Tag Archives: CR-6100

Make Your Vertical Pump Shaft Bearings Last Longer

DuPont™ Vespel CR-6100 resists seizing, can run dry, has high impact resistance, and a low wear rate for a long life under a wide range of process conditions.

Vertically Suspended Pumps

Vertically suspended pump types (API types VS1-VS7) use long, flexible shafts which are supported by a series of product-lubricated shaft bearings. Vespel® CR-6100 is a great upgrade for these components.

 

Typical Vespel Services

Vertically suspended pumps can be divided into two general categories: discharge through column (API Types VS1, VS2, VS3, VS6, and VS7) and separate discharge (VS4 and VS5).

 

Discharge through column pumps tend to be used in light, flashing products like butane, LPG, and natural gas liquids, or in water condensate or cooling water intake service. In flashing services, it is not uncommon for these pumps to run dry temporarily at start up, which can be a challenge for the shaft bushings. In many of these pumps the flexible shaft can create very large loads, leading to high wear rates of traditional materials.

 

Separate discharge pumps tend to be used as sump pumps. In API Type VS4 pumps, the shaft bearings can run dry at start-up until the flushing fluid arrives. Sometimes, the external water flush is turned off; sometimes the flush lines from the process fluid are plugged; sometimes the bearing grease is insufficient. In a chemical sump, the mix of chemicals can cause corrosion issues.

Vespel® CR-6100 Replaces Traditional Materials

Most vertical pump shaft bearings are made from either bronze/cast iron, carbon/graphite based materials, or stainless steel alloys. Bronze/cast iron bearings can have a high wear rate. Carbon/graphite bearings can break. Stainless steel bearings can seize.

 

Vespel® CR-6100 can replace all of these materials in process conditions from cryogenic to 500 F (260 C). Vespel® CR-6100 is low friction with a low wear rate. It is durable and impact resistant so it resists breakage during installation, transport, and operation. Plus, Vespel® CR-6100 does not seize like metal parts and is capable of surviving the run dry conditions which can occur with the flashing process fluids.

 

Documented Results

Consider the results from a long term study at an oil refinery. The plant upgraded 22 vertical pumps to Vespel® CR-6100 wear parts. The pumps were operating in light hydrocarbons, flare knock out drum, and several stop/start services like product transfer, comprising many “bad actors” in the plant. Looking at the number of repairs within this population for 5 years before Vespel® CR-6100 and 5 years after, the plant found the following.

 22 Vertical Pumps Number of Pump Repairs MTBR for the Population
5 Years Before

Vespel® CR-6100

40 2.75 years
5 Years After 

Vespel® CR-6100

8 13.75 years

Final Notes

Next time you are rebuilding a vertically suspended pump, consider upgrading the shaft bearings to Vespel® CR-6100. Contact Boulden with your process conditions and we will be happy to let you know if Vespel® CR-6100 is a good fit for your pump.

 

The Vespel® CR-6100 installation guide will walk you through the installation process. Vespel® CR-6100 is easy to machine and install, and Boulden is always happy to help if you have any questions. Finally, we have large quantities of Vespel® CR-6100 in stock and ready for immediate delivery in North America, Europe, and Southeast Asia.

 

Helpful Vespel Links:

Standard Stock Sizes of Vespel® CR-6100

Vespel® CR-6100 Product Data Sheet

Vespel® CR-6100 Machining Guide

3MW Boiler Feed Pump Case Study

 

Todays Photo

Bernkastel-Kues, Germany

 

Contact Us Today To Learn More About Vespel and Boulden Company!

The Final Installation Steps: Length and Clearance

Upgrading pumps with composite wear componentsSetting the final dimensions of your DuPont™ Vespel CR-6100 component

Review

We have discussed how to measure your pump, prepare the metal parts, and establish the press fit for your Vespel® CR-6100 installation. The final two dimensions you need to establish are the part length and the clearance.

The Part Length

Vespel® CR-6100 has an extremely low coefficient of thermal expansion in the radial plane (perpendicular to rotation). This is one of the principal reasons it performs so well in centrifugal pump components. The low coefficient of thermal expansion is achieved through the use of radially-oriented, long carbon fibers.

Conversely, the coefficient of thermal expansion along the axis is relatively high. Therefore, the part length for a Vespel® CR-6100 component should account for the axial thermal expansion at operating temperature. Table 4 of our installation guide provides the details on how to make this adjustment.

Table 4 of our installation guide provides the details on how to make this adjustment.

The Clearance

The clearance for the part is set depending on the diameter and component type. Tables 2a and 2b in the installation guide show the clearance recommendations for horizontal pump components such as pump wear rings, throttle bushings, center bushings, inter-stage rings, balance bushings, and throat bushings.

Tables 2a and 2b provide recommended minimum clearance for horizontal pump components.

Tables 3a and 3b show the clearance recommendations for vertical pump components like vertical pump shaft bearings, wear rings, and throat bushings.

Tables 3a and 3b provide recommended minimum clearances for vertically suspended pump parts.

The best way to set the clearance is to press the component into place, and then final machine the bore to the desired clearance. This is shown in steps 5a-7a in our installation guide, pages 8-9.

Where final machining after the press fit is not practical, you can design the component to have the correct clearance after the press fit. For most component geometries, you can assume the Vespel® CR-6100 will reduce at a 1:1 ratio with the press fit. This method is shown in steps 5b-7b in our installation guide, page 9.

Some sites have implemented a hybrid method. They measure the inside diameter of the Vespel® CR-6100 case wear ring after installation, and then machine the metal impeller wear ring to set the desired clearance.

Conclusions

Installing Vespel® CR-6100 is an easy upgrade to make your pumps more reliable, safe, and efficient. Follow the steps in our  installation guide and you can make your pump even better than the day it was new. If you need material, Boulden carries inventory of stock sizes in the USA, Europe, and Singapore.

Until next time, please feel free to contact Boulden with your application details or to request a quote. We’ll be happy to answer any questions you might have.

 

Helpful Links:

Standard Stock Sizes of Vespel® CR-6100

Vespel® CR-6100 Product Data Sheet

Vespel® CR-6100 Machining Guide

3MW Boiler Feed Pump Case Study

Today’s Photo

Rock of Gibraltar – was one of the Pillars of Hercules and was known to the Romans as Mons Calpe.

 

Contact Us Today To Learn More About Vespel and Boulden Company! 

Measuring Your Pump

Upgrading pumps with composite wear components

Which information is needed in order to upgrade your pump to DuPont™ Vespel® CR-6100?

Review

Using Vespel® CR-6100 wear parts with reduced clearance can help your pumps be more reliable, efficient, and easier to operate. Which measurements and which process data do we need to assemble for the upgrade?

Dimensions Needed for a Quote

Let’s start with the 3 dimensions we need to determine material sizes and availability shown in Figure 1:

  • “R” Outside diameter of the rotor running against the Vespel® CR-6100
  • “B” Inside diameter of the bore the Vespel® CR-6100 will press into
  • “L” Length of the bore
  • Alternative: the O.D., I.D., and Length of the existing parts

If we have those 3 dimensions for each part plus the quantity of each part required, we can provide a quote

Dimensions of Design

Figure 1: Dimensions for designing a Vespel® CR-6100 part

To design parts for fabrication, we will need the dimensions of the mating hardware. While many wear parts have a simple O.D., I.D., and Length profile, some parts have additional features for which we will want the dimensions:

  • Some pump wear rings have profiles like an “L”, “T”, or “Z”. In those situations, we need to know each of the diameters and widths of any of the “shoulders” or “ribs” of the parts
  • Is the pump axially or radially split?
  • Are any of the parts are axially split?
  • For vertical pump shaft bearings, it will be helpful to know if there is any groove profile required-spiral grooves, axial grooves, how many, what diameter, how deep…
  • What is the existing material and clearance of the vertical pump shaft bearings?

Process Conditions

Vespel® CR-6100 works in most process services. It is manufactured from Teflon™ PFA and carbon fibers, so it is chemically resistant to nearly all process chemicals and it has a broad temperature range. There are only two general limitations:

  • Temperature range is cryogenic -300 F (-200 C) to 500 F (260 C)
  • Avoid abrasive slurries, slops, and bottoms services

To design the parts, the pump operating temperature is required in order to determine the correct press fit for the Vespel® CR-6100 parts.

 

Differential Pressure

If the components are going into a high-energy pump, such as a multi-stage horizontal charge pump or boiler feed water pump, we recommend that the patent-pending Boulden PERF-Seal™ design be used on all horizontal multi-stage pumps. The PERF-Seal™ design is fabricated from Vespel® CR-6100 and increases the efficiency gain and rotor damping associated with the upgrade. If the PERF-Seal™ is not used, we will need to know the differential pressure across the components in order to verify that they are designed correctly.

 

Figure 2: PERF-Seal center bushing from a boiler feed water pump

Conclusions

In the ideal situation, you can supply the dimensions of the parts required, the pump cross-sectional drawing, and the API data sheet for the pump. From this information, we can confirm that the service is a good fit for Vespel® CR-6100, quote the material or machined parts required, and make a recommendation on how to install Vespel® CR-6100 into the pump.

Please feel free to contact Boulden with your application details and dimensions. We’ll be happy to provide a budget estimate or a fixed quote depending on the information available. Once you decide to go forward with the upgrade, we have whatever material you need in stock in the USA, Europe, and Singapore.

Todays Photo

Petronas Towers, Kuala Lumpur, Malaysia

Helpful Links:

Standard Stock Sizes of Vespel® CR-6100

Vespel® CR-6100 Product Data Sheet

Vespel® CR-6100 Machining Guide

3MW Boiler Feed Pump Case Study

If you need any material or have any questions. Please contact us today. Until next time.

Contact Us Today To Learn More About Vespel and Boulden Company!

 

 

When to Reduce the Clearance in Your Pump with DuPont™ Vespel® CR-6100

The industry “rule of thumb” says to reduce the wear ring clearance by 50%, but this isn’t always true.

Vespel® CR-6100 Upgrade Review

When you upgrade your pumps to Vespel® CR-6100, there are two steps:

  • Eliminate the metal-to-metal contact points in the pump
  • Reduce the running clearance (of the wear rings and throttle bushings)

However, you don’t always need to reduce the clearance. It depends on what you are trying to do and which component you are looking at. So, to determine whether or not to reduce the clearance, ask two questions:

 

What Problem am I Trying to Solve with Vespel® CR-6100?

Vespel® CR-6100 can be used to improve pump reliability and performance in many ways. Some benefits require reduced clearance, some do not. The following table gives some examples of where reducing clearance is needed vs. where it is not needed.

 

Reduced Clearance Required

Reduced Clearance Not Required

 

 

Is There Differential Pressure Across the Part?

Reducing the clearance can generally produce two beneficial effects in your pump:

  • Efficiency Improves: The leakage across the part will be reduced, improving pump efficiency and reducing the operating cost of the pump.
  • Improved Rotor Stability: The Lomakin Effect in the pump will be increased, increasing the hydraulic forces produce by the wear rings.

Both of these factors are driven by differential pressure across the part.

 

If the specific component you are upgrading to Vespel® CR-6100 is not exposed to differential pressure (i.e. vertical pump shaft bearing) there is no need to reduce the clearance.

 

Wear rings, throttle bushings, center bushings, balance bushings are all exposed to differential pressure. These are the parts where you want to reduce the clearance to obtain performance and rotor stability improvements. The rule of thumb is to reduce the clearance to 50% of the API minimum for metal parts. For most pumps in the hydrocarbon processing industry, this works.

 

These benefits are augmented using the patented PERF-Seal™ design from Boulden, which further reduces leakage across the part and dramatically increases the hydraulic damping from these components.

 

Exceptions to the 50% Wear Ring Clearance Rule

Because pumps come in all shapes and sizes, there are some places where we need to make exceptions and reduce the clearance by less than 50%.

  • Throat bushings-the throat bushing clearance often helps to control the mechanical seal flush rate. We recommend using the clearance recommended by your mechanical seal OEM to set the clearance of this part.
  • Wear rings in vertically suspended pumps-You don’t want to have the wear ring clearance tighter than the shaft bearing clearance. Therefore, our recommended minimum clearance for wear rings in vertically suspended pumps is the shaft bearing clearance + 0.002″ (0,05 mm).

Conclusions

Over the years, we have seen pump repair shops use a range of clearance values when applying Vespel® CR-6100 with great results. There is no single “best” way. That said, if you want to increase efficiency, you need to reduce the clearance of the parts exposed to differential pressure. If you are only trying to solve a run-dry or seizing problem, reducing the clearance is optional. For vertical pump shaft bearings, staying with the original design clearance is usually the best answer.

 

In any case, you can use our recommendations as a starting point. We supply these values in the clearance tables in our installation guide which you can download here:

 

Boulden Installation Guide for Vespel® CR-6100

 

Until next time, please feel free to contact Boulden if you would like to discuss the appropriate clearance for your pump upgrade. We’ll be happy to help and we have whatever material you need in stock in the USA, Europe, and Singapore.

 

Helpful Links on Vespel® CR-6100 and Wear Ring Clearance:

Standard Stock Sizes of Vespel® CR-6100

Vespel® CR-6100 Product Data Sheet

Vespel® CR-6100 Machining Guide

3MW Boiler Feed Pump Case Study

If you need any material or have any questions. Please contact us today. Until next time.

Useful Links for using DuPont™ Vespel® CR-6100

Upgrading pumps with composite wear componentsTools to help you improve your pump operability, reliability, and efficiency

20 Years of  Vespel® CR-6100

Our favorite material recently passed a milestone. The first pump ever fitted with Vespel® CR-6100 was upgraded 20 years ago in November 1997.

 

The first pump was a vertically suspended condensate pump at a refinery in California. The pump was notorious for running dry, and it had failed once or twice per year for as long as the maintenance records went back. An engineer at the refinery “found” Vespel® CR-6100 and decided to put it to the test on the condensate pump. The pump survived repeated episodes of running dry and subsequently ran for many years without failure.

 

Since then, over 10,000 pumps across the globe have been upgraded with Vespel® CR-6100.

 

Useful Links For DuPont™ Vespel® CR-6100

When you are using Vespel® CR-6100 in your shop, or if you are recommending your favorite repair shop to perform the upgrade for you, the following links should prove helpful:

Standard Stock Sizes of Vespel® CR-6100

Boulden Installation Guide for Vespel® CR-6100

Vespel® CR-6100 Product Data Sheet

Vespel® CR-6100 Machining Guide

3MW Boiler Feed Pump Case Study

If you need any material or have any questions. Please contact us today. Until next time, be safe, and enjoy the holidays with your friends and family

Todays Photo

Proboscis Monkeys, Borneo

Proboscis Monkeys, Borneo

Contact Us Today To Learn More About Vespel and Boulden Company!

Contact Us Today To Learn More About Vespel and Boulden Company

 

 

 

 

 

 

infbytg

Case Study: DuPont™ Vespel® CR-6100 in 3MW Boiler Feed Water Pump with PERF-Seal™ design.

Better operability, reliability, and efficiency

The PERF-Seal™

A while back, we introduced the PERF-Seal™ design for center bushings, throttle bushings, and pump wear rings.

 

Below you can see the center bushing and case wear rings of a 2-stage pump which was upgraded to Vespel® CR-6100 with the PERF-Seal™ design

Center Bushing of a 2-stage pump.

Center Bushing of a 2-stage pump.

2-stage pump upgraded to Vespel® CR-6100 with the PERF-Seal™ design.

2-stage pump upgraded to Vespel® CR-6100 with the PERF-Seal™ design.

The holes drilled in the PERF-Seal™ create a turbulence field, thereby reducing leakage across the component–acting in a way similar to a labyrinth. However, unlike a labyrinth design, the PERF-Seal™maintains the same hydraulic stiffness as a plain wear ring and discourages tangential whirl of the process fluid.

 

Boulden worked with Mechanical Solutions to create an FEA model of the design and to create a custom test rig to validate the performance of the design. If you are interested in the results of this testing, Contact Boulden and we will be happy to share with you.

 

Boiler Feed Pump Case Study

 

We were approached by a power plant looking to upgrade their 3MW boiler feed pumps. Their process had changed over the years to require frequent cycling and they wanted to use Vespel® CR-6100 to avoid pump seizure. Due to the size of the pumps, increased efficiency was an added bonus.

 

We applied the PERF-Seal™ design to all of the stationary wear components–case rings, throttle bushing, and center bushing. The pump had demonstrated the following

  • No issues stopping and starting the pump during plant cycles
  • 10% lower power consumption during full load operation
  • Motors no longer run in the safety factor during full load operation

The pumps have now been running for 2 years. A full case study was recently published in POWER Magazine and is available here.

 

Until Next Time

 

Contact us if you have a boiler feed water pump you would like to upgrade.

If you need material, we have a huge inventory of standard stock sizes available for immediate shipment.

For details on how to install Vespel® CR-6100 into nearly any pump type, download the Boulden Installation Guide.

Today’s Photo

Skull Island, Trang An, Vietnam

Skull Island, Trang An, Vietnam

Contact Us Today To Learn More About Vespel and Boulden Company!

Contact Us Today To Learn More About Vespel and Boulden Company!

 

 

 

 

 

 

gytinfb

The Effect of Wear Ring Clearance on NPSHR

Recommended reading from the 32nd Pump Users Symposium, 2016

A Short Break

In recent weeks, we have discussed how an upgrade to composite wear rings allows you to avoid pump seizure, and therefore reduce the wear ring clearance in your pump. This reduction in clearance increases the Lomakin Effect in the pump and improves pump efficiency.

One thing we did not discuss is that reducing the wear ring clearance also reduces the pump NPSHR.

In the past, discussion of the relationship between pump NPSHR, wear ring clearance, and cavitation has led to many questions. Unfortunately, the answers to these questions are somewhat restricted due to limited testing on this topic.

Last year, there was a paper which provided some clear data on this subject. The authors used a pump test stand, two different impeller configurations, and wear rings at various clearances. We recommend taking a look at the following paper for greater technical insight into the relationship between wear ring clearance and pump NPSHR.

The Influence of Impeller Wear Ring Geometry on Suction Performance

by Thomas Leibner, David Cowan, and Simon Bradshaw

Published at the 32nd Pump Users Symposium

Houston, TX, September 2016

Until Next Time

In the near future, we will return to our series on upgrading pumps with Vespel® CR-6100, addressing how to upgrade specific pump configurations.

Contact Boulden For More Information

Until then, if you have a pump operating at less than 500 F (260 C) where you want to reduce the NPSHR, contact Boulden today. We have a huge inventory of Vespel® CR-6100 standard sizes in stock ready for immediate shipment almost anywhere in the world.

For application and installation details, download the Boulden Installation Guide for Vespel® CR-6100

7 Rules for Using Vespel® CR-6100

Upgrading pumps with composite wear componentsWe just completed our series on upgrading pumps with DuPont™ Vespel® CR-6100, getting into details on how to upgrade various horizontal and vertical pump types. We discussed reducing the clearance of the wear rings, upgrading throttle bushings with the PERF-Seal design, and upgrading vertically suspended pump shaft bearings.

Today, let’s try to condense it all down into a short list of guidelines which we can apply to just about any pump. Follow these rules and we can ensure we are using Vespel® CR-6100 properly and improving our pump reliability.

7 Rules for Using DuPont™ Vespel® CR-6100 

  • Stay under the temperature limit of 500 F (260 C)
  • Only stationary parts, mounted in compression
  • Shoulder on the low pressure side to retain the part against differential pressure
  • Avoid extremely abrasive services such as slurries, bottoms, or slops
  • Press fit, clearance, and axial length of part from the Boulden Installation Guide
  • Pump rotor must turn freely when the pump is assembled and ready for commissioning
  • Use PERF-Seal™ design for throttle and center bushings of multi-stage pumps

What do you think?

Did we miss anything? Contact us to let us know your ideas.

Until next time, if you have an application you would like to discuss, contact Boulden.

Need Vespel CR-6100 or other materials?

If you need material, we have a huge inventory of standard stock sizes available for immediate shipment.

For details on how to install Vespel® CR-6100 into nearly any pump type, download the Boulden Installation Guide.

Todays Photo

Borobodur, Indonesia

The Borobudur temple. The largest buddhist temple, and most visited site in Indonesia

 

Contact Us Today To Learn More About Vespel and Boulden Company!

Contact Us Today To Learn More About Vespel and Boulden Company!

 

 

 

 

 

 

gytinfb

Upgrading Pumps With Composite Wear Components Part: 10

Upgrading pumps with composite wear componentsPart 10: Vertically Suspended Pump Installation Tips

Review

We have discussed how upgrading your pumps with Vespel® CR-6100 helps to eliminate pump seizures, allowing you to reduce wear ring clearance, which improves pump efficiency and improves pump reliability by increasing the Lomakin Effect in the pump.

Quality repair and installation practices are an essential counterpart to the success of upgrading pumps with Vespel® CR-6100. This is true of all pump types–horizontal and vertical. When you are finished with the overhaul, the rotor should turn freely.

Vertically suspended pumps with their multiple fits and pilots require some additional consideration. To ensure the best possible results in these pumps, below are some tips which have been passed on to us from our customers.

Vespel CR-6100 for LPG Pumps

Vertically suspended LPG pumps fitted with Vespel® CR-6100.

 

Mechanical Alignment of Pump Components

Multi-stage vertical pumps pose a challenge for the shop performing the overhaul because there are multiple fits and pilots. Keeping the whole pump assembly concentric and square will give you the best results with your upgrade.

Good practices should be followed from the machine shop through the final alignment in the field.

In the machine shop:

  • Ensure all pilot fits within the pump are 0.002″ (0.05 mm) or better.
  • Ensure all mating faces of assembly elements are square.
  • If possible, assemble the pump in a vertical position.
  • Install Vespel® CR-6100 shaft bearings, bowl bearings, and wear rings, then final machine with the lathe indexed to the pilot fit of the part-this will ensure all bores at wear interfaces are concentric within the assembly. (Alternatively, all wear part fits can be machined concentric to the pilot fits prior to the installation of the Vespel® CR-6100 components.)
  • Install the Vespel® CR-6100 shaft bearings with the same clearance as the original design for the pump. If the original clearance is not available, See Table 3a (imperial) or 3b (metric) in the Boulden Installation Guide for recommended minimum clearances for vertically suspended pump shaft bearings.
  • When the assembly is complete, make sure the rotor turns freely within the pump with no hard rubs. If there are hard rubs, disassemble, try to find the source of the rub and correct the concentricity of the misaligned component. If clearances are very tight, consider a slight increase of the bushing clearance and re-check to make sure there is no hard rub.
  • Our recommended clearance for Vespel® CR-6100 wear rings in vertically suspended pumps is the shaft bushing clearance plus 0.002″ (0.05 mm) or 50% of the API minimum clearance for metal parts-whichever is larger.
  • If the pump is operating in very cold liquid (temperature below 0 C), increase the clearance at the shaft bearings by 0.002″ (0.05 mm) above the minimum values shown in table 3a or 3b.

In the field:

Generally, vertically suspended pumps incorporate a rigid coupling and the pump does not have its own rolling element bearings. The purpose of the rigid coupling is to make the pump shaft and motor shaft act as one unit with the pump relying upon the rolling element bearings in the motor. When dealing with a rigidly coupled vertical pump, traditional alignment methods can introduce misalignment. You also cannot rely upon the register fits from the motor to motor mount to the pump to be concentric.

Here are some tips for aligning a vertical pump with line shaft bushings and no rolling element bearings. (The motor bearings carry the axial load and coupling is rigid)

  • The pump must hang as close to plumb (vertical) as possible. This requires inspection of the base plate at the sump to ensure it is flat and level, and inspection of the mounting plate on the pump to ensure it is also flat and square to the assembly. If the pump is hanging “at an angle” the shaft will bend as it tries to hang plumb and pump life can be reduced.
  • Install the pump without the seal installed
  • Verify that the pump is level on the base
  • Install the motor on the pump.
  • Mount a dial indicator on the motor shaft, reading the ID and face of the seal chamber
  • Correct any radial misalignment by moving the motor and/or motor mounts in their fits. Squareness should be corrected by machining mounting faces (shims are sometimes used).
  • Lock the motor in position (installing 2 dowel pins is a proven method).
  • At this point, you may want to couple the pump and check for any run-out.
    • Any run-out that shows up after the alignment is likely due to a fault in the coupling
    • If resistance is still encountered after alignment and run-out are corrected, the source of rubbing is likely eccentric pump internals, which will need to be corrected back in the shop.
  • Install the seal (if the motor must be removed to install the seal, care must be taken to ensure motor returns to aligned position)
  • Install the rigid coupling (Coupling should be dimensionally checked and checked for trueness in the lathe before installation)
  • Measure the shaft run out between the coupling and the seal. This should be as close to zero as possible. The purpose of the rigid coupling is to make one shaft out of the driver and driven shafts. The end of the motor shaft is the zero point, so just a small run out at 15 cm below the coupling translates into huge side loads on the shaft bushings 1-2 meters down the assembly.

Side note: if you experience misalignment of the rigid coupling, the evidence will likely be wear of the bushing and/or shaft concentrated at the top bushing in the pump.

If you have anything to add to the above notes, please contact us. We’d love to hear your thoughts.

Conclusion

We hope you have found this series on how to upgrade your pumps with Vespel® CR-6100 helpful. In future weeks, we’ll have a couple of bonus sections on special topics. Until then, if you need any Vespel® CR-6100, contact Boulden. We have whatever size and quantity you need in stock and ready for immediate delivery.

For information on how to install Vespel® CR-6100 into nearly any centrifugal pump type, download the Boulden Installation Guide.

The Sydney Opera House , just out of frame is the Sydney Harbor Bridge

The Sydney Opera House, just out of frame is the Sydney Harbor Bridge

 

Contact Us Today To Learn More About Vespel and Boulden Company!

Contact Us Today To Learn More About Vespel and Boulden Company!

 

 

 

 

 

 

 

 

 

 

 

 

ytfbing

Upgrading Pumps With Composite Wear Components Part: 2

Part 2: Reduce Clearance–The Lomakin Effect

Welcome back to our series on upgrading pumps with composite materials. In part 1, we discussed how using composite materials like Vespel® CR-6100 in your pumps allows you to eliminate the metal-to-metal contact points in the pump and minimize the risk of pump seizure:

  • In the shop during assembly
  • In the field during alignment
  • During slow-roll, start-up, and shut down
  • During off-design events like dry-running or low flow

Part 2: Reducing Clearance-The Lomakin Effect

Minimizing the risk of seizure in your pump sets the stage for reducing the clearance at the wear parts in your pump. Reducing clearance can be a significant pump reliability upgrade due to a phenomenon known as the “Lomakin Effect“.

Your Wear Rings are Bearings

During pump operation, the flow created by differential pressure across the wear parts in the pump (wear rings, throttle bushings) creates a force called The Lomakin Effect. The force arises from an unequal pressure distribution around the circumference of the component during periods of rotor eccentricity. This force counteracts shaft deflection in the pump.

Figure 1 shows how shaft deflection creates this force. As the fluid enters the clearance between the rotor and wear component, it accelerates as it passes from the high pressure end to the low pressure end. Due to the eccentricity of the rotor, there is more clearance on one side of the wear part than the other. There will be more flow and a locally higher velocity on the side of the wear ring with more clearance and lower velocity on the side of the ring with less clearance. Higher velocity results in lower pressure; lower velocity results in higher pressure, creating a net corrective force which acts in the direction opposite of the shaft deflection. In other words, when your pump experiences shaft deflection, there is a hydraulic “stiffness” (Lomakin Stiffness) which is generated to counteract the shaft deflection.

Figure 1: The Lomakin Effect

Figure 1: The Lomakin Effect

Using Vespel® CR-6100 you can typically reduce the clearance at the pump wear rings by 50% compared to the API recommended minimum for metal wear parts. The Lomakin Stiffness is inversely proportional to clearance; therefore, a 50% reduction in clearance doubles this force. Potential benefits for your pumps include:

  • Less shaft deflection
  • Lower vibration levels
  • Fewer mechanical seal leaks
  • Longer bearing life

Which Pumps?

The Lomakin Effect is generally beneficial to all centrifugal pumps, but some pump types often show significant vibration reductions and reliability improvements with reduced clearance:

  • Multi-stage horizontal pumps
  • Older overhung pumps with long, thin shafts (high L/D ratios)
  • Two-stage overhung pumps

Conclusion

Reducing the clearance at the wear components can be a major reliability upgrade for your pumps. The reduced clearance increases The Lomakin Effect which improves pump rotor stability. The net result is a pump which runs with potentially lower vibration, fewer seal leaks, and longer bearing life.

Reducing the clearance also increases pump efficiency, which we will discuss in Part 3.

Until then, if you are working on a pump with a long, thin, flexible rotor, contact Boulden to discuss upgrading the wear parts to Vespel® CR-6100 and reducing the clearance. We have a huge stock of Vespel® CR-6100 standard sizes in the USA, Europe, and Singapore available for immediate delivery to your workshop.

For application and installation details, download the Boulden Installation Guide for Vespel® CR-6100