About to buy a pump and gearbox


So I did my last 4GPM flat work job today. Had enough. Takes too long.

Time to use one of my GX390’s to its potential.

I’ve got a nice deal on an InterPump WS202 and a RS500 gearbox. This combo is reportedly going to give me 5.5GPM @ 2900psi.

Before I buy it tomorrow, WILL it actually help me surface clean?

I get the house washing would be better, same as the rinsing of the flat work, but will the added GPM but REDUCED psi (from a 4@4ish) help me at all?

@Innocentbystander I’d appreciate your comments on the figures please (not so much the brand - I heard you don’t like ‘em!)


…and the nozzles people with 5.5GPM use in a 20” SC would be helpful as the chart says 6.5/2 = 3.25 and there isn’t one :slight_smile:





What? No wise monkeys :joy:


Wise monkeys are asleep at this hour. I on the other hand am not all that wise.:smirk:


Yeah, @DisplacedTexan pointed out the time difference just yesterday!

Hopefully someone will post something tomorrow before I buy it :+1:t2:


I get 6.6gpm at 2300 with my gear drive pump on gx390. I pretreat and post treat and can move much faster than with my 4/4. I use 25035s in my SC. The very dirty areas I have to go over twice and sometimes have to post treat with a pump sprayer in spots. I also use an injector bypass which seems to get me more flow when rinsing and using SC


Thanks Barry :+1:t2:

So it seems as though I won’t be much better off with more GPM then :frowning:

I currently don’t go over stuff twice - I just want to walk faster than a snails pace.

I have 3000-3500 @ 4GPM. Ideally I’d like just over 3000 and 5-5.5GPM.

Thanks for taking the time to reply :blush:


I believe Udor makes a 5gpm 3kpsi pump. I wouldn’t go back to 4gpm if you paid me…it’s way to slow for house washing and concrete cleaning. Even at 5gpm you’re working much more efficiently. I walk pretty fast behind my 16 inch Eagle Wash. A typical driveway that took me 1 hr now takes 35-40 min. Everything is faster. Even with my 4gpm I would zip over everything perpendicular to even everything out and I do the same now. And I know I’m not hurting any concrete with 2300 psi.


Cheers again Barry. I was hoping for some input from some more of the regulars, but hey…

Forums are funny places.


My 5.5 at 2900 is quicker at flat work than my old 4gpm .
However I feel in my area another 500 psi really makes a difference on dirtier concrete- I have 60m hose so I’m losing a fair bit of that 2900psi.
It really outshines the old 4 at house washing, particularly rinsing.
For 99% of flat work I’m using my 8gpm machine.
The difference in cleaning time is massive.
If u haven’t bought the 5.5 yet get an 8gpm instead, I could have made heaps more money if Ihad just got one earlier.


Thanks @AUSSIE you’ve pretty much confirmed what I was thinking.

2900psi absolute max, minus my 165’ hose and fittings etc. it’s going to be 2500-2700 tops.

Not enough to do the commercial flatwork significantly better than the 4@4 I guess.

The GX390 is the problem I have, not the pump…

Cheers bro :call_me_hand:t2:


Update for anyone considering something like this.

I spoke to a knowledgeable guy who’s been in the business for 30+ years. He told me a lot of stuff, but basically…

Using manufacturer figures only - to eliminate hose length, fittings etc.

My 4@4 is 60,000 cleaning units.

My potential 2900@5.5 is 63,000 cleaning units.

Rinsing would be better, flow at the SC nozzle tips would increase from 7.5LPM (2GPM) to 10.5LPM (2.75GPM) at a reduced pressure though.

All in all it’s not worth it to invest in my GX390 which is halfway through its life-cycle anyway.




I would tag specifically who you want if you expect any sort of timely responses. It’s almost busy time again. This is defanitly not my forte. Wish I could be of more help.


You can talk to all the knowledgeable guys in the world…the only way to really know if you’ll benefit from it is to do it or talk to others that have done it. Direct drive pumps are terrible anyway. Gx390s last years if you take care of them. Anyone that’s swapped out a 4/4 pump with a 5.6 gear drive will tell you there’s a large difference. More so in housewashing and a good upgrade in concrete cleaning as well. A gx390 is not meant for any commercial work anyways…that’s all 8+ gpm stuff.


@Sharpe I did :wink:

Hey Barry :blush: in my specific case, $1500 on a GX390 to get marginally different results is false economy. That’s all I’m saying. I know the GX390 is a great engine, I have a few of them.

The next step for me is to use that money and buy a GX690 set up :+1:t2:


Honda needs to step up with a GX 500.


Apparently they’ve stopped making the GX630 and the GX660 will replace it.


Good move Steve , you wont regret it here’s an example of a job I did 3 weeks ago-
7000m2 (23000sqft for some) concrete around a staff accommodation complex.
Took 4 days for me and two helpers, one guy non stop surface cleaning with 8gpm and the other moving his hose etc while I did edges, rinsed and post treated with the 5.5 @ $3.50 per m2
This is a bit above my normal m2 charge for a combination of reasons including : narrow pathways, moving furniture, drainage issues in lots of areas , filthy concrete, access issues +more…

Anyway if I was running the 5.5 on SC we would have probably been there for another couple of days.
When I add up what that would have cost regarding added labour and operating costs plus a couple of days not making more money on other jobs then I see the value of 8gpm efficiency in the flats.


I found this machine - but it’s too far away :frowning:

It would be ideal!