The disposition and configuration of the grooves 45 is such that the seal at {TAIL ~ sealing element} 49 is disestablished prior to disestablishment of the metal to metal seal between {HEAD ~ the gate face} and the righthand end of seat element 38, so that high pressure differentials are not imposed across the elastomeric seal 
The disposition and configuration of the grooves 45 is such that the seal at { TAIL ~ sealing element } 49 is disestablished prior to disestablishment of the metal to metal seal between { HEAD ~ the gate face } and the righthand end of seat element 38 , so that high pressure differentials are not imposed across the elastomeric seal
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