Propeller shaft Mechanical seal

[PanChatzi]

The mechanical seal consists of two parts:
1. The moving part which rotates with the shaft and sits tide on the shaft. It is fixed on the shaft with screws
2. The non moving ceramic part which is sittin on the shaft loose.
Question : is there any rule of thumb how loose the ceramic part should sit on the shaft?
I am grateful for any comments. I am currently mounting a PSS mechanical seal on a 2'' shaft in my boat.

 

[rafiki_]

Welcome to this forum. You will get a mix of great help, interesting posts, and some rubbish. I can’t help with your request, but others on here will. Have you checked the specification supplied with your seal?

 

[Tranona]

These are the instructions for installation shaftseal.com/downloads/pss-type-a-pro-seal-instructions.pdf As yyou see the "fixed" graphite face is not "loose" but is effectively part of the bellows. The bellows must be compressed exactly in accordance with the instructions as it is the pressure that creates the seal. The static pressure is set at a level which allows the shaft to move fore and aft as you go in and out of gear while still maintaining enough pressure on the faces to prevent leaks.

Hope this helps.

 

[PanChatzi]

These are the instructions for installation shaftseal.com/downloads/pss-type-a-pro-seal-instructions.pdf As yyou see the "fixed" graphite face is not "loose" but is effectively part of the bellows. The bellows must be compressed exactly in accordance with the instructions as it is the pressure that creates the seal. The static pressure is set at a level which allows the shaft to move fore and aft as you go in and out of gear while still maintaining enough pressure on the faces to prevent leaks.

Hope this helps.

Thank you for the answer. I have followed exactly the mounting instructions. Before compressing the graphite and bellow as per instruction, I notice that the graphite flange is not sitting tight on the shaft. I guess this is normal, because the shaft has to move freely inside the graphite flange during operation, I just don't know how if in my case the fitting is too lose.

 

[Tranona]

Thank you for the answer. I have followed exactly the mounting instructions. Before compressing the graphite and bellow as per instruction, I notice that the graphite flange is not sitting tight on the shaft. I guess this is normal, because the shaft has to move freely inside the graphite flange during operation, I just don't know how if in my case the fitting is too lose.

It does not need to sit tight on the shaft. Clearance is required because the shaft can move in all directions. If you have the correct unit for your shaft size then you have nothing to worry about.