The ISO symbols are based on the SKEY. Usually a 4 letter sequence that is mapped to the block in the Iso Symbol seed file. You will also need to fill in the Iso Symbol Type field too. That will generally be "VALVE", "FLANGE" etc.
The SKEY and Type can be defined on the "General Properties" Tab of the item in the Catalog Editor. Its on the right down the bottom of all the fields. And then the SKEY can be mapped to a block in the "IsoSkeyAcadBlockMap.xml" file in the Isometric folder of your project.
You can make your own to suit your needs. Usually the first 2 characters of the SKEY is the definition of the component type. ie: EL for Elbow. Then the last 2 characters for the end connections. But any combination will do. Then you can create a block for the ISO representation of the item, and map the block in xml file that was mentioned in the earlier post.
How do you create a valve that is SW x THRD, used for drain valves. I need to create them for GATE, GLOBE, BALL, PLUG. And what would be their 4 SKEYname. Is there any scale when you are creating the. I saw the size of the GateValve & the SocketWeld and they are diffrent size. These valves are always in sizes 1/2" thru 2" and I can't belive that they are not in the catalog already. Any help would be great.