I'm repairing an old brass hot water valve for my washing machine. I've removed the old packing material and replaced it with new graphite packing rope. I've tightened the packing nut until it is firm, but when I test the valve, water still leaks out between the nut and the valve stem. When I continue tightening the packing nut, the graphite packing squeezes out between the valve stem and the packing nut, and the valve continues to leak. What am I doing wrong?
(I have tried doing the recommended "wrap the packing rope twice around the stem". I have also tried manually pushing the rope down into the void between the stem and the valve to minimize air gaps. Neither approach seems to make a difference.)