The poppet works on the following principle. Thus the fluid is allowed to flow through in one direction only. Check valves are designed so as not to tolerate leakage. The purpose of the light spring is only to keep the poppet on the seat. The following Poppet type valve is used in submarines.
Most manufacturers use sharp-edged, very hard seats and soft, maybe plastic, poppets.
Parallel seats are very good except that they are too prone to trapping contaminants between the seat and the poppet. All rights reserved worldwide.