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.