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Upgrading Pumps With Composite Wear Components Part: 8

Upgrading pumps with composite wear components

Part 8: Vertically Suspended Pumps (API Types VS1–3, VS6, VS7)

Review

To date, we have addressed how to install DuPont™ Vespel® CR-6100 into the various horizontal pump types to eliminate metal-to-metal contact points in the pump and minimize the risk of pump seizure. This allows a reduction of clearance which improves efficiency and rotor stability.

This segment will discuss how to use Vespel® CR-6100 in vertically suspended pump types (API types VS1-VS7). These types can be further broken down as “discharge through column” (VS1, VS2, VS3, VS6, VS7) and “separate discharge” (VS4 and VS5).

Which Parts?

In vertically suspended pumps, we can upgrade the same components as horizontal pumps (wear ringsthrottle bushingsthroat bushings) for the same reasons-to eliminate the metal-to-metal contact areas in the pump and reduce the clearance resulting in improved reliability and efficiency.

Today we will focus on the components which are unique to vertically suspended pumps-the vertical pump shaft bearings: line shaft bearings, bowl bearings, and bottom bearings. Vespel® CR-6100 is ideally suited to this application, particularly in services which suffer from a lack of lubricity or may run dry at startup. Vespel® CR-6100 does not seize like metal alloys, it can survive running dry, and it can withstand mechanical impacts and thermal shocks so it doesn’t break like carbon or graphite.

Multi-stage LPG pump bowl assemblies being upgraded to Vespel® CR-6100.

Multi-stage LPG pump bowl assemblies being upgraded to Vespel® CR-6100.

One thing of note is that vertical pump shaft bearings do not have differential pressure across the parts, therefore, they do not impact pump efficiency. Because the clearance of these components tends to be rather tight, to begin with, a further reduction in clearance can easily lead to assembly issues with a limited upside associated with the tighter clearance. Therefore, our recommendation for these parts is to install the Vespel® CR-6100 into the spiders or bowl assemblies with the press fit shown in our installation guide, then final machine to the original design clearance.

In our installation guide, you will find two clearance charts–one for horizontal pump types, one for vertical pump types. Because we don’t want the wear ring clearance tighter than the shaft bushing clearance, we simply recommend making the wear ring clearance 0.002″ (0.05 mm) larger than the shaft bushing clearance in these pumps. In short, we highly recommend that you download the Boulden Installation Guide for Vespel® CR-6100.

Discharge Through Column

Vertically suspended pumps are often selected because the service offers poor suction conditions such as light hydrocarbon service or condensate. In a long-term study, a refinery upgraded 22 vertical pumps to Vespel® CR-6100 wear parts. The pumps were operating in light hydrocarbons, flare knockout drum, and several stop/start services like product transfer. In the 5 years prior to upgrading the pumps, this population of pumps comprised many “bad actors” with poor reliability. In the 5 years after upgrading the pumps to Vespel® CR-6100, there were only 8 repairs on the entire population of pumps and the MTBR of this group of pumps increased to more than 10 years!

The combination of excellent reliability with ease of machining and installation along with immediate stock availability has made Vespel® CR-6100 the material of choice in these applications.

Vertically suspended pumps assembled with Vespel®CR-6100 shaft bearings, wear rings, bowl bushings and bottom bearings

Vertically suspended pumps assembled with Vespel®CR-6100 shaft bearings, wear rings, bowl bushings, and bottom bearings

Vespel® CR-6100 can handle significant periods of dry running with minimal wear, making it easier to bring the pump online. When you upgrade your wear rings to Vespel® CR-6100 and reduce the clearance, you might also find the pump easier to start due to a reduction in the NPSHR (Net Positive Suction Head Required).

To be continued…

In the next two issues, we will address vertically suspended pumps with a separate discharge (API Type VS4) and then we will discuss installation and assembly issues unique to vertically suspended pumps.

Until then, if you have a vertical pump which is giving you headaches, consider upgrading the wear parts to Vespel® CR-6100. Contact us today. We have the Vespel® CR-6100 in stock in a wide range of sizes available for immediate delivery to nearly anywhere in the world.
For details on installing Vespel® CR-6100 into nearly any centrifugal pump type, download the Boulden Installation Guide.

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Gardens by the Bay, Singapore

Gardens by the Bay, Singapore

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: 6

Upgrading pumps with composite wear componentsPart 6: Between Bearings, Axially Split Pumps

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).

Upgrading your pumps with Vespel® CR-6100 wear parts allows you to eliminate the metal-to-metal contact points in the pump and reduce the clearance at the wear parts. This simple change allows you to minimize the risk of pump seizure and helps to improve pump reliability and efficiency.

Axially Split Pumps

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

Single and two-stage BB1 style pumps are often used in product transfer, water, or low NPSH applications. Upgrading the wear rings (and inter-stage bushing in two-stage designs) with Vespel® CR-6100 will help maintain rotor stability and improve efficiency. Reducing wear ring clearance can also help reduce the pump NPSHR

Multi-stage BB3 designs are used in several ideal applications for Vespel® CR-6100: boiler feed water, naphtha charge, amine stripping, and product pipeline and shipping applications. These pumps are designed with inherently flexible rotors which rely upon the Lomakin Effect for rotor stability. Upgrading these pumps with Vespel® CR-6100 and reducing the clearance can reduce vibration levels and make your pump more reliable.

These designs also experience significant efficiency gains when you reduce the clearance at the wear rings, center bushing, and throttle bushing. Most of the multi-stage designs will show at least 3-4% efficiency gain and several customers have reported efficiency gains in excess of 5%.

Solid or Insert?

The first question to address with an axially split assembly is whether or not to make the components out of solid Vespel® CR-6100 or to use Vespel® CR-6100 as an insert into a metal holder (figure 1).

Figure 1: Operating temperature determines whether or not you need to install Vespel® CR-6100 as an insert in these pumps.

Figure 1: Operating temperature determines whether or not you need to install Vespel® CR-6100 as an insert in these pumps.

Consider that Vespel® CR-6100 has a coefficient of thermal expansion which is about 60% less than carbon steel in the radial plane. In a hot pump, the metal parts are going to thermally expand more than the Vespel® CR-6100 parts. We compensate for the thermal expansion difference by installing the Vespel® CR-6100 with a press fit into a metal holder. As the metal holder expands, part of the press fit is relieved, and the Vespel® CR-6100 “follows” the growth of the metal parts.

Therefore, if your pump operating temperature is > 140 F (60 C), the Vespel® CR-6100 needs to be installed as an insert into a metal holder to maintain the clearance up to pump operating temperature. If it is an ambient temperature application, you can install Vespel® CR-6100 as a solid component or as an insert, whichever is easier for you.

One advantage of using inserts in these pumps is that during a repair, you can often salvage the used metal parts, machine the bores and reuse the old parts as holders for the Vespel® CR-6100 inserts. This can save time and reduce the cost of upgrading the pump with Vespel® CR-6100.

Split Parts

Another feature unique to axially split pumps is that the center bushings and inter-stage rings might also be axially split (Figure 2).

Figure 2: Split center bushing with PERF-Seal™ design insert.

Figure 2: Split center bushing with PERF-Seal™ design insert.

When the parts are split, we apply the same rule concerning solid or insert parts based on operating temperature. If the pump is operating at ambient temperature, the parts can be manufactured from solid Vespel® CR-6100; if the pump is operating at elevated temperature, we need to install the Vespel® CR-6100 as an insert with a press fit.

The press fit for split parts is achieved by modifying the metal components such that they bolt together. The bolting force is sufficient to create the press fit of the Vespel® CR-6100 component.

If you need to fabricate split parts, please contact Boulden and we will send you specific instructions based on your application details.

Center and Throttle Bushings

Another unique characteristic of multi-stage axially split pumps is that the center and throttle bushings can be exposed to high differential pressures. For these components, Boulden has developed a patent-pending design called the PERF-Seal™ (also shown in Figure 2) which improves the performance and dramatically increases the differential pressure capability of composite materials used in these positions.

Boulden recommends the PERF-Seal™ design for all center and throttle bushings in multi-stage 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.

Until next time…

In the next months, we will discuss radially-split between bearings pumps and vertically suspended pumps.

Until then, if you have an axially 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.

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Todays Photo

Chris Froome in Mondorf Les Bains, Luxembourg, ville-départ, Tour de France, Stage 4 on July 4th, 2017. Walking distance from Boulden’s European Office

Chris Froome in Mondorf Les Bains, Luxembourg, ville-départ, Tour de France, Stage 4 on July 4th, 2017. Walking distance from Boulden's European Office

Chris Froome in Mondorf Les Bains, Luxembourg, ville-départ, Tour de France, Stage 4

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: 5

Upgrading pumps with composite wear componentsPart 5: Upgrading overhung pump types with DuPont™ Vespel® CR-6100.

Review

So far, we have discussed how upgrading your pumps with composite wear parts can help avoid galling and seizing, which allows you to reduce the clearance in your pump. This small change increases the Lomakin Effect and makes your pump more reliable. Reduced clearance also improves pump efficiency, leading to a lower pump life cycle cost.

Last month, we highlighted that Vespel® CR-6100 is installed in compression in the stationary parts of your pump–wear rings, throttle bushings, throat bushings, and vertical pump shaft bearings–and can be used in nearly all process chemicals from cryogenic temperatures to 500 F (260 C).

Today, we start discussing how to install Vespel® CR-6100 to upgrade your overhung pumps, which typically make up the majority of the centrifugal pump population in a process plant. For most designs, there are only three parts to upgrade to Vespel® CR-6100: two case wear rings and the throat bushing.

Manufacturer Case Wear Rings from Vespel® CR-6100

You can usually manufacture the case rings from solid Vespel® CR-6100 and press them directly into the case and head of the pump. Because the pump casing can often be quite large and difficult to handle, it is generally easiest to design the case rings such that they do not require final machining. The way to do this is to assume there is a 1:1 ratio between the press fit and the closure of the inside diameter during the press fit.

For example, if your case rings require 0.020″ (0.50 mm) press fit, machine the inside diameter 0.020″ larger than the final target dimension before the press fit. After the ring is pressed into place, the inside diameter will decrease by 0.020″ and will match the target dimension (give or take a small tolerance).

Alternatively, you can use a metal ring as a “holder”. First, press the Vespel® CR-6100 into the metal ring and then final machine the Vespel® CR-6100 to the desired clearance. This is sometimes a better choice for case rings with very large radial walls or rings with “L” shaped profiles (See Photo 1). By using an insert you can use standard stock sizes of Vespel® CR-6100.

case rings with Vespel CR-6100

Photo 1: Insert into “L” profile case ring

Vespel® CR-6100 can be used for the Throat Bushings

Several mechanical seal flush plans require a close clearance throat bushing to increase the seal chamber pressure, to isolate cooled seal flush fluid from hot process fluid, or to isolate clean seal flush fluid from dirty or corrosive process fluid. Vespel® CR-6100 can be used for the throat bushing.

To set the clearance of the throat bushing, consult your mechanical seal supplier. They should recommend a clearance based on your seal flush plan such that your seal operates with the correct pressure and flow rate of seal flush.

Which Pumps

Reducing the clearance at the wear rings will improve the efficiency of all of your overhung pumps. That said, some pumps can be considered with higher priority than others.

The first place to look is older pumps with long slender shafts with high L/D ratios (see Photo 2), especially two-stage overhung pumps. These pumps were typically built for packing and have been converted to mechanical seals. These designs often excessive shaft deflection, making it difficult for seals to meet current reliability and emissions standards. Closing the wear ring clearance will add stability to the rotor and provide the seals a better operating environment. On the two-stage overhung pumps, you can also upgrade the bushing between the stages for additional support.

Overhung pump

Photo 2: Overhung pump with high L/D ratio

Next, look at your largest overhung pumps. These pumps will typically have higher radial loads when running away from their design point and potentially experience more shaft deflection. Plus, they will consume the most power, generally offering the best payout for efficiency gains.

Finally, consider upgrading your OH4-vertical inline, rigidly coupled pumps. Because these pumps have no bearing housing, they rely upon the motor bearing and the wear rings for radial stability. Reducing the wear ring clearance can often improve the reliability of these pumps.

Upgrading Pumps to be continued…

In the next months, we will discuss upgrading horizontal between bearings pumps and vertically suspended pumps.

Until then, if you have an overhung 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 material required for the upgrade in stock is a wide range of sizes available for immediate delivery.

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Upgrading Pumps With Composite Wear Components Part: 4

Upgrading pumps with composite wear componentsPart 4: Which services, which machines, which parts to upgrade?

Review

In the first part of this series, we discussed how upgrading your pumps with composite wear parts can help avoid galling and seizing, even when a pump runs dry. Because composite parts do not gall or seize like metal parts, this allows you to reduce the clearance at these components in your pump.

In Part 2, we discussed how reducing the clearance at the wear ringsthrottle bushings, and center-stage bushings increases a stabilizing force in your pump called The Lomakin Effect. This force helps to reduce vibration and shaft deflection, leading to longer seal and bearing life in your pumps.

In Part 3, we discussed how reducing the clearance in your pump also improves pump efficiency, leading to a significant reduction in the life cycle cost of the pump.

Today, we start the discussion on how you can upgrade pumps, by looking at the specific services and components to upgrade with Vespel® CR-6100.

Service Conditions

Vespel® CR-6100 is manufactured from carbon fibers and Teflon™ PFA resin. It is chemically resistant to nearly all process fluids used in the hydrocarbon processing and petrochemical industries. Vespel® CR-6100 has been used in a wide range products including (but not limited to): refined hydrocarbons, aromatic hydrocarbons, LPG, amines, sour water, caustic, ammonia, MEK, demineralized water, hydrofluoric acid, and boiler feed water.

The temperature range of Vespel® CR-6100 is cryogenic to 500 F(260 C). It has been used in liquid methane and ethane pumps at -230 F (-150 C), along with liquid nitrogen and liquid hydrogen at even lower temperatures. At the upper end of the temperature range, Vespel® CR-6100 has been used in a wide range of hydrocarbon processing services such as gas oil and naphtha.

In general, composite materials are used for refined process fluids and relatively clean utility services. Vespel® CR-6100 is superior to metallic components in avoiding seizure, running with tighter clearance, and resisting wear due to internal contact between rotating and stationary components. Conversely, if you are dealing with a slurry service where abrasive wear is the main problem facing the pump, composite materials have some limitations. Please contact Boulden to discuss your application conditions.

Which Components

Vespel® CR-6100 will generally be used as the stationary wear parts in the pump. As we noted in the previous parts of this series, our objective is to eliminate the metal-to-metal contact points in the pump and replace them with metal-to-composite contact points. Vespel® CR-6100 is used for the stationary parts because it is stronger in compression than in tension. The rotating parts in the pump remain metal–with no special requirements for surface finishes or hardness beyond the original design of the metal parts.

Table 1 shows which parts are typically converted to Vespel® CR-6100 based on the pump type:

Overhung Pumps Between Bearings Pumps Vertically Suspended Pumps
Case wear rings Case wear rings Case wear rings
Throat bushings Throat bushings Throat bushings
Inter-stage bushings Line-shaft bearings
Center-stage bushings Bowl bearings
Throttle bushings Bottom bushings

Beyond centrifugal pumps, Vespel® CR-6100 can be used for a wide range of product-lubricated components such as agitator bearingsAPI Separator bearings, and gear pump bearings.

Until Next Time

In the next several segments of this series, we will discuss how to install Vespel® CR-6100 by pump type, discussing the differences between radially and axially split pumps, specific considerations for vertically suspended pumps, and some unique situations you might encounter.

Until then, if you have a pump operating at less than 500 F (260 C) where you want to improve the reliability or efficiency, 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

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Upgrading Pumps With Composite Wear Components Part: 3

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Part 3: Reduce Clearance–Improve Pump Efficiency

Welcome to Part 3 in our series on upgrading pumps with composite wear parts.

In the first part of this series, we discussed how upgrading your pumps with composite wear parts can help avoid galling and seizing. Because composite parts do not gall or seize like metal parts, this allows you to reduce the clearance at these components in your pump.

In Part 2, we discussed how reducing the clearance at the wear rings, throttle bushings, and center-stage bushings creates a stabilizing force in your pump called The Lomakin Effect. This force helps to reduce vibration and shaft deflection, leading to longer seal and bearing life in your pumps.

Today, we will discuss how reducing the clearance in your pump also improves pump efficiency.

Background

According to a major centrifugal pump OEM, energy consumption accounts for 44% of the life cycle cost of a centrifugal pump. You can reduce this cost by upgrading the wear components to a composite material like Vespel® CR-6100 and reducing the clearance in your pump.

The specific components where you want to reduce the clearance are the pump wear rings, inter-stage rings, center-stage bushing, and throttle bushing. These components form the barriers between high-pressure and low-pressure areas within the pump. The differential pressure across these components creates internal recirculation within the pump, resulting in a loss of pump efficiency (Figure 1).

 

Leakage wear rings

Leakage past the wear rings (QL) creates efficiency loss

 

 

 

 

 

 

Which Pumps Produce the Biggest Gains?
When you upgrade these components to Vespel® CR-6100, you can typically reduce the clearance by 50% compared to the API minimum for metal parts. If you reduce the clearance by 50%, you reduce the internal recirculation by approximately 50%, leading to a significant efficiency gain.

If we consider only efficiency gains, horizontal multi-stage pumps usually offer the best return on investment from an upgrade to Vespel® CR-6100 with reduced clearance. These pumps have multiple leak paths across wear rings, inter-stage rings, center bushings, and throttle bushings. Because they have many stages, these pumps also tend to consume a lot of power. Consider the following cases where process plants have reduced the operating costs of their multi-stage horizontal pumps:

  • A power station upgraded a 3MW boiler feed water pump with Vespel® CR-6100 along with the Boulden PERF-Seal™ design and reduced clearance and recorded a 7% efficiency gain compared to a newly rebuilt pump with original clearances.
  • A refinery upgraded their hydrocracker charge pumps with Vespel® CR-6100 along with the Boulden PERF-Seal™ design and reduced clearance and recorded 4% more through put to their hydrocracker-a hugely profitable upgrade.
  • A product pipeline company upgraded their LPG shipping pumps with Vespel® CR-6100 and reduced clearance, resulting in a 4% efficiency gain.

Another area to consider is process pumps which are marginally undersized, requiring parallel pump operation to achieve 100% of the target process rate. Sometimes, a modification as simple as reducing the wear ring clearance can get you back to one-pump operation with a full-capacity spare pump.

The PERF-Seal™

To further increase the efficiency gain associated with reduced clearance, the components can be modified with the Boulden PERF-Seal™ design. Internal testing has shown that the PERF-Seal™ creates an additional reduction in flow across throttle bushings, center-stage bushings, and wear rings beyond what can be achieved with reduced clearance alone.

Conclusion

When you eliminate the metal-to-metal contact surfaces in your pumps and use Vespel® CR-6100 stationary wear components, you can then reduce the clearance. This reduction in clearance improves pump efficiency and lowers the operating cost of the pump. Numerous field examples exist where customers have saved tens of thousands of dollars on their annual pump operating costs with this simple upgrade.

If you have a pump where improved efficiency will save you money, 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

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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.

 

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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.

How Much Money Can You Save Increasing the Efficiency of a 500 kW (700 HP) Pump?

According to a major centrifugal pump OEM, energy consumption accounts for 44% of the life cycle cost of a centrifugal pump. With a multi-stage horizontal pump, improving pump efficiency by using Vespel® CR-6100 can make a significant contribution to reducing this cost.

The efficiency improvement from DuPont™ Vespel® CR-6100 results from reduced clearance at the internal wear components in the pump: pump wear rings, inter-stage rings, center-stage bushing, and throttle bushing. These components form the barriers between high-pressure and low-pressure areas within the pump. Because Vespel® CR-6100 is a non-seizing material, the clearance at these interfaces can be reduced, reducing internal leakage losses from high-pressure to low-pressure areas, and thereby increasing efficiency.

For a typical multi-stage horizontal pump (API types BB3, BB4, or BB5), reducing the clearance at the wear components will create a 3-5% efficiency improvement. Just looking at the efficiency gain, upgrading these pumps to Vespel® CR-6100 can be a compelling investment.

Cost of Upgrading a 500 kW (700 HP) pump

Consider a recent application at a refinery where the plant engineers upgraded an API type BB3, 7-stage unit charge pump with Vespel® CR-6100. The fluid pumped is gas oil at 23 ⁰C (73 ⁰F) with a total differential head of 1371 meters (4497 feet). The pump has a rated power of 508 kW and uses a double-suction first stage impeller, a center bushing between the 4th and 7th stage, and a throttle bushing at the 5th stage suction.

Fully upgrading this pump with Vespel® CR-6100 requires 8 wear rings, 4 inter-stage rings, 1 bushing between 1st and 2nd stage, a center bushing, and a throttle bushing. The wear rings of this pump are 200 mm diameter (8”) and the inter-stage rings and bushings are approximately 140 mm (5.5”) diameter. Using the geometry of the actual parts from the pump and including Boulden’s PERF-Seal™ design for the center and throttle bushings, the estimated cost for all of the stationary wear parts in this pump manufactured from Vespel® CR-6100 is $15,800.

Savings

How much the customer saves is a function of the cost of power. Table 1 shows the annual savings from a 4% efficiency gain from a 508 kW pump based on different power costs:

Local cost of power ($/kW-hr) $0.05 $0.08 $0.10 $0.12
Annual Savings (4% of 508 kW) $8,970 $14,400 $17,900 $21,500

If we only account for the energy savings in this pump, the upgrade to Vespel® CR-6100 pays for itself in a range of about 20 months in regions with low cost power to less than a year in regions with higher power costs. If you are interested in saving money with your charge pumps, boiler feed pumps, amine pumps, or product shipping pumps, contact Boulden today to discuss an upgrade to Vespel® CR-6100 in your service.