Types of Ball Valves & Applications

There are types of ball valves according to the different clarifications. The followings are the commonly used ball valve types and applications.

Ball Valve Types: Short Pattern vs Long Pattern

Depending on the end-to-end dimension of the valves, two types of ball valves are available. They are short pattern and long pattern ball valves.

The end-to-end dimension and weight of short-pattern ball valves are less compared to long-pattern ball valves. However, During piping design, a long pattern dimension is selected for ease of connection to pipe flanges. Also, short-pattern ball valves are not available after a specific size and flange rating. So, long pattern ball valves are the only option in such cases.

Types of Ball Valves: Soft Seated vs Metal Seated

Depending on the seat materials of the valve, two types of ball valves are found; Soft Seated and Metal Seated Ball Valves.

Soft, non-metal seated ball valves satisfactorily cover most of the applications. Soft seated ball valves use a thermoplastic material such as PTFE, NBR, etc. However, abrasive media, high pressure, and temperature can severely stress the polymeric seals leading to damage. Because of this reason metal-seated ball valves are developed in the 1960s.

Metal seated ball valves use metal as seat material such as satellite, carbide, etc. Tight shut-off, no jamming, smooth control, good corrosion and wear resistance, wide temperature range, stability under pressure, etc are the advantages that a metal-seated ball valve provides with its soft-seated counterparts.

Soft Seat Ball Valve Design

Thermoplastic or Elastomeric seats are inserted in a metallic holder (seat ring) to provide soft seating action in a ball valve. The main features of a soft-seated ball valve are

• Provide a good sealing ability.
• Lower in cost than metal seated valves.
• Limited temperature rating.
• Should not be used in dirty services, particularly on floating ball valves.
• Soft seat materials used are – PTFE, Nylon, Devlon, PEEK, etc.
• It is generally accepted a leakage of ISO 5208 Rate A

 

Metal Seat Ball Valve Design

The main features of metal-seated ball valves are

• Direct metal-to-metal contact between seat ring & ball.
• Ball Valves are used for abrasive services and for services where soft seated valves can not be used due to temperature limitations.
• The ball & seat contact surfaces are hard-faced to improve resistance to wear & prevent scratching caused by the solid particles contained in the process media.
• Metal sealing may be obtained by tungsten carbide coating (up to 200 deg. C), chromium carbide coating (above 200 deg. C), electroless nickel plating (ENP), or stellite hard facing.
• Acceptable leakage of ISO 5208 Rate D.
• Metal seats do not bed in as easily as soft seals under pressure. hence, ball and sealing rings to be precisely machined.
• Metal-seated ball valves are posed to pitting, fretting, stress corrosion cracking, and intercrystalline corrosion damages.

Ball Valve Types: Side entry, Top entry

From perspective of Ball Valve Body Styles, they are divided into three types of ball valve designs. They are Side entry or top entry ball valves.

Side entry or end entry ball valve design

In the case of a side entry ball valve, the ball is assembled from the side part. They normally have two pieces or three pieces of the body. Each part of the body is assembled by a bolt/stud similar to joining a two-piece of flanges. Side entry ball valves are usually made by forging the metal. Each piece of the body is forged separately and then assembled together to get the complete design. This construction is robust in design and minimizes the defects caused by casting valves. Side entry ball valves are also easy to assemble and the trim component is also easy to align. Another advantage of the side entry ball valve type is that they are easily available from almost all vendors rather than a casting product that still needs some additional testing.

Top Entry Ball Valve Design

The main design features of top entry ball valve types are

• Maintenance and repair of such ball valves are possible in-situ, by removing the top flange. This minimizes maintenance downtime.
• Limited space is required around the valve for maintenance.
• Available in welded as well as flanged end connections, but welded ends are preferred to reduce potential leak paths and minimize the ball valve weight.
• Heaviest and most expensive construction.

Welded Body Ball Valve Design

The main design features of this type of ball valve design are

• Welded body ball valve construction eliminates body flanges, reduces potential leak paths, and increases resistance to pipeline stresses.
• The minimum number of leak paths is hence beneficial in fugitive emission and vacuum applications.
• Compact and lightweight design
• The body draining & venting feature allows the ball valve maintenance technician to test each seat ring sealing ability with the ball in either the fully open or fully closed positions.
• Sealant injection fittings access directly to each seat ring. This enables the technician to top up the quantity of lubricant inside the valve sealant injection system on a periodic basis.
• Valve cleaner can also be injected into these fittings to flush out the old grease in the ball valve and to clean critical seal faces on the ball.
• Heavier sealants are also injected through the sealant injection fittings during an emergency when a critical seal is required.
• Applications – Oil & gas pipelines, compressor stations, measuring skids, etc.

Floating or Trunnion Ball Valve

The major design features of a floating ball valve are

• Ball valve design in which the ball is not rigidly held on its rotational axis & is free to float between the seat rings.
• In the closed position, the ball is pushed against the seat by the pressure of the fluid from upstream and hence can pressure seal the downstream of the valve.
• Ball seats on the downstream seat only.
• Seat loading increases at a higher pressure and for larger sizes and becomes excessive, for the soft seated valve.  Also, the higher the size the heavier the ball, and the less likely it is to be moved by pressure. Hence the need for a trunnion-mounted ball valve design comes into the picture.
• Floating design ball valves have lower manufacturing costs.

Trunnion Mounted Ball Valve

The major design characteristics of a trunnion-mounted ball valve are

• The ball is fixed in position by the stem & the trunnion which are supported by bearings in the body.
• The seat is spring-loaded onto the ball, giving reliable sealing at low pressures
• The key feature of this ball valve is that the ball does not shift as it does in a floating valve to press the ball into the downstream seat.  Instead, the line pressure forces the upstream seat onto the ball to cause it to seal.
• As the area on which the pressure acts is much lower, the amount of force exerted on the ball is much less, leading to lower friction values and smaller actuators or gearboxes.