As we all know, the flow rate and flow rate 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 a certain internal relationship with the pressure, temperature, medium concentration and other factors of the valve. The flow area of the valve is directly related to the flow rate and flow rate, which are two interdependent quantities. When the flow rate is constant, the flow rate is large, the flow channel area can be smaller; when the flow rate is small, the flow channel area can be larger. On the contrary, the flow rate is small when the flow area is large, and the flow rate is large when the flow area is small.
1. The flow rate of medium is large, the valve diameter can be smaller, but the resistance loss is large, and the valve is easy to be damaged. High flow rate will produce electrostatic effect on flammable and explosive media, causing danger; low flow rate, low efficiency, uneconomic. For high viscosity and explosive media, the flow rate should be smaller. The flow rate of oil and high viscosity liquid depends on the viscosity, generally 0.1 ~ 2m / s.
2. In general, the flow rate is known and the flow rate can be determined by experience. The nominal diameter of the valve can be calculated by flow rate and flow rate.
3. Valve diameter is the same, its structure is different, fluid resistance is not the same. Under the same conditions, the greater the resistance coefficient of the valve, the more the flow rate and flow rate of fluid through the valve decrease; the smaller the resistance coefficient of the valve, the less the flow rate and flow rate of fluid through the valve decrease.
The common flow rates of various media are shown in the table below:
| 流體名稱 | 使用條件 | 流速（m/s） |
| 飽和蒸汽 | DN＞200 DN=200～100 DN＜100 | 30～40 25～35 15～30 |
| 過熱蒸汽 | DN＞200 DN=200～100 DN＜100 | 40～60 30～50 20～40 |
| 低壓蒸汽 | ρ＜1.0（絕壓） | 15～20 |
| 中壓蒸汽 | Ρ=1.0～4.0（絕壓） | 20～40 |
| 高壓蒸汽 | Ρ=4.0～12.0（絕壓） | 40～60 |
| 壓縮氣體 | 真空 Ρ≤0.3（表壓） Ρ=0.3～0.6（表壓） Ρ=0.6～1.0（表壓） Ρ=1.0～2.0（表壓） Ρ=2.0～3.0（表壓） Ρ=3.0～30.0（表壓） | 5～10 8～12 10～20 10～15 8～12 3～6 0.5～3 |
| 氧氣 | Ρ=0～0.05（表壓） Ρ=0.05～0.6（表壓） Ρ=0.6～1.0（表壓） Ρ=1.0～2.0（表壓） Ρ=2.0～3.0（表壓） | 5～10 7～8 4～6 4～5 3～4 |
| 煤氣 | 2.5～15 | |
| 半水煤氣 | Ρ=0.1～0.15（表壓） | 10～15 |
| 天然氣 | 30 | |
| 氮氣 | Ρ=5～10（絕壓） | 15～25 |
| 氨氣 | 真空 Ρ＜0.3（表壓） Ρ＜0.6（表壓） Ρ≤2（表壓） | 15～25 8～15 10～20 3～8 |
| 乙炔水 | 30 5～6 | |
| 乙炔氣 | ρ＜0.01（表壓） ρ＜0.15（表壓） ρ＜2.5（表壓） | 3～4 4～8 5 |
| 氯 | 氣體 液體 | 10～25 1.6 |
| 氯化氫 | 氣體 液體 | 20 1.5 |
| 液氨 | 真空 Ρ≤0.6（表壓） Ρ≤2.0（表壓） | 0.05～0.3 0.3～0.8 0.8～1.5 |
| 氫氧化鈉 | 濃度0～30% 濃度30%～505 濃度50%～73% | 2 1.5 1.2 |
| 硫酸 | 濃度88%～93% 濃度93%～100% | 1.2 1.2 |
| 鹽酸 | 1.5 | |
水及粘度相似液體 | Ρ=0.1～0.3（表壓） Ρ≤1.0（表壓） Ρ≤8.0表壓） Ρ≤20～30（表壓） 熱網(wǎng)循環(huán)水、冷卻水 | 0.5～2 0.5～3 2～3 2～3.5 0.3～1 |
| 水及粘度相似液體 | 壓力回水 | 0.5～2 |
| 水及粘度相似液體 | 無壓回水 | 0.5～1.2 |
| 自來水 | 主管Ρ=0.3（表壓） 支管Ρ=0.3（表壓） | 1.5～3.5 1～1.5 |
| 鍋爐給水 | ＞3 | |
| 蒸汽冷凝水 | 0.5～1.5 | |
| 冷凝水 | 自流 | 0.2～0.5 |
| 過熱水 | 2 | |
| 海水、微堿水 | Ρ＜0.6（表壓） | 1.5～2.5 |
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