I’m a lifelong figure skating fan. If someone were to ask me why, the first thought that comes to mind is the power and elegance in it. There is a convergence of power, speed and grace, where these coincide to create the breathtakingly captivating experience we see on the ice. If you’ve ever watched a performance, you’ll quickly see that circular motions are what make the shows. What now? You’re not into figure skating, so you say? Try it, try it, and you may! In that case, let’s get on a race track and rev up your engines. If neither figure skating nor cars are gonna do it for you, so much more is governed by circular shapes that there aren’t enough hours in the day to cover it.
- For those of us involved with water stewardship, circles are everywhere. They are in all places water transport and water treatment. I work in a pump shop. We call it rotary equipment. It’s only in these last few months that circles being in every facet of water stewardship has become a stark observation. It really came together for me in this last week, while I was taking a close look at pump stuffing box drawing. The diameter for gland, shaft, lock nuts, and bearings among other things, are all specified with diameter symbols throughout the page.
- Some people have visions of sugar plums dancing in their heads. I was looking at the page, seeing nothing but diameter symbols everywhere because each of these components is circular. We wanted to know what it would take to possibly fit a cartridge type mechanical seal into the tight clearance, possibly boring through the box to accommodate a packing-to-seal conversion.
- In tandem, I was overhearing an inquiry for a sump basin diameter. I walked out into our shop and looked at the wall of gaskets, baskets of o-rings, and shelves of couplings, pipes, fittings, impellers, and yes, at FRP basins being prepped for pump station installations. It was this unreal recognition. There are just circles, circles, and nothing but more circles all over the place. You have to leave the shop to get away from them, even for one moment! When calculating new installations and retrofits, this has implications for how it’s done.
If we know a diameter, calculating a circumference is straightforward. Here are some basic definitions:
- Radius: A straight line extending from the center of a circle to one end of the circle (diameter / 2).
- Diameter: A straight line across the center of a circle, from end-to-end (2 * radius, since a radius is half of a diameter).
- Circumference: The linear distance around the circle. (2 * pi * radius), or (pi * diameter).
- pi: A little over 3x the diameter of a circle. 3.14….
Why are there so many circles in the structures of water stewardship? It turns out that circles are the most efficient shape for handling pressure because pressure force is evenly distributed around a circumference. With other shapes, pressure forces concentrate at the corners, requiring expensive non-standard inefficient reinforcement. So, let’s say we have flow through a square. Is the velocity the same or is it slowed down? Well, if pressure is not evenly distributed, it can’t accelerate the same.
- From the above example, we know that circumference is (2 * pi * radius). For circular motion, here’s how it’s determined:
- Average speed = distance/time = (2 * pi * radius)/time. In other words, circumference is the distance we’re talking about here divided by time, which gives us the average speed.
I’ve been talking about circles in terms of their mechanics. Bacteria and other buildup such as scaling also love to hide in corners and crevices that come from shapes other than circular. This, too, means circles are a winning shape.
All of this had me curious about the larger picture above and beyond water. Circles are elegant and the most powerful of any shape to be found in the universe and beyond. They might be the shape of choice in water stewardship, but they didn’t start there. That shape is found everywhere in nature, and its use in water stewardship is simply a mirror to it. Everything from atoms to cells to the earth, planets, sun, moon, and even black holes are all circular shapes. It’s only fitting that the shape of the basic building block of life is also the best conductor to what flows through it.
That’s fascinating. And beautiful.
Volts, amps, watts, kilowatts, and power. I don’t know about you, but until today, nothing has earned my ire and frustration quite as much as trying to clearly understand the difference between these electrical terms once and for all: volts, amps, watts, kilowatts, and power. They’re all to do with electricity, but what exactly do they each mean, and how do they all fit together? Today is the day for closing this loop!
A practical example involving all of these terms makes it easy to grasp them. Let’s say we have a motor with a dual rating of 230V/460V. Will running a motor at its higher voltage rating save money by using less amperage?
It won’t because we pay for power in watts or kilowatts. Volts are units measuring electrical potential, while amps are a unit of measurement for electrical current. Power is the combined value of amps (electrical current) and volts (electrical potential), and it turns out be the same for each “rated value” (meaning the 230V or 460V voltage values rated to the motor on its nameplate). Power, which is (amps * volts) is measured in watts or kilowatts.
So, for example, if we’ve got:
*14 amps run at 230V, (14 * 230) that’s 3,220 watts, or 3.2 kw of power
*7 amps run at 460V (7*460) is also 3,220 watts, or 3.2 kw of power
What’s interesting to note is that the higher voltage rated value of 460V is double that of the lower value of 230V. It takes half the amps (i.e., running electrical current) to get the same power (measured in watts or kilowatts) with 460V (of electrical potential) to attain 3.2 kw of power.
Running current at the higher rating can only save money on installation costs because smaller diameter wires can be run at the higher rating than are required for the lower rating.
This explanation, which I was lucky enough to stumble on in web research, finally had each term making clear sense, while showing how it all fits together in practical terms.
This is the source article via El Paso Electric: http://c03.apogee.net/contentplayer/?coursetype=md&utilityid=elpaso&id=12592
I’m not sure I ever really understood the underlying dynamics involved with hydraulic or liquid cavitation until now. I only knew that it involves pressure and equipment damage potential. Thanks to the common sense writing in Mike Volk’s publication, Pump Characteristics and Applications, it finally makes sense. Let me start by saying that there is no way to grasp this topic without learning something totally new to a lot of us.
Cavitation involves vapor pressure creating bubbles that collapse in implosion. I kept seeing images of bubbles headed toward pump impeller eyes in various books with the caption: “cavitation”. That was a start in the right direction in grasping this. It turns out that actually getting it means learning a little about thermodynamics. Those bubbles are boiling water! Now, wait a minute. How can that be? We are talking about ambient temperature water that is boiling, not high temperature water over a stovetop.
If you’re like me, you might have only known about raising temperature as a means to get liquid boiling. This is where it gets interesting. There is another way to get water or another liquid boiling starting with a lower or even ambient or cold temperature, and that is to lower pressure below vapor pressure. I was reading this in awe because I’ve gone through life without this fascinating and useful information. It turns out that pressure and heat are correlated. Raising or lowering either of these, pressure or temperature, has a direct impact on when cavitation happens.
I’ll use a few examples from Mike Volk’s book in my own words on this. So, if we’re talking about 14.7 psia, which is baseline sea level atmospheric pressure, water boils at 212 degrees F. That sounds familiar so far. Now, let’s go climb a mountain where the psia is lower than sea level atmospheric pressure and boil water via raising temperature at that higher level elevation. Water will actually boil at several degrees lower than 212 F, so that means the temperature level is relative to pressure level.
Now, let’s take the psia in the other direction. Let’s say we have 100 psia with a 300 degree temperature. That liquid will not be boiling at 300 degrees with that higher psia. Incredibly, it will just remain in a liquid state. You need to raise the temperature higher to get boiling in that case, and this is how pressure cookers work. Drop the pressure to 67 psia on it and it will boil. At 60 degrees F, vapor pressure is 0.2563 psia, so if pressure is dropped below that, cavitation results. That boiling water with vapor bubbles collapsing and imploding throughout equipment in a significant pressure drop situation even at ambient temperature causes cavitation!
There are predictable causes for water pressure dropping below vapor pressure in equipment such as a pump. Those causes for pressure loss are a topic for another time. And, I’ve been talking about water here. This topic applies to any liquid. If it’s liquid other than water, specific gravity needs to be factored in and taken into account. Thanks for reading!