Packing is a simple but cost-effective way to minimize leakage from around pump shafts. Over time though, it needs periodic adjustment to take up wear. Eventually, when the pump packing material no longer seals effectively, it must be replaced.
This blog provides an overview of packing and discusses the options for pump packing materials.
Sealing Around the Shaft
A fundamental challenge in pump design is to prevent the fluid being pumped from escaping along the impeller shaft. Mechanical seals are an option, but they add complexity and cost. As a result, most pumps rely on compression packing.
Packing involves surrounding the shaft with a braided, rope-like material. This is pushed into a region of the pump housing called the stuffing box. A cylindrical packing gland is passed over the shaft and used to compress, (or stuff), the packing material around the shaft. The gland, sometimes called the follower, is bolted into place to maintain compression on the packing. As the packing wears, these fasteners are tightened to maintain the seal.
Friction, Heat and Leakage
As the packing material presses against the shaft, rotation generates heat from friction. To prevent overheating, the packing gland is tightened to a level that allows a very small leak. Thus the fluid being pumped the both lubricates and cools the packing-shaft interface.
This creates two challenges: the packing material must withstand sliding contact with the shaft, and it must also have appropriate chemical compatibility.
Options for Pump Packing Materials
The principal material choices are fabric reinforced rubber and graphite. Homogeneous rubber with no reinforcement works in some applications while expanded PTFE with graphite fiber is used in others.
At Hennig Gasket & Seals we carry a wide range of Garlock pump packing materials. Their Chevron® line has solutions for most packing needs, while for abrasive liquids Garlock SLUDGE-PAK® is often the answer.
Packing material selection is driven by shaft speed in surface feet per minute, and fluid type and temperature. For advice on what will suit your application, please have this information to hand when you contact us.
