There is a huge misconception about what a gear driven power washer is. Because it is “almost” directly coupled to the engine and not assembled as a belt drive, people assume it cannot pull water from a tank. This is incorrect.
I ran my first gear driven machine in 2017 because I had a fleet washing contract that required I get a machine immediately rather than later. What did Fred and I do? Build a quick gear driven system that took us only a few days to get up and running, rather than a belt drive that would have taken a week for us to construct.
I was hesitant about this process because my first machine was belt driven and I had no issues with the system that we built that had been in use for 2 years. But the amount of time it took to fabricate it to Fred’s standards was unreasonable for this situation and I needed something immediately.
We ran our gear driven system to wash garbage trucks and the 2 5.5 gallon machines we built were “somewhat” a success. Originally we used a Predator and a Duramax engine to save on cost and for fast delivery. The Duramax shook so much that after 2 jobs the fuel tank rattled off and most of the bolts on the engine were loose (this is after 12 hours of use). The predator lasted about 1 month and then the muffler broke off while running and shot a blue flame, causing my cleaning technicians to shut down. We switched our engines to Kohler and these issues stopped occurring.
The gear driven system had nothing to do with the engines failing, they were just extremely tempting because of the cost of the engines (at the time 289$ free shipping).
I spent in the ball park of 6 hours of my time to take off the gear assemblies, replacing the engines with new ones and spending the time to haggle with harbor freight to get a refund on the predator engine. The 6 hours I wasted cost me more than just buying 2 Kohler engines from lost opportunity.
Back to gear drives! I ran a Comet RWS5535 (https://washmart.com/collections/pumps/products/comet-rws-5535-s-solid-shaft-pressure-washer-pump) with a Comet gear box from 2017 to… It still runs today. This bottom machine has ran for 5 years, and is used weekly. The hour usage on it is approximately 1200-1500 hours (it has generated in the ballpark of 150,000$ over this time frame for my cleaning accounts).
When I then built another trailer with 2 more gear drives (this time with Kohler CH730s) We have run the same 2 engines and the same 2 Comet RWS6040 pumps since 2018. We have had to change the unloader valve twice and the two machines have been running for nearly 2000 hours. This machine has been rented, abused and beat down and still going!. This convinced me that gear driven units weren’t as bad as I had been advised.
Now what is the difference between a gear drive and a direct drive? A direct drive is directly coupled to the engine and generally runs anywhere from 3000 RPM to 3600 RPM (3400 RPM is the industry standard). What does this mean? It means that the RPM on the pump is so high, that it will struggle to create a vacuum (venturi effect) and can sometimes have difficulty pulling water. What we have found with direct drive pumps is that many CAN pull from a tank without positive pressure, but the lifespan on the pumps is greatly reduced. CAT makes a DX model pump that actually was designed to pull water from a tank, and does this well for a direct drive.
A gear drive is an intermediate piece between the pump and the engine reducing the RPM ratio. If you have a 3600 RPM engine (in the USA this is standard) and run a gearbox rated at 1750 RPM, you will have nearly a 2 to 1 ratio (meaning the pump is rotating at 1750ish RPM) and the pump can pull water from a tank with ease, without positive pressure. This is the same principle as when you use a 6 inch pulley on the pump and a 3 inch pulley on the engine. You will get approximately a 1750ish RPM with a belt drive when you use this pulley ratio.
One thing we have found with direct drives is they are actually very reliable pumps as long as they are not left running without being used. If you don’t release the trigger gun and allow the water to travel, a direct drive that has a closed loop will recirculate the water causing the water to get hotter every time it recirculates. Eventually the temperature gets over 150 degrees and begins to melt your water seals and check valves (the non metallic parts).
Gear driven machines are an interesting wrench in our industry. Where a belt driven machine is what I consider a more reliable system (when built properly) it has one major drawback, power transfer. What we have found is that with a gear driven IGX800 we can get 4200 PSI at 8.5 GPM when pairing with the AR XWAM8G35 (https://washmart.com/collections/pumps/products/xwam8g35n-pump) . When we ran the same pump and engine as a belt drive the maximum we could get was 3700 PSI at 8 GPM. And why is this substantial? It is substantial because they both use the same amount of energy but one does produce more work. What we have recommended is if you are a sole operator and mechanically adept at fixing your own equipment, gear drive is the way to go. If you are running a larger company with multiple trucks and using multiple operators I recommend going with a belt driven system.
Direct drives are still great tools as backup power washers and we always recommend to our customers that they have 1 inexpensive direct drive cart on standby in case their primary rig goes down. We have been running the same Comet ZWD4040 (https://washmart.com/collections/pumps/products/zwd4040) on a direct drive Kohler since 2017 and the amount of hours on it is unknown (but heavy).
Some people have had entirely different results with the products above I have mentioned and it is fair that some of this information can become “subjective”. But with the volume of work we put out this has been our experience. Between Fred and I, there is extensive experience between building and using the equipment.
When we ran the same pump and engine as a belt drive the maximum we could get was 3700 PSI at 8 GPM. And why is this substantial? It is substantial because they both use the same amount of energy but one does produce more work. What we have recommended is if you are a sole operator and mechanically adept at fixing your own equipment, gear drive is the way to go. If you are running a larger company with multiple trucks and using multiple operators I recommend going with a belt driven system. Direct drives are still great tools as backup power washers and we always recommend to our customers that they have 1 inexpensive direct drive cart on standby in case their primary rig goes down. We have been running the same Comet ZWD4040 on a direct drive Kohler since 2017 and the amount of hours on it is unknown (but heavy). Some people have had entirely different results with the products above I have mentioned and it is fair that some of this information can become “subjective”. But with the volume of work we put out this has been our experience. Between Fred and I, there is extensive experience between building and using the equipment.