2 Step gun not pulling soap

I built a 2 step gun based on the other thread floating around, but Im having some problems with it pulling soap. Itll pull through both lines with a soap nozzle but not with my high pressure nozzle. When I pull soap with a true soap nozzle, itll surge back and forth between a fan pattern and somewhat high pressure 0° soap.

Via Hydrochem:

pressure set at 2000psi at the gun

Machine is 5.5 gpm

25 degree 7.0 nozzle

What am I missing?

Here’s a pic of the gun

That seems quite complicated, what’s the purpose of having a 2 step gun as opposed to one?

The theory is that you use a two step soap combo to eliminate brushing. Also applying it at high pressure is supposed to use less soap

Brushing for oxidation removal? I don’t know what else you’d need to brush for

They’re used in fleet washing to apply acid, soap, etc.


Yep, what @marinegrunt said. Note that this is posted in the fleet washing section.

@TaderzNgravy, have you done your maths on injector size vs. nozzle size? You need something like a 30% pressure differential to draw soap. Due to that issue, I think the high pressure 2-step guns max out at 1800 psi or so, that would be a size 8.5 nozzle on your machine.

Btw, nice job on building the gun. Do you have a link for that 3-way valve? And did you happen to piece the check valve and injector together with an adapter you found, or just bought it prebuilt?

I used a downsteam that has 1/4 npt instead of compression threads then replaced the ball and spring with a check valve. The 3 way valve is on amazon, id have to look back through my orders.

Whats the formula to figure out my pressure differential? It’d be nice to leave the machine at 3000 psi for surface/building cleaning and use an oversized orifice to drop it to 2000psi and pull soap

One of those charts shows the sizes in inches.

First thing you’ll want to do is find your maximum pressure injector. That is, the smallest size injector that will still allow 5.5 gpm of flow. That will likely be an injector with a size 7 orifice, .067” or 1.70mm. You might have to go one size smaller and drill it out with a 1.7mm bit.

5.5 gpm with a size 7 orifice generates 2500 psi. Multiply by .7 (subtracting 30%; taking a quick math shortcut here) = 1750 psi.

Use the chart to find the proper high pressure tip: 8.5.

That should theoretically pull soap at maximum pressure. You could even experiment and see if it will still pull with an 8.0 tip.

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Links, pretty please. Would love to know who sells those non-fangled injectors :rofl:

Compression threads? Is that what those are? I couldn’t get them to match up to anything. I even tried compression fittings :man_shrugging:

I had to improvise:

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I’ll grab an 8 or 8.5 tomorrow to try it out. Honestly, the injector came with my bandit so I have no idea who makes it. The two gp injectors I have are compression threads I think

That’s funny. They really like to pack weird off-brand injectors with these budget machines. Like, “Wow, you really gonna break the bank if you go all out on gp hi-draws, huh?” :joy:

But sometimes the off brand stuff is handy.

I zoomed in on your pic, I see it’s a 2.1 injector. That’s only generating 1000 psi @ 5.5 gpm. So the smallest you could probably go and still pull soap would be with a 13 or 13.5 tip :confused:

Btw, here’s another great reference:

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Soaping at 1500 psi ,rinsing at 2400 psi. 5.5 gpm. 4008 nozzle.

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Looks like somebody is getting ready to market his elixirs.


Thats great. It looks like we used almost identical parts aside from you using a stainless downstream injector.

I don’t quite follow…



Is there some way of accounting for pressure loss through the injector, and through the bypass fittings?

It still seems like you would need different tips to be getting those pressure points.

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Fancy charts don’t always show real world results


What do you mean? It’s on the internet. It absolutely has to be true. No if’s, and’s or but’s about it.

This ain’t window cleaning. No amount of meters, charts, filters or anything else makes one iota of a damn when you get out into the real world and put it into practice.

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Nope , One tip soaps and rinses, pic #1 is soaping, #2 is rinsing.


Ain’t that the truth. These calculators are based off of perfect world scenarios, not accounting hose length, diameter, plumbing restrictions, wear and tear etc, in other words everything matters to get a result.