Impeller and Case Wear Rings for Pump Repair Shops

Case wear rings and impeller wear rings: where each one sits

Nickerson Company says wear rings “provide protection for the more expensive and highly-engineered impeller and casing” (source 2). The stationary one is the case ring, or casing ring, and the rotating one is the impeller ring. On a closed impeller, Gene Vogel of EASA writes, “there will be a casing wear ring and possibly an impeller wear ring which is fitted to the outside diameter (OD) of the impeller suction eye,” and impellers “may also have rear wear rings which are important for controlling axial thrust” (source 1). Nickerson Company says rings “may be installed on the impeller skirt, in the pump casing, or both” (source 2). Name the position on the print: case ring, impeller suction ring or impeller rear ring.

Not every impeller has a ring to replace. Carver Pump’s summary of API 610 says impellers “can have either renewable wear rings or an integral wear surface” (source 3). Where the surface is integral, some repairs cut it down and fit new rings. RepairEngineering describes a job in which the “original wear ring surfaces were machined undersized to clean-up the worn material and to allow for the installation of new replaceable wear rings” (source 4). A ring for that job is quoted to the size you measured after the cut, with the fit you want on the print.

The sleeve under the packing or seal has its own page, pump shaft sleeves, and the liner for an end-bell bore is on bearing housing sleeves. The rest of a rebuild is on wear parts for pump and motor repair shops, and plates, bushings and other parts around the pump are on machined pump parts.

Case ring, casing ring, wear ring, impeller ring: the names on a pump print

A parts list, a pump maker’s drawing and an old repair ticket can name the same two rings in different ways, and “wear ring” on its own can mean either one. Whatever the print calls them, put the position beside the name so the quote is for the ring you mean.

Why a wear ring wears, and what the replacement has to restore

In Gary Dyson’s words in Pumps & Systems, a ring’s job is “to provide a restrictive annulus between different pressure regimes within a centrifugal pump,” and abrasive wear opens it two ways. When the gap is large enough to pass the particles, “the particles pass across the wear ring clearance driven by differential pressure.” When it is smaller than the largest particles, “material is removed from the clearance due to crushing and abrasion until the clearance increases” (source 5).

An open ring costs the pump. Terry Henshaw wrote in Pumps & Systems that “wear ring clearances significantly impact the performance of centrifugal pumps, particularly those with lower specific speeds” (source 6). Heinz Bloch’s checklist in Chemical Processing says impeller rings “should be replaced when the new clearance reaches twice the original value” (source 7). At that point the ring is a reorder.

The clearance is also a trade. Henshaw: “To reduce the chance of galling and seizing between mating rings, users want the clearance to be large,” but a larger clearance “has numerous undesirable side effects” (source 6). Which way to go is the pump maker’s call or yours. It goes on the print as a number.

How a wear ring clearance is specified, and where the number comes from

Vogel writes in Pumps & Systems that wear ring clearances “are always specified in diametric measurements”: the inside diameter of the stationary ring less the outside diameter of the rotating ring, with the running clearance on each side half of that (source 9). A print that gives a clearance should say which kind of figure it is, and the two diameters it sits between.

The number itself has a few places to come from, listed in the table. Vogel says the pump maker’s tolerances are “always the best guidance” for fitting replacement rings, and Nickerson says it is “always better to follow a manufacturer’s guidelines” (sources 9, 2). Where the pump was built to API 610, the standard for centrifugal pumps in petroleum, petrochemical and natural gas service, the standard carries a chart of minimum running clearances keyed to wear ring diameter (sources 6, 9). That chart gives minimums, not maximums (source 9). API 610 is a copyrighted standard, so the chart is not reprinted here; it is API Standard 610, Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries, 12th edition (source 10).

Published rules then add to a base clearance for the conditions. Bloch’s repair guidelines build the clearance from a base value and an amount per inch of ring diameter, with further additions for high pumping temperature and for galling-prone materials such as stainless steel (source 7), and Vogel’s guidelines for new rings add for galling materials too (source 9). The number that applies goes on the print.

What a wear ring print should carry

A ring is a plain turned part, and almost every number on its print is one you read off the pump or the pump maker’s drawing. The quote is made from the print as drawn, and MI CNC Parts does not set the fit or the running clearance. The table lists what each ring’s print needs and why it varies from pump to pump.

What to send: the print, or a new sample part

Send the print if there is one. Files: Any file type; STEP + PDF ideal. Add the material of each ring if you know it, your yearly usage, and the pump make and model, which help place the ring. Photos of the rings in place help when the position is not obvious.

When the print is gone, it may survive elsewhere: the pump maker’s drawing, or an earlier quote or PO number from MI CNC Parts, though for plenty of old pumps “dimension data is simply not available,” as Vogel notes (source 1). Where nothing survives, a new sample part starts the job through reverse engineering, which turns it into a print. Send a new part, not the worn one. Wear changes the sizes that matter. The sample ships back with the parts. Drawing the print from the sample is quoted as its own line the first time, and reorders use that drawing.

For a case ring the mating part is the impeller or its ring, and for an impeller ring it is the case ring. A new mating part helps confirm the fit. It ships back with the parts.

Materials for wear rings: bronze, stainless, steel or non-metallic

Wear rings are quoted in bronze, stainless and steel. Bronze rings are quoted in the grade the print names, and custom bushings lists the bronze grades quoted. Stainless is quoted in 304, 316 and 17-4 PH. Steel rings are quoted to whatever grade the print gives, and the steel page lists the usual ones.

Some prints name a non-metallic ring instead of metal. API 610, in Carver Pump’s summary, asks for “special attention” to “compatibility with the fluid, distortion, thermal gradients, and special clearances” with non-metallic rings (source 3), so the material and its clearance are print decisions. Other alloys and plastics quoted on request. Name the grade on the print.

If the print calls for a hardness on either ring, name it there. Hardness can be arranged and quoted. A finish called out on the print is quoted with the part.

Fits, locking and tolerances: what the print says and what is quoted

How a ring is held goes on the print too. Bloch lists “dowelling, set screws that are threaded in the axial direction partly into the impeller and partly into the wear ring, or tack-welded in at least two places” for impeller rings, and “doweled or spot welded in 2 or 3 places” for case rings (source 7). Carver Pump puts a limit on the hole: it “cannot exceed one-third the width of the wear ring” (source 3). Pressing the ring in, drilling the hub for set screws and any tack weld are assembly steps, and they stay with you.

Typical machined tolerance is ±0.005 in, ±0.001 in on critical turned diameters, and down to ±0.0002 in on wire-EDM and other finished features; ground features are quoted to ±0.0001 in. Ring diameters, fits, locking holes and the running clearance are quoted from the print.

Reordering rings, and blanket orders

If you rebuild the same pump models again and again, the drawing does the work the second time. Reorders at the same revision: send the last quote or PO number and it’s requoted. Ask for more than one quantity, such as 1, 25 and 100, and the quote shows each.

A case ring and its impeller ring can go on one quote, each line at its own quantity, so both diameters sit on one print at one revision. A year’s usage of one ring size can be quoted as a blanket order and delivered in releases. Price, release schedule and lead time per release are set in the quote.

No minimum: one piece to production runs of 10,000. A single ring is a normal order, and small-batch CNC machining covers how quantity affects the quote.

Lead time, quotes and what comes with the rings

Quotes come back in 24-48 hours. Rush: 1-2 weeks. Standard: 4-6 weeks (typical). Extended: 6-8 weeks, for jobs that aren't time-sensitive.

Every part is inspected against your print before it ships. If a part doesn’t match the print, it’s remade or credited. Parts are supplied as replacements by fit and dimensions. No OEM logos, part numbers or markings are copied. Checking the running clearance and the rebuild stay with you.

Sources

All accessed 1 October 2026. Where a figure here differs from your print, the print governs.

1. Gene Vogel, EASA, “Wear ring considerations for centrifugal pumps,” EASA Resource Library, October 2018: easa.com/resources/resource-library/wear-ring-considerations-for-centrifugal-pumps-1 (casing, suction and rear wear rings; missing dimension data).

2. Nickerson Company, “Wear Rings 101: Basics, Location, Fit, Clearances & Material Selection,” 19 May 2022, nicopumps.com/wear-rings-101/ (where rings are installed; ring materials by position).

3. Carver Pump Company, “API 610 Pump Wear Rings: What to Consider when Choosing,” 30 October 2020, carverpump.com/what-to-consider-when-selecting-wear-rings-for-your-api-610-pumps/ (integral wear surfaces; the hole limit; non-metallic rings).

4. RepairEngineering, “Pump Impeller Repair,” 27 December 2013, repairengineering.com/impeller-repair.html (surfaces cut undersized for new rings; rings left with excess material).

5. Gary Dyson, “Wear in Centrifugal Pumps,” Pumps & Systems, 26 December 2019: pumpsandsystems.com/wear-centrifugal-pumps (the ring’s job; how abrasive wear opens the clearance).

6. Terry Henshaw, “Effect of Internal Clearances on NPSHR,” Pumps & Systems, 17 December 2011: pumpsandsystems.com/effect-internal-clearances-npshr (clearance and pump performance; the galling trade; API 610 clearances plotted by ring diameter).

7. Heinz P. Bloch, “Pump repair and restoration guidelines,” Chemical Processing, 18 December 2005 (excerpted from Bloch and Budris, Pump User’s Handbook: Life Extension): chemicalprocessing.com/processing-equipment/fluid-handling/news/11360994/pump-repair-and-restoration-guidelines (when to renew a ring; securing methods; added clearance for galling-prone materials).

8. Tyler Wall, “Pump repair: Working with close tolerance fits,” Plant Engineering, 11 July 2023, on Gene Vogel’s 2023 EASA convention session: plantengineering.com/pump-repair-working-with-close-tolerance-fits/ (interference or clearance fit by pump type; the anti-spin retainer).

9. Eugene Vogel, “Wear Ring Clearance for Centrifugal Pumps,” Pumps & Systems, 7 June 2019: pumpsandsystems.com/wear-ring-clearance-centrifugal-pumps (diametral specification; the pump maker’s tolerances first; the API 610 chart as minimums; the galling addition).

10. American Petroleum Institute, API Standard 610, “Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries,” 12th edition (cited by title only; the standard is copyrighted and not reprinted).

11. Ken-ichi Kajiwara, “Liner ring for a pump,” US Patent 5,295,786, granted 22 March 1994: patents.google.com/patent/US5295786 (liner ring or casing ring; wearing ring or impeller ring).

12. Engineers Edge, “Centrifugal Pumps Wearing Ring Review”: engineersedge.com/pumps/wearing_rings.htm (wearing rings attached to the impeller and/or the casing; page undated).