What Are the Threshold Value of Valves?

The term threshold value of valves is also called the critical value, which refers to the lowest or highest value that an effect can produce. This term is widely used in various fields, including architecture, biology, flight, chemistry, telecommunications, electricity, psychology, etc., such as ecological threshold. 

Among them, the threshold is used in chemical system engineering to calculate the optimization problem. It is often unreasonable for people to make a decision subjectively, and an arbitrary value is often not determined to obtain the optimal value. Therefore, certain mathematical limits must be given to the range of independent variables in the calculation. All points that meet these limits (thresholds) constitute a feasible region of the optimization problem.

In addition, I would like to take this opportunity to discuss with you the aspects of this veritable threshold in heating, cooling, and domestic hot and cold water systems:

Valve PN value (Nominal Pressure)

Rated pressure, or nominal pressure, refers to the highest pressure that the material of the valve body is designed to withstand under certain media, temperature, and connection conditions. Its unit is bar. For the convenience of calculation, 1 bar is equivalent to 1 kg. Valves marked PN 10 have a rated pressure of 10 kg. If the system exceeds this pressure value, the valve may be damaged or its life may be shortened.

Maximum working pressure of the valve (Max. Working Pressure)

The maximum working pressure of a valve is usually lower than the rated pressure, which is closely related to the operating temperature. PN16, a valve with a maximum working pressure of 10 kg and a maximum working temperature of 80 ° C may withstand a pressure of 16 kg at a system temperature of 40 ° C, and may only have a pressure of 12 kg at 60 ° C. The maximum working pressure here refers to the pressure value that can be achieved under the extreme conditions of the highest temperature. This information conveys a very common phenomenon to everyone. When the system is compressed, there may be no valve leakage up to 6 kg and 16 kg. After operation, the lower pressure even leaks. This is because the system enters a dynamic state cycle with temperature. Therefore, most systems are actually testing the valve PN value, not the maximum working pressure value.

Some valves that are under significant pressure, such as automatic exhaust valves, have not only the maximum working pressure, but also the maximum exhaust pressure. This pressure value is often ignored by design and installers: the general perception is that there may be gas accumulation , or the automatic exhaust valve installed on the top of the riser can automatically remove the gas. But in fact, when the water pressure at the installation site exceeds the maximum exhaust pressure, the floating ball of the automatic exhaust valve will rise completely to drive the valve stem to close the exhaust port, even if there is gas accumulation, it cannot be ruled out. The exhaust pressure of the automatic exhaust valve varies from manufacturer to manufacturer and from model to model, ranging from 2.5-10 kilograms. Generally, the parts that exceed 10 kilograms need to be manually vented.

Max. Differential Pressure

This is mainly for regulating valves in closed-cycle systems (heating / air-conditioning), such as two-way thermostatic valves. These thermostatic valves usually use mechanical thermostats, thermoelectric actuators or three-point electric actuators to control the opening and closing of the valve. When the water flow passes through the two-way valve, the resistance of the internal passage of the valve or the piston will cause the pressure loss of the water flow. This pressure loss value is the pressure difference between the upstream and downstream of the valve. When this pressure difference is higher than the design value of the valve, noise, seat wear, cavitation, and failure to close will occur.

Valve Kv Value

This is vital data for valve selection, calculation of resistance and flow. The Kv value refers to the flow rate (m3 / h) of the water flow (at a temperature of 4 ° C) that passes through the valve when the pressure difference between the front and rear of the valve is the largest. The Kvs value is easy to be confused with the Kv value. The latter refers to the flow characteristics of the valve when it is fully open, while the former is the flow characteristic of the maximum opening degree under various opening degrees. Therefore, the Kv value is more used for regulating valves. Kvs value is more commonly used for on-off valves. Through this formula, the pressure loss of the valve at a certain flow rate can be calculated. It is essential data for calculating the total pressure loss of the system and selecting the corresponding pump. If the Kv value of the valve is too low, it will inevitably cause excessive pressure loss, which will not only fail to provide the design flow, but may also generate noise and even cause the system to fail to cycle.

Valve Authority

The so-called valve authority is the importance of the valve (mostly regulating valve) in the system. Valve weight is a coefficient that is defined as the ratio of its own pressure loss to the total pressure loss of the system loop when the valve is fully open. The ideal valve weight is between 0.33-0.5, that is, the pressure loss of the regulating valve is equal to the sum of the pressure losses of other pipes and components, or not less than half of the sum of other pressure losses.

Knowing the professional knowledge of valve thresholds, we can more professionally select the required valves from the dazzling valve product market. Knowing the professional knowledge of valve thresholds, we can more professionally select the required valves from the dazzling valve product market. If you really do not know how to choose, I suggest you log in to the following website, you can definitely get what you want.