a helical spring used to hold closed a valve in the cylinder head of an internal-combustion engine
any spring that closes a valve after it has been opened mechanically or by flow pressure
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Examples from the Web for valve spring
Historical Examples of valve spring
The engine had to be stopped three times, twice due to valve-spring collar failures and once due to a valve head breaking.