When it comes to using a pressure washer for cleaning, the debate often centers around two critical metrics: volume and pressure. Whether you are using a power washer to clean cars, trailers, concrete, or sewer lines, both volume and pressure play significant roles in the effectiveness of your cleaning efforts.
Higher flow rates are associated with more efficient rinsing and moving of dirt/debris. High-pressure is important when you need to cut through grime or film on a surface. However, the most important thing to consider is the specific job requirements and then determine the cleaning method that will be most effective.
There are several factors. Let's dive into the details to understand which is more important and how to balance these two metrics for optimal cleaning.
What’s More Important for Cleaning: Volume or Pressure?
It is difficult to say whether you should prioritize volume or pressure without knowing the specific application. The needs of cleaning tasks vary so the answer will differ depending on the nature of your job. There are several cleaning tasks where flow rate is often more critical than PSI, but there are also tasks where higher pressures should be prioritized.
Volume and pressure provide different benefits in the cleaning process. Volume is most beneficial when there is a large amount of debris which needs to be rinsed away. This is commonly needed when cleaning out stock trailers that contain manure or rinsing out tanks that had sediment left behind.
To illustrate the effect of larger volumes of water when cleaning, consider a flat surface with a small pile of dirt spilled on it. If you were to pour a few ounces of water onto the pile of dirt, you would have very little cleaning effect. In fact, this would likely just make things worse. However, if you were to pour a five-gallon bucket of water on the pile it would have a drastic effect on the dirt. The more water used the more it will rinse and push away the dirt.
Pressure is also vital, especially in scenarios requiring concentrated cleaning. Pressure is most beneficial when the cleaning process involves material that is difficult to remove. This is typically needed in scenarios such as preparing surfaces for painting which often requires removal of old paint or grime.
Let’s look at some specific examples:
Tank Washout
- Requirement: High flow, medium pressure
- Reasoning: The goal of tank washout is to move and remove material efficiently. This task requires a large volume of water (high flow) to carry away debris and residues. The pressure does not need to be extremely high, as the primary objective is volume movement rather than breaking up tough deposits.
This video shows high-flow, medium pressure cleaning in action:
Concrete Cleaning
- Requirement: Low flow, high pressure
- Reasoning: Cleaning concrete surfaces, such as driveways or industrial floors, requires breaking up tough, stuck-on dirt, and stains. This task benefits from high pressure (3,000 to 4,000 psi) to effectively dislodge and remove stubborn grime, while a moderate flow rate (3-4 gallons per minute) may be sufficient to carry the debris away.
Cleaning Units: A Practical Comparison Tool
To compare the effectiveness of different pressure washers, we can combine the flow rate and pressure output of each using a metric known as cleaning units. This is calculated as:
Cleaning Units = Pressure (PSI) × Flow (GPM)
Example 1:
- Pressure washer with 4 GPM and 3,000 psi
- Cleaning units: 4 × 3,000 = 12,000
Example 2:
- Pressure washer with 3.5 GPM and 3,500 psi
- Cleaning units: 3.5 × 3,500 = 12,250
These examples show that despite different flow rates and pressures, the cleaning units are quite comparable (12,000 vs. 12,250). Another important aspect of comparing pressure washer is the horsepower (HP) needed to operate the pressure washer. This is a topic that is covered in this guide to horsepower sizing.
Compare Pressure Washer Options Here
Understanding Flow Rate & Pressure
Flow Rate measures the flow rate of water coming out of your pressure washer. Essentially, it indicates how much water is being used per minute. This is typically measured in GPM (Gallons Per Minute). A higher GPM means more water flow, which can help rinse away dirt and debris more effectively.
Pros of High Flow
- Faster cleaning by covering a larger area with more water.
- More effective rinsing action, removing debris efficiently.
Cons of High Flow
- Higher cost for machines with higher GPM ratings.
Pressure (Pounds per Square Inch) measures the pressure of the water coming out of the nozzle. Higher PSI means more forceful water, which is crucial for breaking up tough grime, stains, and dirt on surfaces. PSI helps in dislodging dirt but may not be as effective alone without sufficient water flow to wash the dirt away.
Pros of High Pressure
- Better at breaking up tough dirt and grime.
Cons of High Pressure
- Splatter
- inefficiency
- may damage delicate surfaces
The Relationship Between GPM, PSI, & Nozzle Size
It’s important to note that GPM, PSI, and your nozzle size are interrelated. The relationship between pressure and flow rate in a pressure washer system is inversely proportional when other factors like the nozzle size and pump capacity remain constant:
- Increasing Flow Rate (by enlarging the nozzle or enhancing pump capacity) leads to a decrease in Pressure.
- Decreasing Flow Rate (by reducing the nozzle size or lowering pump capacity) leads to an increase in Pressure.
Understanding this relationship is crucial for optimizing the performance of a pressure washer to match the specific cleaning tasks and ensuring efficient and effective cleaning results.
Balancing GPM and PSI: Spray Nozzle Orifice Size Matters
If we compare two machines that produce 3000 PSI but one delivers 8 GPM and the other only 2 GPM, the one with the higher flow will provide more efficiency. This is provided that you use the proper size spray gun and nozzle to accommodate the flow of the machine.
While both a 2 GPM and an 8 GPM machine can produce the same PSI, the water output volume makes a significant difference in cleaning efficiency. The orifice size in the nozzle adjusts to maintain the PSI:
- A 2 GPM machine requires a smaller orifice to build up pressure with less water.
- An 8 GPM machine has a larger orifice, allowing more water to flow while maintaining the same pressure.
This means that an 8 GPM machine can clean surfaces much faster and more thoroughly than a 2 GPM machine, even if both are rated at 3000 PSI.
What to Consider When Selecting a Pressure Washer:
- Focus more on GPM for general cleaning efficiency.
- Ensure PSI is adequate for the types of surfaces and dirt being cleaned.
- Higher GPM models are ideal for professionals and large cleaning tasks.
- Higher GPM means faster cleaning times and better rinsing.
- Adequate PSI ensures dirt and grime are effectively broken up.
Shop High-Volume Pressure Washer Units:
Conclusion
When choosing a pressure washer, it's essential to consider both GPM and PSI. However, for most cleaning tasks, prioritizing GPM over PSI can lead to faster, more efficient cleaning. By understanding and adjusting these metrics, you can optimize your pressure washer’s performance for any cleaning job.
