Pressure cooker and hammer: what they have in common

1. Step 1. Pressure cooker — has part — Safety valve. Papin invented the safety valve precisely for his digester.
2. Step 2. Safety valve — is part of — Boiler. A mandatory safeguard for boilers.
3. Step 3. Boiler — is part of — Steam hammer. A boiler supplies the steam.
4. Step 4. Steam hammer — evolved from — Hammer. A steam hammer is a hammer lifted by steam, used to forge huge parts.

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