Why do belt driven pumps last up to twenty times longer than direct driven pumps?


Why do commercial grade belt driven pumps outlast direct driven pumps?  Imagine the cost of buying a new pump once a year for a decade instead of buying a single machine that lasts.  The upfront investment, along with regular maintenance, will cost less money in the long run.  Let’s take a look at what makes belt driven pumps last so much longer.

Belt driven pumps (as seen in Figure 1) can rotate up to one million (1,000,000) times less per day compared to a direct drive pump (as seen in Figure 2). Rotational speed is measured by “RPMs” (Rotations Per Minute). RPM indicates how many times a pump or motor makes one complete 360° rotation within one minute. Why is that important to know before you buy a pressure washer? Consider driving a truck on highway at 65 MPH with the truck stuck in 1st gear.  Now imagine the damage that would do to your vehicle. That is what it is like for a high-speed direct drive pump if it is used on a daily basis. Belt drive pumps are the opposite; they’re like driving in 5th gear when on a highway.  There are no problems because everything is running at a much lower RPM!

The heat coming off of a typical air-cooled single cylinder engine is normally around 250°F, possibly up to 900°F on a twin cylinder engine (Figure #1). A direct driven pump is mounted directly to the back of an air cooled engine running at 250°F to 900°F. That extreme amount of convection heat is transferred directly into the pump. On figure 1, you’ll also notice that the muffler is very close to the pump and unloader. This means radiant heat from the muffler is also transferring to the pump assembly. Finally, you have metal-to-metal heat transfer, since the pump driven by the crankshaft of the engine. Altogether, that is enough heat to cook a turkey.

Belt drive pumps (figure 2) have no extreme heat transfer problems. The pump is not directly connected to the engine, nor is it in the path of the 350°F to 900°F airflow of the engine. Ambient temperature air is drawn in from the front recoil side of the engine, and then passes over the outside cooling fins of the engine. It exits the muffler side of the engine around or above 350°F. Take a look at the belt drive pressure washer in figure 2. See how the muffler is on the left side of the fuel tank and in rear of the engine where the heat exits the engine? Notice that the belt driven pump is mounted on the far right side of the frame. This is the best setup.

Vibrations from the direct drive pump mounted to the engine also can increases pump wear and can often damage the crankshaft of the engine. When we pull the pumps off the engines, very often the crankshaft keyways are damaged. Some pumps even fuse themselves to the engine, requiring them to actually be cut off for repairs.

I have tested all different types of pressure washer pumps, but nothing last longer than an industrial grade belt driven pump.

Light Duty vs Heavy Duty Pressure Washer

If you have any questions, please post them in the comments, call me at 800-666-1992, or email me at dans@hcsclean.com!

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