Electric Pressure Washer: How does PSI and GPM translate to foam?

[JPW]

Does anyone know what the "sweet spot" is for gaining the best foam when it comes to looking at pressure washers and their PSI and GPM ratings? And just to be clear, I'm not referring to their advertised PSI, since those seem to be heavily inflated in most cases, but when testing with a gauge in the real world with something like a 15-degree tip? Also, this is taking into account you are using a high-end foam cannon with an optimal orifice.

What I don't understand is what happens in relation to the resulting foam as PSI increases or decreases and everything else remains constant. The same holds true for GPM. Do you always want more GPM? I wouldn't think so and in some cases I might think that the less GPM, the better, because the more GPM you have might cause the foam to become more diluted as it reaches the car. Personally, I would want the foam to have a little "dwell time" before it starts to run. Does that make sense? If anyone can shed some light on this it would be appreciated.

[opie]

Does anyone know what the "sweet spot" is for gaining the best foam when it comes to looking at pressure washers and their PSI and GPM ratings? And just to be clear, I'm not referring to their advertised PSI, since those seem to be heavily inflated in most cases, but when testing with a gauge in the real world with something like a 15-degree tip? Also, this is taking into account you are using a high-end foam cannon with an optimal orifice.

What I don't understand is what happens in relation to the resulting foam as PSI increases or decreases and everything else remains constant. The same holds true for GPM. Do you always want more GPM? I wouldn't think so and in some cases I might think that the less GPM, the better, because the more GPM you have might cause the foam to become more diluted as it reaches the car. Personally, I would want the foam to have a little "dwell time" before it starts to run. Does that make sense? If anyone can shed some light on this it would be appreciated.

I have a karcher 3000 psi 2.5gpm gas pressure washer. When i turn the pressure regulator down my foam cannon reacts with poor foaming action, compared to when i turn up the pressure then the foam is really thick like its supposed to be

[Azure]

My experience with foaming with my first pressure washer was that using DI water resulted in thicker foam. My first pressure washer was a sun joe SPX3001. I never got foam output like you'd see in YouTube videos. When I upgraded to a Comet 1700, my foam output was super thick with the same brand and amount of soap. With that, I'll say it's higher GPM's that make a difference compared to PSI. If your water is super hard like mine (~450ppm), it'll reduce the foam output consistency.

[JPW]

Thanks for the replies. It sounds like increasing the pressure and the GPM can result in more foam. It is confusing because as I think about it, wouldn't increasing the GPM with everything else constant increase the pressure? Wouldn't the pressure regulator that opie mentioned actually be pushing more water through the nozzle to gain the additional pressure? So confusing.

[PaulMys]

Wouldn't the pressure regulator that opie mentioned actually be pushing more water through the nozzle to gain the additional pressure? So confusing.

Think of it this way: Take your garden hose with no sprayer end on it, and turn it on full-blast while holding it horizontally. See that high volume of water flow out, but only about a foot or so before it loses momentum and arcs toward the ground?

Now put your finger over the end and block off about 3/4's of the opening. It shoots out way further, right?

Now ask yourself which one of these methods had the greater flow (volume-wise)

[JPW]

Think of it this way: Take your garden hose with no sprayer end on it, and turn it on full-blast while holding it horizontally. See that high volume of water flow out, but only about a foot or so before it loses momentum and arcs toward the ground?

Now put your finger over the end and block off about 3/4's of the opening. It shoots out way further, right?

Now ask yourself which one one of these methods had the greater flow (volume-wise)

lol...great analogy. I was feeling sort of stupid for a second (happens often), but I guess what we need to know is exactly what the pressure regulator is doing in his pressure washer. If you changed out the tip from a 45 degree nozzle to a 15 degree nozzle, then yea, I would totally get that. The pressure would be higher with the 15 degree nozzle because it is having to push the same amount of water through a smaller orifice. This is closer to the analogy you provided. But do we really think that is what is happening inside the pressure washer to provide more pressure?

Using your same example, let's say you only turned the water half-way on providing only half the volume of water. Then you changed it to full to provide the full volume of water. Without putting your finger over the end of the hose, what do you think might happen? I would expect the arc of the water to extend further when the full volume of water is applied and thus probably providing more pressure as well. I think. I seem to remember pressure doesn't always fit what common sense might tell you. I think Bernoulli's principle is what could give us exact measurements. Ultimately, I probably need to think less and do more. Ryobi, Greenworks, Dewalt, and Craftsman all appear to have similar pressure washers with similar resulting pressure and GPM. I think I'll just go with one of those and be done with it. My brain hurts.

[PaulMys]

lol...great analogy. I was feeling sort of stupid for a second (happens often), but I guess what we need to know is exactly what the pressure regulator is doing in his pressure washer. If you changed out the tip from a 45 degree nozzle to a 15 degree nozzle, then yea, I would totally get that. The pressure would be higher with the 15 degree nozzle because it is having to push the same amount of water through a smaller orifice. This is closer to the analogy you provided. But do we really think that is what is happening inside the pressure washer to provide more pressure?

Using your same example, let's say you only turned the water half-way on providing only half the volume of water. Then you changed it to full to provide the full volume of water. Without putting your finger over the end of the hose, what do you think might happen? I would expect the arc of the water to extend further when the full volume of water is applied and thus probably providing more pressure as well. I think. I seem to remember pressure doesn't always fit what common sense might tell you. I think Bernoulli's principle is what could give us exact measurements. Ultimately, I probably need to think less and do more. Ryobi, Greenworks, Dewalt, and Craftsman all appear to have similar pressure washers with similar resulting pressure and GPM. I think I'll just go with one of those and be done with it. My brain hurts.

Lol.

Yeah, try not fry your onion on this one.

[SNP209]

Go to youtube and look up "obsessed garage pressure water test" its a comprehensive test featuring the vast majority of the brands out there. A lot of your questions will be answered.

[JPW]

Go to youtube and look up "obsessed garage pressure water test" its a comprehensive test featuring the vast majority of the brands out there. A lot of your questions will be answered.

Thanks, but geesh. He has separate videos for each product line? I literally laughed out loud when I saw someone's comment, "Have I really devolved so much that I've spent an hour watching a video on a $200 pressure washer." I could relate.

This guy does seem to have a ton of tests, but all I really wish he (or someone) would do is create a spreadsheet with every electric pressure washer and their gauged pressure with different nozzles. That way you could quickly narrow down the most powerful pressure washer for your price point. Who knows, maybe this guy actually has that somewhere, but at the moment I don't see him providing it anywhere. He has a cool web site.

[WaxMaster1]

The only tip you want is the 40°.