Surprise BSE Change

Thermal Growth – No Problem

Recently a power plant was installing a new coupling after an extended outage. A new pump shaft and element were installed during the outage, and significant work was performed on the turbine. The original distance between shaft ends (DBSE or BSE) was 14.0 inches, and the FLEXXOR Coupling spacer was designed for this dimension. However, the correct amount of thermal growth and equipment thrust was unknown at that time.

Thermal Growth Determination

Before the installation could continue, a discussion about thermal growth and thrust position ensued. The team realized that the net result of the shaft movement would amount to a different BSE than was expected. The difference in shaft position was about 0.100 inches. Since the allowable axial movement of the coupling was +/- 0.090 inches, it was crucial to set the hubs and shafts properly so that the running BSE would not be in a position to overly stretch or compress the coupling.  


Correcting the Axial Position of the Coupling Hub

Once the correct shaft spacing was determined, the hubs needed repositioning. Since the pump side hub was already fixed in its position by the shaft taper, the adjustment needed to happen on the turbine side where the shaft was straight. Luckily CouplingCorp had designed the hubs to have some adjustability in the axial position of up to 0.250 inches. So, within minutes, the Anderson Clamp Hub was loosened, repositioned, and re-tightened in the new position. 

Thanks to the ease of use of the Anderson Clamp Hub, the mechanics overcame a last-minute hurdle with no sweat. No heat or hydraulics were needed, and one mechanic could make the adjustment very quickly.

How CCA Saved a Customer Millions

A CouplingCorp customer came with a problem that can be common. The original shaft attachment device they were using had a set screw to hold it in place on the shaft. Over time the vibrations of the hub on the shaft caused micro fretting between the set screw and the shaft. This small movement created a weak spot on the shaft which eventually caused shaft failure.

Stress Risers in Shafts

In any shafts that carry high torsional load, a stress riser can be catastrophic.  In this particular case, the shaft was also carrying a cantilevered load which added to the stress on the outer surface of the shaft.  The micro-cracking that happened at the set screw contact point was enough of a stress riser to cause a full crack even on a shaft running at relatively low speeds.

This is a cautionary tale for any shafts that have surface irritations like this or other intentional features.  For example, keyways in shafts are often problematic if the inside corners do not have an appropriate fillet.  It’s always good to inspect shaft to avoid surprises.

The customer wanted to find a mechanical device without a set screw which would be easy to install, simple to uninstall, and, most importantly, it had to be customized to fit a unique geometry which supported a bearing. Luckily CouplingCorp was able to create the perfect solution. The Anderson Clamp Hub™ is a mechanical clamping device that has a fully customizable flange which was able to handle a tight tolerance bearing surface.

Design Flexibility

One distinct advantage of the Anderson Clamp Hub is the ability to access the loading screws from either end as chosen by the user.  Sometimes it can be very helpful to access the loading screws from the shaft end side because there is more wrench clearance.  With some other keyless devices, loading screws are typically found on the back end of the hub where they can be very close to the bearing housing which leaves very little room for access.  In other cases, it can be more helpful to have the loading screws on the other end, which is achievable with the Anderson Clamp Hub.  This design freedom gives the user a much more user-friendly device.

By working with CouplingCorp on this application, the customer was able to solve the shaft failure problem.  In the process of making that change, they were able to save millions of dollars in warranty parts on their entire installed base.

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FLEXXOR Coupling Reduces Vibrations in Gas Compression Application

Reduce vibration in reciprocating compressors

For several years a gas gathering company dealt with high vibrations on the motor driving a 6 throw, 5400 HP reciprocating compressor. Over that time, they made several attempts to reduce the levels, but none were successful. On the output end of the motor, the vibrations amounted to 0.291 inches per second (7.39 mm per second). In this case, torsional excitations did not appear to be a problem. The company wondered if there was a simple way to reduce vibration in reciprocating compressors.

The engineers involved decided to look at the bending stiffness of the coupling. The existing coupling was a typical disc-style, but it was relatively stiff in the axial and angular (bending) orientations. They decided to try the FLEXXOR coupling, which was a more forgiving coupling style.  The difference between the original disc coupling angular spring rate and the FLEXXOR is approximately 10 times lower. 

Immediately after installing the FLEXXOR coupling, the vibrations on the motor output end dropped to 0.065 inches per second (1.65 mm per second) which is over 4 times lower. See the before and after vibration data sheets below. These were the lowest levels ever recorded on that particular unit. Since then, the system maintained the low vibrations through all ranges of operation.

The installation was also performed very quickly using the Anderson Clamp Hub which eliminated the need for any heat or hydraulics.   This keyless hub also eliminates the need for shims to help with axial positioning of the equipment.  The hub can easily be set and then reset to handle any changes in the equipment spacing.  After 6 years of running, this application is still operating with no problems. Over the longer term the reduced vibrations and bending moments should also help enhance the life of the bearings and seals.  The company continues to use the FLEXXOR coupling as a way to reduce vibration in reciprocating compressors and help their various equipment continue to run reliably.

New Year’s Resolution: Coupling Weight Loss

A large industrial manufacturer came to Coupling Corp with a low torque application designed to run at 75,000 RPM.  This was no problem for the FLEXXOR coupling.  But to make things harder, they wanted the coupling to mount on their straight cylindrical shafts.  Normally a spline would be typical for that speed of equipment.  Consequently, Coupling Corp used the world-renowned Anderson Clamp Hub™ to grip on the straight shaft.  With the extra weight of the shaft and hub, the overhung moment would be a critical concern. 

Each piece of the coupling was analyzed in finite element analysis (FEA) to determine possible failure modes and safety factors because of the high speed.  As is the case with most high-speed applications, there were many iterations in both the coupling and user equipment designs to achieve the overall system’s optimal dynamics.  A big part of those iterations was the overhung moment reduction process for the coupling (a.k.a, Weight Loss). 

Luckily for this little coupling, no gym membership was needed.  Instead, the Coupling Corp engineers worked through many details to achieve the overhung moment targets given by the customer.  The coupling ended up being constructed almost entirely of titanium.  Coupling Corp engineers even had to design a custom titanium bolt with a minimized head for the least amount of overhung mass.

In the end, the coupling achieved its weight loss goals.  More importantly, the customer had a successful high-speed test.

If your rotating equipment application requires special design considerations or a custom lightweight coupling, please contact us today.

Can Your Chiller Coupling Stand Up To The Heat?

It can with York* Replacement Couplings from CCA

Every year as the temperature rises and chiller systems are beginning to run, CouplingCorp gets calls from customers whose York* compressors have an unexpected problem.  This past year a customer had an original York coupling fail, causing a bent quill sBroken quill shafthaft. To make matters worse, the quill shaft was threaded into the compressor shaft so hard that it could not be removed (see picture).  Not to worry – CouplingCorp was able to take the compressor wheel and machine away from the old quill shaft.  Then a new replacement FLEXXOR coupling and quill shaft were installed.  Luckily for the customer, CouplingCorp made this happen in a matter of days, and the chiller was back up and running.

Coupling Corporation provides a full range of replacement couplings for

York Compressor Coupling replacement

New FLEXXOR coupling with Quill shaft in place of the York Compressor Coupling

York* Compressors along with many other manufacturers.  Some sizes are in stock for emergency turnaround service, and others can be manufactured very quickly.  If you aren’t sure what you need, Contact CCA and let us help you determine what type and size of coupling you need.

For more information on the benefits of CouplingCorp’s York* Compressor Coupling Replacement, visit the page on our website.  Also, included is a chart to help match part numbers.  York Compressor Replacement Data Table 

Sick of Needing to Find your special York* Wrenches?  Try our Thread-less Quill Shaft Option

The preferred option for most customers when installing a new coupling is to also switch out their existing quill shaft with a new CCA quill that has a straight, smooth end where the coupling mounts.  This has several benefits:  it completely eliminates the threads; it completely eliminates the need for spacing shims, and it eliminates the need for the special York wrench.

Coupling Products for All Applications

No matter what application you have, CouplingCorp has a solution.  See our product menu at the top of our website.  Some of the categories include Flexible Shaft CouplingsAnderson Keyless SolutionsRigid CouplingsVertical Pump Couplings, and more.

We are the most customer responsive, innovative, engineering-driven company in the power transmission industry. We are focused on providing unique, durable, and high-quality custom coupling solutions beyond a catalog.

No matter what size or speed your application is, Contact a CouplingCorp engineer to help determine the optimal product for your application. If you have specifications for your application, please use our simple online forms for either Horizontal Applications or Vertical Applications.

* York is a trademark and/or a trade name of Johnson Controls, Inc

No More Bearing Failures After Coupling Change

A power plant had six identical feed pumps powered by 3500 HP motors. The equipment was initially specified and connected with gear couplings. The plant personnel had grown accustomed to performing the maintenance on these gear couplings by greasing them at regular intervals. Unfortunately, they had also become accustomed to replacing pump bearings as well. Every nine months to a year, the bearings were cracking due to fatigue, resulting in the need for frequent replacement.

After some research, plant personnel realized that the misalignment between the motor and pump was about 0.035”, much higher than the coupling was rated to handle. They determined that the bearing failures were occurring because of high load stemming from high coupling forces. The plant desired to improve the alignment; however, since the majority of the misalignment resulted from thermal cycles in the system, there was no simple way to accomplish this.

There was some resistance among plant personnel to make any changes due to bearings failing on a regular, consistent basis. They looked at it as the “devil you know” versus the risk of unknown results. Eventually, the plant decided to make a change, starting with upgrading the couplings to allow for the higher misalignment.

Coupling Corp was called in to design a coupling that could handle the high misalignment without adding bending loads to the bearings. A close-coupled FLEXXOR coupling was designed to fit the application and was capable of handling an offset misalignment of about 0.060” without any maintenance. More importantly, the spring rates of the new FLEXXOR coupling were roughly 1000 times lower than the original gear coupling.

Flexible Couplings Extend Seal and Bearing Life

Close-coupled, Reduced-moment FLEXXOR coupling

Close-coupled, Reduced-moment FLEXXOR

The newly installed couplings immediately yielded positive results. Despite this, the site mechanics continued to check the bearings every few months to look for cracks as they had for so many years during routine maintenance checks. Eventually, they realized that the couplings were doing their job very well, and the system was running smoothly without any bearing failures.


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Does This Look Familiar? It Doesn’t Have To.

After many years of struggling with maintenance and vibration issues, a pipeline company decided to upgrade their couplings. The pipeline was powered by 4500 HP motor-driven pumps running at 1800 RPM. They came to Coupling Corporation of America for several reasons. First, the FLEXXOR coupling would allow them to have a high-performance coupling with low spring rates that could handle the rigors of remote locations, including unpredictable misalignments. Second, they really wanted the convenience of the Anderson Clamp Hub so that their mechanics could easily remove and install the hubs when it was time for maintenance.

After designing and manufacturing the couplings and hubs for the fleet of pumps, CouplingCorp was on site for the first installation to ensure a good fit and provide training for the staff that would install the remaining couplings and perform maintenance in the future.

Before the new FLEXXOR couplings could be installed, the original gear couplings had to be removed from the motor and pump shafts. In many cases, we don’t have the pleasure of watching the original hub being removed from the shaft, but in this case, we were privy to seeing an all-too-common sight in the world of heated hubs. The motor hub was not cooperating when it was heated, and it was not pulling off the shaft using a hydraulic piston. After several head-scratching sessions, more men, more torches and more hydraulic pistons were applied to the hub, the hub still would not move. In addition, the site engineers were even worried that the bearing might have to be compromised due to the enormous amounts of heat being applied to the shaft.

After several hours of hard work in the hot sun, the hub started to move with the help of several sledgehammers (joining the torches and hydraulic pistons). To make things more exciting, the leftover grease from the gear coupling came running out in a blaze of glory, giving the hub removal the feel of a bonfire!

The following video shows the excitement of the moment.


Several hours after the fire was extinguished and the hub was fully removed, the motor shaft temperature had finally dropped to a workable range. The mechanics pulled out the new Anderson Clamp Hub and received the on-site training covering how to properly install and remove the hub. Once ready, the new Anderson Clamp Hub was installed on the shaft in about 30 minutes – without the need for a bonfire!

This type of success story is common here at Coupling Corporation of America. The Anderson Clamp Hub has been in the field for over 20 years, providing customers with a simple way to connect their couplings to their shafts – whether straight, tapered, or keyed.  Before your mechanics embark on their next fiery adventure, let Coupling Corporation help you upgrade to a safer, faster coupling.

Pelletizer Coupling Success

A plastics manufacturer came to CouplingCorp about 10 years ago with an interesting problem.  On their plastic pelletizer machines, the cutting knives were powered by a 120 HP motor.  The machine used a gear coupling to transmit torque between the motor and the knife drives.  While this coupling application seems to be very simple on the surface, there was a major complication.  During the process of operating the pelletizer, the knives wear down as they constantly cut plastic.  The amount of this wear can vary for different size/model of the pelletizer, but it is a significant amount of movement that changes the length of the coupling as it wears.  For example, when new knives are installed, the Distance Between Shaft Ends (DBSE) might be 10.75 inches (273mm).  By the time the knives have worn to the point of being replaced, the DBSE could be down to 10.06 inches (255.5mm).  This means the coupling must accept an axial change of 0.690 inches (17.5mm).  Even for a gear coupling, this is a large amount of movement.

The user wondered if it was possible to replace the gear coupling with a maintenance-free, non-lubricated coupling.  But, they worried about whether a flexible coupling could handle the large movement without putting too much axial force on the hydraulic knife positioning system.  In other words, if the coupling was too stiff, the axial force generated by the coupling would be larger than the hydraulic force used to position the knives to cut the right size pellets.

CouplingCorp looked at the situation to determine if such a coupling could be produced.  After doing an analysis of the axial forces found in the gear coupling during operation, it was determined that the FLEXXOR coupling would have a lower axial force than the original gear coupling did.  The final hurdle was a large axial movement, and with the use of some high-misalignment diaphragms, the problem was solved.  The coupling was designed to handle +/- 0.384 inches (9.7mm) of axial travel which is a total range of 0.768 inches (19.5mm).  With this axial capacity, the user was able to stretch the coupling to accommodate the new knife position, and then gradually the coupling would move through the neutral position to a compressed position as the knives wore down to their lower limit.

The user installed a first coupling, and it worked as predicted.  After a trial phase, the same coupling was implemented on all pelletizers at the plant.  The coupling has been running successfully for many years without any maintenance.

Introducing Our New Blog “Misaligned and Running Fine”

Coupling Corporation of America (CCA) is pleased to announce the addition of a new, informative blog section to our website called, ” Misaligned and Running Fine.”

Starting this month, we will release periodic success stories providing details on how CCA products have helped our customers save time and money by reducing vibration and equipment failures. These informative success stories stand the test of time, and we believe many viewers could benefit from the sharing of this information.

Respectful of your time, the information will be brief and to the point. We hope this information adds value to your organization. Our first success story is: “How CCA Saved a Customer Millions.”

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