PetroStreet

In relation to process plants , Can valve be installed on vertical lines in piping ..?

Yes valves are installed in vertical lines also, no issues.
It is preferable to install the valves in horizontal runs so that fluid may drain when the valve is closed. It is normally considered where water can freeze inside the line due to cold climatic conditions.

Gate valves with their gate in horizontal plane may not have complete drain as some of the fluid may be present inside bonnet cavity. This can be problematic if line is chemically cleaned sometimes and the chemicals will remain there. This may lead to some pressure binding or any possible chemical reaction.