hi good day for you

actually i fell tired in understanding tandem seal arrangement and plans

*does tandem seal used as pressuerized and non pressureized seal ?
 
*some manufacturers used plan 53 with tandem seal
on other hand i read in some books plan 53 used in conjunction with double back to back seal whet is right ?
   
* when do we must used plan 52 , why dont we used plan 53 all the time to prevent any leak , why there is a plan 52 from the base is it related to avoide diluting for examble  ?

finally
*if there is any leak from the primary seal in the tandem seal in plan 52 we know the leak will mix with the buffer fluid its mean what will buffer now the dangerous pumped product , how can we Separate the buffer fluid from dangerous Product?
according to my information the buffer tank must be vented to flare how ?

thank you all    

 
 

Plan 52 is non pressurized.  What appears to be a tandem seal may in fact be designed as a double pressurized seal.  Plan 53A, B or C is designed for double pressurized seals.  A double seal can be arranged Back to Back, in Tandem or face to face.  Refer to API682 for more descriptive infomation.  Double seals are used where product is not to be released to atmosphere and it sounds like your product needs a double pressurized seal.  Leakage of barrier fluid will be to process and atmosphere, approx (5-10cc/hr).  You cannot use a Plan 52 and seperate the pumped product from the Buffer Fluid.  It is very important to use a compatible buffer fluid with the pumped fluid.  Most Plan 52 systems in refineries, chemical and petrochemical plants are hooked to the flare.  Normally the vessel has a fitting (screwed or flanged) at the top and this is piped into the flare system via a check valve to prevent anything coming back into the vessel.   

 

thanks a lot
but when we have to chose unpressurized seal instead of pressurized seal if both are used for dangerous or toxic application
your cooperation is highly appreciated  
 

Just for this reason API 682 makes the designation of dual pressurized seals (Plan 53A, B, C, 54) and dual unpressurized seals (Plan 52). As stated, the dual pressurized seals can be back to back, tandem, or face to face. When to use either a pressurized seal or unpressurized seal depends on your site and regional regulations. Typically, a plan 52 is an option for low emissions services and must be vented to the flare. You would not want to use it in a truly toxic application as any leakage past the primary seal is going to contaminate your buffer fluid & seal reservoir. A good example of misapplication of a plan 52 system is in HF service, which I have seen a few times in past refinery experience - not a good idea as having a contaminated reservoir of buffer fluid leads to all kinds of disposal and exposure issues. If you have a truly toxic fluid that you need to contain and in which absolutely no leakage to atmosphere can be tolerated, then you want the pressurized system. This is not the only determining factor. In most hot, heavy, hydrocarbon services often the only way to achieve zero emissions would be with a dual pressurized seal as well. These applications require a good bit of engineering to manage the support system details and evaluation of the heat load on the seal. Unfortunately, there is no cookie cutter answer for you when to use each - you need to determine if the specific application warrants the additional measure of pressurization or not.  

Do you mean we have to chose pressurized seal instead of unpressurized seal only if we want to avoid having reservoir contain a very toxic or dangerous fluid ?   

thanks for your valuable informations >

No, that's not the only time to choose a pressurized seal. There are many applications in which a pressurized seal has advantages over an unpressurized. What I described is the most obvious case where it would be preferred which is in a toxic or hazardous service. Again, YOU need to determine which standards, requirements, and general mandates are in place which will lead YOU to this decision.

why dont you tell us what the application is that you have and we can make comments for you.

thanks alot bk19702


i have condensate gas application
actually i dont have any problem
but i want to understand the plans more ..
thanks flexibox