Other good information on this pump is like, okay, so maybe Joe in the facilities group says, "Hey, this pump we got in the system, I need to be able to get a little more gallons per minute out of it." So when you pull that little curve out, you say, "Okay. Can I run this pump at a few more gallons per minute?" So the next question would be, "How much more do I want to run it?" Okay? So Joe comes back and says, "Oh, you know, I only need a couple hundred more gallons a minute." So that's taken this curve right here to this 1,000 gallon mark, okay? 

And looking at that 1,000 gallon mark, as you see, where the curve intersects it at that 1,000 gallons, I'm going to probably be down to about maybe 110 or 108 feet of head. So the question has to be answered, "Will this affect the pump operation?" As a betting man, I'd say no, because it's not that far outside the bars, okay? And see you're still running between 80% and 76% efficiency. So that's not bad enough to call, call out on an alarm or anything like it. So you can go back to your engineer and say, "Yeah, we can boost the system up to there." So how are we going to do that? Well, you're going to have to take some elevation plumbing out of there. You're going to have to take some restrictions out of there. You might have to outsize the pipe. These are all things that you look at down the line later. What I do want to point out on this pump curve, you'll notice there's a thing over here on the left-hand side that says, "NPSH." That's the blue line that kind of rises as you go to the right of the curve. One has to be careful there, because as you go to the right of the curve on there, your net positive suction head required goes up.

And at certain points on this chart, physically the pump will handle it. But gravity-wise and physics-wise, you might cause the pump to cavitate when you go to the right-hand side of the curve, okay? There's two types of cavitations that will show up in my pump. There's called NPSH cavitation, and there's a bunch of other things that go along with that. Then you got your NPSH cavitation, and you also have your high head cavitation. So there are certain portions that pop in there. So cavitation's another one of those subjects that we talk about, "Is my pump cavitating?" when you're working on the pump. So it's a pretty obvious thing, just kind of hangs out there and starts making all kinds of racket. So the other thing you got to be careful of when I boost that flow rate from 800 to 1,000 gallons a minute is, "Do I have enough horsepower?" If you got 25... Well, let's zoom in on this picture here to take a little closer look. And if you're looking at this pump curve, you see at 1,000 gallons a minute, I'm probably at a 30 horsepower driver. But if I should happen to go past the 1,000 gallons per minute, and I'm going to exceed that 30 horsepower threshold. So I could have problems...oops sorry...I could have problems with that pump on overloads if I only have a 30 horsepower driver. So those are things to consider.

So let's take some time and go ahead and troubleshoot our pump now. All right? So...what you're looking at right here is a head and flow curve, okay? And this head and flow curve is put together. This is what my impeller's capable of doing, the solid black line, okay? And the best efficiency point you see here pops up with the orange line air on. That's the point where, if I stay close to that point, that's the pump that's not going to give you problems. You're not going to have problems with it. In fact, you'll probably go walking out in the facility to make sure somebody hasn't removed it from the plant, because it hasn't given you any problems. So I always tell that one as a joke, too, because I hear people say, "Oh, I got this pump. It's not given me electric problems for 20 years. I have to walk by it every once in a while just to make sure it's still there." So those are kind of those funny parts. 

Now, that little purple line that popped up in there, that's my minimum flow limit. That's the point of no return. If I try to operate that pump to that portion of the curve, I'm going to get high temperature on my fluid. I'm actually going to be putting heat into my fluid, and I'm going to get what's called low flow cavitation. So once that fluid stops moving in that pump, the impeller starts to beat the fluid to death, so if you can imagine that the fluid's not moving, but I'm beating the impeller to death. You'll also notice as we go through the left of that best efficiency point, we see this what's called discharge recirculation. That's where the water decides it wants to go for another ride through the merry-go-round impeller, and it decides it likes that better than it does going any place else in the system. So a certain percentage of that water's actually going to hang out and re-pump. It's never going to come out. When you go even lower, you start getting into what's called suction recirculation. I might have a typical installation where the supply fluid is above the centerline of the pump, what we call flooded suction. You'll get some suction recirculation going on there. And then, obviously, when you start doing that, you're going to get low impeller life out of it. You see that there on the bottom?

Low impeller life occurs because we've got this suction recirculation, you've got discharge recirculation, you got low flow cavitation. All these things are going to take its toll on the impeller over a period of time. So, that being said, what can typically happen to you when you go to the left of the curve? You go to the right of the curve, you notice we kind of get the same thing. Down here, and the first thing you're going to hit is low seal and bearing life. On the left-hand side of the curve, you get low seal and bearing life. But one thing that you're going to get when you go to the right of the curve, besides the low seal and bearing life, is you get those big word cavitations. Now, I ask this question, I throw it out there, I wish all of you can answer this, does everybody know what cavitation is? I ask that question, and the first word out of people's mouth is they go, "Oh, it's air." No. Unfortunately, it's not air. It's actually steam. You're boiling that fluid off into vapor by creating a low-pressure area less than atmospheric, and you hit the vapor point of the fluid where it changes state from a liquid to a gas. And it's interesting because cavitation bubbles can form inside of a pump, but it's only at one particular point on that curve that the cavitation bubbles become destructive. 

And, to quote some wild and crazy YouTube videos that are hanging out there, "Cavitation is an area of low pressure, that when it implodes, it focuses on area of pressure the size of about...I like to say roughly the size of a point end of a needle, at about 60,000 PSI." And that little point end of a needle actually goes in there and plastically deforms the material. And if any of you have ever played with a ball-peen hammer and a piece of metal and just kind of beat on it, on a plate, you'll get these little metal flakes that come off of it. That's what cavitation does to your impeller. It's like taking a ball-peen hammer and hitting a piece of soft steel, and you start getting metal flakes out of it. So cavitation's a destructive force. I always tell people, "You want to look at an impeller to look at cavitation damage, it kind of looks like acid erosion or like some...well, I'll just say it, little people went after it with a jackhammer?" I guess, I always tell people it looks like a midget went after it with a jackhammer, a little microscopic-sized person.


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