Stuffing box (Pdf): Definition, parts, types, advantages, disadvantages, applications

In this article, I have explained the following topics related to stuffing box.

• What is stuffing box?
• What is the function of stuffing box?
• How does the stuffing box work?
• What are the parts of stuffing box?
• What are the types of stuffing box?
• What are the advantages and disadvantages of stuffing box?
• What are the applications (Uses) of stuffing box?

What is stuffing box?

The stuffing box is a packing assembly or a shaft seal that is used as a sealing device to prevent leakages of air or water or steam from rotating or sliding shaft. They are mostly used in the pump to prevent fluid leakage. The image of a standard or basic type stuffing box is shown below.

Function & working principle of stuffing box

The main function of the stuffing box is to prevent leakage from the rotating shaft. The entire packing assembly is fitted over the rotating shaft. When the gland packing is tight, the compression of packing rings inside the stuffing box assembly prevents fluid leakage from the rotating shafts. Due to continuous friction, the assembly may get heat, show the entire packing assembly is lubricated by introducing lubricant via lantern ring. By default, the stuffing box leaks few drops per minute while the sleeve is rotating and it is designed in such a way.

The parts and types of stuffing boxes are discussed below.

Stuffing box parts

The stuffing box assembly consists of five major components. They are

Now let’s briefly see about each part of stuffing box assembly.

Stuffing box casing

In some types of pump, stuffing box casing is actually a part of that pump casing, whereas in other types of pump it is bolted and fitted along with pump casing. Some variant of stuffing box casing has a hole to pass sealing liquid to the packing area. The throat bore of the stuffing box casing is concentric to the shaft and it is designed to hold a specific size of packing rings.

Throat bush

The main purpose of the stuffing box bush or throat bush is to reduce the clearance between the shaft sleeve and the stuffing box bore. It is located at the bottom of the stuffing box and just below the first internal packing ring. The clearance between the stuffing box and the shaft sleeve can be adjusted by replacing the throat bush. Some pressure breakdown will happen across it.

The pressure of the packing in sealing determines the life of the packing therefore the lower pressure increases the life of the packing in sealing. To avoid unnecessary wear on the shaft the throat bush keeps away the solid particles entering the packing area. Throat Bush protects the stuffing box from wear and saves the replacement charges for the expensive component.

If the clearance between the shaft sleeve and stuffing box is larger, the internal packing ring might extrude into the clearance. This may reduce the effectiveness while the backing gets tightened. The removal of packing ring and bush will be more difficult during repair or maintenance.

Gland packing rings

The gland packing rings are made by square braided or inter braided fibrous material such as graphite composite, polytetrafluoroethylene, leather, cotton, rubber or fabric. It is often saturated with the lubricating medium in the stuffing box assembly. The packing rings placed in between the throat bush and lantern ring are called as internal packing rings. External packing rings are placed in between gland follower and lantern ring.

These packing rings are compressed in stuffing box assembly. It is also used for avoiding fluid leakage. The packing should not be over tightened because due to friction the packing can overheat. This result in the degradation of packing rings, wear on the shaft sleeve and leads to excess leakage. To avoid this mess there must be certain lubrication.

There are mostly 3 internal and 3 rings in the packing assembly, this number differs and depends and the amount of pressure to be sealed. The gland packing Puller is required to remove the gland packing ring while dismantling the stuffing box assembly.

The selection of packing gland rings is very important because an improper selection may result in frequent failure of packing rings. There are several factors considered while selecting packing ring. Some of the important factors are shaft speed, chemical condition of the fluid, pressure, temperature, dimension of the stuffing box etc. These factors are mostly considered while selecting packing gland rings.

Gland follower (or) Packing Gland

The other name of gland follower is packing gland, gland etc. The main purpose of gland follower is to hold the packing rings in a steady manner inside the stuffing box. There are several types of gland followers are available. The two basic types of gland followers are split glands and split glands.

The gland follower is mostly in split type. The split type gland follower makes the removal and tightening process easier just by loosening and tightening the gland follower nuts. It makes the process of changing packing rings smoothly and easily. In some types of gland follower, there will be a path for introducing calling liquid. This type of gland follower with a hollow cavity is mostly used in boiler and other related applications.

Lantern ring

The lantern ring is also called as seal cage. A lantern ring is a part of a stuffing box assembly which is similar to the gland packing rings. The lantern ring is made of either bronze, stainless steel or plastic materials. It is a circular ring and has a hole in its outer diameter.

The lantern ring is placed between the internal and external gland packing rings and the drilled part of the lantern ring is placed straight to the opening in the stuffing box. It helps to pass the lubrication fluid inside the stuffing box and also act as a seal to prevent air leakage. It helps in separating gland packing rings such as internal and external packing rings.

Types of stuffing box

Basically, the stuffing boxes are classified into four types.

• Basic (or) Standard stuffing box
• Stuffing box with the condensing chamber
• Stuffing box with lantern ring
• Dirty service stuffing box

Basic (or) Standard stuffing box

A basic stuffing box or standard type stuffing box is a basic variant that is used in most common applications. Due to its simple construction of parts, it is named as a basic stuffing box. It is constructed with a ring-shaped chamber that contains the gland packing rings and throat Bush at the bottom. The main advantage of the basic stuffing box is the removal process of packing rings is easier.

Stuffing box with condensing chamber

This variant of the stuffing box has a condensing chamber for cooling purpose. There is a hollow path in the gland follower to introduce cooling liquid and this act as a condensing chamber. This type of stuffing boxes is mostly used in boilers and their related applications.

Stuffing box with lantern ring

This variant has a lantern ring in it. It is mounted in between the set of internal and external gland packing rings. In this variant, the lantern ring act as an additional seal and also helps in introducing lubricating liquid inside the packing. Air leakage inside the packing can be reduced while using this variant.

Dirty service stuffing box

The construction of a dirty service stuffing box is more similar to the basic variant stuffing box. While comparing the basic variant it has an additional component called a wiper ring, placed before the stuffing box bushing. The wiper ring helps to prevent the wear on the shaft sleeve and Bush due to the formation of contaminants.

Advantages of stuffing box

• It is simple and compact in design.
• It is a low-cost sealing device.
• In case of any emergency situation packing rings inside the assembly can be easily replaced.
• It has only small leakage losses.
• The maintenance is simple and easy.
• It is easy to flush and lubricate.
• It is robust in structure.

Disadvantages of stuffing box

• Overheating and thermal stress cracking might occurs.
• Excessive friction in packing rings occurs due to shaft deflection.
• In pumps, the failure of the stuffing box occurs due to friction and vibration.
• Wear in shaft sleeve occurs due to radial and axial moment.
• The design of the stuffing box is not suitable for handling toxic and flammable liquids like liquid fuels, liquid ammonia, liquid $ \displaystyle C{{O}_{2}}$, etc. To handle toxic and flammable liquids a special design of the sealing system is required.
• Coolant is required during high temperature application and overheating.

Applications (Uses) of stuffing box

• It is mostly used in water pumps, slurry pumps and it is absent in the pumps that handle toxic and flammable liquids.
• It is used in propellers of the boat to prevent the entry of seawater.
• It is also used in boilers, steam engines to prevent steam leakage from the piston cylinders.