Understanding the Importance of a Pressure Washer's PSI and GPM
Many guys ask me, "What is the difference between a pressure washer and a power washer?" In truth, those of us in the industry generally use these terms interchangeably, but one pressure washer manufacturer, Hydrotek, does make a distinction. According to Hydrotek, a power washer is a lighter-duty version of a pressure washer.1 When I tell guys this, the next question usually comes back, "What is considered a light or heavy-duty pressure washer?" This can be even more subjective, but it is based on the pressure washer PSI rating.
To the average homeowner just using a power washer to clean their decks and siding, a 1,500 PSI (Pounds Per Square Inch) unit may seem like high pressure. I mean, that is more pressure than the garden hose, and it can knock the dirt off of their surfaces. On the other hand, to the contractor using a pressure washer to clean parking lots with a lot of tar and grime, a rating of 1,500 PSI would seem week. The contract cleaner would probably consider a unit rated high pressure, which is more in the ballpark of 4,000-7,000 PSI. With that in mind, here is a general breakdown:
1,000 - 1,900 PSI: This PSI is on the low end, and is considered a residential unit. This type of pressure washer is good for the average homeowners to handle most household and automotive cleaning jobs, and is usually a hand carry electric model.
2,000 - 2,900 PSI: This is a moderate strength unit used heavier residential tasks. These units are commonly sold as either electric or gas pressure washers.
3,000 - 6,900 PSI: These high pressure models are what professional pressure washers and contractors usually use. They are commonly used in commercial and industrial settings, and can run on either gas or diesel.
7,000 - 50,000 PSI: These ultra-high pressure washers are also known as water blasters. Water blasters are used in industrial and engineering settings to clean and alter large equipment, buildings and structures such as bridges.
PSI rating isn't the only spec to keep in mind when pressure washing, however, there is also the GPM rating (Gallons Per Minute). It is said in the pressure washing industry that the pressure (PSI) does the cleaning, but the water flow (GPM) cleans it faster. Pressure washer PSI and GPM work together to provide the most efficient cleaning. Getting the job done faster also means saving fuel, so not only can a good pressure washer save you time, it can also save you money."
To illustrate the importance of this concept, we have a spec known as CU (Cleaning Units). CU is simply a number derived from multiplying a machine's PSI and GPM, but it is a representation of the amount of time a pressure washer will take to clean a surface.2 The higher the CU, the less time it will take to clean, and again, the more time you save, the more money you save.
A 2,000 PSI rated machine that runs at 4 GPM will produce a CU of 8,000 (PSI X GPM = CU). Similarly, a 2,500 PSI rated machine that runs at 2 GPM will result in a CU of only 5,000. In this case, because it has a higher CU rating, the lower PSI machine will get the job done faster. Of course, you cannot use 500 PSI to clean a house or 1,200 PSI to clean a parking lot, but when comparing pressure washer machines, it is important to consider all the factors that determine the eventual output in order to find the model that best suits your needs and budget.
Sources:
- How to Pressure Washer Your House
- Q & A about Pressure washers
Sources:
- How to Pressure Washer Your House
- Q & A about Pressure washers
