A modular valve assembly can include a core spool module and a plurality of end connection modules. The end connection modules can be configured to be secured to the core spool module at one or more of a core inlet or a core outlet of the core spool module to provide one or more respective, different flow configurations for the modular valve assembly. The core spool module can include a bonnet portion that is integrally formed with the core inlet and the core outlet and a seat ring configured to provide a seal against flow of process fluid through the modular valve assembly.