The ball valve is a type of plug valve with a ball-shaped closure member. The seat corresponding to the ball is circular to ensure circumferentially uniform seating stress. The majority of ball valves feature flexible seats that readily conform to the surface of the ball. Thus, the concept of the ball valve is superb in terms of sealing.
The flow-control characteristic resulting from a circular port moving across a circular seat and the double pressure decrease between the seats is good. However, if the valve is left partially open for a long time under conditions of a high pressure drop across the ball, the soft seat will tend to flow around the ball orifice's edge and may seal the ball in place. Therefore, ball valves for manual control are best adapted for stopping and starting flow as well as moderately restricting it. If flow control is automatic, the ball is constantly in motion, preventing this failure from occurring ordinarily.
Because the ball travels across the seats in a wiping motion, ball valves can manage fluids containing suspended particulates. However, abrasive substances will damage both the ball surface and the seats. As the fibres tend to encircle the ball, lengthy, robust fibrous material may also be problematic.
The majority of ball valves have a reduced bore with a venturi-shaped flow passage that is approximately three-quarters the nominal valve size. Consequently, the pressure loss across the reduced-bore ball valve becomes
Therefore, the expense of a full-bore ball valve is typically not justified.
However, there are instances in which a full-bore ball valve is necessary, such as when the conduit must be scraped.
Seat Materials for Ball Valves
The most essential seat material for ball valves is PTFE, which is chemically resistant to nearly all substances. This characteristic is coupled with a low coefficient of friction, a broad temperature range of application, and exceptional sealing properties. PTFE's physical characteristics include a high expansion coefficient, susceptibility to cold flow, and poor heat transmission.
Therefore, the seat must be designed with these properties in mind. Other plastic materials for ball valve seats include filled PTFE and nylon, among others. Nevertheless, as the seating material gets harder, the sealing reliability tends to decrease, especially at modest pressure differentials. Elastomers such as buna-N are also used for the seats, but their fluid compatibility and temperature application range are limited. In addition, elastomers have a tendency to cling to the ball if the fluid lacks sufficient lubrication.
For services where plush seating is inappropriate, metal and ceramic seating is used.
Failure of Ball Valves
In industrial applications, ball valves are one of the most prevalent valve types. They are renowned for their superior sealing abilities, minimal operating torque, and extended service life. However, as with any other mechanical device, ball valves are susceptible to malfunctions. This article will discuss the causes of some common problems with ball valves.
Leakage
One of the most common issues with ball valves is leakage. It can be caused by a variety of factors, including broken or worn-out sealing components, improper installation, or excessive pressure or temperature. A leak can result in product loss, safety risks, and environmental contamination.
Corrosion
Ball valves are susceptible to corrosion when exposed to harsh chemicals, corrosive vapours, or high humidity environments. It can cause damage to the body, stem, or ball of the valve, resulting in diminished efficacy or failure. By selecting suitable materials for valve construction and performing routine maintenance, corrosion can be prevented.
Deposits and Contamination
Accumulation of deposits or contamination within the valve may result in decreased flow capacity, an increase in pressure drop, or obstruction. It can be the result of improper installation, improper cleansing, or the use of inappropriate materials. Regular maintenance and cleansing can prevent these issues.
Sticking or Binding
Sometimes, ball valves can become caught or bind, preventing them from opening or closing correctly. This may be caused by extraneous objects lodged in the valve or internal components that have been compromised. By installing suitable filters and strainers and performing routine maintenance, this issue can be avoided.
Actuator Failure
Ball valves with actuators may fail due to a faulty actuator, electrical or pneumatic failure, or valve or actuator damage. This may result in loss of control, diminished performance, and even safety risks. Regular testing and upkeep of the actuator can prevent such malfunctions.
Ball valves are dependable and effective valves that are utilised in a wide range of industrial applications. However, they can experience issues or failures that result in diminished performance or safety risks.
Understanding the common issues with ball valves and their underlying causes can aid in preventing these problems and ensuring safe and effective operation. Regular maintenance, inspection, and testing can aid in identifying and resolving potential problems before they escalate into major issues.