Stainless steel vacuum valve

The basic characteristics of vacuum valve are high gas seal (reliable sealing); the resistance to air flow is as small as possible (that is, the flow conductivity of the valve is as large as possible); the wear resistance of sealing parts is good, which can be used repeatedly and has a long service life; the valve body material and sealing parts have small amount of gas discharge; the operation is flexible, easy to clean and install, reliable in performance and convenient in maintenance. In addition, the ultra-high vacuum valve is required to be able to withstand high temperature baking (450 ℃), and the throttle valve is required to be able to adjust the gas flow evenly.

It has been known for a long time that some materials, such as activated carbon, have strong air absorption capacity. It has been further understood that most metal and non-metallic materials have this ability more or less. This is a very important physical phenomenon in vacuum technology, especially in ultra-high vacuum technology. It can provide an important means for people to obtain, improve or maintain the vacuum degree of the system. The outgassing of materials is an important part of the total leakage of vacuum valves. The main sources of gas are: the gas adsorbed on the inner surface of the vacuum valve parts; the gas diffused from the metal interior and the gas released from the metal surface due to some chemical reaction. The amount of outgassing of stainless steel is very small. It is only about 1 / 10 of copper and about 1 / 100 of aluminum.

Stainless steel diaphragm valve is one of the earliest regulating valves, which has the following characteristics:

(1) The medium of diaphragm can not be cut off by soft rubber valve.

(2) Because of the corrosion resistance of rubber, there was no better corrosion-resistant material before the 1960s. It was usually used as a corrosion-resistant material to promote application, even today.

(3) The flow path is simple and has the function of “self-cleaning”, which can be used for unclean media.

(4) However, when used as a corrosion resistant control valve, the front part of the quick opening characteristic has to be used. Its effective stroke is short and the regulating quality is poor.

(5) Such as a fatigue test piece, forced to fold up and down, easy to damage, because the diaphragm is an unreliable part, resulting in a shorter valve life, which is a fatal defect. Because of this, the author has emphasized in recent years that stainless steel diaphragm valve should be eliminated and replaced by ball valve and full function ultra light valve.

(6) When the valve is closed, the medium force pushes the diaphragm to the top. The unbalanced force is large and the actuator thrust is large. Therefore, it is necessary to select a very large and heavy actuator to make the valve heavy, which is twice as heavy as the ball valve and 3-4 times as large as the full-function ultra light valve.

(7) In particular, more and more corrosion-resistant materials are needed, especially in the end of 1980s, the fluorine lined plastic process was solved, and the fluorine lined ball valve came out. Because fluoroplastics are more resistant to corrosion and temperature than rubber, and the ball core of ball valve is ten times stronger than that of stainless steel diaphragm valve. Therefore, it is suggested that in the occasion of cutting off and regulating corrosive medium, diaphragm valve should not be selected as far as possible, and corrosion-resistant fluorine lined ball valve, butterfly valve and PTFE single seat valve should be selected.

As an example, in the water treatment system, the valves used in the desalted water plant, 10 years ago, both at home and abroad, used fluoroplastics lined diaphragm valves. Their service life is about one year, and the short is 3-6 months. Therefore, the diaphragm is constantly replaced. After using the ball valve recommended by us for water treatment, this problem has been solved very well. The service life is as long as 7-8 years, and generally it can be used for 3-5 years. The stainless steel diaphragm valve is developing towards industrial corrosivity.

Stainless steel diaphragm valve advantages :

1. The opening and closing parts of elastic sealing shall ensure no internal leakage;

2. Streamline flow passage makes pressure loss small;

3. There is no stuffing box, so there is no leakage;

4. The valve body and cover are separated by the middle diaphragm, so that the valve cover, valve stem and other parts above the diaphragm are not eroded by the medium;

5. The diaphragm can be replaced and the maintenance cost is low;

6. The diversity of lining materials can be applied to various media, and has the characteristics of high strength and good corrosion resistance.