DBB Valve High-Pressure Pipeline

Description

DBB ball valve has double shut-off, double break, and discharge functions. Double off, double cut and discharge function valves are applicable to aviation kerosene, light oil, natural gas, liquefied gas, pipeline gas, chemical media, and other pipelines, and are ideal devices for cutting off media.

The key to the working principle of the double shut-off and double break and relief function valve is the action of the two sealing slides installed on the cock. The valve is equipped with an automatic relief device (optional). After fully closing the valve, it can prevent abnormal pressure rise in the valve chamber and check the effect of the valve. The valve switch indicator is synchronized with the switch position to accurately display the valve switch status.

However, the ball valve with the DBB structure has a single ball and a double ball. Note: both forging and casting have a DBB structure

Features of DBB ball valve:

1. During the opening and closing process of the valve, the sealing surface of the valve body and the sealing surface of the sliding plate does not have any contact. Therefore, the sealing surface is free of friction and wear, the valve’s service life is long, and the opening and closing torque are small.
2. During the maintenance of the valve, it is not necessary to remove the valve from the pipeline, but only to disassemble the valve bottom cover and replace a pair of slides. Which is very convenient for maintenance.
3. The valve body and plug are reduced in diameter, which can reduce the cost.
4. The inner cavity of the valve body is plated with hard chromium, and the sealing area is complex and smooth.

So if you want to know more about it, please contact us!

Interpretation of DBB and DIB valves and test methods

1. Overview

The interpretation of DBB and DIB is a frequently discussed topic in valve circles. Here we mainly interpret the DBB and DIB valves defined in API 6D 24. Before the text, we will first explain two words describing the function of the sealing valve seat: “blocking” and “isolation” Blocking means that a sealed valve seat can only seal the pressure from one direction of the valve seat. Isolation means that a sealed valve seat can seal the pressure from both ends of the valve seat.

2. Interpret DBB and DIB through definition and test

The DBB valve has two sealed seats. When the valve is closed, open the valve blowdown or vent device. Both ends of the valve are simultaneously pressurized. The valve seat can block the pressure at both ends of the valve. From the definition of DBB, it can be seen that DBB valve needs to have two conditions and one function.
Condition 1: one valve needs two sealed seats.
Condition 2: the middle chamber of the valve needs to be provided with a discharge device. (venting, blowdown, etc.).
One function is to open the middle chamber discharge device of the valve. Both ends of the valve are simultaneously pressurized. The sealing valve seat can block the pressure at both ends of the valve.
The specific test method is also specified in the inspection and acceptance regulations for DBB valves in Appendix H₉ of API 6D 24. Combined with the definition of DBB valve. We can correctly interpret the DBB valve.

DBB valve inspection method:

1. First, the valve is half open. We completely fill the valve and valve chamber with test medium (freshwater).
2. Then close the valve. Open the discharge device (blowdown or venting) in the valve cavity. Overflow the test medium from the discharge port.
3. Both ends of the valve are pressurized at the same time. Until the valve shell material is 1.1 times the rated pressure at 38 ℃.
4. Check the valve leakage through the discharge port in the valve cavity. The acceptance criterion for a soft seal is zero leakage. The leakage of the hard seal shall not be greater than Class D in iso5208.

It should be noted that: The valve seat of DBB valve has no isolation function. DIB valves have dib-1 and dib-2.

Note:

DIB-1 valve must be installed with an automatic safety relief valve outside the valve chamber. Because the valve seat of a dib-1 type cannot automatically relieve pressure. When the pressure in the valve chamber accumulates, the valve may explode. The relief pressure of the external relief valve shall be 1.1-1.33 times the rated pressure of the valve shell material at 38 ℃. The reset pressure shall not be less than 1.05 times.
DIB valves have two sealed seats. When the valve is closed, open the valve blowdown or vent device. One end of the valve is pressurized, and the sealing valve seat can isolate the pressure at one end of the valve.
Both sealing seats of dib-1 valve are sealing seats with isolation functions.
One end of the two sealing seats of dib-2 valve is a sealing seat with a blocking function. The other end is a sealing valve seat with an isolation function. (Normally, the sealing valve seat with blocking function is set at the upstream end of the valve).

From the definition of DIB, it can be seen that DIB valves also need to have two conditions and one function
Condition 1: one valve needs two sealed seats.
Condition 2: the middle chamber of the valve needs to be provided with a discharge device (venting, blowdown, etc.).
One function is to open the discharge device in the valve cavity. One end of the valve is pressurized. The valve seat can isolate the pressure at one end of the valve seat.

Dib-1 valve inspection method:

1. Firstly, the valve is half opened, and the valve and valve chamber is completely filled with test medium (freshwater).
2. Then we close the valve and open the discharge device (blowdown or venting) in the middle chamber of the valve. This allows the test medium to overflow from the discharge port.
3. Pressurize one end of the valve to 1.1 times the rated pressure of the valve shell material at 38 ℃.
4. Check the valve leakage through the discharge port in the valve cavity. The acceptance criterion for a soft seal is zero leakage. The leakage of the hard seal shall not be greater than Class D in iso5208.
5. Relieve the pressure and repeat steps 3 to 4. Inspect the other end of the valve.
6. Relieve the pressure and empty both ends of the valve. The cavity of the valve is filled with medium. Pressurize the valve cavity to 1.1 times the rated pressure of the valve shell material at 38 ℃.
7. At the same time, observe the leakage at both ends of the valve. The acceptance criterion for a soft seal is zero leakage. The leakage of the hard seal shall not be greater than Class D in iso5208.

Dib-2 valve inspection method:

1. Firstly, the valve is half opened, and the valve and valve chamber is completely filled with test medium (freshwater).
2. And then close the valve and open the discharge device in the chamber of the valve. (blowdown or venting). All these make the test medium overflow from the discharge port.
3. Pressurize one end of the valve to 1.1 times the rated pressure of the valve shell material at 38 ℃.
4. Through the discharge port in the valve cavity, we can check the valve leakage. And its acceptance criterion is zero leakage. The leakage of the hard seal shall not be greater than Class D in iso5208.
5. Relieve the pressure and repeat steps 3 to 4. Then we need to inspect the other end of the valve.
6. Then relieve the pressure, and the operator shall empty the valve isolation valve seat end. Thus, the valve seat end and the valve cavity are blocked from being filled with medium. Pressurize the blocking valve seat end and the valve cavity to 1.1 times the rated pressure of the valve shell material at 38 ℃.
7. At last, we observe the leakage at the isolation valve seat end. The acceptance criterion for a soft seal is zero leakage. The leakage of the hard seal shall not be greater than Class D in iso5208.

3. Conclusion

API6D version 24 not only requires the structure of DBB and DIB valves. At the same time, there are clear provisions on the functions to be met. The sealing seat structure required to achieve the functions of DBB and DIB valves needs to be designed by the valve designer. At the end of the article, identify a common misunderstanding. That is, the double valve (double ball valve) is a DBB valve. We think this statement is wrong. The double valve (double ball valve) cannot meet the definition of DBB valve.