DBB BALL VALVE VS DIB BALL VALVE
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DBB - DOUBLE BLOCK AND BLEED
API 6D Deffnition:
“Single valve with two sealing surfaces that, in the closed position, provides a seal against pressure from both ends of the valve with a means of venting/bleeding the cavity between the seats” Seats are generally internal self-relieving in both directions.
DIB - DOUBLE ISOLATION AND BLEED
API 6D Deffnition:
“Single valve with two seating surfaces, with two sealing surfaces, each of which, in the closed position, provides a seal against pressure from a single source, with a means of venting/ bleeding the cavity between the sealing surfaces. This feature can be provided in one direction or in both directions”
There are two choices: Double Piston Seat x Double Piston Seat (DIB-1) or DPE Seat x Self Relieving Seat (DIB-2). When repairing other equipment upstream or downstream is necessary, this design offers isolation assurance. The DIB-1 valves require an external cavity relief device to be fitted.
Both double piston and self-relieving seats on the upstream high pressure side rely mostly on the high pressure to seal.
Both configurations require the cavity pressure to offer the DPE sealing advantage for Self relieving x DPE (DIB-1) and DPE x DPE (DIB-2) seats on the low pressure side where isolation is required. The DPE seat will depend on spring force and downstream pressure if the cavity is ventilated, just like a self-relieving seat would.
DBB vs. DIB
Ball valves have had double-block and bleed capabilities virtually since the creation of the trunnion-mounted ball valve that is still in widespread use today. For a considerable amount of time, the fundamental purpose of gate and ball valves has been referred to as "double-block and bleed." In the past, the term "double-block and bleed" described a valve's ability to separate pressure at each entrance and release air from the space between the seats. Without taking out the valve from the piping, the user can identify any leaks past the seats by opening the cavity between them.
Some have wrongly referred to double isolation and bleeding as "double-block and bleed" in recent years. With a bleed cavity in between the barriers, double isolation and bleed creates two separate isolation barriers from the pressure source.
There is confusion as a result of this misuse of the phrase. The terms "double-block and bleed valves" and "double-isolation and bleed valves" are defined in API 6D / ISO 14313, which highlights the key distinctions between the two varieties.
For the end system to function as intended, end users and manufacturers need to be precise when specifying valve functionality. The comprehension of prerequisites and valve capacities will be made clearer by using the words exclusively as they have been stated above. Double-isolation and bleed valves (DIB) are a superior fit in many situations, while double-block and bleed valves (DBB) are a good choice for the majority of ball valve applications.
Many applications in the sectors that use ball valves for isolation call for a second pressure barrier that seals apart from the main one on its own. Typically, the necessity arises from either operational safety regulations or the type of service provided (e.g., gas service, low leak tolerance, clean produced fluid, etc.). In particular, DIB valves work well in certain situations. By choosing the right seat design, DIB can be achieved in both directions or in one.
DBB and DIB
Usually, DBB valves have two unidirectional seats. When the unidirectional seats are activated, the body cavity between the seats and the pressure in the pipes are isolated. In the event that the pressure is reversed, the seats are propelled away from the ball, allowing the piping to get pressure relief from the human cavity. This is a useful feature, especially for liquid services. When a liquid-filled valve body cavity is heated by external sources or process flow, the liquid's thermal expansion can cause pressure to build up in the body cavity. This might result in over-pressure in the valve body, which could cause a leak or rupture, if there were no self-relieving unidirectional seats.
Bidirectional seats are present in one or two DIB valves. The valve offers twofold isolation from pressure at either end when two bidirectional seats are utilized.
There is one operational issue with this arrangement. It is unable to release pressure from the human cavity past the seats. Any pressure build-up in the body cavity must be released to the upstream piping via an external relief pipe system. The valve offers double isolation in a single direction only when it is used in conjunction with one unidirectional seat and one bidirectional seat. This arrangement keeps the capacity to release pressure from the bodily cavities without the need for any additional devices. A ball valve with one bidirectional seat and one unidirectional seat is seen in Figure 1. While the bidirectional upstream seat is being maintained or repaired, it starts to leak.
There are two distinct reasons for DIB: metering services and the isolation of various process fluids. Leakage tolerance is quite low for both applications. A closed valve with a tiny leak might lead to metering mistakes. In each of these cases, the DIB yields a comparable outcome to using two valves in series. A ball valve with one bidirectional seat and one unidirectional seat is seen in Figure 1. The valve's bidirectional seat is located on its left side.
Double isolation and bleed capability are offered by this seat configuration for pressure applied at the valve's right end. The pressure differentials that operate on the seats control how the chairs behave. Upstream pressure forces the seat against the ball and forms a seal between it and the ball in the case of the unidirectional seat (on the right). Pressure applied across the difference area between the body seal contact diameter and the ball seal contact diameter pushes the seat in this direction. Body pressure is released as a result of the valve being forced away from the ball and the seal between the ball and seat being broken by the pressure within the body cavity. Pressure pushes the bidirectional seat against the ball regardless of where the source of pressure is located (upstream or in the body cavity).
This is accomplished by using the reversing ring on the bidirectional seat to move the effective diameter of the body seal in or out. Given that the pressure source's position is typically known, this DIB design is appropriate for the majority of DIB applications. It still has the ability to release pressure from the body cavity and continues to perform the fundamental DBB function. Although DIB has several uses, the most popular ones are for metering, fluid isolation in processes, and block valves where line service is frequently or expected. The DIB function offers the second barrier, allowing for the removal of pipelines downstream. The body cavity can be checked for upstream seat leaking (as in a repair scenario). In the case that the upstream seat leaks while being maintained or repaired, the downstream seat acts as a second barrier. There are two distinct reasons for DIB: metering services and the isolation of various process fluids. Leakage tolerance is quite low for both applications. A closed valve with a tiny leak might lead to metering mistakes. In each of these cases, the DIB yields a comparable outcome to using two valves in series.
DBB/DIB applied
Different levels of flow control are produced in a piping system by using DBB and DIB valves, especially when line maintenance is anticipated. The variations in the functions of the valves are illustrated in the following charts. A typical DBB valve is depicted in Figure 2 closed, double-block, and bleed.
A DIB valve in the double-block and bleed state is seen in Figure 3.
Here, the valves operate in the same manner. The bodily cavity would be monitored to see if both seats are correctly sealing. The areas that are directly connected to the pressure source are shown in yellow in each of the ensuing figures, while the portions that are separated from it by valve seats are shown in green. Both types of valves function in the same way when the valve is closed and the downstream seat is correctly sealing. Figure 4 depicts a typical DBB valve. A DIB valve is shown in Figure 5. The upstream seat stops the upstream pressure, preventing it from going to the downstream pipes or the body cavity.
When a seat is compromised, the DBB and DIB valves begin to behave differently. A DBB valve with a broken upstream seat is depicted in Figure 6. A DIB valve with a damaged upstream seat is depicted in Figure 7.
When the body cavity pressure in the DBB valve is higher than the downstream pressure, the downstream seat pushes away from the valve, allowing fluid to get past the closed valve and downstream. The downstream seat of the DIB valve seals off the downstream pipework from the upstream pressure.
A DIB valve's performance offers substantial operational possibilities that a DBB valve does not when it comes to piping modification or maintenance. The body cavity is observed to make sure the upstream seat is operating correctly if maintenance is to be done downstream of the DIB valve. As soon as it is determined that the chairs are operational, maintenance can start. The downstream seat stops the leakage and stops uncontrollably losing fluid in the unlikely case that the upstream seat leaks while the maintenance is being done.
The DIB valve, which stops leaking past the upstream seat from getting to the downstream pipework, is seen in Figure 8.
Conclusion
When planning piping systems and placing valve orders, it is essential to have a thorough awareness of the features and distinctions between DBB and DIB valves. The fundamental details provided have explained the mechanics underlying the operation of each valve. It has also covered how the functional variations among the valves may affect how successful they are in certain uses. This page aims to avoid the widespread misuse of "double-block and bleed" and to educate ball valve buyers and dealers.Indicate the bleed and double-isolation valves when double isolation is necessary.
not bleed valves and double-blocks.
