Glanded Pumps, unlike Glandless Pumps, require shaft seals to separate the fluid handled from the drive motor. Two seal systems are generally in use:
Packed Gland Seal
The packed gland seal - the conventional shaft seal - is, due to it's intense maintenance requirements, only rarely used and then mostly in conjunction with long coupled bed plate mounted pumps. Their use with use within inline pumps is restricted to some special design versions.
Specific operating conditions require distinctly different types packed gland seals. They are subject to constant observation and maintenance adjustments. Proper lubrication of the gland packing requires a certain leakage rate which at average working pressures/temperatures and normal water quality amounts to a mean rate of 10 drops per minute. Special manufacturers recommendation's are to be observed individually. Service life expectancy is between 1 and 2 years, this can sometimes extend to several years on favourable conditions. Extremely bad water conditions (sediments, additives, overheating) can however drastically cut short their service life.
Packed glands should preferably be used in conjunction with shaft sleeves in order to avoid damage to the shaft by aggressive fluids or due to improper treatment of the packed gland.
The maintenance free mechanical seal has virtually become standard equipment of glanded direct coupled monobloc pumps.
They operate without any visible water leakage and do not require any maintenance whatsoever during their service life, which runs between 1 and 2 years, maximum 3 years. However, extremely bad water (sediments, additives, overheating) can also severely shorten their service life. In such cases it is advisable to check their suitability or the necessity for special designs with the seal manufacturers.
The following mechanical seal configurations have proved to be the most suitable for building services:
- bi-directional operation
- Flexible shaft attachment by means of an elastomeric bellows (automatic compensation of seal seat wear by means of the integrated spring)
- hard / soft material combination (ceramics or hardened metal to carbon) offering optimum lubricating qualities.
- attachment to a bronze or stainless steel shaft sleeve.
Note:- Packed glands and mechanical seals are parts which are subject to wear. Dry running is not admissible, as it will lead to destruction of the seals.
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