Please double check my math!


#1

So I just put together a new Udor pump with Honda Gx390. It puts out 6gpm. In 1:15 it draws 1/2 gallon through the injector. So out of 15 gallons it has 1 gallon of solution. So if I was to pull straight 12.5 it would hit the wall at about 1.87%. Which is strong for most of the houses around here. If I do a 50-50 solution that’ll put me right about .9% on the wall. Which has worked for most jobs so far. Does all of this sound correct?


Upgrade indecision
#2

Ok I realized where I was making a mistake. I believe I am actually putting .83% on the wall if I pull straight 12.5.

Its been a long day and i realized i have only had coffee to drink so far lol


#3

@Deanswc is this machine able to shoot as high as your other machines? Is it a belt drive, gear drive?
I have an old gx390 and was thinking of putting a 8gpm on it.


#4

Pro tip know your ratios but we’re not putting a man on the moon. As time goes buy you really just know what it takes to clean a surface


#5

What model pump is this? I’ll be replacing the pump on my 390 soon. How much psi are you getting?


#6

Udor sales rep said to use GC3017s or for gear drive GC3017GR for 8 gpm


#7

This would be for house Washing only I’m guessing. No way this would be sufficient for flatwork? I would be curious to know what height this combination would reach.


#8

Theoretically, it should reach the same height as any 8 gpm machine using identical plumbing and shooter tip.

Most sources say you need 2000-2500+ psi at the SC for effective flatwork cleaning. So this setup would not be sufficient for that purpose. You might get 1800 psi at the pump.

On a side note, I bet we’re 5-10 years away from seeing 2-speed gearboxes for pressure washers. You could run it at a lower speed for lower gpm with a higher PSI for flatwork (or for higher concentration DS’ing), and then switch to the higher gear for faster rinsing.


#9

@BillC @Harold
https://www.dultmeier.com/products/search/4388

This is the pump that I added to my engine. It shows that I have 3000 psi at the gun surprisingly. Not sure how but that’s what the numbers show. It was late by the time I finished setting the unloader and did a bucket test and pressure test. I can check what the height and distance was when I go back to the shop. But from what I remember it looked pretty good.


#10

@Deanswc that’s great! 3000psi how much extra was the gearbox?


#11

It came together with the pump for $716.


#12

Wow.

They charge separately for it here in Australia!

The gearbox for that exact same pump is $633 on top of $1349 for the pump.

Shocking.


#13

It’s a 5 gpm pump and not a 5.5 gpm pump which is why you’re getting 3000 and not 2500.

The 390 is an 11HP engine so you’re actually losing a little psi along the way.

There’s no real difference from 2500 to 4000 psi anyway. And that’s a great deal on that pump.


#14

Yeah I figured I would get about 2800 but what surprises me is it also puts out 6gpm as well as 3000psi. I am very happy with the purchase. Since I only do residential at this point I would rather have 2 of these than 1 8gpm.


#15

That’s awesome!


#16

I thought the gx370 was 11hp, looks just like the 390, but isnt.


#17

GX390 net horsepower is 11.7. Stated horsepower is usually not what you’re actually getting. GX390 is stated 13 HP


#18

Bucket test? I can see 2800 or 6gpm, but not both


#19

@Innocentbystander I can do a video of it when I go back to the shop this week. Maybe I am doing something wrong but that’s what it showed. When I did the bucket test I took everything off the end of the hose and then timed how long it took to fill up a 5 gallon jug with the pump running. It was filling at 1 gallon every 10 seconds. Maybe I need to use a certain tip to test this?

Then to check the PSI I put a pressure gauge between the end of the hose and the gun. When I let off the gun and restrict the flow the guage goes up to 3000. Is this the correct process to check?


#20

Without any back pressure on the pump, the engine has nothing to struggle against. I have a hunch that it tends to rev a little higher without any load. So the most accurate way to do a bucket test is with a full pressure tip and a bucket with a lid with a small hole in it to hold the splashback.

Real world house washing, though, you’re using low pressure tips. So less load on the motor, and a little more output from higher rpm. But the difference is likely negligible.

For pressure test, take your reading with a full pressure tip, with the trigger pulled. The 3000 psi you saw isn’t sustained. It’s the spike pressure where the unloader kicks in. Use a nozzle chart to select the tips for 5@3000, and then 6@3000. See what you get from each.

Usually the unloader is set a couple hundred psi higher than the rated pressure for the machine.