Valve Trim
The replacement or removal of internal valve parts that come in contact with the media flow are termed a
"Trim Change". These parts include valve stems, seats, disc, spacers, pivot pins, and internal springs. Other
 areas  of the valve body like the bonnet or packing gland that come in contact with the flow media are not
considered valve trim. Those areas do not experience the same conditions and forces that valve trim does.

Trim performance is determinded by the disc and seat interface. Because of the trim alloys and their unique
mechanical and chemical properties, the basic motion, flow control and sealing requirements are possible.     Trim components may be constructed of an number of alloys based on properties needed to with stand sever conditions such as erosion, corrosion, thermal extremes and high pressure service.

Properties of the flow media are an important cosideration in selecting suitable valve trim materials. Flow
rates, viscosity, velocity, temperture, pressure and chemical composition are all points to consider. Also,
concentration of solution, agitation and impurities can greatly effect the long term life of any valve trim.

                                                                            API Trim Number Chart

 TRIM        MATERIAL        SEAT DISC        BACKSEAT       STEM 

 1​           410              410              410            410​​
​              For service in clorine, bitumin & sour gas service

  2           304             304              304            304
              For service in cryogenic service

   3          F310             310              310           310
  
              For service in paper mills, plastic service, plastic colorazation etc.

  4           410- Hard        410-Hard           410           410
                                                 750 BHN
              For service in coal plants ,timber processing