One way is to ask for an open, preliminary and unbinding offer, asking for quality valves. describing the application.
The offer should include different material suggestions and solutions as well as suppliers pro and con regarding materials and quality. The purpose is to find the markets best alternatives and new technical solutions, without locking everything up to 'older/common' descriptions.
Necessary norms for the applications must be included. Above could be used as preliminary bidder qualification.
Good luck!