Leakage　in　isobaric　energy　recovery　devices　(ERDs)　is　inevitable.　Three　seal　structures　are　introduced　and　studied　for　a　fully-rotary　valve　energy　recovery　device　(FRV-ERD)　to　reduce　leakage.　Effects　of　pressure　difference　and　geometrical　parameters　of　seal　structure　on　leakage　are　investigated　and　compared　for　different　seal　structures.　Results　show　that,　as　the　key　component　of　this　ERD,　the　fully-rotary　valve　(FRV)　achieves　its　best　seal　performance　with　the　bilateral　seal.　For　the　FRV-ERD　of　design　parameters,　both　the　efficiency　and　required　clearance　are　improved　by　using　the　bilateral　seal　to　replace　the　original　seal.　The　calculated　efficiency　is　improved　from　89.48%　to　92.05%　at　the　clearance　of　30　mu　m　under　operating　pressure　and　the　required　clearance　increases　from　18.1　mu　m　to　20.4　mu　m.　Based　on　the　results　of　the　optimized　bilateral　seal,　an　approximate　leakage　rate　equation　is　proposed　and　can　be　used　for　design　calculation.　The　performance　of　FRV-ERD　with　the　optimized　bilateral　seal　is　improved　greatly.　Compared　with　FRV-ERD　with　the　original　seal,　the　efficiency　of　FRV-ERD　with　the　optimized　bilateral　seal　is　improved　from　89.48%　to　96.33%　at　the　clearance　of　30　mu　m　under　operating　pressure,　and　the　required　clearance　increases　from　18.1　mu　m　to　29.5　mu　m,　easing　machining　difficulty　greatly.