Basic concepts and terms of valve hydrodynamics-2

1.2.11. Pressure

压力——液体单位面积上所受的垂直作用压力称为压力。通常用P表示。常用单位有巴、帕斯卡、兆帕、大气压等。换算关系：1bar=1.02kgf/cm2=100000Pa=0.1MPa。

Pressure the vertical acting pressure on a unit area of a liquid is called pressure. Usually expressed as P. Commonly used units are bar, Pascal, MPa, atmospheric pressure, etc. Conversion relationship: 1bar = 1.02kgf/cm2 = 100000pa = 0.1MPa.

绝对压力、相对压力和真空度

Absolute pressure, relative pressure and vacuum degree

以绝对零压力作为基准所表示的压力，称为绝对压力。

The pressure expressed on the basis of absolute zero pressure is called absolute pressure.

以当地大气压力为基准所表示的压力，称为相对压力。相对压力也称表压力。

The pressure expressed on the basis of local atmospheric pressure is called relative pressure. Relative pressure is also called gauge pressure.

相对压力为负数时，工程上称为真空度。真空度的大小以此负数的绝对值表示。

When the relative pressure is negative, it is called vacuum degree in engineering. The vacuum degree is expressed as the absolute value of this negative number.

绝对压力、相对压力与真空度的相互关系 如下所示：

The relationship between absolute pressure, relative pressure and vacuum degree is as follows:

1.2.12.流阻系数和压力损失

1.2.12. Flow resistance coefficient and pressure loss

由于流体存在粘性，流体流动中与管道壁面以及流体自身的摩擦所造成的阻力称为沿程阻力，沿程阻力所造成的流体能量损失称为沿程损失。沿程阻力系数常用λ表示。

Because of the viscosity of the fluid, the resistance caused by the friction between the fluid flow and the pipe wall and the fluid itself is called the frictional resistance, and the fluid energy loss caused by the frictional resistance is called the frictional loss. The drag coefficient along the path is usually expressed as λ.

局部损失

Local loss

当流动边界发生急剧变化时，比如在流动方向发生改变的弯管处、管径改变的变径处、产生额外阻力的阀门等局部阻力存在而产生的能量损失，称为局部损失。

When the flow boundary changes rapidly, such as the bend where the flow direction changes, the change of pipe diameter, the valve where additional resistance exists, the energy loss is called local loss.

产生局部损失的原因是：流动断面发生变化时，断面流速分布发生急剧变化，并产生大量的旋涡。由于流体的粘性作用，旋涡中的部分能量转变为热能使流体升温，从而消耗机械能。

The reason for the local loss is that when the flow cross-section changes, the velocity distribution of the cross-section changes sharply, and a large number of vortices are produced. Due to the viscous effect of the fluid, part of the energy in the vortex is transformed into heat energy, which makes the fluid warm up and consumes mechanical energy.

管道进口、管道的突缩、突扩部分、阀门、弯头等管件部分均会发生局部阻力。

Local resistance will occur at the pipe inlet, the pipe's sudden contraction, expansion, valve, elbow and other pipe fittings.

局部损失与管长无关，只与局部管件有关

The local loss is not related to the pipe length, but only to the local pipe fittings.

局部阻力系数常用ξ表示。

The local resistance coefficient is usually expressed by ξ.

局部阻力的分类：

Classification of local resistance:

流向改变

Flow direction change

1.2.13.流量系数Cv、Kv

1.2.13. Flow coefficient CV, KV

流量系数Cv，指温度为60°F的水在规定的开启位置下压力损失为1磅时流经阀门的流量，单位是g/min（每分钟美制加仑）。

Flow coefficient CV, in g / min (US gallons per minute), is the flow of water at 60 ° F through the valve at a pressure loss of 1 pound in the specified open position.

流量系数Kv，指温度为5℃~40℃的水流过在规定的开启位置下压力损失为1巴的阀门时的流量，单位是m3/h（每小时立方米）。

The flow coefficient kV refers to the flow of water with a temperature of 5 ℃ ~ 40 ℃ passing through the valve with a pressure loss of 1 bar under the specified opening position, and its unit is m3 / h (cubic meter per hour).

Cv=28 Kv /24

Cv=28 Kv /24

1.2.14.噪声

1.2.14. Noise

噪声是发生体做无规则振动时发出的声音。通常是指那些难听的，令人厌烦的声音。引起人们烦躁，甚至危害人体健康的声音。噪音的波形是杂乱无章的。

Noise is the sound produced when the body vibrates irregularly. Usually refers to those unpleasant, boring sounds. Causes people to be agitated, even harms the human health the sound. The noise waveform is chaotic.

从环境保护的角度看，凡是影响人们正常学习，工作和休息的声音，人们在某些场合“不需要的声音”，都统称为噪声。如机器的轰鸣声，各种交通工具的马达声、鸣笛声，人的嘈杂声及各种突发的声响等，均称为噪声。

From the perspective of environmental protection, all the voices that affect people's normal study, work and rest, and people's "unwanted voices" in some occasions are collectively referred to as noise. For example, the roar of machines, the motor and whistle of various means of transportation, the noise of people and all kinds of sudden sounds are called noise.

一般，阀门噪声在距离阀体1米处测试不超过85分贝。

In general, the noise of the valve shall not be more than 85 dB at the place 1 m away from the valve body.