Detailed valve flow coefficient and cavitation coefficient

Valve's important parameters are the valve's flow coefficient and cavitation coefficient, which are generally available in valve data produced in advanced industrial countries and even printed in samples. Valves produced in China have basically no information in this regard, because the information obtained in this respect needs to be tested before it is proposed. This is one of the important manifestations of the valve gap between China and the world.

First, the flow coefficient of the valve The flow coefficient of the valve is an indicator to measure the flow capacity of the valve. The larger the value of the flow coefficient, the smaller the pressure loss when the fluid flows through the valve.

Calculated in terms of KV: In the equation: KV - Discharge coefficient Q - Volumetric flow m3/hΔP - Pressure loss of the valve barP - Fluid density kg/m3

Second, the valve cavitation coefficient with cavitation coefficient δ value, to select when used as control flow, choose what kind of valve structure type.
In the formula: H1—after valve (outlet) pressure mH2—the difference between saturation vapor pressure corresponding to atmospheric pressure and its temperature mΔP—the pressure difference before and after the valve
Because of the different configurations of various valves, the allowable cavitation coefficient δ is also different. as the picture shows. If the calculated cavitation coefficient is greater than the allowable cavitation coefficient, it is available and no cavitation will occur. If the butterfly valve allows a cavitation coefficient of 2.5, then:
If δ>2.5, cavitation does not occur.
When 2.5>δ>1.5, slight cavitation occurs.
When δ<1.5, vibration occurs.
When δ < 0.5 continues to be used, it will damage the valve and downstream piping.
The basic characteristic curve and operating characteristic curve of the valve are invisible to the valve when cavitation occurs, and it is impossible to reach the operating limit at that point. Through the above calculations at a glance. Therefore, cavitation occurs because the liquid is vaporized when the rotor pump passes through a tapered section during the accelerated flow of the liquid. The resulting bubbles then burst in the open section of the valve, and its performance is threefold:

(1) Noise (2) Vibration (In severe cases, damage to foundations and related structures, resulting in fatigue fracture)
(3) Destruction of materials (erosion of valve bodies and pipes)
From the above calculation, it is not difficult to see that there is a great relationship between the generation of cavitation and the pressure H1 of the valve. Increasing H1 will obviously change the situation.

Improve methods:
a. Install the valve at the lower point of the pipe.
b. Install an orifice plate on the rear of the valve to increase resistance.
c. The valve outlet is open, and the direct reservoir will increase the space for bubble bursting and reduce cavitation.

The above four aspects of the analysis and discussion, summed up the gate valve, butterfly valve main features and parameter list for easy selection. Two important parameters play a decisive role in the use of valves.