Seal failure index

3.0 Reciprocating rod glands

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	Figure 1 Scoring on chrome-plated rod of 240 bar methanol pump as the result of overtightening the gland
Main Characteristics	Shows scoring on the rod of a 240 bar methanol ram pump at the point where it passed through the filled ptfe packing. The local safety authority required that there should be no leakage of methanol. Scoring occurred when the gland was tightened up to stop the leakage. The problem was solved by fitting a lantern ring at the centre of the packing and supplying a low viscosity lubricating oil. A similar failure occurred on a 3-row ram pump discharging light aldehydes at 250 bar using glass-fibre reinforced ptfe chevron rings to seal the rods. The pump had been specified to operate without leakage. Predictably the seals failed. Automatic packings require adequate viscosity in the pumped liquid and wetting of the rod to ensure lubrication of the rings. The viscosity of the light aldehydes was inadequate and failure was inevitable, even with self-lubricating ptfe rings.
Cause
Note	Lubrication of the glands on reciprocating rods is essential. If adequate lubrication is not provided, severe scoring of the rod results even with packings of self-lubricating materials.
Possible Confusion with Other Types of Damage
Comment

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