There are by some counts more than 250 American manufacturers of pressure washers, with more  than a few claiming to be the largest. A manufacturer producing mostly small inexpensive units for home use is seldom a good choice for a large pressure washer that will receive heavy duty use. Manufacturers that are too small will seldom offer competitive prices, engineering that will provide adequate safety and efficiency, or emergency service. Some pressure washers look like a haphazard collection of ill-fitting metal parts while others seem to be mysterious boxes with blinking lights. Since they are all designed to do exactly the same thing, how do you pick one that's right for you?
Gallons, Pressure, and Horsepower
Although higher pressure may seem more impressive, more cleaning time will usually (but not always) be saved by using more of the unit's horsepower to pump more gallons per minute. The same 2 hp motor will produce 2.1 gpm at 1400 psi, or 3.0 gpm at 1000 psi. With a typical nozzle, the actual surface impact of the 3 gallon flow can be nearly 20% greater than the impact of the 2 gallon flow, even though the 2.1 gallon flow is being delivered at greater pressure. Specialty nozzles can also increase impact dramatically.
Looked at another way, once enough pressure is generated to break the bond between dirt and surface, the only real way to reduce cleaning time is to flush the loose dirt away faster with more water.
In choosing a pressure washer, remember that the amount of work it will do is limited by the horsepower of the unit. Unfortunately, nearly all manufacturers exaggerate gallons per minute or pressure, leaving the horsepower rating of the motor as the most reliable way to compare competing units. A small unit with a 2 hp motor is a full one-third more powerful than a similar one with 1½ hp. More power means less time spent cleaning.
A typical commercial car wash gun produces 2 to 3 gallons per minute at around 1000 pounds pressure, requiring 1½ or 2 electric horsepower. Units producing 3 gpm at 1500 psi are popular in industrial installations. The minimum recommended for a pork producer is 2000 psi with 4 gpm flow. This would require an electric motor larger than 5 hp. Most companies use a 5 hp motor and mislead you a little, delivering only about 3.6 gallons at 2000 pounds pressure.
Remember, buying a unit that is too small or otherwise inadequate will cost many times the price difference in extra clean-up time and repairs.
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Belt Drive vs. Direct Drive
The larger the pressure washer, the more often you clean, and the longer you spend cleaning each time, the more you need belt drive. One leading pump manufacturer privately admits warranty claims on direct driven pumps are 4 to 5 times higher than on similar pumps that are belt-driven! Belt driven pumps usually operate at lower RPM with a larger oil capacity. A pump coupled directly to a motor or engine places strain on the motor and mounting bolts and will absorb extra heat and vibration that will shorten the life of the unit. Most direct drive pumps do not really contain enough oil to do the best job coping with the extra heat. With direct drive, anything that happens to the motor happens to the pump and vice versa. Even "high quality" direct drives are frequently assembled without due care, will require more maintenance, may be more difficult to repair (pumps nearly impossible to remove from engine or gear shafts are common), and will require major repairs more often. Direct drives can be built cheaply in a compact and efficient package. But small inexpensive direct drives, called "hobby washers" in the industry, may have a life expectancy of only 100 hours! Improvements such as gear reduction drives, shock absorbing mechanisms and more precise machining, have made direct drives better, but at a cost that begins to rival belt drive. For continuous or frequent use they cannot overcome the inherent advantages of a quality belt drive.
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Water Pumps
The GENERAL brand of pump dominates the pressure washer market. The CAT brand of pump is common in the car wash market. Other brands of pump may be OK, but be sure parts and service for them will be conveniently available at reasonable cost. It's a good idea to call the pump manufacturer and find out if the pump model on the unit you are considering is actually rated for the gallons and pressure claimed by the pressure washer manufacturer. Over-speeding or over-pressuring a smaller pump to make it perform like a larger one is an easy way for a manufacturer to cut his costs at your expense.
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Accessories, Parts & Repairs
Don't take parts availability and service as a given! One manufacturer refuses to supply you with a parts diagram or a parts list and doesn't I even list pump oil type in the owner's manual! Another will void your warranty for using a pressure hose or accessory not bearing its own (very expensive) brand name. Are the fittings standard and commonly available? Some dealers will threaten your warranty if you don't buy your cleaning chemicals from them.
All pressure washers have wear items that will require repair or replacement, despite what any salesman tells you. Unloader valves will need replacement and high quality pumps will require new packings after several thousand hours of use, even under the best conditions. Most conditions aren't the best.
Poor water quality and equipment abuse are the most significant causes of premature wear in items like pump check valves and packings, the unloader, and the hot water coil. Look for brand name components and easy accessibility to things like pump check valves, the unloader and burner components. Beware of pressure washers with pumps and parts available from only one source! You will pay dearly for the all the proprietary parts inside that sleek box for which no substitutions can be made!
The right accessories, such as rotating nozzles, brushes, hose reels, and the proper chemicals, will increase the productivity of your unit dramatically. If you have many different employees cleaning, consider an automatic shutoff system for your unit, but beware of shutoff systems that may cycle your unit on and off should a leak develop while the unit is unattended. Your dealer should be knowledgeable about products and techniques that will save you time and money.
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Hot Water
Are you sure you need a hot water unit? The water heating coil is the most expensive single component of a hot water pressure washer. Find out if the brand or model you are considering is known for coil troubles and look for the longest warranty. Make sure it can produce water that is hot enough to meet your needs while providing protection from overheating.
The coil should be made of boiler-grade pipe, not "tubing," and should be Schedule 80 if the unit operates at 2000 psi or more. Coils smaller than one-half inch ID are prone to liming that lowers operating pressure and fuel efficiency and must be periodically removed. Coils that are too short will yield lower fuel efficiency and water temperature, as well as generating dangerous excess heat around the lightly protected burn chamber. Coils wound too close together make them susceptible to sooting that will reduce efficiency and interfere with proper combustion. There are wide variations in burner design and efficiency, but there is no difference in burner efficiency between vertical and horizontal coils.
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