Understanding PSI (Pounds per Square Inch)-Pressure Washer


Water pressure from the pressure washer is measured in pounds per square inch or psi. This pressure is the amount of force delivered to the surface being cleaned, and is the critical factor in breaking debris from that surface. PSI is determined by the orifice size of the nozzle tip and the flow rate (gallons per minute). For labeling purposes, the standard nozzle size for measurement is a #4 orifice, which delivers 4.0/gpm at 4,000psi. As nozzle sizes increase or decrease, psi fluctuates accordingly.  The nozzle chart in our catalogue lists the psi with different flow rates and nozzle sizes. Nozzle selection depends on the work, and the amount of pressure a surface can withstand before it is damaged.

While psi is a constant at the tip of the nozzle, the pressure decreases as its distance from the targeted surface increases. Experienced power wash contractors understand how to manipulate these distances for maximize both cleaning power and their time.

Because the pressure that contractors need varies a great deal, they get the most out of their equipment by adjusting the distance between the nozzle and the surface being cleaned. For less pressure and heat in the application, they hold the nozzle back, thereby increasing the distance from the surface. For increased pressure and heat, they hold the nozzle closer. Larger contract cleaners will use pressure washers that produce 4 to 6 GPM at 3,000 to 3500 psi at 200⁰ F for concrete cleaning. Vehicle washing can be accomplished using 1,500 to 2,000 psi.

Heat provides a tremendous advantage when cleaning grease and oil. A few Vent-a-Hood cleaners will use steam heated to 310⁰ F, while others will use units that deliver 3,000psi at 200⁰ F. However, some vent cleaners use electric, 1,000 PSI cold water washers hooked up to hot water (they must hand scrape more for this to be effective).

The psi for decks and other wood surfaces varies from 200 to 3,000, and must be carefully tested first, as too much pressure will cause the wood to fur. If this happens, you will need to sand the affected areas with fine sand paper or steel wool to knock off the furred surface. Many professional deck cleaners use a variable pressure wand (like the ST-54 36″ Double Lance Wand) so they can adjust the pressure as necessary. Using low pressure, and letting the chemical (like Powerwash.com’s DSR-49 Deck and Siding Restorer or DSR-50 Deck and Siding Restorer plus Stripper) do the work helps avoid furring. Test the effect of pressure on the underside of the deck.

Pressure Washing Tips, Tricks, and Techniques

Pressure Washer
  • Before pressure washing make sure to always fog or presoak the surface with a detergent, degreaser, or chemical presoak. Presoaking reduces wash time and chemical cost.
  • Hot water is a better solvent than cold water.
  • Always rinse detergent off the surface before it dries.
  • Commercial contractors generally use 4 to 6/gpm at 1500 to 3,500/psi for most cleaningapplications. An exception to this is wood cleaning. Here 500 to 2,000/psi is preferred with chemical cleaning to reduce the furring of the wood. Water flow rates of less than 4 gallons per minute – found on general consumer (homeowner) units – are not high enough to be competitive because of increased cleaning time, which raises labor costs.
  • Chemical dilution is largely a matter of personal preference. For most mobile power washing work, chemical costs run from three to five percent of gross sales, labor accounts for 30 to 45 percent, and fuel for heat is two to four percent. If chemicals and heat costs are reduced, labor costs increase because of increased work time. A slight increase in chemical and fuel costs actually reduces labor costs, because work time decreases.  Work smarter – soap and heat are cheaper than labor – not harder.
  • Washers with chemical injection before the pump, start out with the metering valve open 1/4 turn. Then adjust as needed.
  • W-200 Spray Wax is similar to spray wax used in coin-operated car washes. Apply the wax hot and follow with a cold rinse for fine surfaces like cars and pickups. On heavier surfaces, like homes and trailers, the cold rinse is not necessary. The application of wax extends the life of the wash job, makes subsequent cleaning easier, and enhances the overall appearance. Note: Because the application of wax will extend the life of a wash job, some contractors choose not to use it because they prefer to wash more often. Thereare two sides to this. While the use of wax may reduce your income because of the extended life of your cleaning, the enhanced appearance and extended life may generate more business because of the perceived quality of the work.
  • For fleet washing, wax in the rinse water reduces dirt adhesion and lessens subsequent washing time. In heavy concentrations, wax reduces cement adhesion on concrete trucks.
  • The tips provided in this section will reduce brushing to about five percent of the total workload. Typically, contractors only brush in the spring or the fall, or as needed.
  • Brushing once or twice per year at a specified time allows the contractor to prepare and schedule extra, short-term, help for those designated times.
  • For Environmental Power Washing Techniques read Report 507.


How do I clean clogged nozzles in pressure washers?


1. Always disconnect your spray wand from the gun before cleaning your nozzles!
2. Clear the nozzle with a small rigid piece of wire such as a paper clip.
3. Flush the nozzle backwards with water.
4. Reconnect the wand to the gun
5. Restart the pressure washer and depress the trigger on the spray gun.
If the nozzle is still plugged or partially plugged, repeat number 1-4.

If the previous procedure does not clear the nozzle, replace with a new nozzle.

What is Power Washing?


Power washing, or pressure washing, is the growing application of high pressure water spray. Produced by specially designed pumps, this spray is a hundred times more powerful than the typical garden hose. On concrete it is used to remove unsightly mold, bubble gum, and other dirt stains. Wooden decks are returned to the look of new wood, void of graying and fatigued finishes. And on houses, the appearance of siding (namely aluminum and vinyl) is greatly improved by removing pollution, mildew, and other signs of neglect.

Generators Residuals

Gasoline Generator GEN-13000-1MSE

Take Control of the Situation

The next time a severe storm rolls through the area, don’t be left in the dark, without the ability to cook, heat water, do laundry, or keep your family happily occupied. Instead, be prepared with the purchase and installation of a cost-effective residential generator from the knowledgeable professionals at GraciHart Electric. No longer will you and your family be uncomfortable and bored during power outages. Our line of residential generators power on automatically in the event of an outage, and operate quietly and dependably for days, some models can even operate, uninterrupted for weeks. If you prefer, we can elevate the equipment above flood lines. Another notable advantage to installing a generator for home use is that in the event of an electrical power outage your home’s security system will remain functional, keeping your family and property safe and sound.

The next time your neighborhood loses power during a thunderstorm, don’t let another outage inconvenience you and your loved ones. Call on GraciHart Electric and let us help you choose a residential generator that will meet all of your emergency power needs.

Service Question of the Day!?


Describe the most common types of jobs you do for your clients.

We service on industrial equipment, water reclamation, oil water separators, closed loop water treatment systems, car wash equipment, waste water evaporators, wash water evaporators, generators, pumps, hot water power washer, construction equipment, soaps, chemicals, degreases, bioremediation products, & hot & cold pressure washer parts rentals repairs.

Generator Fun Facts

Portable Generator
Portable Generator

–If you actually want to plug something in to your generator which lives more than 20 feet away, prepare to spend as much on heavy gauge power cords as you would for yearly passes to the water slide park for a family of four.


–They are every bit as heavy as you feared. Luckily, they have wheels. This is when you’ll discover that the place you want to put your generator does not have pavement.


–You apparently need about a million watts of generator capacity if you plan on actually using a major appliance–like, say, your electric razor. That’s because–at least according to the “sizing charts” that accompany generators–even the most innocuous appliances are given to wild streaks when–like the Hulk when you make him angry–they surge to 20 times their original power. That fridge you’ve been monitoring at 22 watts all year? According to lore, it can surge up to 1750 watts when something (the defroster?) sets it off. Consider yourself warned.


–GFCI outlets and computers don’t mix. This is the big one, and really the whole excuse for writing this post. You see, a GFCI outlet (Ground Fault Circuit Interrupter) is standard on most portable generators, and is used to make sure you don’t kill yourself by taking the genny with you as you take a quick dip in the pool. The idea is, if it ever sees even a tiny disparity in the generated power vs. What it senses on the neutral wire, it’ll throw the breaker so that your loved ones will be safe as they fish your body out of the shallow end.