I’m a curious person. I can’t help it. I like to understand the details about things even if they don’t affect me. I made the ‘mistake’ of downloading the CAT Pump catalog and looked through it, and as a result I have 2 different pump scenarios I want to understand.
Scenario #1. Say you have two pumps. They both have the same flow. It could be anything, but let’s just say 4 GPM. They’re both designed to turn the same (or very close to the same) RPM, but one has a maximum pressure of 2000 PSI, and the other 4000 PSI. If you were to look at the pumps side by side, would the 4000 PSI pump be beefier looking? What allows it to have twice the maximum PSI?
Scenario #2. Similar to above, but in this case they have the same maximum PSI, but one pump has 2x the flow of the other. Say 4 GPM vs. 8 GPM. Again, without seeing them in person, I’m envisioning the 8 GPM pump being bigger. And what allows it to have twice the flow?
Thanks for indulging me. I don’t know why I let this stuff rattle around in my head, but I do.
Scenario 2, bigger plungers suck in more and spit out more. They are quite a bit bigger compared to a 4gpm pump.
Pumps are designed to be paired with an appropriate sized engine to produce the relevant psi specs for the gpm of the pump. Take away hp you lose psi, reduce plunger size you lose gpm (smaller pump).
Yes, the higher the psi or gpm pump the larger the engine that’s needed. Imagine putting an engine out of a Ford Focus into a Peterbilt. There wouldn’t be near enough power to move that semi the way it was designed to move. There’s an equation you can use to figure out how many hp you need to run a certain size pump. It’s on the forum somewhere.
If you’re looking at a pump with double the max psi of another and you cross section the higher psi manifold you will indeed see thicker cylinder walls. They higher psi pumps also have better webbing to accommodate the added stress
Lol I wasn’t prepared or willing to get the vernier calipers out and record my findings to answer his question, judging by his question and comparing pumps side by side I think he assumed a physically bigger pump puts out more psi, witch of course isn’t the case. Horsepower does that regardless of cylinder wall thickness or webbing, what you mentioned are support elements of design not so much the aid in making pressure.
Thanks for the replies. Another somewhat related question…
Take a typical pump - say 4 GPM, 4000 PSI. You don’t need 4000 PSI for most stuff, so you bring the PSI down by using larger orifice tips. I get that. I might be wrong on this, but it seems like guys typically bring the PSI down to the 2500 range? Is that correct?
What I don’t understand is… why not just get a 4 GPM, 2500 PSI pump in the first place instead of reducing a higher PSI pump down to the pressure you want to use it at?
Would the 2500 PSI pump use the same size tips that you used with the 4000 PSI pump in order to bring it down to 2500?
That is correct in the residential side of washing. With commercial concrete cleaning you usually throw all you have at it since it’s normally higher psi concrete and often dirtier.
Most 4/4K pumps are installed on GX390s. A 4/2500 pump on the same engine would produce higher pressure than the unit was designed for. If a person was confident that they’d never need over 2500 psi then they could install a 5gpm pump on the 390 and achieve about 2500 at the pump outlet.
As others stated, you can have gpm or psi but not both unless going up in hp.
There are some who purchase a 5.5 gpm 2500 psi washer. Although, you’re always better off going for the higher specs if you can afford it. I’d rather have machine that can put out 3500 psi in case I get a job where I need that. Even with a 3500 psi washer I can always get whatever lower pressure I want via nozzle selection. You might run into situations where 2500 psi just won’t cut it. Where the 2500 psi comes from is that it will clean pretty much all residential concrete. That’s not always true though and especially for commercial concrete. Although, it will work for 99% of residential work. I’d shoot for an 8 gpm 3500 psi if you can afford it. It also depends on what you plan on cleaning though. Better to have it just in case you need it.
Thanks. It’s not crucial that I know the answer to this, but just to satisfy my curiosity, what kind of “dirty” in a commercial setting requires 3500 PSI?
Gum and such will require more psi but I also think that the reason youd use more psi on commercial concrete is because you can. Commercial concrete is usually stronger than residential and the added psi may increase cleaning speed
