The valve keeper (also known as a valve collet or valve lock) is a small semi-cylindrical and tapered metal component. Always used in pairs (two keepers per valve), it fits into the grooves of the valve stem and locks into the upper spring retainer. On the Kubota twin-cylinder diesel engine used in Aixam and Minauto vehicles, these small retainers have the critical task of keeping the valve spring compressed to ensure the valve remains properly closed.