Under pressure to choose the right pressure washer? The following guide will help you determine which pressure washer is right for you and alert you to issues to be aware of when buying and using pressure washers.
Choice:
PSI vs. GPM vs. CU, Electric vs. Gas, Hot vs. Cold, Belt Drive vs. Direct, Camshaft vs. Axial Pumps. There are many options when choosing a pressure washer that can complicate your decision. The important thing to keep in mind is to match your needs to the equipment, which will keep your projects running smooth, and keep your overhead costs low.
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. The real challenge is to match these to your applications.
Pressure washers rated at 1300-2200 PSI are for only light, occasional chores such as cleaning a small area, lawn equipment, cars, trucks, mud or dirt. Models rated at 2200-3000 PSI are designed for more frequent users and for larger jobs such as cleaning vinyl and wood siding easier, whether the surface is being prepared for painting or to remove dirt and grime. Units rated at PSI 2200-3500 are for professional use on heavy-duty projects. Contractors and commercial users turn to this category to clean their heavy equipment, construction sites, paint preparation and other demanding projects. Some units are rated above 3500 PSI, however there are few advantages or applications for this extreme pressure.
Electric vs. Gas
Pressure washers are either electric or gasoline powered. Electric pressure washers are low maintenance and quiet. These generally are for light duty. They are handy where you need to work on small confined area, however you need to run power to them and have a pressurized water source. Also the National Electrical Code and Underwriters Laboratories now require ground fault circuit interrupters (GFCIs) be use when operating an electric pressure washer.
Gas models are recommended for tasks that require more power, such as paint prep, heavy vehicle cleaning, or cleaning heavily soiled concrete.. Gas models start with PSI of 1750 and go as high as 4000. They also offer more portability, as they are not limited by electric cords. Also some gas models can draw water from a source other than the garden hose, which allows you to work away from a water line. All gas models have 4-cycle engines and run on regular unleaded gas.
Heated Water vs. Un-Heated Water
Most pressure washers spray unheated water which is fine for most applications. However if you need to remove very heavy grease then you may need to have to opt for a Hot Water Pressure Washer, utilizing either a propane or diesel burner. The downside is that you should expect to pay a lot more for these. Also, the heater is an additional part that requires maintenance and care. Do not run heated water through cold water systems, since this can damage the pump O-rings and gaskets.
Pumps: Belt vs. Direct, Wobble, Axial, Camshaft
The water pump is really the heart of the pressure washer system. The main difference between belt drive and direct drive pumps 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. Direct drive pumps are directly mounted to the engine or motor, which eliminates the extra cost of gearbox, pulleys, belts, etc. Expect to pay 10-30% premium for belt drives given the same PSI, GPM, pump brand, and horsepower. However there is little actual difference in the pumps.
The basic pump models are 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). The axial pump is similar to the wobble, but features a larger oil reservoir and larger bearings to allow the pump to run cooler to extend life. The axial pump also has larger cylinders, which enable it to generate higher PSI and GPM ratings than a standard wobble. Although performance is improved, the axial still is effected by piston spring resistance that translates in to lower performance and efficiency versus a camshaft pump.
The camshaft pump offers many benefits over the "wobble" and "axial-style" pumps. Due to the use of connecting rods and positive action pistons (like a car engine), a camshaft pump is much more efficient (85% efficient) than an axial-style pump, which must overcome spring tension and friction to generate pressure. Another benefit of this design is that a camshaft pump generates much less heat and therefore runs cooler than an axial-style pump, and heat is the number one cause of failure in a high-pressure pump. For this reason, a camshaft pump can easily provide 1,000 hours or more of operation before needing any maintenance, whereas an wobble or axial-style pump typically has a life span of 200-600 hours, after which the pump often can not be repaired economically. Also, when a camshaft pump does require maintenance, the easily accessible pump head, replaceable cartridge-type valves, and ceramic piston sleeves makes repair quick and easy.
Operation
As in all power equipment make sure the operator uses the proper safety gear such as eye, foot, hearing protection. The unique hazard for pressure washers is the water stream, which can cut the body or inject toxins into the bloodstream. Also when using detergents it may be necessary to protect the exposed skin and to use a respirator to prevent inhalation of the cleaning agents. Only use chemical solutions recommended by the manufacture.
Tips on Proper Spraying Techniques
Operator error is the leading cause of user dissatisfaction when it comes to power tools, and pressure washers are no exception. There are three ways to control the cleaning power of your pressure washer:
Adjust the throttle on the gas engine to control speed. Some units also may have a regulator knob on the pump that can adjust the pressure (if so equipped).
Adjust the spray pattern at the nozzle. Choose the widest pattern possible for spraying when starting the job and adjust the pattern to a narrower angle until you find a suitable pattern. Remember to temper power with coverage ability when spraying.
Finally, the easiest way to regulate the cleaning power of your pressure washer is distance from the surface you are cleaning. Begin several feet from the surface and slowly move closer, adjusting the spray pattern as necessary. Hold the nozzle a uniform distance from the surface to ensure that no part of surface is cleaner that another.
Nozzles and Tips
Many units feature nozzles with a variable spray pattern (0-60 degree angle), while others have individual quick connect tips with a pre-set spray angle. The size of the nozzle influences both pressure and flow rate. The spray angle of the nozzle also plays an important role. The wider the spray angle, the lower its ability to cut through dirt.
A wide pattern (40-60 degrees) will distribute the impact of water over a large area, resulting in excellent cleaning action with reduced surface damage risk. The optimum angle for spraying water against a cleaning surface is 45 degrees.
A fan pattern (15-25 degrees) balances stripping power and washing. It is useful for moving dirt and is the best choice for cleaning large flat surfaces such as patios and driveways.
At 0 degrees, a narrow stream pattern delivers a high impact force resulting in maximum deep cleaning in concentrated area. The narrow stream is best suited for concrete masonry or brick and can be used to remove paint or tough dirt.
Detergents
Detergents can dramatically reduce cleaning time and assist in the removal of tough stains, grease, bugs and dirt. Apply them with a low-pressure spray and allowing them to soak into the surface to break down the dirt and grime. Many detergents are customized for pressure washer use on specific cleaning tasks. Only use detergents intended for pressure washers. Thicker detergents such as dish soap will clog the chemical injection system and potentially damage your pressure washer. Be aware the EPA prohibits point source discharge of pollutants without a permit. While this may not be an issue on the job site when using only water, if you are cleaning equipment with detergents in shop or storage yard on a continuing basis, you should check on obtaining a permit and/or installing a waste water recover system.
Maintenance:
Engine maintenance is the same as on other gasoline powered equipment. Check your oil level daily, some models have automatic low oil shutdown switches to protect the engines. When storing over the winter, in addition to standard engine storage preparation such as draining gasoline (or adding a fuel stabilizer), distributing oil through the spark plug hole, you should also prime your water pump with anti-freeze. (Follow the manufacturer instructions from the manual). If using detergents, flush the water pump with clean water after each use. On gas models slowly pull the start rope five times to purge water from the pump.
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