The Difference Between DIB and DBB Ball Valves
In the 2002 version 22 API6D, only DB defined, short for Double block and bleed,there don’t have DIB.
In the 2008 version 23 of API6D, Its included DBB and also DIB(for Double isolation and bleed).
DBB and DIB are two valve seat functional forms, both are double-seat structure, DBB each seat can resist a direction of force, called the single piston effect seat (self-relief seat), can be discharged to the middle chamber.Each seat of dib-1 can resist the force in two directions, called double piston effect seat, this structure shall be equipped with a cavity pressure relief device.Dib-2 is DBB at the inlet end of the valve seat, and DIB at the other end of the valve seat, which is also called single or double piston effect valve seat.
With the function of DBB ball valve is designed according to API 6 d standard, used in long distance pipeline gas/liquid. DBB double block with emissions, namely the overpressure in the valve cavity when the seat all hold the ball up and down, the inlet and outlet seal at the same time, either gas or liquid medium, medium cavity must be equipped with safety valve, to ensure that the pressure relief, and emissions to the atmosphere environment.
_6 R! L % D2 x corresponding, the other is the upstream valve seat seal, the pressure relief into the downstream line when the valve cavity overpressure, the valve cavity does not set the safety valve.
BY ALLAN:
For general trunnion mounted ball valves, both seats have self-relief function (it can be thought that this seat design is a one-way sealed seat design, the same can be pushed, two-way sealed seat is not self-relief function).See below.
Self-releasing conditions:
Δ P = Pc - > 0.33 PI PI
> 1.33 PI (Pc)
F = Δ D1 P * > Fs
= 0.33 PI * D1 > Fs
When the center chamber pressure exceeds 1.33 times of the valve pressure rating of the material at 38℃, the medium pressure pushes the valve seat away from the ball with the help of the area difference formed by the sealing surface of the valve seat to complete the pressure relief.
What does DBB do?Double Block and Bleed, as shown below.
When the valve is closed, there is a medium (liquid or easily condensing gas) in the body cavity, and the pressure in the middle chamber should be less than or equal to the upstream and downstream pressure (if greater, the pressure in the middle chamber will be released to the upstream and downstream through the self-relief valve seat).Only in the middle chamber media abnormal boost (such as rapid gasification caused by pressure surge), the valve seat on both sides of the self-relief function failure or unable to self-relief, for safety reasons, the valve body cavity must be set up a pressure relief valve, for emergency relief of abnormal pressure in the middle chamber, in case of design. When the pressure relief in the middle chamber is lower than the upstream and downstream pressure, the self-relief valve seat under the action of spring force and medium pressure, to achieve the sealing between the valve seat and the ball, to prevent the upstream and downstream medium discharged to the outside of the valve through the middle chamber relief valve.
This is the general fixed ball valve DBB design principle, but the situation rarely occurs, so fixed ball valve pressure relief valve is not mandatory design requirements.This is provided only if the medium has the above characteristics (abnormal boost may occur) or if the customer specifically requests it.Of course, some manufacturers regard this as a standard design, but the disadvantage is that there is one more possible leak point and the valve pressure test also adds to the trouble.
This can only seal the seat, also known as the "single piston" seat, that is, can only seal in one direction, the opposite direction can not seal. A sealed seat in both directions is called a "double piston" seat.
Realization of double piston effect function:
Double-piston effect valves achieve the function of a single seat, whether channel pressure or cavity pressure, the seat is moving towards the ball, to achieve double-sided sealing, as shown in the figure below. It is designed so that the sealing surface of the seat (dotted line in the figure) is between the two static pressure surfaces (the upper and lower contact surfaces of the o-ring in the figure).
Safety relief valves must be provided in the body cavity if both sides of the seats are "double piston effect" seats, i.e. neither can self-relieve.This is DIB minus 1.See the following figure for the safety relief valve.
The setting pressure (take-off pressure) of the relief valve shall be between 1.1 and 1.33 times (NEWAY 1.25 times) of the pressure rating of the relief valve at 38 ° c of the material.
If the ball valve upstream is a "single piston effect" seat, downstream is a "double piston effect" seat, if the pressure in the middle chamber is abnormal boost, can be through the upstream "single piston effect" seat self-relief function to release the pressure out.That's DIB minus 2.In this case, it is not necessary to set the cavity safety relief valve.
If the ball valve upstream is the "double piston effect" seat, downstream is the "single piston effect" seat, if the pressure in the middle chamber is abnormal boost, can be through the downstream "single piston effect" seat self-relief function to release the pressure out.
Generally speaking, from the perspective of technology, it is more reasonable and safe to release abnormal pressure in the middle cavity to the upstream, so the former design will be used, while the latter design is basically of no practical value and no use.
Thus, we can deepen our understanding and distinction between Block and Isolation.A Block is like a plug that can only seal the pressure on one side, while Isolation is an absolute partition that can cut the pressure (medium) on both sides.This is why gate valves can also be called Isolation valves, rather than Block valves, because they cut off the media pressure on both sides.
DBB and DPE are compared, as shown in the figure below.
So what's the benefit of using DIB?Why this new technology/design?
Because the use of DIB can make the ball valve into a valve with two really sealed in a valve, improve the sealing reliability of the ball valve.
Identification of seat on valve body:
Upstream SPE seat (single seat one-way) downstream DPE seat (single seat bidirectional)
