Inkscape is very useful SVG image editor that can help us to create a device image of any kinds. The image can be used for building SCADA or HMI. You can follow the video tutorial to know details about Inkscape.
How to draw a valve for automation system
=> Draw a rectangle, select it
=> Edit path by node (F2)
=> Path | Object to Path, drag a corner and make a shape like valve
=> Object | Group
=>Make the shape that fits to the screen (File | Document Properties | Custom Size | Resize page to drawing or selection)