Mechanical Seal Selection Guide
Seal types, face materials, secondary seals and application checks to discuss with your seal supplier.
In one line: Select a mechanical seal by working through the fluid, the temperature and pressure, the speed and shaft size, the equipment condition, and the cost of failure. Use these checks to discuss the seal type, face pair, secondary seals and support requirements with the supplier.
Check the cleaning cycle as well as the process fluid. Installation, equipment condition and operation are part of the assessment alongside the seal specification.
The Five Step Method
1. Define the fluid
Record the product, concentration, solids and every cleaning or flushing fluid. Check compatibility for the complete duty.
2. Fix temperature and pressure
Record normal and maximum temperatures, chamber pressure, vacuum and pressure changes. Confirm the selected assembly limits; do not apply a universal pressure cutoff.
3. Take the speed and dimensions
Record shaft or sleeve diameter, speed in rpm, chamber bore and depth, available axial space and gland fixing details. Check these against the seal drawing.
4. Assess the equipment
Check alignment, shaft movement, equipment condition and the installation requirements with a qualified person. A new seal does not remove these checks.
5. Price the failure, not the seal
Compare actual quotations with your own estimates for downtime, maintenance and lost product. Treat calculator results as scenarios, not guaranteed savings.
Compare options on lifetime cost with the total cost of ownership calculator.
Seal Types and Checks Before Selection
Component seals
Separate rotating and stationary parts, with the working length set during installation.
Check: Confirm the selected design, working length and fitting procedure.
More detailCartridge seals
Typically assembled on a sleeve and gland, with the seal setting established before installation.
Check: Follow the manufacturer procedure, including the handling of setting parts.
More detailSingle seals
One sealing face pair between the rotating and stationary parts.
Check: Check fluid hazards, lubrication, materials and operating limits.
More detailDual seals
Two seals with a specified buffer or barrier arrangement.
Check: Check containment requirements and the complete support system.
More detailMetal bellows seals
A metal bellows provides flexibility without the sliding secondary seal used in a pusher design.
Check: Check the particular assembly materials and operating limits.
More detailSplit seals
A split construction can allow installation without dismantling the equipment.
Check: Confirm access, dimensions and the selected design procedure.
Gas lubricated seals
Non contacting designs use a gas film between the faces.
Check: Check the gas supply, pressure control and application requirements.
Lip and oil seals
Radial shaft seals can retain lubricant and exclude contaminants.
Check: Check the actual pressure, speed, temperature and material limits.
More detailHow do I choose mechanical seal face and O ring materials?
Choose the face pair and secondary seals together. They must suit the fluid, concentration, solids, temperature, pressure and speed. Include every cleaning and flushing fluid, not only the product the pump normally handles.
Carbon, silicon carbide and tungsten carbide are different face material options, not a simple good, better, best list. The pairing and material grade matter. Check the manufacturer's limits for the selected design, including its lubrication and cooling requirements.
O rings need their own compatibility check. EPDM, FKM and FFKM are not interchangeable, and the material family name alone is not enough to select the compound. A general temperature rating is not approval for your chemical or cleaning cycle.
Send the complete duty before changing a material. If an old seal has hardened O rings, damaged faces or repeated leakage, use failure photographs alongside the duty and installation information, not instead of them.
Does a cartridge seal solve a material problem?
No. Cartridge describes how the seal is assembled. It does not identify the face pair, elastomer or metal grade. The assembly still needs the correct materials and support for its operating duty.
Read the seal face material guide and FFKM guide for more detail.
Face Material Pairings
| Pairing | Role | Duty check | Design check |
|---|---|---|---|
| Carbon with silicon carbide | Check the pairing | Confirm compatibility with the fluid | Use the selected design's lubrication and operating limits |
| Silicon carbide with silicon carbide | Check the grades | Assess solids and operating conditions | Do not assume dry running capability |
| Tungsten carbide with carbon | Check the grades | Confirm pressure, speed and fluid compatibility | Use the manufacturer's limits for the assembly |
More information on material selection in the seal face material guide.
Secondary Seals: Check the Compound
| Secondary seal | Compatibility check | Limits |
|---|---|---|
| NBR (nitrile) | Check the exact compound | Verify fluid, temperature and operating requirements |
| EPDM | Check chemical compatibility | Do not transfer another material's rating to EPDM |
| FKM | Check formulation and compatibility | Different formulations can have different properties |
| PTFE encapsulated | Check jacket, core and geometry | Confirm suitability for the selected seal design |
| FFKM | Check the particular compound | A broad family description is not application approval |
Compatibility must be checked for the exact compound and duty. Read the chemical compatibility chart and FFKM vs FKM.
Selection by Application
Water and wastewater
Check solids, operating conditions and whether adequate liquid lubrication is available. Choose the face pair and secondary seals for the specific fluid and equipment.
Chemical processing
Check the product and every cleaning fluid, concentration and operating condition. Select materials and containment arrangements for the particular duty.
Food, dairy and pharmaceutical
Check the required hygienic design and documented material approvals. Include the actual cleaning and sterilisation conditions in the specification.
Oil, gas and refining
Confirm the purchaser requirements, any API 682 scope, material compatibility and the required seal support system.
Paints, inks and dispersions
Record the solids, fluid properties and operating conditions. Confirm the face pair, secondary seals and support arrangement for that particular duty.
High temperature and hot oil
Check every material and the selected assembly temperature limits. A metal bellows construction does not remove the need to verify lubrication and support requirements.
Six Ways Selection Goes Wrong
- Specifying on the pump model alone, ignoring what actually goes through it
- Leaving cleaning fluids and conditions out of the compatibility check
- Using the average temperature instead of the peak
- Choosing a component seal where nobody has a setting procedure
- Choosing a replacement before checking the failure evidence and equipment condition
- Leaving the required lubrication and support arrangement out of the specification
If a seal is already failing, diagnose it before you reselect, using the seal troubleshooting guide.
Free PDF: 40 Reasons Mechanical Seals Fail
Field diagnostic reference covering installation, material, operating and maintenance causes.
Seal Selection, Questions Answered
How do I select a mechanical seal?
Use the fluid and all cleaning conditions, temperature, pressure, speed, equipment dimensions and condition as the starting point. Check the selected seal manufacturer's limits, material compatibility and support requirements. Compare the consequence of failure and the quoted options; price alone does not confirm suitability.
What is the difference between a cartridge seal and a component seal?
A cartridge seal typically arrives assembled on its sleeve and gland. Component seals are fitted as separate parts, with the working length set during installation. Cartridge construction reduces setting work and can reduce assembly errors. Both require the correct installation procedure. Compare actual quotations and installation requirements rather than assuming one is always cheaper overall.
When do I need a double mechanical seal?
Consider a dual seal when the process hazards, containment requirements or lubrication conditions call for it. API 682 Arrangement 2 uses an unpressurised buffer system; Arrangement 3 uses a pressurised barrier system. Confirm the arrangement and support system for the duty. A second seal does not by itself guarantee zero leakage or protect against every cause of failure.
What is a balanced mechanical seal?
Hydraulic balancing changes the ratio of the pressure loaded area to the seal face area and reduces hydraulic face loading. Balanced designs are used in higher pressure and speed applications. There is no universal 10 bar changeover rule: verify the selected design's pressure, speed, material and lubrication limits.
Which seal face materials should I choose?
Choose the face pair for the fluid and operating duty. Carbon, silicon carbide and tungsten carbide have different properties; the pairing and grade matter. Check the selected design's limits and lubrication requirements rather than choosing a material from its name alone.
Which elastomer should I use with my seal?
Check the exact compound against the process fluid, concentration, cleaning fluids and operating conditions. EPDM, FKM and FFKM are not interchangeable. Temperature limits apply only with compatible media, and the material family name alone does not confirm suitability.
What information do you need to specify a seal?
Send the pump make and model, shaft or sleeve diameter, chamber dimensions, fluid and concentration, temperatures, seal chamber pressures, speed, solids and cleaning conditions. State any required standards or approvals. Include photographs and the old seal reference where available. Suitability and compliance must be confirmed for the selected assembly and duty.
What is API 682 and does it apply to me?
API 682 specifies requirements and recommendations for shaft sealing systems on centrifugal and rotary pumps used in petroleum, natural gas and chemical industries. It includes a classification by categories, types, arrangements and orientations. Confirm the required edition and scope with the purchaser and seal vendor. A reference to API 682 is not proof that an assembly complies.
Can I fit a seal to an old or obsolete pump?
A replacement or conversion may be possible, but it requires inspection of dimensions, equipment condition and duty. Send the old seal reference, photographs and dimensions before choosing a replacement. Do not assume that every obsolete seal can be matched or that a cartridge will fit the existing chamber.
Why does the same seal keep failing?
Repeated leakage can involve the seal, installation, equipment condition or operating duty. Check the failure evidence alongside alignment, shaft movement, lubrication, material compatibility and operating limits. Do not diagnose the cause from recurrence alone or assume that replacing the seal will remove it.
What does the wrong seal actually cost?
Compare the quoted seal and installation cost with your own estimates for downtime, lost product, maintenance and any disposal or cleanup. Use the total cost of ownership calculator for a scenario comparison, not a prediction of seal life or guaranteed savings.
How do I discuss selection with Acumen?
Send the duty and equipment details to discuss selection with Acumen. Confirm the scope and any charges before agreeing work. Refurbishment and replacement can be compared once the seal condition and quotations are known.
Send the duty, get the specification
Send pump details, fluid, temperature, pressure and speed. Compare selection, refurbishment and replacement options once the duty and condition are known.