The flow coefficient and cavitation coefficient of the valve are detailed in the comparison table of pressure and temperature of the valve material

The flow coefficient and cavitation coefficient of the valve are detailed in the comparison table of pressure and temperature of the valve material

The important parameter of the valve is the flow coefficient and cavitation coefficient of the valve, which is generally available in the data of valves produced in advanced industrial countries, and even printed in the sample. Our country produces the valve basically does not have this aspect information, because obtain this aspect of the data need to do the experiment to be able to put forward, this is our country and the world advanced level of the valve gap one of the important performance.
A, valve flow coefficient
The valve flow coefficient is a measure of the valve flow capacity index, the greater the flow coefficient value, the fluid flow through the valve when the pressure loss is smaller.
According to KV value calculation formula
Where: KV — flow coefficient Q — volume flow m3/h δ P — valve pressure loss barP — fluid density kg/m3
Two, valve cavitation coefficient
The cavitation coefficient δ value is used to determine what type of valve construction to choose for flow control.
Where: H1 — pressure mH2 — difference between atmospheric pressure and saturated vapor pressure corresponding to temperature M δ P — difference between pressure before and after valve M
The allowable cavitation coefficient δ varies among valves due to their different configurations. As shown in the figure. If the calculated cavitation coefficient is greater than the allowable cavitation coefficient, the statement is valid and cavitation will not occur. If the allowable cavitation coefficient is 2.5, then:
If δ2.5, cavitation will not occur.
At 2.5δ1.5, slight cavitation occurs.
At delta 1.5, vibrations occur.
Continued use of δ0.5 will damage the valve and downstream piping.
The basic and operating characteristic curves of valves do not indicate when cavitation occurs, let alone the point at which the operating limit is reached. Through the above calculation is clear. Therefore, cavitation occurs because when the rotor pump passes through a section of shrinking section in the process of liquid accelerated flow, part of the liquid is vaporized, and the bubbles generated then burst in the open section after the valve, which has three manifestations:
(1) Noise
(2) vibration (serious damage to the foundation and related structures, resulting in fatigue fracture)
(3) Damage to materials (erosion of valve body and pipe)
From the above calculation, it is not difficult to see that cavitation is greatly related to the pressure H1 after the valve. Increasing H1 will obviously change the situation and improve the method:
A. Install valve low in line.
B. Install a orifice plate in the pipe behind the valve to increase resistance.
C. The valve outlet is open and directly accumulates the reservoir, which increases the space for bubble bursting and reduces cavitation erosion.
Comprehensive analysis of the above four aspects, summed up the gate valve, butterfly valve main characteristics and parameters list for easy selection. Two important parameters play an important role in valve operation.
Valve material pressure and temperature comparison table valve industry insiders know that the selection of valve materials need to choose according to the valve engineering pressure and applicable temperature, different materials in the pressure and temperature environment are not the same, we look at the control relationship.
Insiders in the valve industry know that the selection of valve materials needs to be selected according to the engineering pressure and applicable temperature of the valve. The pressure and temperature environment of different materials are not the same. Let’s take a look at the contrast relationship among them.
Valve material pressure and temperature comparison table
Valve material pressure and temperature comparison table
Grey cast iron:
Gray cast iron is suitable for water, steam, air, gas and oil with nominal pressure PN≤ 1.0mpa and temperature -10℃ ~ 200℃. The common grades of gray cast iron are: HT200, HT250, HT300, HT350.
Malleable cast iron:
Suitable for nominal pressure PN≤ 2.5mpa, temperature of -30 ~ 300℃ of water, steam, air and oil medium, commonly used brands are: KTH300-06, KTH330-08, KTH350-10.
Ductile iron:
Suitable for water, steam, air and oil with PN≤4.0MPa and temperature of -30 ~ 350℃. Commonly used brands are: QT400-15, QT450-10, QT500-7.
In view of the current domestic technology level, each factory is uneven, and users are often not easy to test. According to experience, it is recommended that PN≤ 2.5mpa, steel valve is safe.
Acid resistant high silicon ductile iron:
Suitable for corrosive media with nominal pressure PN≤ 0.25mpa and temperature below 120℃.
Carbon steel:
Suitable for water, steam, air, hydrogen, ammonia, nitrogen and petroleum products with nominal pressure PN≤32.0MPa and temperature -30 ~ 425℃. Commonly used grades are WC1, WCB, ZG25 and quality steel 20, 25, 30 and low alloy structural steel 16Mn.
Suitable for water, sea water, oxygen, air, oil and other media with PN≤ 2.5mpa, as well as steam media with temperature -40 ~ 250℃, the commonly used brand is ZGnSn10Zn2(tin bronze), H62, HPB59-1 (brass), QAZ19-2, QA19-4(aluminum bronze).
High temperature copper:
Suitable for steam and petroleum products with nominal pressure PN≤ 17.0mpa and temperature ≤570℃. Commonly used brand ZGCr5Mo, 1 cr5m0. ZG20CrMoV, ZG15Gr1Mo1V, 12 crmov WC6, WC9, etc. Specific selection must be in accordance with the valve pressure and temperature specifications.