Sealing arrangement using flexible seals

Abstract

A sealing arrangement is provided between relatively rotatable bodies of a machine in which, in operation, a relatively high pressure (P 1 ) exists on one side of the sealing arrangement and a relatively low pressure (P 2 ) exists on the other side, the pressure difference (P 1 -P 2 ) being up to a predetermined maximum pressure difference (ΔP max ). The sealing arrangement includes a series of seals, the pressure dropping across each successive seal from the high pressure side of the sealing arrangement to the low pressure side. At least two of the seals are flexible seals, e.g. brush or leaf seals. Each flexible seal 14 is designed to function under a pressure drop (Δp) up to a predetermined maximum pressure drop (Δp max ) across the flexible seal 14 and to provide a given resistance to fluid flow. Each flexible seal 14 is capable of recovering from an abnormal condition, due to normal operation of the machine, in which the resistance of the flexible seal to fluid flow decreases from a normal level to a substantially lower level. The series of seals are arranged in such a manner that the pressure drop across each flexible seal is less than the predetermined maximum pressure drop (Δp max ) when the pressure difference (P 1 -P 2 ) between the high pressure side of the sealing arrangement and the low pressure side is equal to the said predetermined maximum pressure difference (ΔP max ) and another one of the flexible seals has suffered a recoverable decrease in its resistance to fluid flow. In one embodiment the flexible seal 14 is provided with a permanent by-pass path 16 communicating between its upstream and downstream sides.

1 . A sealing arrangement useful between first and second relatively rotatable bodies of a machine in which, in operation, a relatively high pressure (P 1 ) exists on one side of the sealing arrangement and a relatively low pressure (P 2 ) exists on the other side, a pressure difference (P 1 -P 2 ) being up to a predetermined maximum pressure difference (ΔP max ), the sealing arrangement comprising: 
 a series of seals, the pressure dropping across each successive seal from the high pressure side of the sealing arrangement to the low pressure side when in operation;    at least two of the seals comprising flexible seals;    each flexible seal being configured and arranged to function under a pressure drop (Δp) up to a predetermined maximum pressure drop (Δp max ) across the flexible seal and to provide a given resistance to fluid flow;    each flexible seal being configured and arranged to recover from an abnormal condition, due to normal operation of the machine, in which the resistance of the flexible seal to fluid flow decreases from a normal level to a substantially lower level;    the series of seals being arranged in such a manner that the pressure drop across each flexible seal when in operation is less than the predetermined maximum pressure drop (Δp max ) when the pressure difference (P 1 -P 2 ) between the high pressure side of the sealing arrangement and the low pressure side is equal to the predetermined maximum pressure difference (ΔP max ) and another one of the flexible seals has suffered a recoverable decrease in resistance to fluid flow.    
   
   
       2 . A sealing arrangement as claimed in  claim 1 , in which each flexible seal comprises a permanent fluid by-pass path communicating between the upstream side and the downstream side of the flexible seal and provides fluid conductance in parallel to the fluid resistance of the flexible seal.  
   
   
       3 . A sealing arrangement as claimed in  claim 1 , wherein each flexible seal comprises a flexible sealing element and a further element providing a fluid resistance in parallel to the fluid resistance of the flexible sealing element.  
   
   
       4 . A sealing arrangement as claimed in  claim 3 , wherein the further element includes a plurality of by-pass ducts communicating between the upstream side and the downstream side of the flexible seal.  
   
   
       5 . A sealing arrangement as claimed in  claim 4 , wherein the plurality of by-pass ducts comprise grooves, bores, or both.  
   
   
       6 . A sealing arrangement as claimed in  claim 3 , in which each flexible sealing element includes a plurality of apertures extending from the upstream side to the downstream side of the flexible seal.  
   
   
       7 . A sealing arrangement as claimed in  claim 6 , wherein at least some of the plurality of apertures extend to a free end of the flexible sealing element remote from the further element.  
   
   
       8 . A sealing arrangement as claimed in  claim 7 , wherein each flexible sealing element comprises sub-divided separate segments which are spaced apart to form said plurality of apertures.  
   
   
       9 . A sealing arrangement as claimed in  claim 8 , wherein each further element comprises segments which support the respective segments of the flexible sealing element and which are spaced apart.  
   
   
       10 . A sealing arrangement as claimed in  claim 1 , in which the flexible seals comprise brush seals.  
   
   
       11 . A sealing arrangement as claimed in  claim 1 , in which the flexible seals comprise leaf seals or foil seals.  
   
   
       12 . A sealing arrangement as claimed in  claim 1 , wherein the series of seals comprises fin seals individually having a lower resistance to fluid flow than the individual flexible seals.  
   
   
       13 . A sealing arrangement as claimed in  claim 12 , comprising at least one fin seal upstream of each flexible seal.  
   
   
       14 . A sealing arrangement as claimed in  claim 1 , wherein the series of seals is configured and arranged so that the pressure drop (Δp) across each flexible seal is less than the predetermined maximum pressure drop (Δp max ) even when all other flexible seals have suffered their greatest recoverable decrease in resistance to fluid flow.  
   
   
       15 . A sealing arrangement as claimed in  claim 1 , wherein the predetermined maximum pressure difference (ΔP max ) between the high pressure side and the low pressure side is more than 20 bar.  
   
   
       16 . A sealing arrangement as claimed in  claim 1 , wherein the predetermined maximum pressure drop (Δp max ) across each flexible seal is in the range from 10 bar to 30 bar.  
   
   
       17 . A turbine comprising: 
 a sealing arrangement as claimed in  claim 1;     said first and second relatively rotatable bodies; and    wherein the seal arrangement is positioned between said first and second relatively rotatable bodies.    
   
   
       18 . A turbine as claimed in  claim 17 , wherein the turbine comprises a steam turbine.