“Mechanical seal is a device which helps to join system or mechanism by preventing leakage and containing pressure.”
Any conventional mechanical seal consist of two main sub assemblies parts- seal head & mating ring assembly.
along with these mechanical seal sub-assemblies, we must know the parts of equipment which are use to adopt the mechanical seal on a given equipment.
Any single mechanical seal system has normally five leakage path:-
- Between gland plate face & stuffing box face.
- Between shaft & shaft protection sleeve.
- In between mating ring & gland plate.
- Between seal ring of seal head & shaft protection sleeve.
- Between stationary & rotating face.
while designing of any mechanical sealing system these points are carefully look into paths.
Mechanical seal performance is principally base on the health of the lubrication film between two faces.
To maintain this lubrication film, we have to ensure that the seal generates minimum heat & whatever heat is generated it should be dissipated very effectively.
Following point noted while selecting the seal:
- For a given situation, size of the seal selected should be the smallest possible.
- Selection of equipment should be such that the seal box pressure is minimum.
- low speed equipment is use.
- Seal face should have min. coefficient of friction.
- Seal with minimum face pressure is use.
- Hydraulically balance seal is select.
The operation of supplying continuous flow of fresh, clean & cool liquid to the mechanical seal face is known as flushing.
this is desire to ensure proper face lubrication & effective heat dissipation.
disadvantage of flushing are:
- wherever self flushing is use , when volumetric efficiency of the equipment get affect.
- wherever external flushing is use, flushing liquid gets mixed up into the pumpage & it dilutes the pumpage.
To create a barrier between the atmosphere & the seal face, some other media is allowed to occupy the space between the seal face & the atmosphere.
Quenching also helps face heat dissipation. in some applications, the atmospheric air creates problems for mechanical seal faces, hence it it necessary to keep the atmosphere away.
SELECTION OF THE SEAL
In selection, following things are decide:
- Type of the seal
- Metallurgy of the seal
- Size if the seal
- Surrounding of the seal , i.e. what API plan is use.
INSTALLATION & COMMISSIONING OF THE MECH. SEAL
During installation of the mechanical seal following care is require :
- Proper hygienic condition is maintain.
- Trained manpower should be use to install & commission the seal.
- All equipment parameters & dimensions to be ascertained.
- Use of hammer is strictly ward off
- Direction of rotation is check for the unidirectional seal.
- Free rotation of the shaft is ensure.
- Desired API plan is install.
- Static pressure test is achieve .
- Alignment of coupling is check.
Maintenance of the mechanical seals
Once the seal is installed & commissioned, it needs preventive maintenance
- Ensuring the equipment works without any abnormal vibrations.
- the temperature in seal area in the equipment is not raising abnormally.
- Ensuring that no abnormal sound is coming from the seal area.
- Ensuring that flushing liquid & quenching liquid flow rates & pressure are maintained as desired.
- confirm that cavitation doesn’t occur in the pump.