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Mechanical seal failure

Mechanical seal failure

Mechanical seal failure

Hi everybody,
In our plant we use horizontal, multistage centrifugal pumps, 3000-8500 rpm, seal chamber pressure DE side 5-7 bar, seal chamber pressure NDE side 3-4 bar, axial movement of the pump is controlled by a balance disc, fluid demi water with boron content (max 5 g/kg), max temperature 60 °C, sleeve bearings with external oil source.

We use cartridge, single, balanced mechanical seal, API plan 01 and API plan 62, six springs on stationary side, seal faces made of sintered silicon carbide.
Occasionally, after start of the pump, a seal starts to leak heavily on the DE side. After shut-down, the seal is without leakage. After next start and during operation, the seal is without leakage. When we disassemble cartridge seal, there are no damaged parts and following static pressure test is ok. Maximum axial movement of the pump during start is 0,5 mm.
Described behavior appears on several pumps of the same type after maintenance of the cartridge seal - replacement of seal faces, springs and o-rings.

We assume, that problem could be in a dynamic o-ring, which seals stationary seal face made of SiC. Seal manufacturer provides us EPDM 80 5,33 x 116,84 (0,210 x 4,6 inch) o-ring. Groove parameters:
Rod (SiC) diameter 114 mm (4,488 inch)
Bore diameter 115,15 mm (4,533 inch)
Groove (316L SS) diameter 123,8 mm (4,874 inch)
Groove width 7,14 mm (0,281 inch)

O-ring and groove dimensions don’t correspond to standard dynamic o-ring tables (Parker etc) for rod diameter 114 mm (4,488 inch).
Thank you for your ideas.

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