Field of Invention

The present invention cites the use of the single butterfly valve with extremely efficient and super fine controllability with wide rangeability in any industrial flow control applications.

Background of the Invention

In any industrial flow control applications, for higher pipeline size (i.e. above 8” size), generally, butterfly valves are widely preferred. This is because of the less weight, less space, comparatively lower cost than globe valves and higher & wide range of Cv (Valve Flow Coefficient) availability. However, the main problem with butterfly valve is the limited controllability. Widely acceptable control range for the butterfly valves is limited from 30° to 70° opening. Thus, despite having a very significant Cv values for the respective body size, the butterfly valves are practically unusable for wide range control applications. In fact, where the process demands 1:100 controllability, a single butterfly valve is practically not implementable despite having the sufficiently available higher Cv. In such applications, almost everyone chose two control valves in parallel. Most of the applications demand for one Globe Valve and one Butterfly Valve as parallel option. This two valves’ system is used in almost every industry to overcome the controllability problems. e.g. LNG Level Control Application in Recondenser in LNG plants, Feed Water Drum Level Control in Power Plants, etc. In such applications, two or more control valves are used in parallel to overcome the controllability and wide rangeability issue. When two or more control valves are used, in many cases those come with inline manual isolation valves. In case of Drum Level control, three control valves are used with six motor operated isolation valves.

The problem of wider rangeability is widely faced and handled in the way it is Or within limited options available for single control valve with slightly better rangeability. This in turn is not the cost effective solution.

In present market scenario, there are many butterfly valves with wide range of the Cv values depending on different designs or material of construction.

But, the option of butterfly control valve below 4” size is comparatively rare. i.e. below 4” the obvious forced choice is globe control valve, which although has better differential pressure across the valve, however, is the costlier option compared to butterfly control valve.

In butterfly control valves, Cv rangeability is typically approx. 50:1 for higher size valves. Precisely, the practical rangeability in control application will be approx. 5:1 maximum i.e. in the 30° to 70° opening. Beyond these valve-opening ranges, the butterfly control valves are practically not used for fine control applications.

Thus, there are two scenarios, for lower valve sizes, the butterfly valves are not easily available and for higher sizes, the controllability is poor after 70° opening of the butterfly valves and forcefully the higher Cv valves are to selected.

In applications, wherein higher rangeability is needed, two or three control valve assemblies are used. The lower size globe control valves are used in parallel with higher size butterfly control valves. However, the present invention focuses on such applications where wide rangeability with best controllability is needed and shall be solved with a single butterfly control valve giving the extremely cost-effective solution.

Summary of the invention:

The detailed designs of the said invention are provided in the drawings (Page 8 &

9).

This unique“Disc in Disc Butterfly Valve” or“MultiTrim Butterfly Valve” or “1+n Trim Butterfly Valve” design is especially designed to address the controllability problem.

In this invention design example (Drawing - A), there are three discs in a single butterfly valves. Depending upon the controllability requirements, these three discs shall open or close and achieve the required flow conditions.

In the present invention, only single Butterfly Valve with Multiple Trims / Discs are used.

e.g: As per Drawing - A, three discs are indicated. (Depending on the application, there may be three or more number of discs.) In wide range applications, for initial lower range flow control, the smallest trim (innermost disc) shall start opening. As the size of this trim suggests, it is used for small flow control or fine flow control. As soon as the smallest trim reaches 90° opening and if the flow demand increases, then next higher size trim shall start opening. As per Drawing - A, the middle trim (middle disc) shall start opening gradually. The opening of the middle trim shall be as per the flow demand. If the flow demand increases and the middle trim opening leads to the higher flow than the required flow -set-point then this middle trim shall stop opening & the smallest trim shall immediately start closing to meet the flow -set-point. The movement of the smallest trim stops at the moment when flow demand matches set point. If the flow demand is again increased and if it is such a high value that even after 90° opening of smallest trim and 90° opening of the middle trim can not meet the required flow demand then the third i.e. largest trim (outermost disc) shall start opening gradually. Once again, for the fine flow control, smallest trim plays a vital role.

Inherently, the Butterfly Valve has Quick Opening characteristics. Present technological support in terms of Smart Positioners can deliver the Linear Characteristics for Butterfly valves but upto limited opening and limited controllability. Practically, after 70° opening the butterfly valve design inherently loses its controllability. Also, there is limitation in the present days positioners’ resolution, which limits the butterfly valve’s fine movement and that limits the fine controllability for higher size butterfly valves.

However, using this invention design the absolute Linear characteristics is possible for extremely wide range in the same valve size.

Table- 1 shows the example of 3 Discs - Disc in Disc / MultiTrim / Multidisc Butterfly valve. The valve is considered with 32” pipeline data. The three discs are with diameter of 800mm (32”), 600mm (24”) & 400mm (16”). For 32” pipeline, the available cross sectional area for the flow is 502400 mm approx for 100% opening. In Table- 1, the valve percentage openings from 0-100% are indicated against individual discs’ opening area and the total effective area available for the flow against the theoretical area for the respective percentage opening. Here, the valve percentage area means the percentage opening for the highest size of the disc i.e. in this case, it is 32” valve’s percentage opening. It shows the super fine linear characteristics for this invented design Disc in Disc / Multidisc/ Multitrim Butterfly valve. Correspondingly, Chart- 1 shows the Linear Relationship of this valve’s Percentage (%) Opening against Valve Area available for Flow. Here, the percentage valve opening corresponds to different positions of the various discs involved in the design. In this case, initially, i.e. during 0-63% opening, only the inner two discs play the role in the control. From 64% opening, the outermost disc starts opening and actively participate in the control along with the other two discs. From this table, it is clear that the combination of the discs’ different opening positions actually arrives to the exact required percentage opening area and provides the linear characteristic.

Thus, perfect linear valve characteristics is achievable using this invention design Disc in Disc or Multidisc/Multitrim Butterfly Valve through out the valve positions. The most unique aspect of this design is the perfect linear characteristics for the entire opening.

In case, if the more fine control is needed then lesser innermost disc size to be considered. More fine, the control needed for intermediate upper ranges of the flow control, more the number of discs to be selected while deciding the number of discs.

Thus, very low flow control as well as extremely fine flow control during higher flow control ranges can be achieved by the smallest disc and the upper flow ranges are taken care by the bigger discs. The number of trims/discs can be chosen based on the fine control requirements for particular application ranges. The smallest trim/disc size also to be decided based on the smallest flow control range requirements as well as the fine flow control requirements. Thus, the number of discs and their sizes need to be decided based on the specific application requirements.

This innovative butterfly valve design provides multiple flow-paths, which helps to reduce the flow velocities and in turn the noise and that too without compromising on differential pressure (DR).

The valve discs’ movement mechanism is out of the scope of this document. It is addressed separately.

CHART-1