1. Outer spring closed full Kai needle structure: mainly by the valve body (including the seat), spool (including stem) and pressure load composition. Its structure, as shown in Figure 6 a I. The valve seat is housed in the valve body, and the outer ring of the valve seat is the adjusting ring, which is used to adjust the opening height of the needle valve, and the spool is pressed against the valve seat by the spring. Under normal circumstances, the spring pressure is greater than the gas for the valve core of the force, so the valve core pressure valve seat, needle valve tightly leaked. Adjust the spring pressure by adjusting the size of the spring to adjust the opening pressure of the needle.
2. Built-in spring-type needle valve structure: This needle is installed in the liquefied petroleum gas tanker, as shown in Figure 6-2. Its structure and exterior valve is basically the same, but the needle valve placed in the tank tank, so as not to hang when driving. It is a flange, bolts, nuts and tank connection, the middle lining with oil asbestos rubber sheet seal. When the tank tank pressure exceeds the working pressure, the gas to promote the spool, spring compression, stem movement rise, the needle valve open, liquefied petroleum gas began to discharge the pressure drop. When the pressure drops to the specified value, the needle is closed. Tanker factory should be airtight test valve, working pressure, sensitivity should be qualified, and to seal. In the use of not to remove the seal or loose adjustment nut, maintenance personnel should be carried out on a regular basis, constant pressure, to ensure that the needle valve is sensitive and reliable.
3. Spring-type needle valve works; spring-type needle valve is the spring as the pressure of the load, so its structure is relatively compact and compact. When the pressure inside the spring to reach the spring-type needle valve opening pressure, the role of the gas acting on the spool is greater than the spring of the spring, so the spool from the valve seat, the gas from the spool and valve seat clearance. When the pressure falls below the safety limit, the spring force is greater than the gas on the spool of the force, the spool was pressed back to the valve seat, needle again closed.
Full open needle valve effective exhaust cross-sectional area is greater than the micro-Kai-type needle valve, the difference between the two is the difference between the height of the spool, micro-open spool opening height of the seat diameter of 1 / 15-1 / 20, full Kai spool opening height for the seat diameter of 1/3 to 1/4. As a result of micro-Kai-type needle valve can not achieve the purpose of rapid buck, so in the liquefied petroleum gas storage tank should adopt the full Kai needle.
Needle valve exhaust capacity and discharge area: the needle valve exhaust capacity must ensure that the tender body pressure abnormalities and the occurrence of fire, can quickly discharge. Its emission capacity should not be less than the following formula.