Very Useful Handbooks for your work:

Handbook for Control Valve Sizing (Parcol)

[link Point to another website Only the registered members can access]
Masoneilan Control Valve Sizing Handbook

[link Point to another website Only the registered members can access]
Control Valve Handbook, Fourth Edition (Emerson)

[link Point to another website Only the registered members can access]
Flowserve Instrument Engineer's Handbook for Control Valves

[link Point to another website Only the registered members can access]