Mechanical Seal for Pump
MECHANICAL SEALS FOR PUMPS
S. Raghavachari
Consultant
Chennai
Abstract
Mechanical seals are pieces of engineering marvel. Process industries could meet today’s stringent environmental pollution regulations through the effective sealing of even the most difficult fluids. This paper describes different kinds of seals, their design, properties and functioning. Effect of various factors like seal balance, face pressure, temperature and lubrication on performance of seal and probable causes of seal leakage with their corrective action has also been described.
Mechanical seals arrest the leak from shaft where it comes out of the casing. They work satisfactorily to seals almost any liquids, operate under full vacuum to 80 Bar pressure and temperature from 100 to 840oC. It can handle shaft speeds up to 3600 RPM and special designs can handle higher speeds also.
Seal Fundamentals
The rotating shaft carries the flexibly mounted seal head assembly. The pump gland plate carries the mating ring (Figure 1). These two parts perpendicular to the shaft have mating faces of extremely find surface finish of the order of 2 light bands. (A light band is 11.6x10-6 inch or 0.3 microns). Single or multiple springs load the faces, to form a leak tight seal at the running speeds. Single spring design of seals though simple is not common due to the following disadvantages:
Compressing and fitting the large springs are difficult.
Their working length is large requiring larger stuffing box.
The load on the faces is not uniform.
Hence multiple springs are common in use. One of the seal faces is usually carbon because of the following advantages:
Its excellent self-lubricating property reduces power consumption by seals.
Due to its good heat transfer capability, seals transfer.
The friction heat to the pumped liquid and so does not get heated.
The other mating face is usually some hard material like Tungsten carbide, or ceramic
S. Raghavachari
Consultant
Chennai
Abstract
Mechanical seals are pieces of engineering marvel. Process industries could meet today’s stringent environmental pollution regulations through the effective sealing of even the most difficult fluids. This paper describes different kinds of seals, their design, properties and functioning. Effect of various factors like seal balance, face pressure, temperature and lubrication on performance of seal and probable causes of seal leakage with their corrective action has also been described.
Mechanical seals arrest the leak from shaft where it comes out of the casing. They work satisfactorily to seals almost any liquids, operate under full vacuum to 80 Bar pressure and temperature from 100 to 840oC. It can handle shaft speeds up to 3600 RPM and special designs can handle higher speeds also.
Seal Fundamentals
The rotating shaft carries the flexibly mounted seal head assembly. The pump gland plate carries the mating ring (Figure 1). These two parts perpendicular to the shaft have mating faces of extremely find surface finish of the order of 2 light bands. (A light band is 11.6x10-6 inch or 0.3 microns). Single or multiple springs load the faces, to form a leak tight seal at the running speeds. Single spring design of seals though simple is not common due to the following disadvantages:
Compressing and fitting the large springs are difficult.
Their working length is large requiring larger stuffing box.
The load on the faces is not uniform.
Hence multiple springs are common in use. One of the seal faces is usually carbon because of the following advantages:
Its excellent self-lubricating property reduces power consumption by seals.
Due to its good heat transfer capability, seals transfer.
The friction heat to the pumped liquid and so does not get heated.
The other mating face is usually some hard material like Tungsten carbide, or ceramic