Tag Archives: pump suction performance

14 Reasons to Avoid Increased Wear Ring Clearance

If you increase the clearance, the long-term reliability and efficiency of the pump will suffer.

Happy Summer!

We hope you have had a chance to enjoy your summer holidays. From New Orleans to Narvik, it’s hot out there, so be safe, and wear sunscreen.

In our messages, we frequently highlight how Vespel® CR-6100 does not seize and therefore allows you to reduce the clearance at the wear parts in your pumps: wear rings, inter-stage rings, throttle bushings, and center bushings.

Today we want to look at things from another perspective–negative effects which can happen to your pump when you increase the clearance at the wear parts.


What can happen when you increase clearance?

If a process plant has a problem with a pump seizing during operation or galling during commissioning, the traditional response has been to increase the clearance at the wear parts.

Metal Case Ring After a Boiler Feed Pump Seizure


Although increasing the clearance might make the pump operable in the short term, there are several negative consequences from increased clearance.

Hydraulic Effects Mechanical Effects
Lower head Reduced rotor stability
Lower flow Potentially higher vibration
Lower efficiency–increased power consumption Potentially higher shaft deflection
Higher NPSHR–greater risk of cavitation Increased risk of shaft breakage
Higher motor load Potentially shorter seal life
Need to run steam turbines at higher speed Potentially shorter bearing life
Higher likelihood of needing to run pumps in parallel Higher risk of motor over-heating or tripping from excessive load

So, while you don’t want your pumps to seize, increasing the clearance can create some major issues. At a minimum increased clearance drives up the operating cost of the pump and likely compromises the long term reliability of the machine.


The Poster Pump

A while back, one of our clients had an 11-stage horizontal pump which was originally supplied with metal wear components. The pump seized soon after start-up, and the recommendation from the OEM was to increase the clearance. The pump seized again. The second recommendation was to use a “non-galling” metal alloy to address the problem. The pump seized again. The clearance was increased one more time. When the pump was started again, the overall pump vibration levels were beyond alarm limits. The multiple increases in clearance had resulted in a loss of rotor stability to the point that the pump was no longer operable.

The end of the story will be in our next email…



Until next time, if you have a pump in your shop which has galled or seized, contact Boulden to discuss an upgrade to Vespel® CR-6100. We will be happy to work through the details of the upgrade with you and we have material in stock and available for immediate shipment.


Helpful Links for Vespel and Pump Case Studies:

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’

Rossio Square in Lisbon Portugal with famous wave pattern stone pavement.

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






Upgrading Pumps With Composite Wear Components Part: 4

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


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