Nothing, they are still available, we just stopped cataloging and promoting them. After years of experience, testing, and engineering we came to the conclusion that they are best suited for moderate pressures, 2000 - 3000 psi (140 - 210 bar). If the seat is soft enough to conform at low pressures, it is too soft to stand up to todays higher operating pressures and flows. If you have a dirty, medium pressure system that does not experience high flows or temperatures and you require very low leakage rates, you may want to consider the soft-seated valves. One piece of hard debris can make a steel seat leak. A soft seat is able to ingest a lot of contamination before it starts to leak. However, one piece of debris can cause the soft seat to leak at low pressures. Originally, Sun had a tighter leakage specification on soft-seated valves. However, when we made the decision to promote the steel seated valves instead of soft seats, we tightened the leakage specifications of the steel seat valves to match.