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The Structure and Working Principle of the Needle Valve

Aug. 05, 2020

1. The structure of the external spring-closed full lift needle valve: mainly composed of the valve body (including the valve seat), the valve core (including the valve stem), and the pressurized load. In its structure, the valve seat is installed in the valve body, and the outer ring of the valve seat is an adjustment ring to adjust the opening height of the needle valve, and the valve core is pressed against the valve seat by a spring. Under normal circumstances, the pressure of the spring is greater than the force of the gas on the valve core, so the valve core is tightly pressed against the valve seat, and the needle valve is tight and leak-proof. Use the adjusting screw to adjust the spring pressure to adjust the opening pressure of the needle valve.

2. Built-in spring-loaded needle valve structure: this needle valve is installed on the LPG tanker. The structure is basically the same as that of the externally mounted needle valve, except that the needle valve is placed in the tank of the tanker to prevent it from hitting during driving. It is connected with the tank by flanges, bolts, and nuts, and is sealed with oil-resistant asbestos rubber sheet in the middle. When the pressure in the tank truck exceeds the working pressure, the gas pushes the valve core, the spring compresses, the valve stem moves up, the needle valve opens, and the liquefied petroleum gas begins to discharge and the pressure drops. When the pressure drops to the specified value, the needle valve is closed. The needle valve should be tested for airtightness before the tank truck leaves the factory, and the working pressure and sensitivity should be adjusted and qualified and lead sealed. Do not remove the lead seal or loosen the adjustment nut during use, and the maintenance personnel should regularly debug and constant pressure to ensure that the needle valve is sensitive and reliable.

Needle Valve

Needle Valve

3. The working principle of the spring-loaded needle valve; the spring-loaded needle valve uses the elastic force of the spring as the pressurizing load, so its structure is relatively light and compact. When the pressure in the storage and male reaches the opening pressure of the spring-loaded needle valve, the force of the gas acting on the valve core is greater than the elastic force of the spring, so the valve core is pushed away from the valve seat, and the gas is discharged from the gap between the valve core and the valve seat. When the pressure falls within the safety limit, the elastic force of the spring is greater than the force of the gas on the valve core, the valve core is pressed back to the valve seat, and the needle valve is closed again.

The effective exhaust cross-sectional area of the full-open needle valve is larger than that of the micro-open needle valve. The difference between the two is that the height of the valve core is different. The opening height of the micro-open valve core is 1/15-1/ of the inner diameter of the valve seat. 20. The opening height of the full-lift valve core is 1/3~1/4 of the inner diameter of the valve seat. Since the low-open needle valve cannot achieve the purpose of quickly reducing the pressure, the full-open needle valve should be used on the LPG storage tank.

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