Data: 2009-10-09 From www.supply-valve.com

Safety Valves can open and close automatically according to the work pressure, it generally install on closed system or pipeline to pretect safety of the system. When the manifold pressure of the equipment or pipeline surpasses the prescribed value, it will automatically start to release pressure, to make sure the manifold pressure of the equipment and pipeline within the prescribed value, and to aviod accidents.
1. According to the structure, it can be devided into,
(1) Hammer (lever) safety Valves: use lever and hammer to balance the disc pressure. Hammer safety Valves adjust pressure by moving the hammer position or changing the hammer weight. Simple structure is its advantage; Disadvantage is its heavy and bad eturn ability. Safety Valves of this structure can only used for fixed equipment.

(2)Spring safety Valves: use compression spring force to balance the disc pressure and make it seal. Spring safety Valves adjusts the pressure by adjusting the spring compression. The advantage is that it is smaller, lighter and higher sensitivity than hammer safety Valves, and installation position are not strictly limited; The disadvantage is that the force on the Valves stem will change with spring deformation. Also it must pay attention to insulation and heat of the spring. The spring force of spring safety Valves generally must not more than 2000 kilograms. Because too big and hard of the spring is not suitable for high precision work..

(3) Pulsed safety Valves: Pulsed safety Valves consists of main Valves and auxiliary Valves. The main Valves and auxiliary Valves get together to drive the main Valves through the pulse function of auxiliary Valves. Pulsed safety Valves is usually used in large diameter pipelines. Because hammer or spring saftety Valves are not applicable to such big diameter Valves. When the medium in pipelines surpasses the prescribed value, auxiliary Valvess will firstly drive the main Valves, to exhaust the redundant medium.

2. According to the body structureit can be divided into:
(1) Enclosed type: No leaking when exhausts medium, and let out all through the drain pipe.
(2) Semi-enclosed type: When exhaust medium, one part is through the drain pipe, another part is leaking form joint of the Valves bonnet and stem.
(3) Open type: Not lead to the outside when exhausts medium, but directly exhaust from the upper disc.

3. According to proportion the disc maximum open height and seat size, it can be devided into:
(1) Low lift type: The disc open height is 1/20 ~ 1/10 of seat sizes. Because the open height is small, so the requirement of structure and geometry are not strictly like the full bore type, design, manufacturing, maintenance and tests are more convenient, but with low efficiency.

(2) Full bore type: The disc open height is 1/41/3 of seat sizes. Full bore safety Valves gets the help from the gas medium inflation to make disc reach enough momentum and capacity. It uses two adjustment of disc and seat, the exhausted medium forming a pressure area in the disc and two Valves section, to make Valves opens up to the required open height and specified back pressure. This structure is high sensitivity and used more often, but the two adjustable ring position is difficult to adjust, so it must be used carefully.