For a pressure cooker to maintain proper pressure during cooking, the gasket (the rubber or silicone ring that fits inside the lid) must seal tightly. To check how well a gasket is sealing, pour 2 cups of water into the cooker and secure the lid. Bring the cooker up to pressure. If water drips down the sides of the cooker, or if the cooker does not reach high pressure, replace the gasket. Be sure to remove the gasket after each use of the pressure cooker and wash it by hand in warm, soapy water. Look for cracks and other signs of wear: Those are signs that the gasket needs to be replaced.