Mechanical Seal Vs Gland Packing

In this article, we will see the difference between the mechanical seal and gland packing (Mechanical Seal Vs Gland Packing).

Although mechanical seals had been around for many decades and now it replaced gland packing in many application. But still, gland packing’s are used in many applications such as fire water pumps, effluent water pumps, valve packing’s, etc,

[To read more about Balanced and Unbalanced mechanical seal click here]

The major comparison between the mechanical seal and gland packing are listed below. They are

• Emission
• Product loss
• Power Consumption
• Installation Time

Emission

Today, emissions norms in all countries are more stringent and move toward the target of Zero emission.
Because of the emission norms, the mechanical seals are used to meet the requirement and start replacing gland packing.
As per the Clean Air Act of the United States, they are 187 air pollutants listed and the source from which they came. Every year this list is kept on growing. Due to this Act, the companies in the United States are stickily following the Clean Air Act. Similarly the Clean air act of European Union and developing countries like India, Brazil are moving toward stringent.

As per API 682, guaranteed the leakage rate mechanical seal will be as follows
• Vapours – less than 1000 ml/m3 (1000 ppm vol) per pair of seal faces
• Liquid – less than 5.6 g/h per pair of seal faces

In particle, most of the mechanical seal leakage rate is well below the recommended by API 682.

If the above mention emission level is higher than the local emission norms than we need to go for a double mechanical seal.

Gland packings are used for only when the pumping liquid is non-hazardous such as water transfer pumps, stormwater pumps, etc.,

Product Loss

This is one of the major parameters for selecting mechanical seal over the gland packing. By using mechanical seal the loss of product due to leakage in reduced more than 99.95% when compared with gland packing.

As per gland packing thumb rule, leakage of pumping fluid is essential for extending the life of gland packing.

The leakage rate of well tighten gland packing is 10 drops/minutes (but in actual site condition it will very high). Total leakage rate for per day shall be

(10 drops/min) x 60 x 24 = 14400 drops (approximately 0.72 liters)

As per the above estimation, by using gland packing the production loss will be 0.72 litres. If you consider the pump is running for one year, then the product loss will be

0.72 x 365 = 262.8 liters

In the case of mechanical seal (assuming single mechanical seal) the product loss will be no more than 1 litres for a year.

Power Consumption

The amount of power required to drive a mechanical seal is very less compared to the pump having gland packing.
In the case of Gland Packing, the sealing will take place by pressing the gland packing against the gap between the casing and shaft to control the leakage. Also, the number of packing required for the seal is pend on the stuffing box pressure and depth of the stuffing box. Usually, the number of packing rings used for the pumps will be between 3 to 7 packing rings. Usually, the power will increase with an increase in the number of packing rings.

On the other hand, the mechanical seal having primary seal faces which are having very less frictional losses. Due to this mechanical seal will consume 80% power (assuming mechanical seal with pumping ring) less than the gland packing.

Installation time

The Installation time for mechanical seal usually takes seven to eight hours (include flushing system). Normally the installation duration will depend on the size of the mechanical seal.

On the other hand, glad packing installation will take a maximum of one to two hours and it will depend upon the size of shaft and number of gland packing rings required.

Mechanical Seals Vs Gland Packing

Description	Mechanical seal	Gland Packing
Installation time	Installation time is high, due to the pump would have to be taken off-line and disassembled	Gland packing installation time is very less when compared with mechanical seal.
Capital cost	Very high	Very cheap when compared with mechanical seal
Spare cost	Spares to be maintained. High spare cost.	Spare is not applicable.
Skill requirement	Skilled manpower is required for mechanical installations, removal and assembly	Minimal training is sufficient for gland packing installations and removal.
Leakage rate	Very minimal leakage	Leakage will be high
Product loss	Very minimal	Huge production loss when compared with mechanical seal
Power Consumption	Very less power consumed	Power consumption is very high