Simple description: 1.Material: WCB,CF8,CF8M 2.Thread: NPT,BSPT 3.Can relieve pressure automatically. 4.Long service life. A21H Spring Low Lift Thread Safety Valve:Descriptions:1.A21F, A21H-C type are used for the equipment or pipeline of the air, ammonia, petroleum gas, etc. medium whose working temperature are less than 200 °C.2.A21W-P, R type are used for the equipment or pipeline of some ...