The National Board maintains the NB-18 on their web site. This document, among many other pieces of information, records active certificates for each valve series. This document should be consulted first when determining if a valve can be used in a particular service. Under the section of “Listing of Certified Types.”
For instance, Farris’ 2600L series maintains two certificates for media. Certificate number 57068 is the Certificate for the 2600L in liquid service. Certificate number 57260 is the Certificate for the 2600L in Steam & Air/Gas. Since the 2600L has a certificate for Steam & Air/Gas, it can be used in this service.
Keep in mind, not all liquid trim valves with certificates can just be installed in different media. In some instances, a spring may need to be changed. The Farris 2600L uses the same spring for all 3 media.
The Farris 2700 series valve, for instance, has certificates for Steam & Air/Gas (57237) and Liquid (57248). However, this valve has a different spring for liquid compared to the Steam & Air/Gas.