The valve body structure has an overflow port and the decompression speed is fast. The piston seal adopts a V-type seal ring, which is well sealed and wear-resistant. Small size and light weight,portable and convenient to carry with.High accuracy and responsive. Piston structure, rate is 30% larger than traditional diaphragm flow. Easy to install, can be installed reversely vertically horizontally assembly according to customer's preference, appearance is beautiful.