Tony. Thanks for your response. It's greatly appreciated. I apologize, but I'm not exactly able to specifically discern what you are trying to state. I may be completely mistaken, but are you attempting to denote that if the PW output pressure (PSI), obtained via any particular combination of GPM and orifice chosen, is painful to one's hand, then it may be dangerous to the vehicle's paint? I may be confused with your response, and you may very well not be saying this at all. You also might be trying to discuss two separate topics or a combination of both (1 being personal safety, and 1 being safety of the vehicle's paint). I'm not quite sure. If you are discussing personal safety, I appreciate the warnings. I'm actually familiar with pressure washers, but haven't used them yet for a vehicle wash. Looking forward to it though! If you are in fact attempting to say that if it's safe for one's hand, it's safe for the paint, then I would venture to say that is an accurate statement. However, I would politely argue that it is not very scientific in nature. Ha. Some clear coats are harder than others, some people's pain thresholds vary dramatically, etc. I know most people utilize the 40 and 25 angled tips or a combination thereof.
I'm more interested in learning if anyone has done an analysis on the most efficient/effective range of output pressure (PSI) for vehicle cleaning purposes. I have read about the "cleaning unit" calculations (Flow X PSI) and the preferred range for vehicles. However, the articles I have read about Cleaning Units didn't necessarily hit upon the recommended upper PSI limits, especially when using specific orifices to adjust the output. Logically speaking there has to be an upper limit. Obviously, the lower you go, the safer it is, but the less effective it is going to be, which ends up being a fruitless endeavor. One of your statements is a perfect example of the great variation in responses related to this topic. You mentioned that you don't think that 1000 PSI is very effective for cleaning. However, I've also heard that some people like to dial in as close to 1000 PSI as they can, which is their preferred pressure setting. Trust me, if using a size 2 orifice, which gives me a 1440 PSI using the Ryobi 1800 / 1.2 GPM PW, is safe, I'd use that all day long and not worry about it. However, there is the other side of the argument, which might explain why some like to use the lower PSI, despite it not being as effective in initially spraying off the caked on grime, which is flow rate. I've heard some say that GPM flow rate is the more important measure, but that doesn't exactly sound like the best theory as well. With a higher GPM I might be able to push the water and loose dirt off the car quicker, but if much of the dirt hasn't yet been "unstuck" then that's somewhat of wasted effort.
With that said, here are some example numbers: By using a size 3 orifice with the PW referenced above, I would get a 2.01 GPM flow rate, but only 640 PSI. In contrast, if using the size 2 orifice, the flow rate drops to 1.34 but the PSI is sitting at 1440. Or, one could split the difference and go with the 2.5 orifice, where the flow rate is 1.68 and the PSI is 922. Now obviously, the pressures drops as flow rate increases and vice versa. My initial personal thought is like yours, in that I'd rather a higher PSI to really remove the tough grime from the paint/wheels, etc. than more flow that just pushes things around. However, I don't want to push it too far with the PSI hitting the mysterious safe "upper limit", which is why I posed the initial question. There are too many pressure washer threads to comb through. I've dug into a few, without actually finding someone specifically discussing what I'm asking about. I may be blind however, and skimmed right over it, which is probably the case
Ha.
