Mechanical seal

01

Choose faces, materials and secondary seals

EASA, summarising a 2017 convention paper by Gene Vogel, explains that seal faces are lapped flat to within helium light bands, around 0.00003 in (0.00075 mm), so they can develop a hydrodynamic film in which the pumped liquid lubricates and cools them. Face materials include carbon, ceramic, tungsten carbide, silicon carbide, chrome oxide and Ni-resist, chosen for heat capacity, abrasion and corrosion resistance, strength and cost. [1]

Secondary seals, such as elastomers, seal the stationary face to the housing and the rotating face to the shaft; the elastomer must suit the pumped fluid's chemistry and temperature. [1]

Give the supplier the fluid, its temperature, pressure at the seal chamber, solids and vapour pressure, shaft size and speed, and the pump model. Seal choice follows the fluid more than the pump.

02

Choose pusher or bellows, balanced, cartridge or dual

EASA describes pusher seals, whose springs load the faces and whose secondary seal must slide on the shaft, and non-pusher seals using a bellows or diaphragm so the face moves independently of the secondary seal. Balanced seals use a step on the face to control hydraulic force on the faces; cartridge seals reduce the risk of failure from incorrect assembly. [1]

Dual seals have a chamber between two seals filled with barrier fluid that cools and lubricates the faces even when the pump is not running and protects against corrosive or abrasive pumpage. [1]

03

Choose the piping plan that keeps the faces cool and lubricated

John Crane explains that API 682 (4th edition) recognises 32 piping plans that set the auxiliary piping and equipment around a seal to give lubrication, cooling and pressure control and to manage leakage safely; a handful, such as single-flush plans and basic dual-seal systems, dominate everyday use. [2]

It notes that Plan 11 can give a healthy flow but may let gases collect in the seal chamber, especially in vertical pumps; Plan 13 removes gases but may not circulate enough to cool; Plan 14 combines both. For dual unpressurised seals, Plan 75 drains inboard leakage to a monitored containment vessel and needs space below the pump shaft. [2]

Ask the supplier which piping plan it recommends for your fluid and pump orientation, and what the plan needs in pipework, instruments and space.

04

Prevent heat, vibration and dry running

EASA identifies heat and vibration as major causes of seal failure: vibration from bearing problems, shaft misalignment, unbalance, cavitation or misaligned seal parts; heat from face friction that the pumpage or barrier fluid must carry away. Seals are not designed to run dry. [1]

Check pump alignment, bearings and vibration when replacing a seal, and make sure the support system is working before start-up; a new seal on a vibrating pump faces the same causes of failure.

05

Compare what suppliers offer

Suppliers linked to this page list pump mechanical seals, cartridge and agitator seals and seal distribution. [3] [4] [5]

EagleBurgmann lists mechanical seals across industrial processes; HQSeal and Sealcon list mechanical seals for pumps; Ningbo Donglian lists O-ring pump mechanical seals such as its DY41. Confirm whether a seal is an original, an interchangeable design or a repair kit. [3] [4] [5] [6]

06

Trace the seal components

This is a functional reference built from the sources cited; it is not one maker's parts list.

07

Fill the specification fields with values for your pump

A seal quotation needs pump- and fluid-specific values. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

08

Send the pump, fluid and operating data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Pump: [make and model; shaft size; speed; orientation; seal chamber dimensions]
Fluid: [name; temperature; seal-chamber pressure; vapour pressure; solids; hazardous or not]
Seal: [single or dual; pusher or bellows; balanced; cartridge or component]
Materials: [faces; elastomers; metal parts]
Support: [API 682 piping plan; flush source; barrier or buffer fluid]
Condition: [vibration and alignment status; history of failures]
Documents: [seal drawing; materials list; installation instructions]

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