Spring type safety relief valves directory
Structure and function of spring type safety relief valve
Working principle of spring type safety valve
Low temperature spring type safety valve
Backflow valves (Back flow preventer
Vacuum negative pressure valve
Model selection of safety relief valves
Tianjin U-ideal Instrument Co., Ltd
Tianjin, China
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Spring type safety valves' working principle: 
Spring type safety relief valve works through adjusting spring force to prevent medium pressure and realize sealing purpose. Under the condition of spring force greater than medium's normal pressure, valve disc is at the close state, when medium pressure exceeds the set pressure, the spring is compressed, and lead the disc sealing faces separated, the valve open automatically, and relief pressure; When medium pressure reduced to normal pressure, the valve disc go back to valve seat under the spring force, disc sealing faces and valve seat sealed again, the valves close automatically. 
Sealing face's accuracy and cleanness of Valve disc and valve seat direct related to valve's tightness. 
In the range of spring pressure, the valve set pressure can be changed by rotating the adjust screw. 
Change the seal pressure relief angle and lifting force by rotating the adjust ring to achieve suitable reseating pressure, relief pressure and disc's open height. Low temperature safety valve
Low temperature valves are widely used in medium Natural gas, liquefied gas, liquid oxygen, liquid ammonia, liquid hydrogen and liquid nitrogen in -29o C~-196 o C
Valve material selection: LCB, 304, 316, Monel etc.; Spring type is decided by medium. All valve parts are at -196 o C subzero treatment for 24hours. 
Low temperature safety valves are installed on low temperature, ultra-low temperature equipment and storage tank, tanker; The valve is low temperature resistant, good sealing, reliable and open sensitive, assured the cryogenic equipment safety work. If the medium is toxic or inflammable, choose the bellows valves. 
Safety reflux valve (return valve; Reverse flow valve)
Usage
Reflux valves install at the liquid reflux pipe of LPG tank pump outlet. When the front pump pressure greater than rated value, safety reflux valve reduce pressure & back flow. 
Structure
Safety reflux valve include flange parallel type (picture 4) and right-angle type (picture 2). Disc sealing material is PTFE (picture 5), good sealability. Valve open and close function is realized by the inlet and outlet different pressure. 
Working principle
When inlet pressure is greater than outlet pressure of 0.5MPa, spring is compressed, and valve open automatically. When inlet pressure is less than outlet pressure of 0.5MPa, the valve get closed automatically by spring moving. 
Vacuum negative pressure safety valve
Main application
Vacuum negative pressure safety valve is mainly used in negative pressure system. 
Safety valve model selection
Working pressure and medium temperature decide valve's temperature range and nominal pressure; Valves set pressure which define the spring pressure class, medium type and working temperature decide the valve material and structure; Safety valves relieving capacity decide the valve's orifice area