Selection of valves

Use the design pressure you know, and round up to the corresponding standard grade. For American standards, these are typically: 150lb, 300lb, 400lb, 600lb, 1200lb, and so on

As long as your temperature * 0.95 is less than 452 degrees, there is no need to consider temperature when choosing valves that meet US standards

With replies from the 2nd and 3rd floors, your valve’s pressure rating is now determined! Additionally, the valve gaskets must also be of the appropriate pressure rating.

Check it in the mechanical design manual – you’ll understand it right away.

Pressure grades in our country: 0.25MPa, 0.6MPa, 1.0MPA, 1.6MPa, 2.5MPa...... etc. The pressure rating of the valve you choose just needs to be higher than what you require, but from an economic perspective, it is better to select the one with a rating that is closest to that requirement.

It also depends on the fluid in the pipeline; the material should be selected based on its corrosivity

Knowing the temperature and pressure of the pipeline medium as well as which valves to use, one can refer to the manual and select based on the temperature and pressure range. It should be noted that different methods use different temperature bases.

Basically agree; one must be careful in high-temperature conditions, as the pressure rating is also greatly affected by temperature

Since the temperature and pressure of the material are known, it is not difficult to determine the pressure rating of this valve in accordance with European or American standards.

Basically, pay attention to the temperature and pressure curve of the valve body material; by allowing for an appropriate margin under high temperature and pressure conditions, problems should not arise easily

Once the temperature and pressure are known, the pressure rating of the pipes and valves can be determined. The pipe rating tables also provide guidelines for selecting valves based on the design temperature and pressure; in principle, it is sufficient that the pressure rating of the selected valves is higher than the design pressure. Another thing to note is that for gas pipelines, regardless of the design pressure, the valve rating must be 2.5 MPa or higher.

It depends on which system you use; just match it to the pressure rating of that system.

It is mainly determined by the pressure and temperature of the medium in the pipeline. Generally, the pressure rating of valves is higher than that of the medium, as a measure of safety. Additionally, some valves do not come in pressure ratings that are very low; for example, the 1.0 rating is not available for all valves, while the 1.6 rating is usually available

When transporting toxic, flammable, and explosive media, the pressure rating of the valves should be increased by one grade.

Check the table in the valve selection manual; it’s just one table that lists the appropriate pressure ratings for different temperatures and pressures. Just one table

The appropriate type of sealing surface also needs to be selected based on the properties of the material inside the pipeline.

Criteria for selecting valves: 1. The purpose of the valve to be used, the operating conditions, and the method of control. 2. Properties of the working medium: operating pressure, operating temperature, corrosion resistance, presence of solid particles, toxicity of the medium, whether it is flammable or explosive, viscosity of the medium, etc. 3. Requirements for the fluid properties of the valve: flow resistance, discharge capacity, flow characteristics, sealing grade, etc. 4. Requirements for installation dimensions and external dimensions: nominal diameter, connection method and connection dimensions with pipes, external dimensions or weight limits, etc. 5. Additional requirements regarding the reliability, service life of valve products, and the explosion-proof performance of electric actuators. (When selecting parameters, note that if the valve is to be used for control purposes, the following additional parameters must be determined: operating method, maximum and minimum flow requirements, pressure drop under normal flow conditions, pressure drop when closed, and the maximum and minimum inlet pressures of the valve.) ) Based on the criteria and steps for selecting valves mentioned above, to choose a valve in a reasonable and correct manner it is also necessary to have a detailed understanding of the internal structure of various types of valves, so as to make an accurate decision regarding which valve should be given priority.

Steps to select a valve: 1. Determine the purpose of the valve in the equipment or device, and identify its operating conditions: the medium it will handle, operating pressure, operating temperature, etc. 2. Determine the nominal diameter and connection method of the pipeline connected to the valve: flange, thread, welding, etc. 3. Determine the method of operating the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrically actuated or electro-hydraulically actuated, etc. 4. The materials for the housing and internal components of the valve to be selected are determined based on the medium transported through the pipeline, the operating pressure, and the operating temperature: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloys, etc. 5. Select the type of valve: closed-loop valves, control valves, safety valves, etc. 6. Determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc. 7. Determine the parameters of the valve: For automatic valves, it is necessary to first determine the allowable flow resistance, discharge capacity, back pressure, etc., based on various requirements, and then determine the nominal diameter of the pipeline and the diameter of the valve seat hole. 8. Determine the geometric parameters of the valve to be selected: structural length, flange connection type and dimensions, dimensions in the vertical direction of the valve when it is open or closed, dimensions and quantity of the bolt holes for connection, and overall external dimensions of the valve. 9. Utilize existing materials: valve product catalogs, valve product samples, etc., to select appropriate valve products.

Performance indicators of valves – Strength performance: The strength performance of a valve refers to its ability to withstand the pressure of the medium. Valves are mechanical components that are subjected to internal pressure; therefore, they must possess sufficient strength and stiffness to ensure they do not crack or deform over long periods of use. Sealing performance: The sealing performance of a valve refers to the ability of its various sealing elements to prevent the leakage of the medium, and it is the most important technical parameter for valves. There are three sealing areas in a valve: the contact point between the moving part and the two sealing surfaces of the valve seat ； The fit between the packing and the valve stem as well as the packing box ； The connection between the valve body and the valve cover. The leakage in the former case is known as internal leakage, which is what is commonly referred to as poor sealing; it affects the valve’s ability to block the flow of media. For cut-off valves, internal leakage is not allowed. The leaks in the latter two locations are called external leaks, that is, the medium leaks from inside the valve to outside it. Leaks can result in material loss, environmental pollution, and in severe cases, accidents. For flammable, explosive, toxic, or radioactive media, leaks are absolutely unacceptable; therefore, valves must have reliable sealing properties. Flow performance: When a fluid passes through a valve, pressure loss occurs (that is, a pressure difference before and after the valve), meaning the valve presents a certain resistance to the flow of the fluid. The fluid must expend energy in order to overcome this resistance. From the perspective of energy conservation, when designing and manufacturing valves, it is necessary to minimize the resistance exerted by the valves on the flowing medium as much as possible. Operational performance: Sensitivity and reliability of operation. This refers to the degree to which the valve responds to changes in medium parameters. For valves such as throttle valves, pressure relief valves, and control valves that are used to adjust the parameters of a medium, as well as valves with specific functions like safety valves and steam traps, their functional sensitivity and reliability are very important technical performance indicators. Opening force and opening torque: The opening force and opening torque refer to the force or torque that must be applied in order to open or close a valve. When closing the valve, it is necessary to create a certain sealing pressure between the sealing surfaces of the operating element and the seat. At the same time, it is also required to overcome the friction forces between the valve stem and the packing, between the threads of the valve stem and the nut, at the support points at the end of the valve stem, and in other friction-prone areas. Therefore, a certain closing force and closing torque must be applied. During the process of opening and closing the valve, the required opening and closing forces and torques change, with their maximum values occurring at the final moment of closure or the initial moment of opening. When designing and manufacturing valves, efforts should be made to reduce their closing force and closing torque. Opening and closing speed: The opening and closing speed is expressed as the time required for a valve to complete one opening or closing action. Generally, there are no strict requirements regarding the opening and closing speed of valves, but certain operating conditions impose specific demands on this speed. For example, in some cases rapid opening or closing is required to prevent accidents, while in other cases slow closing is necessary to avoid water hammer effects. These factors should be taken into consideration when selecting the type of valve. ℃Valves with a temperature lower than t, below 120°C. Service life: It indicates the durability of a valve, is an important performance indicator for valves, and holds great economic significance. It is usually expressed in terms of the number of openings and closings required to ensure the sealing requirements, or it can also be expressed in terms of the time of use.