Partners or Never the ‘Twain Shall Meet? Pressure Washing and Waterjetting

By Diane M. Calabrese / Published November 2022

Less is more got us to soft washing, but sometimes more is better.

     It’s possible to pare an apple with a butter knife, but why not just reach for a paring knife and save a lot of time? So it is with the continuum from pressure washing to waterjetting. 

     Make that a logical continuum with water flowing at any rate at one end. If it’s flowing, there is pressure. At the other end put the highest psi yet achieved.

     Do the ends of the continuum ever meet? In the sense that there are projects on which both pressure washers and waterjetting equipment play a role, yes.

     “Surface preparation and coating removal is an example of an area where the two tools complement each other,” says Stephen LaViers, who is in regional sales and rentals at Hammelmann Corporation in La Porte, TX. “Pressure washing—less than 5000 psi—is used to remove mold and mildew. Waterblasting—greater than 5000 psi—follows to remove coating and prepare the substrate for new coating.”

     The pressure washer is the wrong tool for coating removal, but it is sometimes deployed (or tried), says LaViers. “Sometimes it takes +30,000 psi to remove a coating,” he explains. 

     Of course, there are situations in which waterjetting technology should never be deployed. “Fiber-glass and wood substrate are not candidates for waterjetting, for instance,” he says.

     Terminology for the points along the pressure-per-square-inch continuum is not as definitive as rock or scissors. We know that at the low-pressure end, professional organizations such as PWNA [Power Washers of North America] aim to clarify that power washing depends on an array of tools, including pressure washers and soft washing systems. But colloquially (and beyond), pressure washing and power washing are used interchangeably. 

     A parallel issue in the psi lexicon involves waterblasting and waterjetting, which are often used interchangeably. Some industry practitioners put waterblasting in a high-pressure range and reserve waterjetting for ultrahigh-pressure tools.

     Pressure range is what LaViers uses to define the difference between pressure washing and waterjetting. He considers less than 5000 psi pressure washing and greater than 5000 psi waterblasting. That demarcation aligns with that used by the WJTA [Waterjet Technology Association].

     Ultrahigh waterjetting introduces another dimension to the use of water as a tool. The psi with which the water moves from an orifice is not the force with which it accomplishes work. That force derives from the velocity at which it moves. The addition of abrasive puts the velocity to good use by conferring momentum—and cutting capabilities—on the abrasive.

     Forty years ago, pressures of 36,000 psi were considered amazing and ultrahigh pressure. Working in combination with abrasives, they allowed breakthroughs in machining, for one. Now, waterjets in the range of 90,000 psi are familiar to all and go-to tools in cutting.

Perspective

  Jimmy Peck, the president of WJTA, also cites 5000 psi as the boundary between pressure washing and waterjetting. But he notes that the demarcation gets a bit murky in general conversation. (To tack back to our analogy, how often do we just say knife and assume the listener will know which sort of knife because of the context?)

     “I think most of the population, or at least a large percentage of it, use those two terms pressure washing and waterjetting synonymously, unaware there’s a difference,” says Peck. “The WJTA sees 5000 psi as that cutoff.” 

     Irrespective of the pressure or the tool, safety is the priority, says Peck. “The same health and safety guidelines that we follow in pressures above 5000 psi should really be followed at lower pressure because even pressures around 100 psi can be enough to penetrate the skin or cause an injury.” 

     And it’s something Peck follows through on daily in his workplace. “Here at MPW Industrial Services, where I’m general manager, we observe the same safety protocols regardless of psi—all levels of water pressure must be respected.” 

     Tools working in tandem sometimes get taken for granted. Pause to think a bit about the frequent need for cleanup following use of a waterjetting tool, and there will often be a pressure washer in the picture.

     “I think there are many examples of where waterjetting is necessary to remove some sort of debris or fouling that requires ultra-high-water pressure,” says Peck. “But, in order to do a final rinse or a final cleaning of the equipment or the affected area, a hot water pressure or water pressure unit is necessary because a high-pressure waterjet is simply too powerful to accomplish this.”

     Peck elaborates with candor, “Typically, the higher-pressure waterjets make a mess. The lower pressure washer is going to help clean it up.”

     The reverse situation is a bit more complex. “If you send a pressure washer, but you really need a waterjet pump, you’ll know quickly because you won’t be able to get the job done,” says Peck.

     “Generally speaking, in industrial cleaning it’s more common to run higher pressure than necessary because people often think higher pressure is always better,” says Peck. “Also, if there are restrictions on water usage, it might be advantageous to use high pressure/low flow versus lower pressure/higher flow.” 

     A thorough understanding of surroundings is needed before using any tool. There may be a setting in which waterjetting tools should not be used. “In general, if waterjetting is going to cause damage to an asset owner’s equipment or it poses a health and safety risk that can’t be contained, then I would say that a waterjetting technology should not be deployed in those situations,” says Peck.

Partners

     We don’t advocate for wasting water, but when watering a garden, most of us have fiddled with the opening of a garden hose. We have blocked part of the aperture with our finger and immediately increased the pressure of the water exiting the hose. If we dropped a little stone into that higher pressure stream, we could propel the stone.

     Direction and speed of the water (its velocity) would determine how much momentum the stone had. Bump that velocity up to the ultrahigh pressure range and add abrasive (as noted in first section), and the abrasive has enough momentum to cut through substrate as tough as granite and steel.

     Results of CNC [computer numerical control] waterjet cutting leave less residue to be cleaned away than does waterjetting to remove coatings, but there’s still cleanup to be done. A pressure washer may be used to help with the cleanup if rinsing tools are not built into the system.

     Of course, the effort to automate and consolidate as many processes as possible means that rinsing (or cleaning) is no longer a stand-alone process. NLB Corporation, located in Wixom, MI, has developed semi-automated systems that put operators of waterjetting equipment in cabs on tracks, which keeps them out of harm’s way when debris flies. It also manufactures robotic systems that can be remotely controlled for jetting in tight spaces.

     Will fully automated waterjetting systems eliminate the need for pressure washing equipment in the same setting? Probably not. Sometimes a plant floor must be cleaned or walls must be washed, and lower pressure machines coupled with surface cleaners and/or wands are the optimal choice.

     Less is sometimes more. It might be possible that a homeowner would try to get a powered street sweeper into a two-car residential garage, but a broom would be the method of choice.

     In terms of function, pressure washers and related tools like sewer jetters (even though they get labelled “jetters”) that operate below 5000 psi are mostly tied to cleaning applications, while waterjetting machines accomplish tasks like coating removal and cutting. Jetters used to unclog sewers operate at pressures lower than 4000 psi in most cases.

     When fats, oils, and greases (FOG) accumulate in sewers, the result is an ugly mess, an invitation to rats to stay and multiply and a prelude to disaster (a sewer backup when the narrowing aperture closes). Sewer jetting tools supported by remote video monitoring prevent many backups (and sewer replacements).

     Despite the tenacity of FOG, using the lowest pressure possible to clean out sewers is the best option. Most sewers (infrastructure) are in a fragile state—corroded, breached in some places, and sometimes still wooden.

     The National Institute of Standards and Technology (NIST), which is part of the U.S. Department of Commerce, has a keen interest in waterjet machining. NIST sees waterjet machining as a way to elevate the level/competitiveness of manufacturing across the country, and it recognizes the environmental benefits of the methods.

     Environmental benefits include the use of less energy and water, containment of residues, and no
generation of heat. In fact, NIST envisions waterjet machining as an integral part of a path toward a robust and revived manufacturing sector in the United States. 

     There’s no doubt waterjet machining and other waterjetting technologies will play such a role, and pressure washing equipment will continue to be a partner in the efforts.

     Clean, cut, unclog, and more—water and pressure get it done.