hydraulics of a pump

What I try to get through when we do these basics around the beginning of the class, we talk about pumps don't really suck. Pumps actually create an area of low pressure less than atmospheric, and that allows the gravity that's around us every day to push that fluid into that pump. And the centrifugal action, the second portion of the two functions, takes place. And it's kind of ironic when you think about this, but you remember back when you were a youngster, and I mean a youngster, somewhere around the five, six-year-old age. And you first got on that merry-go-round, and you're standing in the middle of that merry-go-round, and all you're doing is getting dizzy. And then as you start to go out further and further to the outside and feel this energy that's trying to pull you off that little merry-go-round, and then, of course, you got that 12 or 13-year-old bully that's out there, he's trying to spin that thing so fast you finally can't hang on anymore, and you get thrown off. Well, that's exactly what a centrifugal pump does. A centrifugal action delivers the pump to the outlet, and there are some things to take into effect there as we move along and think about.

Basically a pump is a very simple device, and it's one of those simple devices when it acts up, people get all kind of crazy about trying to figure out why it's not doing things. And I've seen a lot of different things, talked to a lot of different people, and it's interesting to see that when a pump actually fails in my facility how many red flags it starts popping up. We’ll talk about common pump terminology. This is really kind of fun, because when I get into this portion of it, you know, I ask the students when I'm doing the class, "Anybody know what pressure really is?" Pressure is a resistance to flow, okay? And in the hydraulic world, pressure is typically in pounds per square inches, PSI. Now, that's not always true, because when you go north of the boarder, sometimes it will be in bar. If you go across the big pond, they'll actually talk about bar as well. 

And it's kind of funny how we've kind of intermixed some of the metric system in the pumping world as well. So what I tell people is, "Pressure is the force exerted on a confined liquid, and it acts equally undiminished in all directions." That's part of Blaise Pascal's law. And one of the big complaints I hear from customers when they have problems with the pump is they go, "Oh, my pump's not making enough pressure." Okay. Well, what kind of pressure is it supposed to make? Well, all I know is Ralph, the building manager, when he turned this system over to me, he says, "You know, this gauge should read 70 PSI. If it doesn't, you got problems." Well, okay. That might be a good place to start. Been in a lot of mechanical rooms where there's actually a permanent magic marker, you know, a permanent marker's on the gauge that says, you know, "The gauge should be in between these two points as you're walking by it." There's all different kinds of scenarios to, "What should my pump be doing?" But when I don't fit that pressure, then the question is, "What happened?"

Typically what pumps do is they generate fluid flow, and flow rate is the volume of fluid which passes by a certain point. And in the real wide, wide world of pumps, it's usually represented by the symbol Q when they talk about it. But flow rate is kind of like looking at amperage in current flow on an electrical system. Flow rate is expressed usually in gallons per minute in the centrifugal pump world. In the positive displacement pump world, it could be expressed as in ounces per rotation. There's a lot of different scenarios when you get into pumps. You can go into gallons per minute, hundreds of gallons per minutes, millions of gallons per day, acres feet per day. It's actually kind of interesting how many different ways we can actually determine flow rate of a pump. For instance, a lot of your waste treatment facilities, they'll tell you, "Oh, this place handles 165 million gallons a day." It's kind of hard to get your head around that kind of water, but that's a lot, a lot of fluid. Okay, so next is the word "head." Head is actually a measure of work expressed in feet.

This is what the pump does. Now, when you think about centrifugal pumps in the facility, pumps are constant head devices. All they do is generate and apply energy to a fluid and make it move. Doesn't matter if it's pumping salt water, gasoline, water, water glycol. You know, people call it "chiller water," people call it different types of chemicals that we pump in there, sodium hypochlorite. All this fun stuff that we run across in the day-to-day application of, "What does my pump do?"