Abstract

Kermabon expresses his doubts that strong torque is not needed in the valve described by Rosfelder (ibid., v. 36, no. 4, p. 973-976, 1966). To be useful and economical, the "sphincter' type core catchers must be used to close in rather compact layers when, consequently, a rather large amount of energy is required. To operate properly, the lever system used by Rosfelder must be surrounded by sediments presenting some comparison.

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