Centrifugal Pumps and Pressurized Seals

Assume we have an overhung centrifugal pump having the following details:

- operating fluid is propane;

- operating temperature 40 degree Celsius;

- tandem mechanical seal Plan 52;

- suction pressure 21 bar;

- discharge pressure 28 bar;

- 3000 RPM, driver is an electrical motor 75 Kw;

- flow is 318 cubic meter/hour;

- γ is 0.45;

- buffer fuid is diathermic oil.

While operate this pump in some hours the buffer fluid is lost outside or to the connected flare when is connected to flare the seal pot, due the overpressurizing of seal pot reservoir. The question is why the seal pot become presurised? We assumed that some operating fluid is coming in this seal pot. The plan 52 stated that are allowed from zero to very low process emissions. The second question is what does mean very low process emissions? How much quantity ( i.e. how many milliliters per hour ) ? This very low emissions could have a reaction with buffer fluid and in this way generate that pressure which force the buffer fluid outside from the seal pot?

Thanks a lot to all