How to Select a Replacement Mechanical Seal for Grundfos Pumps

Choosing the correct Grundfos pump mechanical seal replacement requires more than matching a pump series or finding a seal that looks similar to the original.

Grundfos pumps may use different shaft seals within the same product family. The correct seal can depend on the exact product number, production date, shaft size, seal arrangement, face materials, elastomer, pumped liquid, pressure, temperature, and operating speed.

Therefore, do not order a replacement only from a general model name such as CR, CM, CH, TP, or NB.

A reliable selection process combines the pump identification data, existing shaft-seal code, physical dimensions, material requirements, and actual operating conditions.

This guide explains how to collect that information, compare replacement options, and reduce the risk of leakage, installation problems, or premature seal failure.

Quick Answer: How Do You Select a Grundfos Pump Seal?

To select a suitable Grundfos pump mechanical seal replacement, follow these steps:

1. Record the complete pump model.
2. Photograph the pump nameplate.
3. Record the Grundfos product number.
4. Check the production year or date code.
5. Identify the existing shaft-seal code.
6. Confirm whether the seal is a component or cartridge design.
7. Measure the shaft or sleeve diameter.
8. Measure the stationary seat and working length.
9. Confirm the seal-face materials.
10. Confirm the elastomer material.
11. Record the pumped liquid and concentration.
12. Record the pressure, temperature, and shaft speed.
13. Compare the replacement drawing with the original seal.
14. Verify the installation and startup requirements.

Whenever possible, search the official pump documentation or service-kit information before removing the old seal.

However, if the part number is unavailable or the pump has been modified, provide a complete seal sample, accurate dimensions, and clear photographs to the replacement supplier. Follow our guide to identify the correct mechanical seal when the original code is missing or unclear.

Why the Pump Model Alone May Not Be Enough

A Grundfos product family may include many different configurations.

Differences can include:

• Motor size
• Shaft diameter
• Number of stages
• Pump material
• Operating pressure
• Seal-chamber design
• Seal-face materials
• Elastomer materials
• Production year
• Regional configuration
• Customer-specific options

For example, two pumps may share the same series name but use different shaft-seal kits.

In addition, previous maintenance work may have changed the original arrangement. A pump may now contain a different shaft sleeve, gland, stationary seat, or replacement seal.

Therefore, buyers should confirm the exact product configuration rather than relying on the series name alone.

Step 1: Record the Complete Pump Identification

Start with the pump nameplate.

Record:

• Pump series
• Full model designation
• Product number
• Serial number
• Production code
• Manufacturing date
• Motor power
• Rated speed
• Frequency
• Pump material code
• Any visible shaft-seal code

Take a clear photograph of the complete nameplate.

Do not crop out numbers that appear unrelated. A product number or production code may help distinguish between different versions of the same pump.

If the plate is damaged or unreadable, check:

• Original purchase records
• Maintenance records
• Service-kit packaging
• Pump manuals
• Spare-parts lists
• Previous supplier quotations
• Equipment database records

The complete product number is often more useful than a general pump series.

You can also check the Grundfos Product Center for product documentation, variants, dimensional information, and recommended spare parts.

Step 2: Identify the Grundfos Pump Family

The pump family helps narrow the seal design, but it does not complete the selection.

Common pump families may include:

• CR and CRN vertical multistage pumps
• CM compact horizontal multistage pumps
• CH and CHI multistage pumps
• TP and TPE inline pumps
• NB and NBE end-suction pumps
• Wastewater and drainage pumps
• Submersible pumps
• Circulation and booster systems

Each family can use different seal arrangements and dimensions.

CR and CRN Pumps

Vertical multistage pumps may use different seal codes according to:

• Pump size
• Shaft diameter
• Pressure rating
• Pumped liquid
• Elastomer material
• Face materials
• Production version

Do not assume that all CR or CRN pumps use the same mechanical seal.

Even when two pumps have similar external dimensions, their shaft seals may have different working lengths, face combinations, or stationary-seat designs.

CM, CH, and CHI Pumps

Compact multistage pumps may use small component or cartridge-style seals.

A small difference in shaft diameter, stationary seat, or working length can make the replacement incompatible.

For example, review our replacement mechanical seals for Grundfos CM and CHI pump applications when comparing seals for these compact multistage pump families.

TP, TPE, NB, and NBE Pumps

Inline and end-suction pumps may use several shaft-seal arrangements according to the pump variant and duty.

Confirm the exact product number and inspect the seal currently installed in the equipment.

Do not assume that an NB seal fits every NBE version or that all TP pumps share one seal design.

Wastewater and Submersible Pumps

These pumps may use:

• Upper and lower seals
• Oil-chamber seals
• Cartridge assemblies
• Hard-on-hard seal faces
• Directional or pump-specific arrangements

When the pump uses two seals, identify each position separately.

Do not assume that the upper and lower seals are identical. One position may require different dimensions, materials, or installation procedures.

Step 3: Find the Existing Shaft-Seal Code

Grundfos documentation and pump identification data may include a shaft-seal code.

Depending on the product, the code may indicate information related to:

• Seal design
• Rotating face material
• Stationary face material
• Secondary-seal material
• Seal arrangement

Record the complete code exactly as shown.

Do not change the order of the letters or assume that similar-looking codes are interchangeable.

A one-letter difference may indicate a different elastomer, face pairing, or seal arrangement.

If you find more than one code in the documents, confirm whether one refers to:

• The complete shaft seal
• A service kit
• An O-ring kit
• A previous replacement
• A regional product variant
• An alternative approved seal

Send the complete code to the supplier together with the pump product number.

Step 4: Confirm the Original Spare-Part or Service-Kit Number

The original spare-part number provides an important cross-reference.

When available, use the official Grundfos Pump Spare Parts Finder to search for the correct spare part or service kit.

Search for:

• Complete shaft-seal kit
• Individual shaft seal
• O-ring kit
• Gasket kit
• Wear-parts kit
• Service-kit number
• Recommended spare parts

A service kit may contain more than the mechanical seal.

It may also include:

• O-rings
• Gaskets
• Washers
• Retaining components
• Installation aids
• Sleeve parts
• Additional pump components

Therefore, compare the kit contents with the parts you actually need.

When requesting a replacement, clearly state whether you need:

• Only the mechanical seal
• The rotating and stationary components
• A complete cartridge
• A full service kit
• Additional O-rings and gaskets
• Installation tools or sleeves

This distinction prevents incomplete quotations and avoids receiving parts that do not cover the entire repair.

Step 5: Identify the Mechanical Seal Design

Grundfos uses different shaft-seal designs and arrangements for varying liquids, pressures, speeds, and operating requirements.

Determine the current seal design before comparing replacement products.

Component Mechanical Seal

A component seal normally consists of separate rotating and stationary parts.

It may include:

• Rotating face
• Stationary seat
• Spring
• Retainer
• Rubber bellows
• O-ring
• Drive component

Component seals require accurate installation length and spring compression.

The installer must also confirm the correct order, orientation, lubrication method, and stationary-seat position.

Cartridge Mechanical Seal

A cartridge seal combines the main sealing components into a preassembled unit.

It may include:

• Sleeve
• Gland
• Rotating face
• Stationary face
• Springs
• Drive collar
• Setting devices
• Flush or vent ports

A replacement cartridge must match the shaft, gland register, bolt pattern, port positions, and available axial space.

Do not remove setting clips or spacers before the manufacturer’s instructions require it.

Single or Double Seal

A single seal has one main sealing interface.

A double seal uses two sealing interfaces and may require:

• Buffer fluid
• Barrier fluid
• Oil chamber
• External circulation
• Cooling or flushing

Never replace a double arrangement with a single seal without engineering approval.

A change in seal arrangement may affect leakage control, lubrication, cooling, safety, and environmental compliance.

Balanced or Unbalanced Seal

Balanced seals reduce the effective hydraulic loading across the sealing faces.

The correct arrangement depends on pressure, speed, face loading, and pump design.

Do not determine whether a seal is balanced only from its outside appearance.

Step 6: Measure the Old Seal When Necessary

If the official part number does not provide enough information, measure the removed mechanical seal.

Use our step-by-step guide if you need to measure a mechanical seal before requesting a replacement quotation.

Important dimensions include:

Measurement	What to Record
Shaft or sleeve diameter	Actual diameter where the rotating seal fits
Rotating seal inside diameter	Bore of the rotating component
Rotating assembly outside diameter	Maximum diameter of the rotating unit
Seal free length	Uncompressed axial length
Working length	Installed axial position and compression
Stationary seat outside diameter	Diameter that fits the pump housing
Stationary seat inside diameter	Central clearance diameter
Stationary seat thickness	Axial thickness of the stationary part
Gland register	Locating diameter of the gland
Bolt pattern	Bolt quantity, hole size, and spacing
Cartridge sleeve length	Overall sleeve dimension
Port position	Flush, vent, quench, or barrier connections

Clean the parts before measuring, but preserve any visible codes and wear evidence.

Used elastomers may swell, shrink, flatten, or harden. Therefore, prioritize measurements from rigid metal, carbon, ceramic, or carbide components.

Also compare the seal dimensions with the actual pump shaft and seal housing.

Do not select the replacement from a used rubber component alone, because its dimensions may have changed during operation.

Step 7: Confirm the Working Length

Working length is a critical replacement dimension.

It determines the installed compression of the spring or bellows.

If the working length is too long:

• Face closing force may be too low
• The seal may leak during startup
• The rotating face may not remain stable

If the working length is too short:

• Spring compression may be excessive
• Face loading may increase
• Friction and heat may rise
• Seal faces may wear rapidly
• The pump may become difficult to rotate

Do not judge working length only from the free length of a used seal.

Instead, compare:

• Original pump drawing
• Seal drawing
• Shaft-shoulder position
• Stationary-seat thickness
• Gland position
• Drive-collar position
• Existing installation marks

For cartridge seals, follow the specified setting procedure and remove setting clips only at the correct stage.

When no original drawing is available, record the existing installation position before removing the old rotating component.

Step 8: Select the Seal-Face Materials

Common mechanical seal face materials include:

• Carbon graphite
• Ceramic
• Silicon carbide
• Tungsten carbide

The correct choice depends on the fluid and operating conditions.

Carbon and Ceramic

This combination may suit clean water and moderate operating conditions.

It can offer an economical solution for light-duty service.

However, abrasive particles may wear the carbon face.

Carbon and Silicon Carbide

This pairing is common in many industrial water and process-pump applications.

Silicon carbide provides strong hardness, wear resistance, thermal performance, and chemical resistance.

Silicon Carbide and Silicon Carbide

Hard-on-hard silicon carbide faces may suit:

• Wastewater
• Fine abrasive solids
• Corrosive fluids
• Crystallizing liquids

However, they still need adequate lubrication and cooling.

Hard faces do not protect a seal from dry running, incorrect working length, shaft movement, or blocked flush lines.

Tungsten Carbide Combinations

Tungsten carbide may provide strong toughness, abrasion resistance, and resistance to mechanical shock.

Its corrosion performance depends partly on the binder grade.

Do not approve a material only from a general label such as “SiC” or “TC.” Ask for the actual grade when the application is demanding.

Review our mechanical seal material selection guide before changing the original face or elastomer combination.

Step 9: Select the Elastomer Material

Common elastomers include:

• NBR
• EPDM
• FKM
• FFKM
• TFE/P
• PTFE-based secondary seals

The correct elastomer must match:

• Pumped liquid
• Chemical concentration
• Operating temperature
• Cleaning chemicals
• Flush liquid
• Oil or grease exposure
• Food or hygiene requirements

NBR

NBR may suit general water and oil applications within its chemical and temperature limits.

However, it may not be suitable for aggressive chemicals or high-temperature service.

EPDM

EPDM is commonly considered for water, hot water, and certain chemical services.

However, it is generally unsuitable for petroleum-based oils and many hydrocarbons.

FKM

FKM often provides improved resistance to oils, fuels, higher temperatures, and many chemicals.

Nevertheless, compatibility must be checked for the exact fluid.

Special Elastomers

FFKM, TFE/P, and PTFE-based solutions may be required for aggressive chemicals or high temperatures.

They can increase the seal cost, but they may prevent repeated swelling, cracking, or chemical attack.

Never identify an elastomer only by color.

Step 10: Record the Pumped Liquid

A dimensionally correct seal can still fail if its materials do not match the liquid.

Record:

• Liquid name
• Chemical composition
• Concentration
• pH
• Solids content
• Particle size
• Viscosity
• Lubricating properties
• Crystallization tendency
• Toxicity
• Cleaning chemicals
• Flush fluid

Do not simply write “water” when the pump handles:

• Treated water
• Glycol mixture
• Chlorinated water
• Boiler water
• Wastewater
• Seawater
• Hot condensate
• Cleaning solution
• Water containing abrasive solids

Small differences in fluid composition can change the required seal materials.

Also record temporary fluids used during cleaning, sterilization, flushing, or shutdown.

Step 11: Confirm the Operating Conditions

Record the actual operating data:

• Normal seal-chamber pressure
• Maximum pressure
• Pressure fluctuations
• Normal temperature
• Maximum temperature
• Shaft speed
• Direction of rotation
• Frequency of starts and stops
• Dry-running risk
• Suction conditions
• Vibration level
• Available cooling
• Flush arrangement

Do not use only the maximum pressure printed in a general pump catalogue.

The pressure acting at the seal chamber may differ from the pump discharge pressure.

Similarly, the normal liquid temperature may differ from the startup, cleaning, or shutdown temperature.

If the pump frequently operates away from its intended duty point, also investigate cavitation, vibration, and hydraulic instability before installing another seal.

Step 12: Check Whether the Pump Has Been Modified

Previous repairs can change the original seal requirements.

Inspect whether technicians have replaced or modified:

• Shaft sleeve
• Pump shaft
• Gland
• Seal chamber
• Stationary-seat bore
• Drive collar
• Impeller position
• Spacer
• Motor or coupling
• Flush piping

A replacement selected from the original product number may not fit a modified pump.

Therefore, compare the current equipment with the original documentation.

If the dimensions do not match, send photographs and measurements of the modified area.

Clearly inform the supplier that the pump is no longer in its original configuration.

Step 13: Compare Original and Replacement Drawings

Before approving production, compare the supplier’s drawing with the original seal or pump.

Check:

• Shaft diameter
• Working length
• Stationary-seat profile
• Seat thickness
• Face dimensions
• Spring arrangement
• Gland dimensions
• Bolt pattern
• Port position
• Rotation direction
• Materials
• Overall axial length

Do not approve the drawing only because the product title contains the correct pump model.

For large orders or critical equipment, mark the confirmed dimensions directly on the approval drawing.

Also record the drawing revision for future repeat orders.

A drawing approved for one pump version should not automatically be used for every pump with a similar model designation.

Step 14: Evaluate the Replacement Supplier

A reliable supplier should ask for more than the pump series.

The supplier should be able to discuss:

• Product number
• Production version
• Seal code
• Dimensions
• Materials
• Pumped liquid
• Operating conditions
• Application history
• Inspection process
• Installation requirements

Ask whether the supplier:

• Has supplied the pump model before
• Has a verified drawing
• Can provide material options
• Can provide inspection records
• Can maintain repeat-order consistency
• Can identify different production versions
• Offers sample approval
• Supports failure analysis

Be cautious when a supplier confirms compatibility from one photograph without asking for dimensions or pump information.

For repeat orders, request that the supplier maintain an approved drawing, material specification, and production record.

Step 15: Decide Between an Original and Compatible Replacement

An original seal may be preferable when:

• The pump is under warranty
• The process requires approved original parts
• The application is highly hazardous
• The seal arrangement is specialized
• Complete operating information is unavailable
• Original documentation and support are essential

A compatible replacement may be practical when:

• The original part has a long delivery time
• The original part is discontinued
• The dimensions can be verified
• The buyer needs a lower cost
• Different materials are required
• The pump has been modified
• Repeat supply is needed
• The supplier has proven experience with the model

A replacement does not need to copy every visible detail, but it must satisfy the critical installation and operating requirements.

The supplier should disclose any important differences in design or materials before production.

Grundfos Pump Mechanical Seal Replacement Checklist

Before placing an order, confirm:

• Complete pump model
• Grundfos product number
• Production date or version
• Existing shaft-seal code
• Original service-kit number
• Shaft or sleeve diameter
• Stationary-seat dimensions
• Free length
• Working length
• Seal design
• Single or double arrangement
• Balanced or unbalanced arrangement
• Seal-face materials
• Elastomer material
• Metal-part materials
• Pumped liquid
• Chemical concentration
• Solids content
• Operating temperature
• Seal-chamber pressure
• Shaft speed
• Rotation direction
• Flush or barrier arrangement
• Supplier drawing
• Required quantity

This checklist helps prevent a replacement that fits physically but fails under actual pump conditions.

Information to Send a Mechanical Seal Supplier

Send the following information with your inquiry.

Pump Data

• Pump manufacturer
• Full pump model
• Product number
• Serial number
• Production year
• Motor power
• Shaft speed

Existing Seal Data

• Shaft-seal code
• Original part number
• Service-kit number
• Complete photographs
• Seal dimensions
• Stationary-seat profile
• Free length
• Working length
• Face materials
• Elastomer material

Application Data

• Pumped liquid
• Concentration
• pH
• Solids
• Temperature
• Pressure
• Viscosity
• Dry-running risk
• Flush or cooling system

Commercial Data

• Required quantity
• Delivery requirement
• Packaging requirement
• Inspection requirement
• Material certification
• Sample requirement
• Repeat-order forecast

Complete information allows the supplier to recommend the correct Grundfos pump mechanical seal replacement instead of selecting the closest-looking product.

Common Selection Mistakes

Ordering from the Series Name Alone

A general model family may include several seal options.

Always confirm the full model and product number.

Ignoring the Production Version

Older and newer pumps may use different parts.

Record the production date whenever possible.

Assuming Similar Seal Codes Are Interchangeable

A small code difference may indicate different face or elastomer materials.

Measuring Only the Shaft Diameter

The shaft size does not confirm the working length, seat profile, or seal arrangement.

Copying a Damaged Sample Without Checking the Pump

The old seal may have worn faces, compressed springs, swollen rubber, or missing parts.

Selecting Materials Only by Price

A lower-cost elastomer or face material may fail quickly in an incompatible liquid.

Ignoring the Working Length

Incorrect spring compression can cause immediate leakage or rapid overheating.

Replacing Only One Face

A new rotating face may not seal correctly against a worn stationary face.

Replace matched faces together unless the manufacturer approves another procedure.

Ignoring Pump Problems

A new seal will not correct:

• Shaft runout
• Misalignment
• Worn bearings
• Cavitation
• Excessive vibration
• Pipe strain
• Dry running

Repair the underlying pump problem before installing another seal.

Installation Checks Before Startup

Before installing the replacement:

• Inspect the shaft and sleeve
• Remove burrs and sharp edges
• Check bearing condition
• Verify shaft runout
• Clean the seal chamber
• Confirm the correct component order
• Use compatible assembly lubricant
• Protect elastomers from threads and keyways
• Keep seal faces clean
• Install the stationary seat evenly
• Set the correct working length
• Tighten gland bolts gradually
• Confirm the direction of rotation

Before startup:

• Prime the pump
• Fill the seal chamber
• Vent trapped air
• Open the required valves
• Start the flush or support system
• Rotate the shaft manually when appropriate
• Check for binding
• Monitor leakage, vibration, pressure, and temperature

Do not allow the new seal to run dry.

Frequently Asked Questions

Can I Select a Grundfos Seal from the Pump Model Alone?

Sometimes, but the model alone may not identify the exact seal.

Use the full product number, production information, seal code, and physical dimensions whenever possible.

Where Can I Find the Pump Product Number?

The product number is usually found on the pump nameplate or in the original purchase and service documentation.

Photograph the entire nameplate before requesting a quotation.

What Information Does a Shaft-Seal Code Provide?

A shaft-seal code may contain information about the seal design, face materials, and secondary-seal material.

Always record the complete code and confirm it with the relevant pump documentation.

Are All CR Pump Seals Interchangeable?

No.

CR and CRN pumps can use different seals according to pump size, shaft diameter, pressure, materials, production version, and application.

Should I Order Only the Mechanical Seal or a Complete Service Kit?

It depends on the pump condition and the required repair.

A complete service kit may include O-rings, gaskets, or other components that should be replaced during maintenance.

Can I Use Different Seal-Face Materials?

Yes, when the new materials are compatible with the liquid, pressure, temperature, speed, and seal design.

Do not change materials without reviewing the complete application.

Can I Change from EPDM to FKM?

Possibly, but only after checking compatibility with the pumped liquid, cleaning chemicals, and temperature.

FKM is not automatically better for every fluid.

Can a Replacement Seal Perform as Well as the Original?

A properly designed and manufactured replacement can provide reliable service when the dimensions, materials, tolerances, and operating limits are correctly verified.

Supplier quality and application review remain essential.

Why Does a New Grundfos Pump Seal Leak After Installation?

Possible causes include:

• Contaminated seal faces
• Damaged O-rings
• Incorrect working length
• Uneven stationary-seat installation
• Dry running
• Shaft runout
• Wrong materials
• Incorrect seal size

For a complete troubleshooting process, review the common causes of a mechanical seal leaking after installation.

Stop the pump and identify the actual leakage path before replacing the seal again.

What Should I Do When the Old Seal Has No Readable Code?

Provide:

• Pump nameplate
• Complete seal photographs
• Shaft diameter
• Stationary-seat dimensions
• Working length
• Pumped liquid
• Pressure and temperature

A complete physical sample can also help with identification.

Conclusion

Selecting the correct Grundfos pump mechanical seal replacement requires a structured verification process.

Start with the full pump model, product number, production information, existing shaft-seal code, and original service-kit reference. Then verify the shaft size, stationary seat, working length, seal arrangement, face materials, elastomer, and actual operating conditions.

Do not select a replacement only by appearance or a general pump series.

Clear photographs, accurate dimensions, application data, and an approved supplier drawing can significantly reduce ordering mistakes and installation problems.

For Grundfos pump seal identification or replacement support, contact Hongteng Seals with your pump nameplate, seal code, dimensions, old-seal photographs, fluid information, and operating conditions. Our team can review the available data and help you select a suitable replacement seal for your pump.