Matters to be paid attention to in the selection of conventional valves - Wuzhong instrument

Valve application requirements

(1) General gate valves, ball valves, and globe valves are prohibited from regulating according to their structural characteristics. However, in process design, it is widely used for mediation. Due to the conditioning application, the valve seal is in a throttling state for a long time, and the impurities in the oil wash the seal, damaging the sealing surface, forming a loose closure or because the operator in order to make the sealing surface that has been damaged to achieve sealing, forming the phenomenon of passing and over-opening the valve.

(2) The orientation of the valve equipment is unreasonable, when the medium contains impurities, there is no filter or filter screen at the front end, so that the impurities enter the inside of the valve, forming damage to the sealing surface, or the impurities are deposited at the bottom of the valve, causing the valve to be closed loosely, and leakage.

Matters to be paid attention to in the selection of conventional valves - Wuzhong instrument

Matters to be paid attention to in the selection of conventional valves - Wuzhong instrument

1. Consider from the perspective of process requirements

(1) For corrosive media, if the temperature and pressure are not high, non-metallic valves should be used as much as possible, and if the temperature and pressure are high, fabric valves can be used to save precious metals. When selecting non-metallic valves, economic rationality should still be considered; For the medium with large viscosity, it is required to have a small flow resistance, and valves with small flow resistance, such as direct flow globe valves, gate valves, ball valves, and plug valves, should be selected. Valves with low flow resistance and low energy consumption; When the medium is oxygen or ammonia and other special medium, the corresponding oxygen special valve or ammonia valve should be selected.

(2) Directional valves should not be selected for double-flow pipelines, but non-directional valves should be selected. For example, after the heavy oil pipeline of the refinery is suspended, the pipeline should be purged in reverse with steam to prevent heavy oil condensation from blocking the pipeline, and the shut-off valve should not be selected here, because when it comes to reverse inflow, the sealing surface of the shut-off valve will be slightly eroded, and the efficiency of the valve will be affected, and the gate valve should be selected.

(3) For some media with crystallization or precipitate, it is not advisable to use shut-off valves and gate valves, because their sealing surfaces are slightly worn by crystallization or precipitation. Therefore, it is more appropriate to choose a ball valve or a plug valve; Flat gate valves are also available, but jacketed valves are preferred.

(4) In the selection of gate valves, open rod single ram and dark rod double ram are more accustomed to corrosive media; The single ram is suitable for media with high viscosity; The habitual deformation of the sealing surface of the wedge-type double ram is better than that of the wedge-type single ram, and there will be no jamming due to temperature change, especially better than the rigid single ram.

(5) Cast iron valves can be used for valves on general water and steam pipelines, but if the steam stops in the outdoor steam pipelines, condensate will form and freeze, thus freezing the valves. Therefore, in cold areas, it is advisable to use cast steel, low-temperature steel raw materials or useful insulation measures for valves.

(6) For highly toxic media or other harmful media with great danger, valves with bellows structure should be selected to avoid leakage of the medium from the packing.

(7) Gate valves, globe valves and ball valves are the most widely used valves, and should be considered when selecting. The flow of the gate valve can be strong, the energy consumption of the transport medium is less, but the equipment space is larger, the structure of the globe valve is simple, the repair is convenient, but the flow resistance is larger, the ball valve has the characteristics of low flow resistance and fast opening and closing, but the use temperature is limited, and the viscosity of petroleum products and other media is large, considering that the flow of the gate valve can be strong, most of the gate valves are selected; In the water and steam pipelines, the globe valve is applied, and the pressure drop is not large, so the globe valve is more used in water, steam and other medium pipelines, and the ball valve can be used under the condition that the operating conditions allow.

2. Consider from the point of view of operation convenience

(1) For large-diameter valves and long-distance, high-altitude, high-temperature, high-pressure occasions, electric and pneumatic valves should be selected, explosion-proof equipment should be selected for flammable and explosive occasions, and hydraulic and pneumatic equipment should be applied for safety and reliability.

(2) For the valves that need to be opened and closed quickly, butterfly valves, ball valves, plug valves or quick-opening gate valves should be selected according to the needs, and general gate valves and globe valves should not be selected. In the case where the operating space is limited, it is not advisable to use the open rod gate valve, and the dark rod gate valve should be used, but it is best to use the butterfly valve.

3. Consider the accuracy of the flow rate

When the flow rate needs to be accurately regulated, the conditioning valve should be selected, and when the accuracy of the small flow rate is required, the needle valve or throttle valve should be selected. When the pressure behind the valve needs to be reduced, the pressure reducing valve should be selected, and the pressure stabilizing valve should be selected when the pressure behind the valve is to be maintained.

4. It can only be considered from temperature and pressure resistance

High temperature and high pressure medium often choose the casting of chromium-molybdenum steel and chromium-molybdenum vanadium steel, about the ultra-high temperature and high pressure medium should consider the selection of its corresponding casting, the induction function of the forging is better than the casting, the temperature and pressure resistance can also be better than the casting.

5. Consider cleanability

In the production and transportation of food and bioengineering, the requirements for valves on the process pipeline need to consider the cleanliness of the medium, and the general gate valve and shut-off valve cannot be ensured. In terms of cleanability, there is no other type of valve that can be compared to a barrier valve.

(1) The barrier valve has a simple structure, a variety of valve bodies and barrier materials, which can be widely used in food and biological engineering, and is also suitable for some difficult to transport and dangerous media.

a. Only the valve body and barrier are in contact with the logistics, and the other parts are all blocked, and the valve can be completely sterilized with steam.

b. Have the ability to drain themselves.

c. Can be repaired online. As a result, barrier valves have become the most widely used valves in food and bioengineering.

(2) Foot valve.

In the case of strict sterilization requirements, there is simply no choice between the discharge valve at the bottom of the tank. The bottom valve is directly welded to the bottom of the tank during the manufacture of the equipment, which is very different from the general selection of making a nozzle at the bottom of the tank, and then connecting the valve on the nozzle, when the valve is closed, the valve core is flat with the inner bottom of the storage tank, so it usefully gets along with the dead angle in the tank, so that all the liquid in the tank can be fully mixed in the fermentation process, and the unique steam sealing system is added, which greatly reduces the possibility of product infection.

Matters to be paid attention to in the selection of conventional valves - Wuzhong instrument

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