The pressure safety valves are used to protect the equipment such as motors, pumps and compressors. The safety valve releases the excess pressure out that can affect the equipment harmfully.
Construction safety valve:
The construction of the pressure safety valve consists of body, team, spring, bonnet and accessories
The Pressure Safety Valve that will be produced in the design must refer to the applicable provisions or standards such as ASME, API or other code recommended in the plant or project process. Another thing to note is the construction of the body and material. he “part” design must consider the allowable tension of the material that will be used and must also conform to the standard specifications.
Valve bodies are usually the type of angle (angle type), usually has an outlet that is larger than the inlet. This is very important to “expand” the fluid such as gas, vapour. Safety or relief valves must always do a “relief” to a lower pressure (usually with atmospheric pressure). To achieve this can be done by increasing the size of the pipe outlet in such a way that it can obtain a back pressure of 10% below the inlet pressure price that is permitted to ensure that the valve will open at a predetermined set pressure price. The valve body must have a connection that is able to use its pressure and temperature of use and not only in its operating conditions but also in its relieving conditions.
Body material, for general use (general purpose), is carbon steel. The alloy steel will be used if the pipe specifications require it or for use in certain atmospheric conditions. For the fluid in the form of air, Bronze Alloy is used to pressuring relief devices that are installed in a storage tank (breather valve) usually will be used material made of aluminium material.
Full nozzle is shown in the picture.
The arrangement of the nozzle on the pressure safety valve is divided into two types, namely full-nozzle and semi-nozzle. The full nozzle between the valve body and the nozzle becomes one so that before discharging all parts of the nozzle and disc are wetted by the fluid. Thus if a special material is needed for the nozzle and disc, it must be followed by the part of the valve body .
Material spring specification influenced by fluid temperature of standard spring material for pressure safety valve is usually carbon steel or alloy steel (tungsten). For temperature between -240°C to 232°C. carbon steel material is used, for temperatures above 2320C tungsten alloy is used whereas for temperatures below -240C (cryogenic) stainless steel is used on closed bonnet.
When the pressure safety valve has reached the set pressure, it will tend to leak, this is due to the mechanical force balance coming from the bottom of the “disc-area” has reached or the same as the “operated spring” style that is on the top of the disc, leakage on this set pressure can be overcome by:
Make the surface “seating surface” as smooth as possible and as precise as possible with a deviation close to 5 micro-inches.
Using an O-ring seat seal that allows you to get more perfect tightness at pressures near the set-pressure price
Bonnet and Yoke
Bonnet is a housing and is a protective spring because therefore the material of the bonnet should be of the same material as the material of the body. so the bonnet is no longer needed to accommodate the spreading “escaping fluid”
Blowdown rings are made with the aim to solve two problems, namely: (1) together with the disc-holder to form a “huddling-chamber” which will prepare “pop-action” in the safety valve (2) by adjusting the blowdown ring will change the pressure difference between set pressure and reseating pressure from the valve.