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- Pressure Washer Tech Talk - The technical aspects of pressure washers
Apex Unlimited.com: Blog Posts
In this section you'll learn more about the technical aspects of pressure washers. We'll review things such as gallons per minute, PSI, CU, pump types, how a pressure washer works, a nozzle chart and many other technical questions-find the answers here. Don't worry, we'll try to keep it in down to earth language as best as we can!
How does a pressure washer work?
Water from a suitable supply is supplied through a garden hose to the inlet of pressure washer. An electrical or gasoline driven high pressure pump generates water pressures in excess of 1500psi and in some commercial models as high as 4000psi.
A high pressure hose delivers the high pressure to the pistol and the lance. With the trigger of the pistol open, the water leaves the nozzle of the lance as a sharp, concentrated jet with high cleaning power. Believe it or not, despite its remarkably better cleaning performance a pressure washer uses dramatically less water than a garden hose thus protecting the environment and conserving water supplies. Typically a garden hose with 60 psi water supply pressure uses up to 600 gallons of water per hour, whereas a pressure washer uses only about 180 gallons per hour but supplied at a pressure of 1500psi and upwards.
What is PSI, GPM and CU?
When you are shopping for a pressure washer, one way to compare units is by the cleaning power of the water. PSI (pounds per square inch) refers to the amount of cleaning pressure the unit is capable of developing. GPM (gallons per minute) refers to the actual flow of water through the unit or rate a which the unit sprays water. Some manufacturers have started to use CU (cleaning units) which is simply PSI X GPM.
While its true that higher pressure (PSI) helps you to clean faster, this isn’t the only factor. The other more important part of cleaning quickly is the volume of water or Gallons per Minute (GPM) the pressure washer puts out. Let’s take an example:
Say you have one pressure washer that cleans at 3.5 GPM and 4000 PSI and one that cleans at 4.0 GPM and 3500 PSI. The one with the higher pressure cleans faster, right? Nope, they actually clean about the same. How do we know? To see the true speed of cleaning you simply multiply the Gallons per minute (GPM) and the Pound Per Square Inch (PSI) and you get the total cleaning units (CU) cleaned by the particular pressure washer. So, back to our example: 3.5 GPM X 4000 PSI= 14,000 CU and 4.0GPM X 3500 PSI=14,000 CU-both pressure washers have the same cleaning power. You can compare the total cleaning units of any pressure washer on our site by plugging in the GPM and PSI numbers and multiplying them.
What are the different pump types: Belt, Direct, Wobble, Axial, Camshaft?
The water pump is the heart of the pressure washer system. Let’s talk about our first two different types of pumps- belt drive and direct drive pumps. The big difference between them is that belt drive pumps run at a lower RPM and are insulated from engine or motor vibration, and therefore may extend the pump live. On the other hand, direct drive pumps are mounted directly to the engine or motor. This eliminates the extra cost of gearbox, pulleys, belts, etc. Look to pay between 10-30% more for belt drives given the same PSI, GPM, pump brand, and horsepower and so forth.
And then there are three basic pump models: the wobble, axial, and the camshaft. The wobble pump has lower performance and efficiency (70% efficient) due to piston spring resistance on each stroke (pistons must push against the pressure in the pump PLUS the resistance from the springs). An axial pump is similar to the wobble, but has a bigger oil reservoir and larger bearings. This helps the pump to run at cooler temperatures and hence allows extended pump life. The axial pump also has larger cylinders. This allows it to generate higher PSI and GPM ratings than a wobble pump. Yes this pump is an improvement on the wobble but the axial pump is still affected by piston spring resistance. This translates into lower performance and efficiency versus a camshaft pump.
The camshaft pump offers lots of benefits over the "wobble" and "axial-style" pumps. Think of a car engine, with its pistons & rods. This is kind of like what a camshaft pump is like. It too has connecting rods and positive action pistons. This allows it to be quite a bit more efficient (85% more) than an axial-style pump, which must overcome spring tension and friction to generate pressure. This design also generates much less heat and runs cooler than an axial-style pump. This is a plus because heat is the number one cause of failure in a high-pressure pump. What does this mean in the long run? Well, a camshaft pump can easily provide 1,000 hours or more of operation before needing any maintenance. On the other hand, wobble or axial-style pumps typically have life spans of 200-600 hours. If the wobble or axial style pumps break down they can’t often be repaired economically. But to their advantage when a camshaft pump finally needs maintenance it has features that allow for easy and quick repair. These features are an easily accessible pump head, replaceable cartridge-type valves, and ceramic piston sleeves.
Thanks for getting an overview of some technical details of the inner workings of pressure washers. We hope this section will make you an informed, educated consumer, which allows you to buy with confidence!