I see dotted lines that are attached to pipes when I put in an isolation valve. What are they for? Can I turn them off?
Why are the isolation valves connected to the middle of pipes by the dotted line? Are they associated to this location on the pipe?
The dotted lines associated with the isolation valve shows what pipe the isolation valve is attached to. It's there because isolation valves do not split pipes and if you accidentally move you isolation valves around the only way you could visually tell what pipe it's associated with is by opening it the properties of the valve. In that respect the dotted line is very important.
If you'd like to turn off the dotted line there is a way to do that. Just double click in the element symbology on "Isolation Valve" and in the properties box that pops up set the property for "Show attached link decorations" to 'False'.
Note that the dashed line has no direct bearing on the spatial reference for the isolation valve itself. The isolation valve will be spatially located at the point where it is placed. For instance, if you place the isolation valve a quarter of the way down a pipe from the start node, the isolation valve will be assumed to be at that point. There is an attribute in the isolation valve properties called "Distance from End Point". This is the distance from the start node of the pipe to the location of the isolation valve.
Whereas about isolation valves not connected to the pipe ends directly, it prevents the need of extra pipes in the model. If you have a valve in the middle of a particular run of pipe, the isolation valve element is associated with that pipe, so you only need to have one pipe element in the model in this case. If you were to use one of the other valve types like a TCV to represent the isolation valve, it would "split" the pipe (since pipes need to be physically connected to other nodes like TCVs), causing there to be two pipe elements to model this case.
It helps in situations where you have a large system with a large number of isolation valves, adding them to the model (for use with the criticality tool for example) could result in a large increase in the number of pipes. This could have implications with licensing (staying within the pipe limit), model size/complexity and asset management (having to work with multiple pipes/labels instead of a single pipe - though our GIS-ID feature, if used, will ensure this is not a problem with GIS synchronization workflows.)