Valve knowledge: commonly used flow rate meters for various media
Mar 12, 2021
The flow rate and velocity of the valve mainly depend on the diameter of the valve, and it is also related to the resistance of the valve structure to the medium. At the same time, it has an internal connection with various factors such as valve pressure, temperature and medium concentration.
The flow channel area of the valve has a direct relationship with the flow rate and flow rate, and the flow rate and flow rate are two mutually dependent quantities. When the flow rate is yiding, the flow rate is large, the flow channel area can be smaller; the flow rate is small, the flow channel area can be larger. On the contrary, the flow channel area is large, its flow velocity is small; the flow channel area is small, its flow velocity is large. If the flow rate of the medium is large, the valve diameter can be smaller, but the resistance loss is large and the valve is easily damaged. If the flow velocity is large, it will have electrostatic effect on flammable and explosive media, causing danger; the flow velocity is too small, the efficiency is low, and it is not economical. For the medium with high viscosity and explosive, the flow rate should be smaller. The flow rate of oil and liquid with high viscosity is selected according to the viscosity, generally 0.1～2m/s.
In general, the flow rate is known, and the flow rate can be determined empirically.
The common flow rates of various media are shown in Table 2-2. The nominal diameter of the valve can be calculated through the flow rate and flow rate.
The valve diameter is the same, its structure type is different, the fluid resistance is also different. Under the same conditions, the greater the resistance coefficient of the valve, the more the flow rate and flow rate of the fluid through the valve will drop; the smaller the valve resistance coefficient, the less the flow rate and flow rate of the fluid through the valve will drop. The flow rate of common media is shown in Table 2-2.
The resistance coefficient of the gate valve is small, only in the range of 0.1 to 1.5; the resistance coefficient of the gate valve with a large diameter is 0.2 to 0.5; the resistance coefficient of the constricted gate valve is larger. The resistance coefficient of the stop valve is much larger than that of the gate valve, generally between 4 and 7. The resistance coefficient of the Y-type globe valve (DC type) is the smallest, between 1.5 and 2. The resistance coefficient of the forged steel globe valve is zuida, even as high as 8.
The drag coefficient of the ball valve is the smallest, generally around 0.1.
The drag coefficient of the butterfly valve is small, generally within 0.5.
The resistance coefficient of the check valve depends on the structure: the swing check valve is usually about 0.8-2, of which the resistance coefficient of the multi-leaf swing check valve is larger; the resistance coefficient of the lift check valve is as high as 12 .
The resistance coefficient of the plug valve is small, usually about 0.4 to 1.2.
The resistance coefficient of the diaphragm valve is generally around 2.3.
The resistance coefficient of the above valve is the value when the valve is fully opened.
| liqud name | Conditions of Use | velocity of flow （m/s） |
| Saturated Vapor | DN＞200 DN=200～100 DN＜100 | 30～40 25～35 15～30 |
| superheated steam | DN＞200 DN=200～100 DN＜100 | 40～60 30～50 20～40 |
| Low pressure steam | ρ＜1.0（KPa ） | 15～20 |
| Medium pressure steam | Ρ=1.0～4.0（KPa ） | 20～40 |
| High pressure steam | Ρ=4.0～12.0（KPa ） | 40～60 |
| compressed gas | vacuum Ρ≤0.3（KPaG） Ρ=0.3～0.6（KPaG） Ρ=0.6～1.0（KPaG） Ρ=1.0～2.0（KPaG） Ρ=2.0～3.0（KPaG） Ρ=3.0～30.0（KPaG） | 5～10 8～12 10～20 10～15 8～12 3～6 0.5～3 |
| oxygen | Ρ=0～0.05（KPaG） Ρ=0.05～0.6（KPaG） Ρ=0.6～1.0（KPaG） Ρ=1.0～2.0（KPaG） Ρ=2.0～3.0（KPaG） | 5～10 7～8 4～6 4～5 3～4 |
| gas | 2.5～15 | |
| Semi-water gas | Ρ=0.1～0.15（KPaG） | 10～15 |
| natural gas | 30 | |
| Nitrogen | Ρ=5～10（KPa） | 15～25 |
| Ammonia | vacuum Ρ＜0.3（KPaG） Ρ＜0.6 （KPaG） Ρ≤2（KPaG） | 15～25 8～15 10～20 3～8 |
| Acetylene water | 30 5～6 |
| liqud name | Conditions of Use | velocity of flow （m/s） |
| Acetylene gas | ρ＜0.01（KPaG） ρ＜0.15（KPaG） ρ＜2.5（KPaG） | 3～4 4～8 5 |
| chlorine | gas liqud | 10～25 1.6 |
| Hydrogen chloride | gas liqud | 20 1.5 |
| Liquid ammonia | vacuum Ρ≤0.6（KPaG） Ρ≤2.0（KPaG） | 0.05～0.3 0.3～0.8 0.8～1.5 |
| Sodium hydroxide | concentration0～30% concentration30%～505 concentration50%～73% | 2 1.5 1.2 |
| sulfuric acid | concentration88%～93% concentration93%～1oo% | 1.2 1.2 |
| hydrochloric acid | 1.5 | |
| Water and similar viscosity liquids | Ρ=0.1～0.3（KPaG） Ρ≤1.0（KPaG） Ρ≤8.0 (KPaG) Ρ≤20～30（KPaG） Heating network circulating water, cooling water Pressure backwater Pressureless backwater | 0.5～2 0.5～3 2～3 2～3.5 0.3～1 0.5～2 0.5～1.2 |
| water | main pipe Ρ=0.3（KPaG） branch pipe Ρ=0.3（KPaG） | 1.5～3.5 1～1.5 |
| Boiler feed water | ＞3 | |
| Steam condensate | 0.5～1.5 | |
| Condensate water | Self-flowing | 0.2～0.5 |
| Superheated water | 2 | |
| Sea water, slightly alkaline water | Ρ＜0.6（KPaG） | 1.5～2.5 |
