PACKING AND PACKED GLANDS

Definition: This is an arrangement where the moving part of a system such as a rotating shaft is sealed from the outside world via packing it with a number of rings of material; any medium from within is prevented from escaping via leakage & the outside world is prevented from entering inside (the packing provides a satisfactory barrier between the interior & the exterior atmospheres. The packed gland is used primarily for sealing process valve shafts (axial movement) and for process pump shafts(rotary movement). The packed gland seal for pump applications is now rarely fitted to new pumps. This is due to it's high maintenance requirement

Explanation: The packed gland is still widely used for stem sealing of various types of valves including gate valves, globe valves, and ball valves. The packed gland provides a low cost option with the capabilities of sealing under a wide range of operating conditions with a wide range of fluids by selecting appropriate packing materials The gland packing generally creeps over time, causing leakage and therefore needs to be regularly tightened to maintain the seal. The packing can be continuously spring loaded using disc springs or similar to extend the maintenance period. A packed gland situation can also be referred to as a stuffing box, packed glands or a gland seal.

Properties Required: The properties of a packing system required for good sealing and trouble free operation include: Compatibility with the working fluid at the operating temperatures Plasticity to conform to the shaft under the influence of the gland force Non-abrasive to minimise shaft erosion Non-corrosive to avoid damage to the shaft of housing Wear resistant Retain properties over time

Packed Gland Assembly

Gate Valve

Packing Material & FORM Types Material - Plastic Material – PTFE Material – Aluminium Material – Graphite MATERIAL - YARN Form - Plaited Form - Braided Form - Twisted Yarn packings can be based on vegetable, animal or synthetic fibres and are based on various types of fibre:

Packing Material Types - Metallic In plaited and braided packings reinforcing wires are used for operation at higher temperatures and pressures.   For high temperatures, woven types of copper and aluminium packing can be produced.  Metal foils of lead, aluminium, graphite and copper can be used to form packings. Combinations of packings having hard metal end rings with softer inner rings are used for higher performance duties including gases and abrasive fluids.

Packing Form Types Cross Section

The Fitting of Packing Packing is generally cut into specific size length pieces, to make a single ring (the size of 1 revolution from around the circumference of the shaft, this piece of packing will surround). This comes off a long roll of material like tape, usually in 10m lengths. It is the fitted into the application in the rings, with the joint of each one facing 180 degrees apart from its neighbour. A metal ring known as a gland bush may in some instances be inserted into the application first, before the packing is put into place.

Packing Retention A metal ring known as a lantern ring are sometimes included between two sets of packings to allow introduction of lubricant, cooling or flushing fluid (this ring would definitely be used where several pieces of packing are being used together) The entire assembled material is held in place by a gland follower which is tightened initially in place by either nuts or bolts. These area adjusted periodically over time to ensure the packing does not allow leakage

Packing Gland Maintenance It will be necessary to conduct regular checks on the Gland Packing assembly to see whether any leakage has occurred; if this is so, it would be necessary to slightly tighten the securing bolts / nuts in an even sequence (DO NOT OVERTIGHTEN AS THIS CAN CAUSE DAMAGE TO THE PACKING BY CRUSHING AND WOULD REDUCE THE WORKING LIFE OF THE GLAND SEAL)

Packed Gland Assembly

Packed Gland Assembly

The Fitting of Packed Gland Material The following youtube clip shows how the correct fitting of packed gland material takes place. Please observe this closely as I will be asking questions about this at the end of the video. http://www.youtube.com/watch?v=xrB1IpCXNQ0&index=1&list=PL8OpMfgxgzguZhwq qfRZs8Bdg1d-ShJM2

References: http://www.aesseal.co.uk/en/product/gland-packing/pump-packing http://www.eriksgaskets.co.uk/Compression-Packing/ http://vulcan-eng.com/gland-packing/ http://www.jdvalves.com/