Technical requirements for Needle Valve

The selection of Needle Valve should meet the use requirements. First of all, we must understand the specifications and models of Needle Valve. When using and identifying, we should pay special attention to whether the sealing surface material, valve body material and nominal pressure meet the requirements, as well as sealing, adhesion and other issues. Needle Valve are generally used for steam. The valve body material is carbon steel and the valve seat material is stainless steel. The nominal pressure of the Needle Valve requires a reference temperature of 120℃, while the Universal Valve body is 200℃. When the medium of the Universal Valve exceeds 200℃, the maximum allowable working pressure is lower than the nominal pressure. Therefore, for boilers with saturated steam pressure exceeding 1.47MPa and superheaters, Needle Valve should be selected according to the working temperature. The number of Needle Valve. For boilers with a rated evaporation capacity of >0.5t/h, at least two Needle Valve shall be installed. For boilers with an evaporation capacity of ≤0.5t/h, at least one Needle Valve shall be installed. Needle Valve must be installed at the outlet (or inlet) of the separable economizer and the outlet of the steam superheater. The Needle Valve should be installed vertically to the ground and installed at the highest position of the drum and header as much as possible. The outlet pipe and valve for taking steam shall not be installed between the Needle Valve and the drum or between the Needle Valve and the header. Verification of the opening pressure of the Needle Valve. The opening pressure of the Needle Valve should be adjusted and verified according to the value specified in the table. For boilers using only one valve, the opening pressure of the Needle Valve is adjusted according to the lower value in Table 1.2-2; for boilers with superheaters, the Needle Valve on the superheater is adjusted according to the lower pressure. For boilers with separable economizers, the opening pressure of the Needle Valve on the economizer is 1.1 times the working pressure of the installation location. For boilers with economizers and superheaters, the opening order of the Needle Valve is: first the superheater Needle Valve, then the drum, and finally the economizer, in order to follow the principle of ensuring good safety performance of components with high working temperatures.

20 November-2024

Structural management of Needle Valve

The Needle Valve is one of the three indispensable safety accessories on the boiler. It plays an important role in controlling the internal pressure limit of the boiler and the safety protection of the boiler. When the pressure in the boiler rises to a value exceeding the specified value, the Needle Valve automatically opens to relieve pressure and discharge steam. When the pressure in the boiler drops to the specified value, the Needle Valve automatically closes. If the Needle Valve is improperly selected or the adjustment does not meet the use requirements, it is easy to cause overpressure and even explosion accidents in the boiler. Therefore, correctly understanding and using Needle Valve is an important part of boiler safety management. The Universal Valve uses the adjustment of the tightness of the spring to control the size of the exhaust pressure. This Needle Valve has a compact and light structure and can withstand vibration without leaking. It is the most commonly used Needle Valve on boilers. However, since the elasticity of the spring changes due to factors such as temperature and time, the reliability is poor, and the Needle Valve must be inspected regularly during use. When the steam pressure acting on the valve disc is less than the weight pressure acting on the valve stem, the valve disc is pressed against the valve seat again to keep the boiler running. The opening pressure of the Universal Valve is controlled by adjusting the distance between the weight and the fulcrum. After the opening pressure of the Needle Valve is determined, the distance of the weight fulcrum can be calculated using the lever principle to determine the position of the weight. The Universal Valve has a simple structure, is easy to adjust, has a flexible action record, and is relatively accurate and reliable. However, the weight is relatively heavy, the exhaust capacity of a single Needle Valve is limited, and the installation requirements are also relatively strict.

19 November-2024

Why do imported metering pumps need to be equipped with a Needle Valve?

As we all know, metering pumps are mainly composed of three parts: power drive, fluid delivery and regulation control. The power drive device drives the fluid delivery diaphragm to achieve reciprocating motion through a mechanical linkage system. The diaphragm (piston) sucks the delivered fluid in the first half of the stroke and discharges the fluid from the pump head in the second half of the stroke. Therefore, changing the reciprocating frequency of the stroke or the stroke length of each reciprocating motion can achieve the purpose of adjusting the fluid delivery volume. Precise machining accuracy ensures the amount of each pump out and thus achieves precise metering of the delivered medium. Nowadays, environmental protection is increasingly valued. Why are Universal Valve equipped on imported metering pumps or dosing pumps? The Needle Valve plays a safety protection role in the system. If there is no Needle Valve, it may even cause an explosion. It can be automatically opened and closed according to the working pressure. It is generally installed on the equipment or pipeline of the closed system to protect the safety of the system. When the pressure in the equipment or pipeline exceeds the specified value, the pressure relief is automatically opened to ensure that the pressure of the medium in the equipment and pipeline is within the specified value to prevent accidents. When the system pressure exceeds the specified value, the Needle Valve automatically opens to discharge part of the gas in the system into the atmosphere so that the system pressure does not exceed the allowable value, thereby ensuring that the system does not cause accidents due to excessive pressure.

18 November-2024

Operation method of Plug Valve adjustment

① Before the Plug Valve leaves the factory, its opening pressure should be adjusted to the set value required by the user. If the user proposes the working pressure level of the spring, it should be adjusted according to the lower limit of the pressure level before leaving the factory. ② Before installing the Plug Valve on the protected equipment or before installation, the user must readjust it at the installation site to ensure that the set pressure value of the Plug Valve meets the requirements. ③ Within the working pressure level range of the spring indicated on the nameplate, the opening pressure can be adjusted by rotating the adjustment screw to change the spring compression. ④ Before rotating the adjustment screw, the valve inlet pressure should be reduced to less than 90% of the opening pressure to prevent the valve disc from being driven to rotate when the adjustment screw is rotated, thereby damaging the sealing surface. ⑤ In order to ensure the accuracy of the opening pressure value, the medium conditions during adjustment, such as the type of medium and temperature, should be as close to the actual operating conditions as possible. The opening pressure often changes when the type of medium changes, especially when the medium accumulation state is different (for example, from liquid phase to gas phase). When the working temperature increases, the opening pressure generally decreases. Therefore, when adjusted at room temperature and used at high temperature, the set pressure value at room temperature should be slightly higher than the required opening pressure value. How high it is depends on the valve structure and material selection, and should be based on the manufacturer's instructions. ⑥ Conventional Universal Valve are used in situations where additional back pressure is fixed. When the opening pressure is adjusted after inspection (the back pressure is atmospheric pressure at this time), the set value should be the required opening pressure value minus the additional back pressure value.

15 November-2024

Characteristics and application fields of Plug Valve

The working principle of Plug Valve is basically the same as that of ordinary Universal Valve. It is a bellows added between the valve seat and the valve body. It is used as an overpressure protection device on equipment or pipelines with unstable back pressure or toxic and corrosive media. The bellows can eliminate the influence of back pressure fluctuations on the performance of the Universal Valve, protect the spring and other internal parts from corrosion by the medium, and effectively prevent the leakage of the medium. 1. The valve seat and valve body are detachable, which is convenient and economical to maintain. 2. The umbrella-shaped recoil disc can effectively increase the lift, and the valve disc can be opened quickly under a small pressure to discharge the medium, thereby achieving the purpose of protecting the equipment. 3. The adjustment ring can adjust the satisfactory opening and closing pressure difference. 4. Reasonable selection of materials for the recoil disc and guide sleeve, valve stem and adjustment screw, and appropriate selection of clearances are made to ensure flexible movement of the valve disc. 5. The sealing surfaces of the valve disc and valve seat are welded with hard alloy, and the surface is finely ground to ensure high sealing and service life. 6. The bellows in the Plug Valve can eliminate the impact of back pressure fluctuations on valve performance, and can also protect springs and other internal parts from corrosion by the medium. 7. The selection and processing of springs and bellows are particular and strictly tested and inspected. The Plug Valve is suitable for equipment and pipelines with air, steam, petroleum gas and other media with an operating temperature of ≤300℃ as an overpressure protection device. When the pressure in the equipment and pipeline exceeds the allowable value, the valve automatically opens and then discharges in full; when the pressure drops to the specified value, the valve automatically closes to ensure the safe operation of the equipment. It is widely used in industries such as electricity, metallurgy, petroleum, and chemical industry, but the Plug Valve is not suitable for use on reciprocating compressors, because the pressure fluctuation of the process fluid before and after the compressor is too large, and the bellows are sensitive to such fatigue stress, so the service life of the Universal Valve will be greatly reduced.

14 November-2024