Tag Archives: boiler feed water pumps

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 Interference Fit – Setting the interference fit value for DuPont™ Vespel CR-6100

The interference fit value for DuPont™ Vespel CR-6100

Review

We have discussed how to measure your pumps and prepare the metal parts. The next step is to machine the DuPont™ Vespel® CR-6100 part to have the correct dimensions.

Remember, Vespel® CR-6100 is used for stationary wear parts like wear rings, throttle bushings, and vertical pump shaft bearings. The rotating components running against the Vespel® CR-6100 remain metal. The Vespel® CR-6100 components are installed with an interference fit (aka “press fit”).

 

Installation Guide for Vespel CR-6100

The Boulden Installation Guide for Vespel® CR-6100 Tables 1a (Imperial) and 1b (Metric) outline the interference fit values for a Vespel® CR-6100 component based on diameter and the pump operating temperature.

If you only want the right value, follow the guide. You can stop reading and contact Boulden whenever you need material or if you would like to request a quote. If you want to know how we arrived at the values, continue reading.

 

Low Coefficient of Thermal Expansion

Vespel® CR-6100 has an extremely low coefficient of thermal expansion–about 60% lower than carbon steel in the radial plane. This property is one of the reasons Vespel® CR-6100 can survive pumps running dry and avoiding seizure.

The low coefficient of thermal expansion is a main factor in the interference fit value. At elevated temperatures, the metal parts will thermally expand more than the Vespel® CR-6100 parts. Therefore, as pump operating temperature increases, the interference fit increases.

 

Vespel CR-6100 Low Modulus of Elasticity

Vespel® CR-6100 parts press in relatively easily due to a very low modulus of elasticity. Vespel® CR-6100 can be used in temperatures up to 500 F (260 C). At maximum operating temperature, the recommended interference fit can be quite high. Due to the low modulus, the material generally presses in without issue.

 

Small Pilot Fit

To facilitate the large interference fit, machine a small pilot or “step” on the leading edge (Figure 1) of the Vespel® CR-6100 component. This will help the part sit squarely in the bore as it is being pressed in (Figure 2).

Figure 1: Pilot Fit on leading edge to facilitate press fit

Figure 2: Press fit operation

No Pins or Screws Required

Once Vespel® CR-6100 is installed with a press fit and a shoulder to retain the part against differential pressure, no further retention of the components is required. There are thousands of pumps running for many years with Vespel® CR-6100 components without retaining pins or screws.

If you insist on using retaining pins with Vespel® CR-6100, contact Boulden and we will discuss the possible designs given your part geometry.

 

Conclusions

When installing Vespel® CR-6100, make sure you are using the correct interference fit. Download our installation guide for the full installation procedure. 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

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!

 

 

 

 

Todays Photo

Grand Canyon, Arizona USA

 

Boulden Company – Conshohocken, PA, USA | 1-610-825-1515

Boulden International, S.ar.L – Ellange, Luxembourg | +352 26 39 33 99

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.

Upgrade to DuPont™ Vespel® CR-6100: 100%

Upgrading pumps with composite wear componentsThere is great satisfaction in doing a job all the way.

100%

In South Africa, when you make a statement that someone agrees with, they say “100 %”–similar to how other English speakers say “absolutely.” With that in mind, we want the pumps upgraded to Vespel® CR-6100 to be upgraded 100% whenever possible.

 

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 wear rings, center bushings, and throttle bushings)

Upgrading your pumps to Vespel CR-6100 Step #1

Our recommendation when upgrading to Vespel® CR-6100 is to convert all of the stationary wear parts to Vespel® CR-6100. All of the rotating parts remain metal, thus eliminating all of the metal-to-metal contact points in the pump. This essentially eliminates the risk of pump seizure.

 

Yet, once in a while, customers try to make a small change instead of fully upgrading the pump. The three partial upgrades we run into are:

Overhung Pumps

Older pumps with long slender shafts (high L/D ratios) create problems for mechanical seals due to excessive shaft deflection. If you want to increase the rotor stability of these pumps using the wear parts, you will want to upgrade the wear rings to Vespel® CR-6100 and reduce the clearance.

 

The reason is that the Lomakin Effect-the hydraulic force which stabilizes the rotor-is driven by differential pressure and the surface speed at the differential pressure interface. Wear rings have significant differential pressure and high velocity, creating a lot of stability from the Lomakin Effect. Throat bushings? Not so much.

 

Horizontal Multi-Stage Pumps

If a horizontal multi-stage pump like a boiler feed water pump seizes, it will usually occur at the center bushing or throttle bushing, depending on the pump type. These two components generally have the tightest clearance in the pump and will be the first points of contact. In these services, there is a temptation to only upgrade the one or two components which seized.

 

While this approach has been successful in reducing pump seizures, there are some limitations. Metal-to-metal contact points remain and thus there is still a possibility of seizure. If all of the wear parts are upgraded, the risk of seizure is essentially eliminated. Furthermore, the wear rings also add to the rotor stability and efficiency of these pumps. Upgrading the wear rings as well as the center and throttle bushings will make for a much better pump. Especially if you use the Boulden PERF-Seal™ design (patent-pending).

Two-stage kerosene pump with all the components upgrade to Vespel® CR-6100 and the PERF-Seal™ design

 

 

Center Bushing of a 2-stage pump.

 

Vertically Suspended Pumps

Vespel® CR-6100 is a great material for vertically suspended pump shaft bearings in LPG, butane, natural gas liquids (NGL), and other flashing products. It can survive running dry at start up with limited wear. It doesn’t break like a carbon part. This application for Vespel® CR-6100 is so common that Boulden carries a huge inventory of standard stock sizes for the dimensions typically used for shaft bearings.

 

What some users miss is the opportunity to also upgrade the case rings of these pumps and reduce the clearance. This addition to the upgrade eliminates the other potential seizing points in the pump. Furthermore, reducing the clearance increase the pump efficiency and reduces the NPSHR–all of this making the pump easier to operate.

 

In Summary

The only partial upgrade above which we do not recommend is trying to stabilize a rotor with a throat bushing. In our experience, this approach is marginally successful at best. The other partial upgrades have worked and there are situations where they are necessary. But, given the choice, why not do the job 100%?

 

The main point is to recognize that the maximum improvement in reliability, safety, and efficiency will be achieved if you upgrade all of the wear parts (Table 1) in your pump to Vespel® CR-6100.

Table 1: Components to upgrade to Vespel® CR-6100

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

Contact Boulden Today for your Vespel® CR-6100 Needs!

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 can provide you all of the details required for your upgrade and have the Vespel® CR-6100 material required for the upgrade in stock in a wide range of sizes available for immediate delivery.

 

Helpful Links:

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

 

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