WHAT IS A BALL VALVE?
A ball valve features a spherical disc to open, close the flow of the fluid passing through the pipeline. Ball valves are the industry standard for pipeline shut-off applications, as the design and the mechanical geometry of this type of quarter turn valve guarantees a very tight and leakage free sealing even after years of operation. Bal valves are classified in two main designs, floating and trunnion, with side or top entry configuration.
The key specifications for ball valves used in petrochemical applications are the API 6D, BS 5351 (forged ball valve) and ASME B16.34 (pressure and temperature ratings), ASME B16.5/B16.47 (flanged ends) and ASME B16.25 (butt welding ends).
Ball valves are largely used in the petrochemical, oil refining, energy, offshore drilling, marine, shipbuilding, renewable energies, pulp & paper. They are less widespread in pharmaceutical, bioprocessing, or food and beverage applications as cleaning is not as easy as other types of valves.
HOW DOES A BALL VALVE WORK?
The ball mounted inside the valve has a hole through which the flow passes freely when it is fully aligned with the two ends of the valve. When the hole is completely perpendicular to the ends of the device, the valve is perfectly sealed.
Otherwise, when the hole is in any other position (perpendicular to the ball valve ends for instance) the flow is totally or partly interrupted. It should be noted that ball valves are not as precise as globe valves to throttle the flow, as they generally have positive (at 0, 45 and 90 degrees) instead of incremental positions.
The actual status of the ball valve (open, closed or partly open) can be detected by looking at the position of the valve’s lever: when the ball valve lever is visually aligned to the pipe, the valve is open; when it is perpendicular to the pipe, the valve is closed; when it is any other position, the valve is partly open (or partly closed) and is modulating the flow.
Ball valves belong to the family of “quarter turn” valves or “1/4 turn ball valve” (together with butterfly and plug valves), as the opening and closing operations are executed by turning a lever connected to the disc by 90 degrees (i.e. the ball).
BALL VALVE TYPES
Ball valves can be classified according to multiple criteria:
- Design-wise, ball valves can be divided into 3 main types, i.e. floating, trunnion mounted and double bleed and block (as represented in the image below)
- Valve ports: ball valves are available in the standard 2 ports design (1 inlet, 1 outlet) or 3 ways design (1 inlet and 2 outlets or vice-versa)
- Bore size: full bore or reduced bore (FB vs. RB), and V-notch
- Body assembly: unibody (the ball body is made out of one single piece of cast or forged steel), 2 pieces or 3 pieces (the body results from the assembly of two or three different parts)
- Ball access: side entry or top entry (depending on the fact that the ball can be accessed, for maintenance, from the side of the valve or from its top)
- Seat type: metal or soft (Teflon)
The meaning of all these terms is discussed below in this article.
BALL VALVE BENEFITS AND ISSUES
Ball valves have different advantages:
- they can be quickly opened and closed with a quarter turn movement
- ensure a very tight seal without the need of high torque forces
- compact design
The ball valve’s disadvantages are:
- a ball valve has poor regulating and throttling performance, as it is designed for pipeline shut-off vs. modulation: throttling causes the partially exposed seat to erode because of the high-velocity flow and pressure experienced by the valve. The wear may lead to a leakage of the valve progressively.
- it is not suited for slurry applications, as the accumulation of suspended particles and debris would lead to wears, leakages or failures of the ball valve. Slurry applications are not recommended as the slurry may solidify in the cavities in the proximity of the ball and seats, increasing the operating torque and creating the conditions for a valve failure (actually, ball valve manufacturers generally recommend a maximum 3% trace solids in the conveyed fluid). Ball valves are way more very efficient with gases and other liquid fluids (even challenging chemicals as dry chlorine, hydrofluoric acid or hydrochloric acid, and oxygen).
- may be difficult to clean (side entry design)
BALL VALVE MATERIALS
Ball valves are available in cast and forged materials. Generally, valves below 2 inches of diameter have 2 pieces of three pieces forged bodies (the most common is ASTM A105 for high-temperature service, ASTM A350 LF2 and LF3 for low-temperature service and ASTM A182 F304, F316 for stainless steel ball valve or higher grades, such as duplex ball valves ASTM A182 F51 and super duplex ASTM A182 F53/F55). Forged bodies are also used for high-pressure ball valves.
Examples of forged ball valves (small size and stainless steel ball valve with a forged body, trunnion mounted).
Ball valves of sizes above 2 inches feature, generally, cast bodies (the most common grades are ASTM A216 WCB for high temp. service, ASTM A352 for low-temperature service and ASTM A351 CF8, CF8M for cast stainless steel ball valves).
BALL VALVE SYMBOL
The ball valve symbol in P&ID diagrams is represented below
FLOATING VS. TRUNNION BALL VALVE
The two most common ball valve’s designs are floating and trunnion mounted:
FLOATING BALL VALVE
In a floating ball valve, the ball is suspended in the flowing fluid and is kept in position by the compression of two elastomeric seats against it.
The shaft is connected at the top of the ball and allows the switch from an open to a closed position with a quarter turn movement (90 degrees).
When the shaft is moved, a load is applied to the ball which gets pressed against its seats.
This design, which is lightweight and economic, suits bore sizes up to 10 inches: above this bore size, the seats of the valve would not be able to withstand heavier and heavier balls and the valve would not operate safely and efficiently.
Floating ball valves allow a bi-directional shut-off of the flow (as the trunnion type).
TRUNNION BALL VALVE (TRUNNION MOUNTED)
Trunnion ball valves have been introduced to cope with the size limitations of standard floating ball valves outlined above. Indeed, in this type of valves the shaft, the ball, and the supporting trunnion act as a single solid assembly able to withstand the heavy loads generated by balls of large dimensions.
Besides a size flexibility advantage, a trunnion ball valve features a lower operating torque compared to a floating ball valve design (which can become a benefit when the valve needs to be actuated, as smaller and economical actuators can be fitted to operate the valve).
A stainless steel ball valve, trunnion mounted type
SIDE ENTRY VS. TOP ENTRY BALL VALVE
What is the difference between a side entry and a top entry ball valve?
These terms relate to the way by which the ball of the valve and its internal parts can be accessed, from the side (side entry) or from the top (top entry).
TOP ENTRY VS SIDE ENTRY BALL VALVE
Floating and trunnion-mounted ball valves are available with a “side entry” and “top entry” design.
The top entry design is specified when frequent inline maintenance activities are expected on the valve.
This is due to the fact that top entry ball valves allow an easier and faster access to the ball and the valve trim compared to side entry valves (which require more maintenance time and space for the same operations).
The main differences between these two ball valve design are:
- Top entry ball valves are manufactured, generally, with cast bodies; side entry valves are manufactured with (robust) forged steel bodies
- Top entry ball valves have a monolithic structure (are made by one single piece); side entry valves have a two or three piece assembly
- Top entry ball valves require more NDT testing than side entry due to their cast bodies;
- Side entry ball valves are easier to assemble and manufacture than top entry, which requires long experience and craftsmanship to work properly
- Top entry ball valves are generally more expensive than side entry ones and have longer lead times due to the casting operations required to manufacture the body
3 WAY BALL VALVE
Generally, a ball valve has two entries (or “two ways”).
However, for some applications, a 3-way ball valve may be specified. A 3-way ball valve has 3 ports (entries), instead of only two.
This multiport design is needed to divert the fluid coming from the main valve inlet to two different directions (instead of just one), each served by two separate valve’s outlet. Another typical application of a 3-way ball valve is to have the main flow line served by two separate and alternative inlets.
The ball of a 3 ways ball valve may have an L or a T design as shown in the picture below. Further, this special type of ball valve is available in floating or trunnion design, with any type of valve end (flanged, socket or threaded connection) and in various materials from plastics, to carbon, alloy, and stainless steel.
FULL PORT VS REDUCED PORT BALL VALVE
These concepts refer to the relation between the bore diameter of the valve and the connected piping system. More in detail:
- A “Full port” ball valve (FB) features a bore size (the hole of the ball) matching the bore size of the connected piping. Full port ball valves minimize the pressure drop that is generated by reduced port valves but they are of course more bulky, heavy and expensive. FB ball valves are better suited, than RB ball valves, for throttling applications.
- A “Reduced port” ball valve (RB) has a bore size that is smaller than the bore size of the connected piping (for example a tube). The media flowing through the valve is, in this case, limited to a percentage (generally between 70 and 80%) of the full flow in the pipeline. Reduced port ball valve create a pressure drop in the pipeline.
BALL VALVE PRICES
Looking for the price of ball valves? Click on the image and check our online ball valves price estimation tool!
The tool estimates the price for ball valves manufactured in Europe and Asia.
Even if our price estimates are reliable, prices shall always be double checked with ball valves manufacturers and distributors.
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