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Ball valves are most widely used valves for flow control in fluid flow lines for wide range of temperature changes (-200°C to 500°C).Most of the outlet valves of chemical plant storage were installed with ball valves for sudden closing and opening purposes. For petroleum and chemical plants it is very convenient to operate with ball valves.
Ball valves are used in situations where tight shut-off is required. The type of seat can vary with the valve pressure rating and materials of construction. Some valve seats are composed of single molded forms, while other seats with higher-pressure ratings often incorporate a trunnion design where each face of the ball is separately sealed. They are wide duty valves, able to transfer gases, liquids and liquids with suspended solids (slurries).
Ball valves are available in a variety of body styles, including one-piece, two-piece, three-piece and flanged body construction. Each of these forms offers specific advantages depending upon the requirements of the given application. Similarly, they are designed using a wide variety of materials, as required by their application. Common valve materials include brass, bronze, copper, cast iron, ductile iron, stainless and other steel types, metal alloys and plastics including PVC and CPVC.
Ball valve consists of a casing, a rotary ball and an external lever (FIG.1). The casing acts as a housing as well as connector. It contains flanges or threads at either ends for connecting ball valve to main fluid line. It houses a ceiling ring for seating of ball. The rotary ball sits in the recess of casing and has a cylindrical hole having diameter equal to that of fluid flow line. The proper alignment of the hole of ball with the main line leads to unrestricted flow area and is achieved by a quarter turn external lever

There are three types of ball valve mainly used for industrial applications
1. Conventional or quarter-turn pierced ball type.
2. Characterised type
3. Ball and Cage type.

Conventional type:
The quarter turn (900) required to fully uncover or cover an opening in the valve body can be imparted to the ball either manually by turning a handle, or mechanically by use or an automatic valve actuator. Actuator used for ball valves may be the same as those used to control the other valve types”Pneumatic, electric (or electronic), hydraulic, or combination. Most of the ball valves on the market are available with built-in, or integral, valve actuators. They are designed so that they can be applied with or without an actuator or so that they can be fitted with other manufactures actuators.
The spherical plug lends itself not only to precise control of the flow through the valve body but also to tight shut off. Thus the ball valve may assume the double role of control and block valve (fig). Special materials used for valves seats help achieve these functions.
The valve body can be configured as two-way, three-way, or split body. Figure illustrates some of the available multi port configurations.
Flow characteristics:
The flow path through a ball valve includes two orifice restriction locations (fig.).Sizing of ball valve proceeds with the possible exception that due to the essential straight-through flow feature, a ball valve can be chosen whose size is equal to the nominal pipe size, which might be an advantage on slurry service. This can only be done if an over sized valve can be tolerated, but at the cost of reduced sensitivity and increased cost. The low-pressure loss and high recovery of a ball valve must be considered in the calculations.
Design parameters of conventional type:
Size and design pressure: ½ inch to 42inch(12.5mm to 1.06m) in ANSI Class 150; to 12 inch (300mm) in ANSI Class 2500.
Design temperature: Varies with size and material, typically from -250 to 6000F(-157 to 3150C), with special designs available from -300 to 18000F(-184 to 10200C)
Capacity: Standard ball: Cv = 30d2 to Cv = 45d2; segmented ball: Cv = 24d2 to Cv = 30d2; Full bore ball: 35d2 to Cv = 100d2
Materials of construction: Body: Cast or bar stock brass or bronze, carbon steel, stainless steel, ductile iron, aluminium, monel, titanium, plastics, glass; also Hafnium-free zirconium(for nuclear applications) and ceramic for abrasives. Ball: forged naval bronze, carbon steel (also plated), stainless steel, plastic, glass, ceramics, alloy 20, Monel, aluminium, titanium. Seats: Teflon, Kel-F (both tetrafluoroethylene), buna-N, neoprene, natural rubber, graphite.
Special feature: Full- ported, three-way, split body, two-directional
Characterised ball valve:
The characterised ball valve category includes the V-notched and the U-notched ball valves and the parabolic ball valve. These valves are introduced partially in an effort to solve the problem of valve clogging and dewatering in paper stock applications. Since then these valves have come into more wide spread use as a result of increased valve rangeability and the shearing action at the sharp edges of the valve as it closes.
In essentially all characterised ball valves the ball has been modified so that only a portion of it is used (fig.) .The edge of the partial ball can be contoured or shaped to obtain the desired valve characteristics. The V-notching serves this purpose as well as its shearing purpose.
This shape or contour of the valveâ„¢s leading edge is the main difference between the various manufacturersâ„¢ products. The ball is usually closed as it is rotated from top to bottom, although this action can be reversed.
Mechanically, the characterised ball valves are very similar to their ancestors, the ball valve. However, because of asymmetrical design, the characterised ball valve has some design problems that are not significant with the conventional ball valves. A typical characterised ball valve is shown in figure in its end and side views. The main parts of characterised ball valve are described below.
The controlling edge of ball valve can be notched or contoured to produce the desired flow characteristics. They are presently available as U-notched, as V-notched and as a parabolic curve. Mechanically this part can create problems by bending under pressure and thus introducing movement into shaft seals.
The stub shafts can be distorted by the bending of partial ball under operating loads.
Flow characteristics:
The flow characteristics are dependent upon the shape of the edge of the partial ball and on the method of installation. The shape of the V-notch at the edge of the valve varies from concave for small openings to convex for large openings. Figure shows this together with the corresponding shapes for parabolic ball valves.
Design parameters of characteristics type:
Size and design pressure: Segmented ball: 1 inch to 24inch (50mm to 600mm) in ANSI Class 150; to 16 inch (400mm) in ANSI Class 300; to 12 inch (300mm) in ANSI class 600.
Design temperature: Varies with size and material, typically from -50 to 3000F(-46 to 1490C), with special units available from cryogenic to 10000F(5380C)
Capacity: Standard ball: Cv = 30d2 to Cv = 45d2; segmented ball: Cv = 24d2 to Cv = 30d2; Full bore ball: 35d2 to Cv = 100d2
Materials of construction: Body, ball, seal ring and shaft are available 316 stainless steel. Chrome plating available for ball and carbon steel for valve bodies. All ceramic valves are available.
Special feature: Depending on contour edge of ball, the flow characteristics vary slightly between suppliers. Slurry design provides for continuous purging for low- activity zone of valve to prevent build-up of solids, dewatering or entrapment.
Positioning of a ball by a cage in relation to a seat ring and discharge port is used for control as shown in figure. The valve consists of a venturi-ported body, two seat rings, a ball that causes closure, a cage that positions the ball and stem that positions the cage. Seat rings are installed in both inlet and discharge but only the discharge ring is active. The body can be reversed for utilization of the spare ring.
Cage positioned ball valve
The cage rolls the ball out of the seat as it is lifted by the stem, positions it firmly during throttling, and lifts it out of the flow stream for full opening as shown in figure. The cage is contoured for unobstructed flow in the open position. Cage design includes four inclined control surfaces. The two surfaces next to the down stream seat lift the ball out of the seat and roll it over the top edge of the seat ring as the valve is opened. As the valve opens farther, the ball rolls down the first two inclined surface to the centre of the cage to rest on all for inclined surfaces. The Bernoulli Effect of flowing stream holds it cradled in this position throughout the rest of the flow. A non rotating slip stem is guided by a bushing at the bottom and a gland at the top of the bonnet. A machined bevel near the base of the stem act as a travel limit and allows for back seating.
Design parameters of characteristics type:
Size and design pressure: ¼ inch to 14inch (6.3mm to 350mm)
Up to 2500 PSIG (17MPa)
Design temperature: -425 to 18000F(-254 to 9820C)
Capacity: Cv = 20d2 (non critical flow)
Materials of construction: Stainless steel.
Special feature: Good resistance to cavitations and vibration.
Ball valves can be mounted on pipelines in three ways.
Screwed end
Socket weld end
In this type of valve, having both end connections are flanged. It can be easy for mounting in line between flanges; after the maintenance or new installations as shown.
Screwed end:
Both end of this type of valve will have female screwed ends and can fixed on the pipe line with male threaded pipes as shown.
Socket weld end:
In this type of valve can be fixed on line by welding on both ends of valve with pipeline. Usually socket or butt welding; and good for high pressure lines in industries as shown.
Ball valve consists of a casing, a rotary ball and an external lever. The casing acts as a housing as well as connector. It contains flanges or threads at either ends for connecting ball valve to main fluid line. It houses a ceiling ring for seating of ball. The rotary ball sits in the recess of casing and has a cylindrical hole having diameter equal to that of fluid flow line. The proper alignment of the hole of ball with the main line leads to unrestricted flow area and is achieved by a quarter turn external lever. The ball rotates about its own centre by one quarter of a circle to achieve full flow to no flow situation. The positions are also assigned as full opens and zero open angles.
If geometry of a quarter of the ball valve is considered for particular ball valve open angle (), the actual flow area is intersection of circular main line and projection of the open end of the ball. The main line is always circular and projected area of the ball is always an ellipse with shifting centre. The shape of the ellipse changes from a line, with zero semi-minor axis for no-flow situation, to a circle for unrestricted flow passage. The intersection point of these circles and ellipse subtends an angle and at the centre of the circle respectively as shown in figure.
The actual flow area is bounded by two curves, each of which is an arc of circle and ellipse. The different angles are connected by following relations:
Cos = Cos / ( 1+Sin )¦¦¦(1)
Tan = (Cos -Cos) / Sin¦¦.(2)
The value of , and varies from 0° to 90° for no-flow to full flow situations. If an non dimensional flow area f is defined as fraction of full flow area opened by a typical ball valve open angle , f can expressed in terms of different angles by relation given below.
f = [ - sin Cos + Sin (/2) - Sin - ( Sin Sin2 )/2] / ......(3)

The fractional flow area f is plottted against ball valve open angle as shown in figure
Variation of flow area with open angle of ball valve
After the mathematical representation of ball valve geometry, flow control analysis is carried out. The developed steady, laminar flow of incompressible Newtonian fluid, across ball valve is analysed using momentum equation. The input flow parameter is shown in the table1.
The pressure head and fluid viscosity is assumed constant and the mass flow rate is calculated for different ball valve opening angles. As ball valve open area varying from elliptical to a circular opening, the flow is analysed using a flow through both circular and electrical cross section. For calculation of flow assumed to be taking through modified circular cross section, the velocity profile is assumed to be parabolic over uninterrupted cross section and cross sectional area is taken as a fraction of fractional flow area, available for the given ball valve open angle. For elliptical cross section , the cross section of parabola is made equal to that of fractional open area, by selecting the major and minor axes of the ellipse, suitably. The results are tabulated on table2.
The discharge for elliptical cross section gives a very small mass flow rate and is not matching to the actual observed flow. The mass flow rate actually observed is matching to circular flow calculations. So, the ball valve flow pattern is simulated as per circular flow cross section assumption and the concept of fractional flow area opened by ball valve can be utilised, while using ball valve for flow control of viscous slurries.
1. Less resistance i.e. free flow
2. It can operate with high viscous fluid even in solid slushy gypsum where as other valve could not be operated.
3. It has only less spare parts and easy maintenance also.
4. It can close or open very fastly in any emergency situations especially in petroleum products where as other valves like gate, globe, plug will take more time and that will cause accident.
5. Ball valves can be widely used because of their low cost, compactness, wide range of size, least effort in operation and unrestricted flow area at full operation.
6. It is also called spherical plug valves and has least maintenance compared to other types of valves.
7. It is not generally used for throttling purposes but can regulate flow area, also. Although flow through the valve is generally expressed in terms of flow co-efficient, flow regulation is achieved by the cross-sectional opening of the valves.
Ball valves have got wide range of applications. Now a day all industries are now replacing older valves by these type because of their advantages.
1. In all domestic services like heating and sanitation in large building such as hospitals and schools in district heating works on distributors, filter plants, transformer stations, before and after thermal meters, in long distance pipe lines.
2. In LPG tank farms
3. In steel works e.g. in cooling systems for blast furnaces
4. In paper making industry: digesters, washing and bleaching plants for fibrous, viscous and also highly aggressive media.
5. In paint and varnish factories, in proportioning mixing and regulating plants.
6. In hydro carbon processing industries.
7. Filling stations for petrol, oils, solvents etc.
8. In plastic industries.
9. In aircraft fuel line.

The geometrical analysis of ball valve is a useful tool for fluid flow rate determination. The mass flow rate matching to actual mass flow rate establishes the relevance of the analysis. The ball valve open angle can be automated as per flow rate requirement, using analysis.
Process and plant engineering, January- March 2001, volume 13.No:4 (article)
Author: Himanshu Shekhar, HMERL,Pune.
Process control, Instrument engineers book by B.G.Liptak.

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