Double Seal Piping Plan Query

[Milkboy]

Hey there

Double (Dual) Pressurised Mechanical Seal which the Barrier Fluid is supplied by another Centrifugal Pump which goes to Barrier In connection.
Barrier Out connection has a needle valve and a gauge to throttle the pressure to get a Barrier of 2 Bar above box.

The barrier fluid then goes to drain (water).

This is not an API Plan.


What are the groups thoughts on this set up as I have seen it a few times and cannot understand why people use it.


TIA




-
Milkboy

 

[JJPellin]

We use a very similar plan on sludge pumps. The pumped product is abrasive and cannot run between the seal faces. We use the water double seal so that the seal faces are lubricated with clean water instead of sludge. This has greatly improved the reliability of the seals in these pumps. In order to get optimum seal life, the pressure must be maintained above seal chamber pressure and the flow rate maintained at 1 gpm per inch of seal size to carry away the heat that the seal generates.

 

[lgoochy]

The API Plan you are describing is 54. Alternatively it can also be classed as quench to drain.
You could recirculate the fluid back to the tank the supply pump is pumping from, however you will need to check the heat load on the seal and that the fluid wont boil due to being constantly recirculated.
Other dangers of this are debris being carried from the process and into the barrier fluid system

 

[Jalink]

Milkboy the configuration you describe can be used for e.g.:
(a) as described by JJPellin to prevent abrasives to come between the seal faces;
(b) to cool/lubricate the seal faces; and
(c) to prevent air ingress in seal cavity with negative pressure.