Flanged Valve - Mating Bore - Valve engineering - Eng-Tips

Hi everyone,
In most of project I was involved in, flanged valves were purchased based on the rating and size of the mating flanges. I mean nothing is said with regard to the schedule of the pipe. I know that internal bore is important when purchasing welding end valves, but I haven't deal with specifying of internal bore when purchasing flanged valves. ASME B16.34 correlates flange thickness (say internal diameter) to the ASME B16.5, which in turn has mixed dimension for internal diameter (depending on the size and rating). For, say 600#, 24", internal bore shall be specified by purchaser.
My question:
Is it possible to have different bore diameter at the mating flanges (for 24", #). If so, what's maximum allowable difference?
Thanks in advance.
'Internal bore' of a ball-valve is normally used for the actual opening in the ball itself. For a reuced bore ball-valve, where the opening in the ball is less than the nominal inner piping diameter, the entering opening of the valve flange will match the full opening of a sheduled standard opening of the counter flange on the pipeline, eg. both at full pipeline diameter. From the ball-valve flange there is normally a cone reduction to the ball opening at a reduced bore bsll-valve.

I do however, from your description, belive that you are actually talking about the allowable difference between the entering hole through the valve's flange compared to the bore of the standardized bore of the pipeline's counter flange.

I do not believe anything is noted down in regulations here as long as the flanges matches (strength of flanges and the general construction of pipeline and valve), but others might correct me here.

If we are talking about ball-valves we have also to consider possible pigging and allowed differences according to pig-type, if there is an abrupt change of diameter from pipeline flange to valve flange.

Else, for all types of valves, we will have to consider increased hydraulic loss, possible cavitation, and actual capacity of the valve for the different pressure and flow data. For some types of (smaller) valves other than ball-valves, flow capacity might vary from valvetype to valvetype, not directly proportional to piping diameter. This is often the case for regulation valves.

There are, for some (larger) types of regulation valves (for instance german 'ringkolben' (needle) valves) from 150 mm up to mm) cases where a valve of lesser diameter is used to give the correct regulation for a larger pipeline. The valve is often then mounted to the upstream pipeline with an abrupt diameter change (most often 1 to 2 valve diameters smaller than the pipeline diameter) given by a flat reducing flange. This will (depending of flow amount) give a better linear flow through the valve than a longer cone reducing tube for many cases.

Concluding on your question: for normal cases 'small' differences might be negliable whereas 'larger' differences might be more complicated, but as said: all depending on flow parameters.

(Others may have things to add or correct.)

The History of Ball Valves

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The humble ball valve is so widely used in industry today that it is considered to be a valve type in its own right, distinct from linear and rotary valves as main groups. However, when it was first introduced in the ’s it was known as a ‘spherical plug valve’.

The use of a ball valve has developed rapidly since the ’s because of the development of machines that are able to accurately produce the spherical polished surface of the ball and the availability of different ball and seat materials. In more recent years the continual development of seat materials together with metal seats made from low wear materials has extended where these valves can be used particularly where abrasive and high temperature media are involved.

What materials can ball valves be made from?

The most common materials for ball valve manufacture are carbon steel grades WCB and LCB for the body and stainless steel grade 316 or CF8M for the ball and shaft.  In special applications the body can be made from stainless alloys in corrosive or low/high temperature applications.

The standard seat material for ball valves is PTFE (Polytetrafluoroethylene) because it is chemically inert to a wide range of fluids and has a coefficient of friction at less than 0.1.

PTFE loses rigidity at high temperatures which is why Ball valves have a pressure/temperature curve supplied by the manufacture showing what temperature is achievable at what pressure.

To overcome the limitations of standard PTFE, special Nylons, Polyether-etherketone (PEEK) and powder filled PTFE’s are used to gain a higher rigidity over the seating face and an increase in maximum service temperature. When temperatures are over 280°c metal seated ball valves are required.

Floating Ball Valve Design

With this design the ball is held between two ball seats by the compression of the seats against it.  To turn the ball 90° or quarter turn the ball is driven by a shaft which connects to a slot in the top of the ball.  The slot allows a little lateral movement of the ball due to the influence of upstream line pressure.  The design principle around floating ball valves is that they are loaded by line pressure against the downstream seat which is why this seat is always regarded as the primary seat.  In some cases the upstream seat can also give a secondary seal if the design has a pre-loading or a spring in the the upstream seat design.

Trunnion Mounted Ball Valve Design

On this design the ball is supported by a trunnion and not the valve seats which allows much higher pressure and temperature ratings. The concept behind this is that the shaft and trunnion are intended as being a one piece construction.  The shaft and trunnion are held in bearings to prevent the ball from moving against the downstream seat.  To facilitate loading the upstream seat is designed to move forward against the ball and thus in a trunnion mounted ball valve the primary seat is formed at the upstream side.  A spring mechanism is also incorporated behind both seats to ensure even seat loading even at low pressures and to provide a secondary seat on the downstream side. As with floating ball valve designs, trunnion mounted ball valves are capable of bi-directional shut off.  One of the main benefits of trunnion mounted ball valves over floating ball valves is a lower operating torque and consequentially this means that actuation costs can be lower.

Different Ball Valve Body Designs

For more information, please visit Flange Ball Valve.

Further reading:
4 Advice to Choose a Globe Control Valve

One Piece Ball Valve Design – The ball is placed into the body through an entry in one of the pipe flanges and secured with a gasket forming part of the raised face. This has inherent strength and minimises leak paths.

Split Body Ball Valve Design – This is also known as a 2 piece or 3 piece ball valve and the body is split in one or two places in the same plane as the valve flanges.  The body is then bolted around the ball. 3 Piece ball valves are common among smaller sizes due to lower manufacturing costs and trunnion mounted ball valves due to component weight.  The big advantage of split body ball valves is the ease of maintenance.

Top Entry Ball Valve Design – This is a rarer design of valve where the ball is inserted through a bonnet in the top of the valve.  The main advantage of this is that the critical parts of the valve can be maintained while the valve remains in the pipeline. It’s often used in welded pipe systems.

Fully Welded Ball Valve Design – This is where the body of the valve is an all welded construction and completely non-maintainable. These are often found used in gas pipelines.

The difference between Reduced or Full Port Ball Valves (also known as Full or Reduced Bore)

One of the most important considerations with a ball valve is port size. Full port generally means the ball port is the same as the inside diameter of the pipe.  One of the advantages of Reduced Bore Ball Valves is that they are lighter in weight and cost less but the disadvantage is a reduced flow and in some cases a 1 piece construction rendering them non-maintainable.

Anti-Static Ball Valves

If the ball is held between seats without any metallic contact between it and other components the flow of fluid can lead to a build up of static electrical charge on the surface of the ball. To prevent this static forming a spark, igniting fluid or causing an explosion valve design standards require a mechanism to ensure electrical continuity between ball, body and downstream pipework.

Anti-Blowout Design

In the floating ball valve design the shaft is not attached to the ball.  It is essential to make sure that the shaft cannot be blown out past the packing if the gland bolting is removed or slackened.

Fire Testing of Ball Valves

As the majority of ball valves rely on soft seats in order to seal properly, engineers are often concerned about whether a ball valve will still operate in the event of a fire which has partially damaged or destroyed the ball seats.  For certain industries like oil, chemical and petrochemical industries it’s a requirement that valve can still operate . Ball valve fire safe standards stipulate the details of fire to which a ball valve must be subjected to before it can be certified as ‘fire tested’. 

Ball Valve Cavity Relief

When a ball valve is closed the body cavity of a ball valve is full of line fluid which can always escape if the pressure is not sufficient to load the ball onto the downstream seat.  In this case an increase in temperature may render the valve inoperable due to the increase in temperature, and as a solution to over pressure relief, a hole can be drilled in the upstream side which renders the valve uni-directional. Cavity relief is part of the design in a trunnion type ball valve but not inherent in a floating ball valve so required adding.

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