should be taken when using a 0° nozzle as it can cause injury to both the user and passersby, as well as damage to surfaces. Nozzles are sized based on the GPM and PSI of the machine.

See also

• Washdown

Further reading

• Steel Structures Painting Council (1995), Surface Preparation and Cleaning of Steel and Other Hard Materials by High- and Ultrahigh-Pressure Water Jetting Prior to Recoating. Pittsburgh, PA. SSPC
• U.S. Water Jet Technology Association, Recommended Practices for the Use of Manually Operated High-Pressure Water Jetting Equipment, St. Louis, MO: US Water Jet Technology Association, 1987