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First time posting, but love the forum. Hopefully this hasn't been asked before. I could only find the question in relation to electric, not gas engines. I own a pressure washing business, and my issue is the commonly used engines for commercial grade washers don't have enough power to get both the maximum psi and gpm at the same time. There would be a significant cost savings if I could tie two predator 459 or duromax 440 engines together on one pump instead of buying one large motor. My plan was to have a mounting plate, either 3/8 aluminum or steel with vibration dampers underneath, and the motors in line, one on each side, with the pump in the middle. Grooved vbelt drive with a 4 groove pully on the pump shaft, and 2 groove pulleys on the engine shafts. That way each engine could operate from its own grooves on the 4 groove pump pulley. My questions are below.

  1. Most importantly, is this design, or maybe another, efficient enough that at least roughly 90% of the combined power would translate to the pump shaft? If not then the idea is likely moot.

  2. Would the vibration be a good deal greater on the pump shaft, and should an idler pulley be installed on each belt?

Hoping that someone can point me one way or the other before I spend 2.5k+ on trying it out. Thanks everyone!

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  • $\begingroup$ By "gas" do you mean gasoline / petrol? You're on an international site and "gas" in many countries means butane, propane, methane or LPG. You might Edit your question to clarify. $\endgroup$
    – Transistor
    Mar 19, 2023 at 18:51

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So check out the centrifugal pulley drives - one common use is in chainsaws and mower drives.

They can deliver lots of power and very low friction when one engine is not needed.

But you might find the pump can do pressure or flow but not both at maximum...

Or, use a larger engine with sufficient power with a variable pump or swash plate pump. Those pumps can be varied from 0 to full output while held at constant rpm.

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  • $\begingroup$ Thank you very much, I'll look into that! $\endgroup$
    – Davidk
    Mar 20, 2023 at 1:54
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That's because those motors are both toys and you want a real commercial grade engine. Hondas, Briggs Vanguards, and Kohlers will run several pumps into dust. 6000 hours at full throttle at the industrial-rated rpm is to be expected (then put new rings, bearings, and valves in and off you go again). They cost \$2000 - $3000 depending on options. They have been really hard to find since Covid but are starting to become more available now.

You already have the geared pump? Which one?

As an example, say you buy a geared pump that recommends an 18-19 hp engine. The default here is 3600 rpm, which is silly. You could get the smallest "big block" Vanguard with a nominal 27 hp rating. The commercial rating is about 22 hp at 2650 rpm. Setting the engine governor for 2650 and gearing the belt drive accordingly will give you years of trouble-free service.

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  • $\begingroup$ If I was running an 8 gpm I'd be happy with the minimal pressure/gpm loss. I prefer higher volume, around 11-12 gpm. Right now I run two udor 38/20 gr pumps, but the honda 690 doesn't put out nearly enough psi for my preference. We can work with it, but I'd like the full psi from the pump. People have been having issues with Hondas, finding both parts and the whole engine, which has scared me off from them. I know the pred may not last as long, but they are readily available and cheap. Plus if I can get more psi out of a pump and save about $1800, then that's a win. I run 1/2 hose as well. $\endgroup$
    – Davidk
    Mar 20, 2023 at 2:02
  • $\begingroup$ That said, I really liked the advice about the gearing, but everything I've read said Hondas are made to run at 3600 rpm and running them slow longer term is bad for them? Is that not correct? $\endgroup$
    – Davidk
    Mar 20, 2023 at 2:04
  • $\begingroup$ @Davidk so gearing can increase or decrease output rpm. Which means the engine can still run at 3600, but what is the power output at 2600? Wasn’t that the point being made? $\endgroup$
    – Solar Mike
    Mar 20, 2023 at 7:22
  • $\begingroup$ The Honda 650 is pretty happy at 3600, but as we already know, it won't do the job even when brand new. And it won't run for as many hours at that speed. You will probably experience a lot of nuisance stalls when you release the handle and the pressure bypass pops. It a good engine, it's just not the right engine for your application. And yes, finding one is a nightmare. $\endgroup$
    – Phil Sweet
    Mar 20, 2023 at 9:06
  • $\begingroup$ Sorry, meant 690. Same deal. $\endgroup$
    – Phil Sweet
    Mar 20, 2023 at 9:14

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