Purpose of mechanical seal setting plates (also called seal tabs)

[Mech5656]

Hello,

I did research on mechanical seals and learned about components but couldn’t find anything on setting plates (also called seal tabs). The way I understand is that the seal tabs prevent the rotating and stationary faces from moving during shipping a pump. If they are not engaged, the faces will move and may get damaged during transportation.
Do you agree?

 

[Artisi]

It's to keep the stationary and rotating faces apart during transport /handling / installation.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[JJPellin]

For API cartridge mechanical seals, the seal tabs do not keep the seal faces apart. They actually lock the seal in the proper running position as far as compression and the seal is set at its ideal running length. The tabs may help a little bit once the seal is installed in the pump to protect the seal during shipment or other work that might disturb the seal. But, the main function is to set the seal at the correct running position during installation. The seal tabs should not be disengaged until the pump thrust bearing is assembled and set. At that point, the thrust bearing will hold the seal rotary and stationary elements in the proper axial alignment.

Johnny Pellin

 

[Mech5656]

Thank you for your responses and both were superb. I understand now.

I have another follow up question. Suppose you send your pump to repair shop (outside), they repair the pump, air test the seals, and ship the pump to you without engaging the seal setting plates. Will you send back the pump and remove and re-evaluate the seals, just because the seals may have been damaged during shipping while pump was on truck?

 

[JJPellin]

I would not. In my experience, the seal tabs provide some minor amount of support to limit shaft movement at the seal. But, it is not enough to save the seal if the shipment was very rough. And, if the shipment was very smooth, the tabs probably were not needed.

If the pump was shipped back as a complete assembly, I would pressure test the entire pump whether or not the seal tabs were locked. I would use a low pressure air test before I installed the pump into the field.

Johnny Pellin

 

[TiCl4]

As JJPellin said, the tabs are there to maintain the correct compression force on the cartridge seal until the set screws can be engaged. They do not space the seal faces apart.

Just be aware that if the seal was removed during rebuilding, they would need to reset the seal compression to the original spacing that is normally maintained with the tabs when the seal is not installed. Normally the OEM does this - removing and reinstalling the same cartridge seal is a dicey proposition.

JJpellin’s suggestion of a low pressure air test is good. Vendors that I’ve dealt with don’t recommend more than 5-10 psig for the seals we have in operation. Other seals may be okay for higher air pressure - consult the OEM for pneumatic testing for mechanical seals.

Also, if the seal is already set on the pump, those tabs are supposed to be removed.

 

[Mech5656]

Thanks to JJPellin and TiCL4 for their responses. Your detailed explanation was extremely helpful in understanding the basics of setting plates.