Steam seal

In a fluid seal apparatus for a member, which fluid seal apparatus includes a plurality of spaced-apart seal rings arranged about said member defining at least a first region, a second region, a third region in communication with the atmosphere and with a low pressure chamber at a pressure below atmospheric pressure, and a fourth region arranged between said first and second regions, which first, fourth, second and third regions communicate with one another and which are sequentially arranged with respect to the member to be sealed, a first source of a first fluid, and a second source of a second fluid, the improvement comprising:

• first means for conducting said first fluid from said first source to said first region at a first pressure, said first pressure being greater than a pressure in said third region;
• second means for conducting said second fluid from said second source to said second region at a second pressure, said second pressure being above atmospheric pressure and greater than a pressure in said third region or a pressure in said fourth region
• third means for conducting a mixture of air and said second fluid from said third region to said low pressure chamber, said second fluid flowing from said second region to said third region and air flowing from the atmosphere to said third region;
• and
• fourth means for withdrawing a mixture of said first and second fluids from said fourth region, said first and second fluids flowing from said first and second regions, respectively, to said fourth region, whereby pure seal steam may be supplied as said second fluid while impure seal steam may be supplied as said first fluid to prevent the leakage of said impure steam.