Tag Archives: Vespel

Diesel Charge Pump Case Study

DuPont™ Vespel® CR-6100 helps the pump survive and keep pumping.

The Diesel Charge Pump

A refinery in North America experienced recurring issues with their diesel charge pumps. The pumps provide feed into the refinery HDS unit. Loss of feed to the unit can result in reduced refinery production and significant losses.

The refinery has 3 total pumps in this service–two pumps running in parallel with an installed spare. The pumps are 1200 HP (900 kW), 13-stage, axially-split, between-bearings pumps (API Type BB3), running at 3550 RPM. The product is diesel fuel at approximately 250 F (120 C).

The original design of these pumps included metal wear rings, throttle, and center bushings. During the previous process upsets, these metal wear parts had seized, requiring expensive pump overhauls. The overhauls required the services of an outside shop, exposing the refinery to production risk due to operating without a spare pump for several weeks.

 

Vespel® CR-6100 is Put to the Test

Earlier this year, the refinery upgraded the first of the three pumps to Vespel® CR-6100, using Boulden’s patented PERF-Seal design for all of the stationary wear parts. The rotating wear parts remained metal, using the original metallurgy and surface finish.

Soon after the upgrade, a process upset caused a temporary loss of flow to the pumps. Figure 1 shows the process flow data during the upset condition. Each box along the x-axis represents one hour and the y-axis represents flow rate. Without sufficient flow to the pumps (blue and cyan lines), minimum flow (yellow line) could not be immediately established, causing the pumps to run at extremely low flow rates for nearly an hour. Partial flow was re-established, but the pumps continued to operate far below the design flow rate for nearly 4 more hours.

Figure 1: Process flow data for the diesel charge pumps during the process upset

 

normal process conditions were finally restored, the pumps were individually shut down for inspection. The pump with metal wear components seized upon shut down had damage to both bearings and required significant repair work.

The pump with Vespel® CR-6100 rotated freely, with the inspection revealing some damage to the thrust bearing. The thrust bearing was replaced in the field and the pump returned to service where it ran at full rate with no evidence of reduced performance or vibration issues.

 

Conclusion

In an ideal world, plant processes always operate per design. Unfortunately, there are times when things do not go as planned. When that happened to this refinery, the pump with Vespel® CR-6100 survived where the pumps with metal components could not.

Beyond surviving this incident, the refinery also reports that the pump is running with lower vibration than the pumps with metal components. With reduced clearance at the wear parts, the pump is almost certainly consuming less power, further reducing the life cycle cost of the pump.

If you have a service causing any issues at your plant, contact Boulden today. We have Vespel® CR-6100 in stock in a wide range of sizes in the USA, Europe, and Singapore and we can assist with any application or design questions you have. If you know what you need, just request a quote. Until next time, be safe.

 

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

October in the forest, Mullerthal, Luxembourg

 

14 Reasons to Reduce Wear Ring Clearance

Use DuPont™ Vespel® CR-6100 to reduce the clearance in your pumps and improve pump reliability and efficiency.

Vespel CR-6100 Review

A couple weeks ago, we looked at all of the negative consequences from increasing the wear part clearance in you pumps: wear rings, inter-stage rings, throttle bushings, and center bushings. In the past, increasing the clearance was a typical response to pump seizure.

Now, there is a better way to address the issue and make your pump more reliable and efficient at the same time. Instead of increasing the clearance of the metal parts, replace the stationary wear parts with non-seizing, non-galling Vespel® CR-6100 and reduce the clearance. With this simple change, all the contact points in the pump become metal-to-composite and the risk of seizure is minimized.

What if you reduce the clearance?

Because Vespel® CR-6100 is non-seizing, you can safely reduce the clearance at the wear parts in your pumps. Even if the pump runs dry, Vespel® CR-6100 will not seize like metal components.

 

 

When you reduce the clearance at your wear parts, essentially every aspect of the pump hydraulic performance improves. Reduced clearance also tends to produce lower vibration levels. In short, the pump will likely be easier to operate, more reliable, and consume less power.

 

14 Benefits of Reduced Clearance using Vespel CR-6100 

 

Hydraulic Benefits Mechanical Benefits
Higher head Increased rotor stiffness
Higher flow–higher potential maximum flow rate Potentially lower vibration
Increased efficiency–reduced power consumption Potentially reduced shaft deflection
Lower NPSHR–lower risk of cavitation Reduced risk of shaft breakage
Reduced motor load Potentially longer seal life
Steam turbine drivers can run at lower speeds Potentially longer bearing life
Reduced need to run pumps in parallel Reduced potential for motor tripping or over-heating

 

The PERF-Seal™

The benefits of reducing the clearance can be augmented using the patented Boulden PERF-Seal™ design. The design is simple to implement, increases the potential efficiency gain from the upgrade, adds a significant amount of hydraulic damping, and generally amplifies the benefits of your upgrade to Vespel® CR-6100. Contact Boulden for details.

Two-stage product shipping pump upgraded with the PERF-SEAL deign

The Poster Pump, continued…

Two weeks ago, we wrote about an 11-stage horizontal pump which had seized several times. Each time it seized, the wear part clearance was increased. After the clearance had been increased multiple times, the pump would vibrate beyond alarm limits and the pump was no longer operable.

The plant upgraded the pump with Vespel® CR-6100 case rings, center bushing, and throttle bushing, using the Boulden PERF-Seal™ design. They subsequently reduced the clearance to less than the original design clearance. After the upgrade, the pump ran without seizing, very low vibration, and a significant efficiency gain.

 

Conclusion

What do you think of our list of benefits from reduced clearance? Is there anything we should add? Anything you disagree with? Let us know your ideas. We will be happy to hear from you.

 

Until next time, if you have a pump in your shop which can benefit from an upgrade to Vespel® CR-6100 and reduced clearance, contact Boulden. We can answer your questions and we have material in stock and available for immediate shipment.

 

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

Place Stanislas is considered to be one of, if not the most beautiful royal squares in Europe. It was added to UNESCO’s World Heritage List in 1983.

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

 

 

Prepping Your Metal Parts

Prepare your pump parts for an upgrade to DuPont™ Vespel CR-6100

Review on Pump Parts and upgrading to Vespel CR-6100

The National Geographic Channel used to run a show called Doomsday Preppers where survivalist families would prepare for apocalyptic disasters and societal collapse. Although that sounds like a lot of fun, at Boulden, we are more concerned with helping your pumps survive adverse process conditions with an upgrade to DuPont™ Vespel® CR-6100.

 

Last month, we outlined the measurements required for a Vespel® CR-6100 installation. When you have decided to go forward with the upgrade, the first step will be to prepare the metal parts to facilitate the installation.

 

Start with a Little Chamfer

Vespel® CR-6100 is used for stationary wear components–throttle bushings, case wear rings, center-stage bushings, inter-stage case rings, vertical pump shaft bearings, throat bushings, agitator bearings, API separator bearings-basically any product lubricated wear part.

 

The material is installed with a significant press fit. To facilitate the press fit operation, the metal bore into which you will be pressing the Vespel® CR-6100 requires a small chamfer or radius (Figure 1). It is very important that any corners or sharp edges are fully broken and smoothed with a stone so that the metal edge does not remove material from the outside surface of the Vespel® CR-6100 during the press operation.

Figure 1: Chamfer or Radius Leading Edge to facilitate press fit. (Note shoulder on low-pressure side.)

 

 

 

 

 

 

 

 

 

Make Sure There is a “Shoulder” or “Step”

For any part exposed to differential pressure, it is important that the design features a shoulder or step at the low-pressure end (shown on the right side of Figure 1) to ensure the differential pressure does not dislodge the Vespel® CR-6100 during operation.

 

Some radially split multi-stage pumps (BB4 and BB5) pumps feature metal wear rings welded into the pump diffusers with no step or shoulder incorporated in the design. In this case, you can consider modifying the diffusers so that the case wear rings have an “L” shaped profile like the rings below which were used in a hydrocracker charge pump.

Figure 2: “L” Shaped wear ring profile for BB4 or BB5 pump type.

 

Conclusions

Vespel® CR-6100 can help you avoid pump seizure during extreme events like running dry. The temperature limit is 500 F (260 C), allowing it to survive infernal heat waves. The material is not affected by electromagnetic pulses. polar shifts, or solar flares. As an added bonus, Vespel® CR-6100 has an indefinite shelf life, making it an ideal material to stockpile in your underground bunker, and the material is likely to hold its value in the case of hyperinflation.

 

In reality, you don’t have to stockpile the material. Boulden carries a huge inventory of stock sizes in the USA, Europe, and Singapore. You can generally receive whatever material you need in a matter of days.

 

To prepare your pump for whatever the future holds, please contact Boulden with your application details and dimensions. We’ll be happy to walk you through the installation details–assuming we have not been wiped out by an asteroid strike.

Todays Photo

All this talk of disaster is making me hungry. This is some excellent Bun Cha in Vietnam.

 

 

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!

 

 

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

Upgrading Pumps With Composite Wear Components Part: 9

Upgrading pumps with composite wear componentsPart 9: Vertically Suspended Pumps with Separate Discharge (API Type VS4)

Review

Last week, we looked at vertically suspended pumps with the discharge through the column. This week, we take a look at vertically suspended pumps with a separate discharge (API Type VS4).

Vertically suspended pumps with separate discharge are generally used for sump pumps or wastewater pumps. It seems that these pumps cause headaches at most plants. The shaft bushings wear out leading to chronic repairs. Over the years, Vespel® CR-6100 has been used in a lot of these pumps, sometimes the pump life has been extended from a few months to several years; sometimes the pump life has not improved. Therefore, it is important to identify the failure mode before making the upgrade. We have used our experience to create the roadmap below.

Define the Service

The first step is to clarify “sump pump” or “waste water pump”, which are generic terms encompassing a wide range of services. Some services are pumping primarily chemicals mixed with water, and some of them are pumping primarily water mixed with dirt. Some of the sumps are so dirty, that the pump suction strainer seems to be immersed in mud. Another variable is that the shaft bearings are flushed with different arrangements. Some of them are flushed with the process fluid, others with clean water, and others are greased.

Given the range of service conditions, there are several different problems which can cause the shaft bearings to fail. However, there are some commonalities. First, by design, the shaft bearings are along the column of the pump with a separate discharge for the process fluid. The 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 grease supply runs out. In a chemical sump, the mix of chemicals can cause corrosion with metal wear parts. Finally, in very dirty sumps where the bearings are flushed with the process fluid, abrasive wear tends to be the main problem.

The Road Map

Considering the above, we have created the following table to guide your selection of where to use Vespel® CR-6100 in sump pump services:

Vespel CR-6100 sump pump services.

Vespel CR-6100 sump pump services.

*Some of the alternatives to consider are switching to a clean water flush or looking at an abrasive resistant, non-seizing combination for the shaft bushings and sleeve. This generally entails a hardened sleeve and an abrasive resistant bushing material. If you have any doubts about whether Vespel® CR-6100 is a good fit for your service, contact Boulden to discuss.

Vertical Pump Conclusion

To finish our discussion of vertically suspended pumps, we will talk about assembly and installation issues which impact pump reliability. Until then, use the above information as a guide on how to use Vespel® CR-6100 in your pumps with a separate discharge. If you need any material, 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.

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

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

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Today’s Photo

Late Night Snack, Thailand

Late Night Snack, Thailand

 

 

 

 

 

 

 

Boulden Company

Conshohocken, PA, USA

1-610-825-1515

 

Boulden International, S.ar.L

Ellange, Luxembourg

+352 26 39 33 99

Upgrading Pumps With Composite Wear Components Part: 7

Upgrading pumps with composite wear componentsPart 7: Between Bearings, Radially Split Pumps (API Types BB2, BB4, and BB5)

Review

DuPont™ Vespel® CR-6100 is a composite material which is used for the stationary wear parts of your pump and can be used in nearly all process chemicals from cryogenic temperatures to 500 F (260 C).

The upgrade to Vespel® CR-6100 wear parts involves two steps: eliminate the metal-to-metal contact points in the pump to minimize the risk of pump seizure, then reduce clearance to improve reliability and increase efficiency.

Radially Split Pumps

Today, we cover the details on using Vespel® CR-6100 to upgrade your between-bearings, radially-split pumps. The components we want to upgrade in these pumps are the case rings, throttle bushing, and throat bushings.

Single and two-stage BB2 style pumps are widely used in refining and petrochemical applications featuring higher temperatures and low NPSH available. Upgrading the wear rings (and inter-stage bushing in two-stage designs) with Vespel® CR-6100 and reduced clearance will help maintain rotor stability, improve efficiency, and reduce the pump NPSHR.

Multi-stage BB4 and BB5 designs are used in several ideal applications for Vespel® CR-6100: unit charge pumps in refinery, petrochemical, and gas processing along with boiler feed water in many different industries. Upgrading the wear rings and throttle bushings of these pumps with Vespel® CR-6100 and reducing the clearance can produce significant efficiency gains of 4-6%. Higher efficiency translates to either lower operating cost as your pump uses less energy to produce the same flow, or increased throughput which can pay for the upgrade in a matter of days

Wear Rings

The key point in upgrading the wear rings in these designs is to ensure the Vespel® CR-6100 is retained against differential pressure. In many designs, the original case wear rings are manufactured with an “L” shaped profile as shown in Figure 1. This shape of this design will, in most cases, retain the rings against differential pressure. You only need to modify the original design to incorporate the press fit required for Vespel® CR-6100 and then final machine the rings after they are pressed into the diffusers.

Vespel® CR-6100 case rings for a hydrocracker charge pump

Vespel® CR-6100 case rings for a hydrocracker charge pump

 

In some pumps, however, the case rings go straight across the diffusers. When they are metal rings, they are usually welded in place. To replace these designs with Vespel® CR-6100, you may need to modify the diffusers to incorporate an “L” shaped profile, or design another method of retaining the components against differential pressure. If you have any questions, contact Boulden with the pump cross sectional drawing and we can help.

Throttle Bushings (aka Balance Drums)

The throttle bushings of BB4 and BB5 pump types can be exposed to high differential pressures. For these components, Boulden has developed a patent-pending design called the PERF-Seal™ which improves the performance and dramatically increases the differential pressure capability of composite materials used in this position.

Boulden recommends the PERF-Seal™ design for all throttle bushings in BB4 and BB5 pumps. Contact us and we can either supply machined parts or provide drawings for you to manufacture the components in your shop for the upgrade.

To be continued…

Our final look at specific pump types will feature vertically suspended pumps. After that, we will cover a few specific topics and wrap up this series.

Until then, if you have a radially split pump where you would like to improve the reliability or efficiency, contact Boulden today. We can provide you all of the details required for your upgrade and have the Vespel® CR-6100 in stock in a wide range of sizes available for immediate delivery.
For details on installing Vespel® CR-6100 into nearly any centrifugal pump type, download the Boulden Installation Guide.

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

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

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

Upgrading Pumps With Composite Wear Components Part: 1

Part 1: Minimize the Risk of Pump Seizure

Welcome to our series on upgrading pumps with composite materials. Over the next few months, we’ll cover the basics of why and how to use composite materials, specifically DuPont™ Vespel® CR-6100, to make your pumps more reliable, efficient, and safe.

Metal Parts Seize

Centrifugal pumps contain contact points between rotating and stationary parts. Most designs use replaceable wear components at these contact points: wear rings, inter-stage rings, throttle bushings, center-stage bushings, vertical pump shaft bearings, throat bushings. In the past, both the rotating and stationary parts would typically be metal.

With metal rotating and stationary components, there is a risk of galling or pump seizure. Galling can cause your pump to stick during assembly in the workshop, during alignment, or when the pump is slow-rolling in the field. This is a nuisance which can cause costly delays, returning the pump to the shop for disassembly, clean-up, re-assembly, and a return to the field. If a pump seizes during full-speed operation due to running dry, low flow, valve failure, bearing failure, shaft breakage, or another off-design scenario, the welding of metal parts together will generally cause the pump to stop abruptly, causing severe pump damage along with the potential for safety and environmental impacts.

 

new boulden

Vertical LPG pump with metal shaft bushings seized, shaft broke, impellers and bowl assemblies destroyed.

Eliminate the Metal-to-Metal Contact Points in Your Pump

At a very basic level, the reason to upgrade the wear components in your pumps to composite materials is because composite materials are completely dissimilar to metal. Due to the totally different material compositions, metal-to-composite contact does not result in seizure like metal-to-metal contact.

So, our first objective when we are upgrading our pump with composite materials is to eliminate the metal-to-metal contact points within the pump. When using Vespel® CR-6100, the rotating parts will typically remain metal and the stationary parts will become Vespel® CR-6100. With this simple change, we now have metal-to-composite contact points in the pump and the risk of seizure is minimized.

Horizontal LPG pump ran dry with Vespel® CR-6100 case rings. No damage to impellers, case, shaft, or bearing housings. Photo: Vespel® CR-6100 wear ring as found during disassembly

Horizontal LPG pump ran dry with Vespel® CR-6100 case rings. No damage to impellers, case, shaft, or bearing housings. Photo: Vespel® CR-6100 wear ring as found during disassembly.

Conclusion

Eliminate the metal-to-metal contact points in your pumps by upgrading the stationary components to Vespel® CR-6100. This simple upgrade will minimize your risk of pump seizure, eliminate nuisance repairs from pumps galling during alignment or slow-roll, and will help mitigate the risks and damage due to off-design operational events including dry-running operation.

Because the risk of pump seizure is minimized, you can now safely reduce the clearance at the wear components, setting up several additional benefits. We’ll talk about reducing the clearance in Part 2.

Until then, if you have had troubles with a pump which galls or seizes, contact Boulden to discuss upgrading the wear parts to Vespel® CR-6100. 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.

Reduce Shaft Deflection by Upgrading Your Wear Rings

The shaft deflection in your pump directly affects mechanical seal reliability. Reducing wear ring clearance is an easy upgrade to minimize shaft deflection.

Consider the faces of your mechanical seals–lapped flat to within one or two light bands of flatness, designed to run with precise alignment and minimal leakage across the faces. Excessive shaft deflection at the seal prevents proper alignment of the faces, potentially allows particles between the faces, and can lead to higher leakage and faster wear of critical components.

Reducing the clearance at your pump wear rings will help reduce shaft deflection and improve your seal life.

What does API say?

API 610 11th Edition (section 6.9.1.3) states: To obtain satisfactory seal performance, the shaft stiffness shall limit the total deflection under the most severe dynamic conditions over the allowable operating range of the pump with maximum diameter impeller(s) and the specific speed and liquid to 50 μm (0.002 in) at the primary seal faces.

The same section goes on to state the variables pump designers can manipulate in order to achieve this target:

  • Shaft diameter
  • Shaft span between bearings or shaft overhang
  • Casing design including dual volutes or diffusers

Finally, there is a provision for the wear rings: For one- and two-stage pumps, no credit shall be taken for the liquid stiffening effects of impeller wear rings. For multistage pumps, liquid stiffening effects shall be considered and calculations performed at both one and two times the nominal design clearances. 

Why does wear ring clearance matter?

That last phrase highlights a major role of pump wear rings. Why does the standard insist that the designer calculate the stiffness effects at one and two times clearance?

The reason is the Lomakin Effect–the bearing effect generated by the differential pressure across the wear rings and throttle bushings in your pumps. The stiffness from the Lomakin Effect is inversely proportional to clearance. If your wear ring clearance doubles, you lose half the stiffness generated by the wear rings.

Conversely, if you use non-seizing composite wear rings from materials like DuPont™ Vespel CR-6100, you can reduce the clearance by up to 50% and double the stiffness generated by the wear rings. Increased stiffness from the wear rings helps to reduce shaft deflection. Field results have shown that pumps running with reduced clearance exhibit lower vibration and fewer seal leaks.

New Pumps Only

It is important to note that the current API standard applies to new pumps. For pumps which already exist in your plant, upgrading the wear rings and reducing clearance is an easy upgrade; whereas, there is little you can do to modify the design of the shaft or volute without a major pump upgrade or replacement.

This is particularly important because the refineries in North America and Europe (along with older plants around the world) continue to operate large populations of pumps from the 60’s 70’s and 80’s. One- and two-stage pumps built during that period frequently have long, thin shafts which suffer from excessive shaft deflection. Multi-stage pumps, including those built to the current standard, also have flexible shafts and rely upon the wear rings to limit shaft deflection.

Upgrading older and multi-stage pumps with Vespel CR-6100 wear rings and reducing the clearance is one of the fastest and easiest ways to improve the reliability of these older pumps. The upgrade will also produce a significant increase in pump efficiency.

Conclusion

Reducing wear ring clearance will help reduce the shaft deflection in your pumps and help improve your mechanical seal performance. Vespel CR-6100 has proven reliable in a wide range of services from cryogenic to 260 C (500 F) in thousands of applications around the world.

Contact Boulden today with your application details, and we can discuss whether Vespel CR-6100 is a good fit for your pump. We have a huge inventory of stock sizes available for immediate delivery almost anywhere in the world.

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