That is true. But a size 4 nozzle is not twice the diameter of a size 2. It’s twice the area.
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Be careful “cleaning” concrete with machines over 20 HP
With the wrong nozzles, 20 HP or greater “cleans” concrete by “removing” concrete.
Ask me how I know.
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You guys are making this so much harder then it has to be.
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Any size machine with wrong nozzle will remove concrete. From your homedepot one to a belt drive anything. Not just 20hp engines
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How long did you run the #2s?
It’s about the only thing in Australia I can get cheap - so about every four weeks 
Or did you mean how long before I decided to try the others? Years.
I’ve got a fair bit of flat work coming up in the next few weeks. I might do a side by side if I get time.
The 25020’s have the pressure to get mould off that the 25025’s just don’t touch.
But - I can walk much faster with the 25025’s if the surface isn’t mouldy compared to dragging your feet with the 25020’s.
Go figure!?
The horsepower just removes it faster with the GPM
Ummmm… huh? ^^^
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I have the same machine. I run 25025 on mine. I believe racer has 25030 on his whisper wash for his 4gpm. I dont notice a difference but when i go to buy some spares ill probably purchase the 25030
Y’all got me curious. I run 4x 2502 on my 4 bar WW / 8gpm. It works. But I just ordered some 25025 for the heck of it
huh? uhm?
It’s really hard to say. There are so many variables that come in to play. I would just stick to what works best for you. Have you checked the pressure lately running a single nozzle?
This has nothing whatsoever to do with horsepower…
You can destroy concrete with a 6.5hp machine. You can also safely clean concrete with a 50hp machine, or a 200hp machine for that matter. Choose the correct tip/tips to produce the right pressure.
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…and flow 
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So @Innocentbystander got me wondering about how much my machine actually put out so I started looking around and found this equation on another forum and if I did my math right my 4 gpm 4200 psi is really barely making 3200 psi with the Honda GX 390. I guess trumping up the specs on these machines is normal but it does make it harder for new guys to get the right equipment to allow the machine to perform at its capability. Here is the equation please if someone sees that my math is off let me know.
4gmp x 3200 psi / 1450 x 1.5= 13.24 hp
I use psi times gpm divided by 1100
4200*4/1100=15.2 horse power required. Vendors lie. Knowledge is power
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I did yours, it put me closer to 3500 either way it wasn’t what I thought I was getting thank you for sharing.
the last part of this thread is very interesting…having been a car sales manager in a previous version of myself I tend to follow the “Don’t Believe the Hype” world view. I just bought the Simpson 4400psi/4gpm /420cc unit.
I found the AAA triplex pump is a 4040 model #, Guessing that’s the 4000/ 4gpm pump?? (LOL) pressure gauges out at pump outlet- 4000psi with trigger pulled with both white and green tip. Will have to bucket test for GPM… I guess I think of it as like car MPG… Lab results in a perfect world.
This unit has worked great on my fence restore project as long as I don’t get too close and cleans more width faster than than my 2800/2.5 Generac. plus old wood gets a dark semi transparent stain anyway, so you refresh and hide defects
this thread also has me curious to see results of my 15 year old driveway and walks on Monday with the Mi-T- M 14" SC with the 2 - 25020 nozzles. sound like with 50ft hose and Hyped up machine specs I should get great results. will take pics. or please correct me if I am wrong
25025 nozzles. Unless you just enjoy watching the cream wash down the drain.
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Quickest best at reasonable cost- place to get them?
and I need the 25025 or 25030 1/4"?? right? manual doesn’t say.
schedule wise, I may just have to turn down unloader a bit, and maybe hit TSC and get the extra 50’ hose and test with pressure gauge before starting
this has all been wand washed in the past and I get pretty close with the white tip on tough areas… haven;t screwed it up yet, but used the smaller generac machine…
