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.

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.