The detachable surface parts in the valve are used to support the fully closed position of the valve core and form a sealing pair. Generally, the seat diameter is the maximum flow diameter of the valve. For example, the seat material of butterfly valve is very wide, all kinds of rubber, plastic and metal materials can be used as seat material, such as: EPDM, NBR, NR, PTFE, PEEK, PFA, SS315, STELLITE and so on. Use elastic sealing material and small actuator thrust to obtain air bubble tight seal, compress the valve seat sealing stress to elastically deform the material and squeeze into the rough surface of the matching metal parts to block all leakage paths. The permeability of the material is the basis for small leakage of the fluid. Materials that are too soft, or exhibit cold deformation (creep) under load, can be stiffened by adding fillers such as fiberglass. If it is used to make thin sheets, it can still meet the requirements of use, and can eliminate cold deformation or permanent deformation. The seal must be carefully secured to prevent rupture and air leakage due to differential pressure. Bonding soft seats to metal parts is one solution, but not a complete solution, as the bond can crack and fail when subjected to thermal shock. A large enough pressure drop will destroy the bonding material.
Ethylene-propylene rubber has excellent water vapor resistance and is estimated to be better than its heat resistance. The high temperature resistant EPDM valve seat has no change in appearance after nearly 100h in superheated steam at 230°C. EPDM valve seat and fluorine rubber, silicone rubber, fluorosilicone rubber, butyl rubber, nitrile rubber, and natural rubber under the same conditions, the appearance of the valve will be significantly deteriorated after a short period of time. Ethylene-propylene rubber also has better resistance to superheated water, but it is closely related to all vulcanization systems. The ethylene-propylene rubber with dimorpholine disulfide and TMTD as the vulcanization system has little change in mechanical properties after being soaked in superheated water at 125°C for 15 months, and the volume expansion rate is only 0.3%. Ethylene-propylene rubber has excellent electrical insulation properties and corona resistance, and its electrical properties are better than or close to styrene-butadiene rubber, chlorosulfonated polyethylene, polyethylene and cross-linked polyethylene. Since there are no polar substituents in the molecular structure of ethylene-propylene rubber, the molecular cohesion energy is low, and the molecular chain can maintain flexibility in a wide range, second only to natural rubber and butadiene rubber, and can still be maintained at low temperatures. Due to the lack of active groups in the molecular structure of ethylene-propylene rubber, the cohesive energy is low, and the rubber compound is easy to bloom, and the self-adhesion and mutual adhesion are very poor. The detachable surface parts in the valve are used to support the fully closed position of the valve core and form a sealing pair. Generally, the seat diameter is the maximum flow diameter of the valve. For example, the seat material of butterfly valve is very wide, all kinds of rubber, plastic and metal materials can be used as seat material, such as: EPDM, NBR, NR, PTFE, PEEK, PFA, SS315, STELLITE and so on. Use elastic sealing material and small actuator thrust to obtain air bubble tight seal, compress the valve seat sealing stress to elastically deform the material and squeeze into the rough surface of the matching metal parts to block all leakage paths. The permeability of the material is the basis for small leakage of the fluid. Materials that are too soft, or exhibit cold deformation (creep) under load, can be stiffened by adding fillers such as fiberglass. If it is used to make thin sheets, it can still meet the requirements of use, and can eliminate cold deformation or permanent deformation. The seal must be carefully secured to prevent rupture and air leakage due to differential pressure. Bonding soft seats to metal parts is one solution, but not a complete solution, as the bond can crack and fail when subjected to thermal shock. A large enough pressure drop will destroy the bonding material.
Ethylene-propylene rubber has excellent water vapor resistance and is estimated to be better than its heat resistance. The high temperature resistant EPDM valve seat has no change in appearance after nearly 100h in superheated steam at 230°C. EPDM valve seat and fluorine rubber, silicone rubber, fluorosilicone rubber, butyl rubber, nitrile rubber, and natural rubber under the same conditions, the appearance of the valve will be significantly deteriorated after a short period of time. Ethylene-propylene rubber also has better resistance to superheated water, but it is closely related to all vulcanization systems. The ethylene-propylene rubber with dimorpholine disulfide and TMTD as the vulcanization system has little change in mechanical properties after being soaked in superheated water at 125°C for 15 months, and the volume expansion rate is only 0.3%. Ethylene-propylene rubber has excellent electrical insulation properties and corona resistance, and its electrical properties are better than or close to styrene-butadiene rubber, chlorosulfonated polyethylene, polyethylene and cross-linked polyethylene. Since there are no polar substituents in the molecular structure of ethylene-propylene rubber, the molecular cohesion energy is low, and the molecular chain can maintain flexibility in a wide range, second only to natural rubber and butadiene rubber, and can still be maintained at low temperatures. Due to the lack of active groups in the molecular structure of ethylene-propylene rubber, the cohesive energy is low, and the rubber compound is easy to bloom, and the self-adhesion and mutual adhesion are very poor.