misunderstanding in plan 52 + 53 + tandem seal !! 2

[mechanicaly1980]

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

 

[BigInch]

Sometimes a little leakage is acceptable.

You don't separate it. It stays mixed forever.

Use some pipe to connect the buffer tank to the flare.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[mechanicaly1980]

thank you biginch

i need some on to answer my questions
with little explanation ..

 

[TD2K]

A tandem seal can be either a pressurized or non-pressurized seal.

I don't have my little cheat book from Flowserve here but from what's I've seen on a quick google for tandem seal flush plans:

Plan 52 is unpressurized
Plan 53 is pressurized

 

[mechanicaly1980]

thanks td2k

i know that Plan 52 is unpressurized,Plan 53 is pressurized

my question was when do we must used plan 52
why dont we used plan 53 all the time ?

 

[longeron]

The answer is that it depends.

The availability of a flare or nitrogen header might help dictate which is used. The lubricity of the process fluid, concentration of solids, how toxic the process fluid is, or how high the seal chamber pressure is might push a user to a pressurized or unpressurized dual seal. Some users are more comfortable with one over the other.

Perhaps your Nitrogen header pressure isn't high enough, and you don't want to use a 53B or 53C. The cost of the reservoir and accessories can drive users one way or the other. Cost is often an issue with a pressurized seal and support skid (essentially a lube oil skid supplying pressurized barrier fluid to the seal) otherwise known as a Plan 54.

Taking a pragmatic approach to each application and consulting your trusted mechanical seal vendor is a good way to tackle the problem.

 

[raronen]

In many situations, either Plan 52 or 53 will work.

In the refining and chemical industries, the choice is based on the following criteria:

If absolutely zero leakage is required, a pressurized plan 53 is required. The challenges with a Plan 53 are:
- Requirement for a dual-balanced seal design (primary seal can withstand reverse pressure). Most bellows seals can withstand reverse pressure. Spring-pusher seals can only withstand reverse pressure with special primary face designs which are often more expensive and less likely to be in stock.
- The pressure source must be very reliable
- The buffer fluid needs to be something that will not contaminate the product
- The buffer gas cannot become entrained in the buffer fluid, causing failure of the secondary seal
- Instrumentation to ensure there is no loss of buffer fluid.

In most cases, near-zero leakage is acceptable, and a plan 52 is preferred because the engineering set-up of the buffer fluid system tends to be simpler and more reliable.

In the wastewater and paper industries there are a lot of dual seals and a pressurized water system is used to flush between the seals. This is probably technically a Plan 54.

 

[Rotator]

You would use plan 52 when contamination of the buffer fluid with the pumped fluid is acceptable; as raronen states a plan 52 is generally simpler.
For example I have seen plan 52 on a heat transfer fluid circulation pump, where to avoid carbon buildup it was important to keep air away from the hot oil leaking through the primary seal. The buffer fluid used was the same heat transfer oil, so contamination was no problem.

 

[GaTechTheron]

Mechanically1980,

If there is ONE thing I learned from getting my degree, I NEED to actually understand what is going on with the different flush plans before I can remember when to use which one, and why. If you are anything like me, then out the Flowserve flip book:

http://pdf.directindustry.com/pdf/f...europe/piping-plan-flip-book-32907-62346.html