Wuzhong instrument valve selection precautions

Valve application requirements

(1) General gate valves, ball valves, and globe valves are prohibited from dispatching according to their structural characteristics. However, in process design, it is widely used for mediation. Because of the scheduling application, the valve seal is in a throttling state for a long time, and the impurities in the oil wash the seal, endangering the sealing surface, constituting a loose closure or because the operator in order to make the existing hazardous sealing surface reach the seal, constituting the phenomenon of passing and over-opening the valve.

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

1. Consider from the perspective of process requirements

(1) For corrosive media, assuming that the temperature and pressure are not high, non-metallic valves should be selected as much as possible. When choosing non-metallic valves, economic rationality should still be considered; For the medium with high 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 works intermittently, the pipeline should be purged in reverse with steam to prevent the heavy oil from condensing and blocking the pipeline.

(3) For some media with crystallization or precipitation, it is not advisable to use globe valves and gate valves, because their sealing surfaces are slightly worn by crystallization or precipitation. Therefore, ball valves or plug valves should be used; Flat gate valves can also be selected, but jacketed valves are preferred.

(4) In the selection of gate valves, the open rod single ram and the dark rod double ram are more accustomed to corrosive media; The single ram is suitable for media with high viscosity; The habit of wedge-type double ram to the deformation of the sealing surface of high-temperature text is better than that of wedge-type single ram, and there will be no jamming phenomenon due to temperature change, especially better than that of 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, it will constitute condensed water 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 risk, 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 in general when selecting. The flow ability of the gate valve is strong, the energy consumption of the transport medium is small, but the equipment space is large, the structure of the globe valve is simple, the repair is convenient, but the flow resistance is large, the ball valve has the characteristics of low flow resistance and fast opening and closing, but the use of temperature is limited, and the viscosity of petroleum products and other medium is large, considering the strong flow ability of the gate valve, most of the gate valves are selected; In the water and steam pipelines, the use of shut-off valves, the pressure drop is not large, so the shut-off valve is used in water, steam and other medium pipelines, and the ball valve can be used under the condition of the working conditions.

Wuzhong instrument valve selection precautions

Wuzhong instrument valve selection precautions

2. Consider from the perspective of operating 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 used 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 choose an open rod gate valve, and a dark rod gate valve should be used, but it is better to use a butterfly valve.

3. Consider the accuracy of scheduling traffic

When the flow is required to be accurately scheduled, the dispatching valve should be selected, and when the accuracy of the small flow 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. Consider the ability to withstand temperature and pressure

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 castings, the general function of the forging is better than the casting, the temperature and pressure resistance is also 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 guaranteed. In terms of cleanability, there is no other type of valve that can compare with diaphragm valves**.

(1) The diaphragm valve has a simple structure, a variety of valve body and diaphragm materials, which can be widely used in the field of food and bioengineering, and is also suitable for some difficult to transport and risky media.

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

b. Have the ability to clean up on their own.

c. Can be repaired online. Therefore, diaphragm valves have become the most widely used valves in the field of food and bioengineering.

(2) Foot valve.

In the case of severe sterilization requirements, the discharge valve at the bottom of the tank leaves few options. The bottom valve is directly welded to the bottom of the tank when the equipment is made, and the general selection of a nozzle at the bottom of the tank, and then the practice of connecting the valve on the nozzle is very different, when the valve is closed, the valve core is flat with the inner bottom of the storage tank, so it is useful to get 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.

Wuzhong instrument valve selection precautions

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