Tag Archives: pump seizure

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

Boulden Company

Boulden Company

 

boulden footer

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.