Abstract: An abradable seal includes an outer ring arrangement and an energiser for urging said outer ring arrangement against an opposing surface, wherein an outermost surface of said outer ring arrangement defines a sealing surface of said abradable seal; wherein said outer ring arrangement is configured such that after a first period of operation said sealing surface suddenly transitions from having a relatively large surface area to having a relatively small surface area, so as to cause a sudden increase in internal leakage across the seal at said transition.

Abstract: An abradable seal includes an outer ring arrangement and an energiser for urging said outer ring arrangement against an opposing surface, wherein an outermost surface of said outer ring arrangement defines a sealing surface of said abradable seal; wherein said outer ring arrangement is configured such that after a first period of operation said sealing surface suddenly transitions from having a relatively large surface area to having a relatively small surface area, so as to cause a sudden increase in internal leakage across the seal at said transition.

Abstract: An abradable seal is provided, comprising an outer ring arrangement and an energiser for urging said outer ring arrangement against an opposing surface, wherein an outermost surface of said outer ring arrangement defines a sealing surface of said abradable seal; wherein said outer ring arrangement is configured such that after a first period of operation said sealing surface suddenly transitions from having a relatively large surface area to having a relatively small surface area, so as to cause a sudden increase in internal leakage across the seal at said transition.

Abstract: There is disclosed a method of monitoring the health of an abradable seal located on a piston of an actuator, the method comprising the steps of: (i) measuring an initial velocity of said actuator piston while said actuator is maintained in a passive condition at an initial time; (ii) operating said actuator; (iii) measuring a subsequent velocity of said actuator piston while said actuator is maintained in a passive condition at a subsequent time; (iv) repeating steps (ii)-(iii) and either: recording or outputting the measured subsequent velocities over time; or determining a health status of said actuator when said subsequent velocity has increased above a predetermined amount.

Abstract: An abradable seal is provided, comprising an outer ring arrangement and an energiser for urging said outer ring arrangement against an opposing surface, wherein an outermost surface of said outer ring arrangement defines a sealing surface of said abradable seal; wherein said outer ring arrangement is configured such that after a first period of operation said sealing surface suddenly transitions from having a relatively large surface area to having a relatively small surface area, so as to cause a sudden increase in internal leakage across the seal at said transition.

Abstract: There is disclosed a method of monitoring the health of an abradable seal located on a piston of an actuator, the method comprising the steps of: (i) measuring an initial velocity of said actuator piston while said actuator is maintained in a passive condition at an initial time; (ii) operating said actuator; (iii) measuring a subsequent velocity of said actuator piston while said actuator is maintained in a passive condition at a subsequent time; (iv) repeating steps (ii)-(iii) and either: recording or outputting the measured subsequent velocities over time; or determining a health status of said actuator when said subsequent velocity has increased above a predetermined amount.