Motor Basics for Pump Enthusiasts

If you’re like me and dealing with pumps and motors on a regular basis, it can be useful to learn a few fundamentals about them. I’m learning these, myself, and just sharing along as I go for any interested parties. Here, motor operation and efficiency optimization will be discussed. Before I start, some of you may be thinking, “Now, wait just a minute. Shouldn’t you be at home baking cookies instead of messing around with motors?” Rest assured, I can still bake a cookie. Behave, and you might get one along with your new motor or motor repair. 

A motor has two main components: a rotor and a stator. Single phase motors operate according to the principle of induction. When alternating current power is applied to the stator, an expanding magnetic field is created that cuts across rotor conductor bars, inducing current in the rotor. When dealing with single phase asynchronous induction motors, 110-240v, the stator field has no rotation. Hence, it cannot start itself. With the stator in permanent position, +/- poles change position once each cycle. Why are single phase motors asynchronous? Synchronous speed here refers to the speed match between rotor and stator. Having the speed match is impossible in single phase induction motors. A rotor will always lag behind a stator in rotations per minute with induction motors. This lag is called slip. Slip is measured in %. The greater the slip, the greater the torque. It looks like this:

  • Slip = [synchronous speed – rotor speed / synchronous speed] * 100%. Motor slip increases as power increases. 
  • To illustrate: Slip = [3,600 RPM stator – 3,450 RPM rotor]/3,600 RPM stator = 3.6% slip.

Because single phase motors are not self starting, there are four means to start these motors. Each has its set of torque/speed curves along with pros and cons to consider for applications these motors will pertain to.

  • Capacitor start/ induction run (CSIR): This type of induction is noisy due to polar operations. CSIR is most commonly found in hard to start applications.
  • Resistance start/ induction run (RSIR): Another noisy motor starter. These are cheap motors for low torque, low power applications.
  • Capacitor start/ capacitor run (CSCR): This is a best choice and is more expensive. The capacitors are in series. The capacitor balances the motor operations.
  • Permanent split capacitor (PSC): This starter offers smooth operation and is a good choice for centrifugal pumps and fans.

Stators are coiled iron or aluminum with silicon steel lamination. Okay, why laminate? To prevent energy losses via hysteresis and eddy currents. Guys, I had no clue what either of these terms meant. Hysteresis is a lag in effect behind its cause. That cause in this case would be energy loss. At least for me, eddy currents are tough to grasp. They’re closed loop reactions back to magnetic fields that created them. What that means in real terms is an energy loss via heat transfer. Copper is used as conducting material in stator coil windings. So, lamination serves to prevent these couple forms of energy loss, preserving motor efficiency. When discussing motor efficiency, we’re really talking about minimizing heat transfer, which is unconverted energy. Put your hand on a hot motor, and this is what we’re talking about. What accounts for efficiency loss?

Pcu1 = losses due currents flowing in stator windings, accounting for 40-45% of motor efficiency losses.

Pfe = losses due to eddy currents and hysteresis in the laminations. These stray losses are small and hard to measure. Iron losses = 30-35% of total losses.

Pcu2 = losses due to eddy currents flowing in the rotor bars and end rings. This accounts for 10-15% of total losses.

Pfrig = friction in bearings and windage losses from the fan. This accounts for 10-15% of losses.

Permanent Magnet Synchronous Motor (PMSM) is a good way to help eliminate loss, but it takes us out of the single phase motors we’ve been discussing thus far. These are also known as Electronically Commuted Motors (ECM). Variable frequency drives (VFD) are required for these types of motors. VFDs can only be operated on three phase motors. These motors are synchronous in that there is no slip between stator and rotor speeds. Without slip, these motors operate at cooler temperatures. These are relatively new to market, since the early aughts. The main difference is that the rotor is permanently magnetized via rare earth permanent magnets. These magnets produce more flux and resultant torque for their physical size as compared to induction types. What this all means is that in terms of reliability, lower operating temperatures reduce wear and tear and maintenance. They extend bearing and insulation life.

This is all I’ve got so far. There is much more to understanding motors, such as learning about electromagnetic fields, the number of magnetic poles within stators, and how they relate to speed. For reference, I took the coursework via Grundfos online training, and got a bit of reinforcement via Wikipedia. Fair disclosure: I took that Grundfos training twice before passing the final exam!

 

Prevent that DI Water Emergency!

DI water systems might lose functionality for a number of reasons. In cases such as these, what steps can be taken to keep and restore DI water systems? While there is no one size fits all solution, there are a few steps that can certainly help both prevent and address DI water system emergencies. 

  1. Have adequate redundancy to that system either online or in standby. Where possible, we can help to explain how to make this happen.
  2. Have critical spares for system components and expendables on hand to minimize downtime. Want a list of spares specific to your system? Ask us. We can deliver on this.
  3. Ensure all manuals, data sheets, and system training has been performed and reinforced. Have regular reviews to bring all relevant parties into the loop. Do you need manuals, data sheets, or system training? Give us a shout. We can help.
  4. Have preventative maintenance contracts in place for all DI water systems. An ounce of prevention is worth a pound of cure, and this applies to water systems as well. Gain peace of mind via regularly scheduled system service checks, remote monitoring, and services. Gain additional freedom to stay focused on your core business by not leaving this to chance!

Peracetic Acid for System Sanitizations: What is it and Why Choose it?

Hydrogen peroxide sanitizations have been around for a long time and they’re well known for getting the job done when it comes to sanitizing DI water systems. Peracetic acid has, too. But, for some people, it might be less known. So, when making the choice for a sterilant, do we do things the way they’ve always been done or do we know and consider all available options? Do we know that we have a choice?

Paracetic acid requires less contact time for killing bacteria and viruses. This matters when production is shut down while a sanitization takes place and time matters. Well, isn’t it, like, a totally different thing than hydrogen peroxide? See the chemical composition above. What this is, is a mix of acetic acid and hydrogen peroxide. In layman’s terms, we’re basically talking about a vinegar and hydrogen peroxide mix. A much smaller concentration of peracetic acid is typically needed versus hydrogen peroxide alone.

That’s one factor in cost savings, being done with the cost of needing to transport it around in drums or carboys. Less product required also means cost savings. And sanitization time can often be cut by up to 2/3! Anyone interested in saving time and money? Peracetic acid gets the job done just fine for many if not most DI water systems, but there are some exceptions. If on autopilot for the way things have always been, peracetic acid might an option worth looking into. It’s biodegradable, too. Check it out!

How Awesome are Conductivity Meters?

Spoiler: they’re pretty awesome. There are a couple of common methods to determining water conductivity. One involves a relatively tedious step-by-step process with a handheld conductivity meter for a reading from a specific sample port in a DI water system at a specific time. Okay, yes I know I’m exaggerating a bit by characterizing it as tedious. But it’s a spot check process rather than a continuous one that involves human interface with a correct procedure followed. It is tedious and downright archaic when compared to the alternative.

And that alternative is to make a small investment in a panel or wall mounted continuous conductivity/resistivity monitor. This second option is superior in countless ways: it’s continuous, automatic, and can be multi-channel, meaning continuous monitoring of potentially more than one spot in a DI water system. There is one observation I’ve made with these. They can last for many years, but not forever. If the display stops working or works partially, it might be time to consider replacing the monitor. It can be awesome to go from one channel to two with today’s monitors. Not only that, but automated reports over time aren’t bad to have access to either.

Stop Those DI Water System Leaks!

One of my most common calls regarding DI water systems is to report a leak somewhere in the system. While walking through a DI water system, someone looked down and found a puddle. Quick, where is it coming from and what can we do about it?

Prevention is key and there are two small and inexpensive additions for any DI water system that can help in trying to prevent leaks. These are pressure regulating valves and leak detectors, and they should be a part of every DI system for practical reasons as well as peace of mind.

Pressure regulating valves are typically found after feed water sources. They regulate to make sure there is enough water pressure… but not too much! Let’s take the case of multi-floor buildings. As the floors increase, the pressure also increases to reach each higher floor. It isn’t consistent by default, and that inconsistency ought not be a risk worth taking. Is the pressure being increased somewhere in the building for a specific purpose, and could this have implications for other locations feed water is flowing into?

There is a way to try to control for this, and that is to set a pressure regulating valve in place after the water feed source along with a small leak detector on the floor below the DI water system. Starting out with the basics goes a long way toward prevention and early identification of leaks. Periodically check the piping, too. Is it showing signs of age or in need of repair or replacement? Get more peace of mind — and save the puddle jumping for outdoor adventures with the kids.

Radial, Axial and Mixed Flow for Newbies

After plowing through a few small texts and online trainings, I’ve started in on Igor Karassik’s Pump Handbook. I’ve heard it referred to as the bible of pumps and it’s a fitting description! I couldn’t even turn three pages before getting stumped. It turns out that dynamic centrifugal pumps are a bucket category for a variety of flow options. First of all, radial and axial are words I had heard, but had never really brought into practical use. That was a problem! And anyone who knows me well enough knows the approach I took to solving it: Merriam-Webster Online. It has been my most frequently visited site for decades.

Where I got stumped was in visualizing this. Both radial and axial refer to force taking place outside of a circumference. If they’re both that, then what? Pump shafts are the circumference in this case, and the water flowing adjacent to them represent the force. It also matters that the direction of flow directly impacts the head-capacity curve and best efficiency point. And when we’re trying to understand that, head is a measurement of how far the pump can pump water from its suction end. There is more that factors in, involving suction lift, specific gravity, and net positive suction head, but those are topics for another post. Head is measured in feet rather than pressure pounds per square inch, though one can convert to the other. It seems useful to measure it as feet of head from a visualizing standpoint. Capacity is maximum volume flow rate through a pump in gallons per minute in our measurement standard.

In radial pumps, water flows at 90 degree right angles from the impeller. That means the water is flowing out to the casing radius, to each side. Higher centrifugal forces are providing higher head and proportionally lower flow. In axial pumps, water flows parallel to the shaft in a perpendicular vertical flow, resulting in lower head with higher flow. Think of it as the water flowing upward in a straight line adjacent to the impeller, where the axial impeller acts as a propeller. What makes that happen is the angle of the impeller vanes. Mixed pumps are somewhere in between, 45-80 degree flow. The head-capacity curve for mixed pumps rises in uniform toward shut off head. Shut off head is what it sounds like, and it’s the reason head-capacity curves are useful in striving for best efficiency, selecting and sizing pumps appropriately to avoid premature pump failure.

Are axial pumps actually centrifugal pumps, then? There a different opinions on this. For the most part, the consensus is to categorize them as a subset of centrifugal pumps. Yes, the flow is vertical rather than radial, but all else aligns in terms of being rotodynamic, which is just another way of saying this classification of pumps is designed for continuous flow rather than at interval displacement.

It is all well and good that directional flows have been defined within centrifugal pumps. This isn’t even close to capturing the full spectrum just within the centrifugal category. It’s a good running start in that direction. And applications for each type are useful to know. It’s a topic for another post. If this information seems like a lot to digest, it was for me, too. If this also helps anyone else, that’s awesome and all the better.

Piping, Systems, and Project Design: Codes, Standards, and Specifications!

One third of global electricity consumption is by industrial electric motors. I just heard this statistic on a recent Pumps & Systems podcast and went in search of verification for it. Holy moly. It turns out that’s true! It’s one of these points that an up until recently outsider like myself may well have never known. How are they and other process instrumentation regulated and why does it matter? It’s important to keep asking the relevant questions and looking for answers, so let’s do it.

Piping, pumps, motors and other equipment have a critical role in global safety, security, and standards of living. This equipment is designed in adherence to rules established by standards organizations, government agencies, and trade association standards. Engineers can also employ their own project-specific specifications. This matters because when a project calls for instrumentation, it’s mandatory to know what the applicable standards are that apply to an informed project design. And there are caveats to be mindful of in this process.

In the interest of saving time, engineers will sometimes recycle codes, standards and specifications from past projects onto a new project. Brian Silowash, author of Piping Systems Manual, has seen this firsthand. It can be problematic if any regulations specified are out of date. Apart from recycled codes, projects tend to have multiple revisions. The danger in printing projects on paper is that various parties may not have the same revisions in hand. A Building Information Modeling (BIM) program can solve that problem by storing project revisions to the internet cloud, allowing all parties associated with projects access to the same revisions.

Though some effort has been made through the years to unify codes and standards, there are still many to sort through by relevant issuing associations. The first photo below shows standards issuing trade associations. My reference text shows eighteen of these associations, though there may be more nationally and internationally. 

IMG_Oct22019at43437PM

This next photo shows one page of individual standards, their issuing organizations, ID numbers and titles pertaining to valves and fittings. We should be mindful that every project is subject to a number of codes, specifications, and standards. 

Codes, standards, and specifications are typically identified like this:

ACRO SPEC-YR

ACRO is the organization that developed the code, standard or specification

SPEC is an alphanumeric identifier

YR is the year of the latest revision 

IMG_2043

I recently came out of a piping and instrumentation diagram seminar session where a wastewater department standard drawing references legends, symbols and abbreviations. The photo below depicts engineer specified project specific instrument letter identification, symbol configuration, and instrument or function symbols.

IMG_2046

While instrumentation and projects are subject to codes, standards, and specifications from many sources and there are pitfalls to avoid, the good news is that these are categorized for searches. Take care to ensure that any recycled codes are current. And save time for all parties affiliated with the project by use of a BIM cloud storage application.

Best regards and thank you for reading.

Jennifer Zadka

 

Sources: Piping Systems Manual by Brian Silowash

On the Job Site: Construction course by Jim Rogers

Affinity Laws in Practice

Merriam Webster defines affinity as: “a likeness based on relationship or causal connection.”  The Affinity Laws are a heuristic governing pump sizing for one pump based on known constants for another of that same pump. Knowing of these laws helps, but really understanding to apply them in problem solving goes a long way. I’ve been holding off on writing this because the topic is one I had been struggling with. It’s important to know, so it’s worth the struggle.

I once had someone tell me, “I’m not paying you to learn all of this theory!” That’s fair enough, but know that the trade-off is between a culture of striving for a good enough versus one that’s striving for excellence. Which standard would you rather hold? If we’re honest, we can’t have it both ways. For this, I challenge you. Be honest. Hold your torches high!

  • Pump performance involves relationships between performance [ie, head, shaft speed, volumetric flow rate] and power. If speed or impeller diameter are known with one pump, performance based on speed or impeller diameter change for a another of that same pump can be determined. Also, if these are known for just one pump with a VFD (variable frequency drive), which is a commonplace scenario, new H-Q (head-capacity relationship) and BHP (brake horsepower) curves with a different speed than published on a pump performance curve can be plotted.
  • There are two sets of Affinity Laws, and both are based on the premise of a pump’s specific speed not being changed once its been calculated. One law holds impeller diameter constant. The other holds speed constant.
  • What’s nice is that this can all be seen on a pump performance curve. These relationships are what we’re typically seeing most manufacturers including in their pump H-Q curves. The curve is designed to provide this information/knowledge as given information. What I’m writing about here is less about that knowledge, itself, and more about understanding relationships based on knowledge.
  • Though you could just see it all on the curve and not bother with knowing the why and how of it, don’t cheat. Learn how it all ties together foundationally. This is like the difference between seeing a movie in just two dimensions versus in all three (seeing versus “seeing”). Wouldn’t it be more far more entertaining to have it all come to life in vivid detail – not once, but every single time?
  • Here are the two sets of Affinity Laws presented in basic and practical terms:

Affinity Laws Set 1.

Holding the impeller diameter, D, constant, let’s solve for speed:

Q1/Q2 = N1/N2

  • Q is capacity (flow in GPM) and N is speed (motor speed). 1 is the first baseline pump; 2 is a second of that same pump with a capacity change having affinity in predicting second pump speed based on capacity change.

What that’s saying is this:

Q1(capacity of baseline pump 1)/Q2(capacity change for pump 2) = [N1(speed of baseline pump 1)/N2(speed change for pump 2)].

Visualizing this, I see two of the same exact pumps sitting side-by-side. Each has the same unchanged impeller size inside the respective volutes. But each pump calls for a different capacity (flow in GPM). How will the flow difference in that second pump change the required motor speed, since capacity and speed are related? We’re about to find out!

Let’s solve an iterative trial and error problem with these known terms, referencing this pump curve:

IMG_Oct12019at75546PM

Using an example pump curve, what speed is required with a full diameter impeller to make this rating: 3000 gpm @ 225′? Here, I’m referencing an ITT Goulds Model 3196 centrifugal pump performance curve, 6 x 8 – 15 at 1780 RPM. (This model has a 6″ discharge, an 8″ suction, and a 15″ full impeller diameter). Let’s try out 2200 RPM to see if it gets to the desired rating:

Holding the impeller diameter, D, constant, let’s solve for speed:

Q1/Q2 = N1/N2

  • Q1 = 3000 GPM; H1 = 225 ft; N1 = 1780 RPM
  • Q2 = Q1 * (N2/N1); Q2 = 3000 * (1780/2200) = 2427 gpm
  • H2 = H1 * (N2/N1) squared; H2 = 225 (1780/2200) squared = 147′

This first test doesn’t work out. We’re trying for a motor speed to accommodate 3000 gpm given an untrimmed full 15″ impeller diameter. 2427 gpm isn’t a high enough flow for the full impeller to make sense on the example 1780 RPM pump curve. It’s below the 15″ full diameter curve line. Ditto for the 225 feet of head requirement. 147′ isn’t a high enough head for the full 15″ impeller size.

We tried a 2200 RPM motor speed for 3000 gpm @ 225′ and it didn’t work out. I’ll try again, this time @ 2000 RPM:

Holding the impeller diameter, D, constant, let’s try again to solve for motor speed:

Q1/Q2 = N1/N2

  • Q1 = 3000 GPM; H1 = 225 ft; N2 = 1780 RPM
  • Q2 = Q1 * (N2/N1); Q2 = 3000 * (1780/2000) = 2670 gpm
  • H2 = H1 * (N2/N1) squared; H2 = 225 * (1780/2000) squared = 178′

Referencing the performance curve published for this pump, 2670 gpm @ 178′ does fall on the curve line for the 15″ full size impeller. (It wasn’t slow enough of a speed to be above the line.) 2000 RPM speed is the test winner! Awesome.

Q1/Q2 = N1/N2

  • For this first set of Affinity Laws (that being the set with the impeller diameter held constant), it’s also true that:

H1/H2 = (N1/N2) squared

  • H1(ft/hd requirement for baseline pump 1)/H2(ft/hd change for pump 2) = [N1(speed of baseline pump 1)/N2(speed change for pump 2) squared].

BHP1/BHP2 = (D1/D2) cubed

  • BHP1(brake horsepower for baseline pump 1)/BHP2(brake horsepower change for pump 2) = [N1(speed of baseline pump 1)/N2(speed change for pump 2) cubed].

In summary, this first set of laws holds impeller diameter as constant. The second set of affinity laws is different. It holds speed constant in order to solve for impeller diameter trim.

Affinity Laws Set 2:

The speed is held constant. Let’s solve for impeller trim.

  • Flow in GPM is the same as shaft speed (1780 RPM, for example).
  • Head is shaft speed squared. (1780 * 1780 RPM).
  • Power (BHP) is the cube of shaft speed (1780 * 1780 * 1780 RPM).

Q1/Q2 = D1/D2

  • Q is capacity (flow in GPM) and D is impeller diameter (imp dia). 1 is the first baseline pump; 2 is a second of that same pump with an imp dia change having affinity in predicting second pump imp dia based on capacity change.

What that’s saying is this:

Q1(capacity of baseline pump 1)/Q2(capacity change for pump 2) = [D1 (imp dia of baseline pump 1)/D2(imp dia change for pump 2)].

Visualizing this scenario, I see two of the same exact pumps sitting side-by-side. Each runs on the same motor speed (1780 RPM, for example). But each pump calls for a different capacity (flow in GPM). How will the flow difference in that second pump change the impeller trim, since capacity and impeller diameter are related? Let’s do this!

In the second set of Affinity Laws (the set holding speed as the constant), it’s also true that:

  • H1/H2 = (D1/D2) squared
  • BHP1/BHP2 = (D1/D2) cubed

To summarize, the first set of Affinity Laws holds the impeller diameter as an unchanged constant in order to solve for motor speed required to accommodate a pump rating. In set one of the Affinity Laws, the problems can be solved by either changing capacity, feet of head, or brake horsepower to solve for speed. The second Affinity Laws set holds the speed constant in order to solve for impeller diameter trim. In set two, the problems can be solved by either changing capacity, feet of head, or brake horsepower to solve for impeller diameter trim.

To conclude, the Affinity Laws are a good rule of thumb, but can have up to a 15%-20% margin of error when solving for impeller trim. Slower motors tend to allow for greater impeller trim while following the Laws than higher specific speed motors. I personally find it interesting that capacity is equal to, while ft/head is squared and brake horsepower is cubed to solve for these variables. It’s so neat and tidy to have these variables line up for solving that way. I hope this information brings value to you. Please feel free to hold onto this for your next learning “curve” adventure!

With warm regards,

Jennifer Zadka

PS: Here’s my reference source: Pump Characteristics and Applications, 3rd Edition by Mike Volk.

The Power and Elegance of Circles

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.