I thought most engine manufactures under rate their HP ratings, which is why a gx390 is able to push 4/4k
Pressure pro and other unreputable companies typically are allowed 15% leeway in actual numbers. That’s why they can legally lie in their advertisements. Math and physics don’t lie though.
In reporting to the EPA, engine manufacturers have some leeway to fudge horsepower ratings by about 15 percent.
Sometimes, the same engine is advertised as having different horsepower ratings depending on how it’s sold.
“There are slight adjustments that get them there, but it’s the same engine,” Hebbard said.
Ariens buys engines from Briggs, Kohler,
CETA goes along with this.
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How often do you change the check valves on your udors?
I bought a box of 6 about 10 years ago. I’ve used half of them between 10 pumps since then. I don’t change the pump oil but every couple of years.
Well, here’s the reply from Udor:
“Very common configuration that is used. They work great together. Have a great day!”
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Thanks for that @dcbrock very kind of you 
I’ve learnt a bit from this post from other too 
The only configuration I’ll go with must have 3000 psi, nothing less. I recently had trouble with mould at 2500psi that the surface cleaner wouldn’t touch (left it sat over it, nothing). Both the wand and my small Mosmatic moved it instantly with just 500psi more.
I get that flow is king so to speak, but there’s a point where that drop in pressure becomes an issue.
Thanks for all the input so far!
Have an awesome day 
Do you not pre and post treat?
I wash concrete with less than 1800 psi, and it always turns out great. The only time i need/want more pressure is on commercial because it can handle it. And even than its not always needed.
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I do indeed. Yet it still happened. This was the surface. The mould was like mini lichen and the surface was very hard. If you look at the bottom right picture, those white spots were after 3500 psi - I still had to spot treat with neat SH.
Sand? What sand?
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I usually use 200 ft of hose for housewashing. If I’m doing concrete I’ll usually take off 100ft of hose to pick up a few psi. I do notice a difference.
With my 4/4 a typical suburb driveway would take me about 1hr or sometimes 1hr 15min…depending on how dirty and if there’s a sidewalk to door. With the 5.6/2500 it takes me about 30-45 min. The cleaning part I have to go over twice/3 times sometimes even with pretreating (if extra dirty). Even with that I still clean quicker with the new pump. But the rinsing is so much faster. There’s some sacrifice when using a gx390 for surface cleaning because you’ll need the extra psi when upping your gpm. Taking the 100ft of hose off has helped some.
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No sand in those gaps my friend. They are 1-2mm gaps on a sloping surface.
Nice try.
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@Barry1 Makes perfect sense. Especially the rinsing, which is half the job right there. Thanks for the positive input
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Can anyone tell me approximately what PSI and flow this pump would give using a GX390?
AR North America RKV55G40HD-F24
It says it needs 15HP to deliver the full 5.5 @4K but the GX390 is only 13HP…
Thank you!
Hey Steve have u tried Spitwater Australia yet? They have general/interpump on their machines.
I have the 21lpm , 15lpm and 29lpm machines.
The 15 has been going strong for years and I got the other 2 in the last 12months . They seem to be ok at this stage.
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Hey Clayton
I’ve got an Interpump WS201, but the oil went milky - it’s about 10 years old, so I think it’s time for a new one!
I’ll have a look at Spitwater, but last time I did, they were VERY expensive for everything - like surface cleaners, machine and even nozzles.
That pump I posted last, works out at $620 delivered. That’s very cheap compared to Australian prices.
If that one is no good, I’ll have to get a reduction gearbox, plus a pump which is getting expensive just for a GX390.
That is direct drive pump which runs at the same rpms as the engine. A gear reduction box will reduce it down 2.2/1 so the pump will run at much slower rpm and cooler (similar to a belt drive). Gear drive pumps also pull water like a belt drive where direct drive you’ll need more gravity pulling from a buffer tank.
The Australian numbers confuse me a bit. I hope you find what you’re looking for there down under.
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You could get 2500 psi or maybe a little more at 5.5 gpm with the GX390. As already stated, that’s a direct drive pump; you’d be better off finding a gear drive.
Btw, 5.5 @ 4k with only 15hp seems very optimistic. I think 17 or 18hp would be more realistic.
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Thanks for the info @Infinity
5GPM @3000 psi is the goal. For me, thats 4 litres per minute more than the 4@4 it has.
As I understand it, the lower speed from the gear drive lengthens the life of the pump - but a gear drive will cost more on top of the pump. The extra cost isn’t worth it to me, unless it was a Udor pump or other expensive one.
If you’re using your PW commercially 40+ hrs a week then yes a gear drive pump is worth the money if you’re upgrading from a direct drive.
Even with an Udor pump…a direct drive pump runs too hot. I heard it explained once…imagine driving 1000 miles in a car in 1st gear…every day…engine won’t last long. But if you drive 1000 miles everyday in 5th gear…you’re fine.
If you’re using it around the house or light residential then direct drive should be ok…especially Udor.
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