The fit clearance between spool and sleeve decreases because of the thermal expansion of the spool caused by temperature increment, so it is possible that spool is deadlocked in sleeve.
油温升高使阀心受热膨胀，阀套与阀心间的配合间隙减小， 阀心有可能被卡死在阀套里。
2
The outer circle of the thermal fuse is riveted with a copper sleeve.