Placing the grinding heads centrally over the valve seat also produces a more effective cross-hatch pattern . This is the π www . valve-world . net Valve World June 2024
VALVE GRINDING
Portable valve grinding equipment , designed for field work , is frequently used in the workshop as well
Portable valve grinding equipment needs to produce excellent results despite its compact size
Early equipment for field use was heavy and cumbersome . Some still is . But over the years , designs have , in general , significantly improved , to the point where some users even prefer to use their portable equipment in the workshop as well .
Different machine designs
Grinding a valve seat can take a while and it is best to be patient . Pushing the machine down with great force will not speed up the grinding process , it will only build up heat and wear down the abrasive material quicker . It is the cutting action of the grains in the abrasive material that do the work , not the weight or pressure applied of the machine . So , it is best to leave the machine to do its work . Material needs to be removed evenly from the valve seat . Sometimes , a solid flat disc is applied across the entire seat . This will
remove more material from the outside of the seat , as a solid plate has a higher speed the further out on the diameter you are , making the seat slightly convex . It can also cause longitudinal scratches that result in inaccurate flatness across the entire seat . To avoid this scenario , many machines have hubs with several individual , smaller grinding heads , each one of them grinding across the entire surface of the seat in a uniform manner . A gear driven system uses a planetary gear in the hub that transfers mechanical power to the grinding heads using small diameter shafts . With this design , the centre of each grinding head is placed centrally over the valve seat . The alternative is to use friction driven grinding heads . These have the centre of the grinding head on the inside of the valve seat , with only a small portion of its surface in contact with the seat . There are no shafts connecting the hub with the grinding heads . When the hub turns , the friction between the grinding head and the valve seat causes the grinding head to spin . The shaft driven design tends to be more reliable . Friction drive can only transfer a limited amount of torque , which can cause individual grinding heads to slow down or stop altogether , resulting in inaccurate flatness of the valve seat .
Grinding discs with grit abrasive ( top ) are used for quick removal of material , while discs with micron material ( below ) are used to produce a smooth surface
Effective cross-hatch pattern
Placing the grinding heads centrally over the valve seat also produces a more effective cross-hatch pattern . This is the π www . valve-world . net Valve World June 2024
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