By Jim Newman
In the industrial world, valves are used to isolate or shut off systems. There are ball, gate, globe and plug valves, which are used for the majority of services. Other valve types, such as knife gate and pinch valves, have a much more specific application. For this discussion I will focus on the ball valve and why it is preferred.
Ball Valve Functionality
The ball valve is a simple device. It has a 90 degree operation and is easy to determine which position the valve is in: when the handle is cross line, the valve is closed; when the handle is in line, the valve is open. The 90 degree operation means there is no stem that rises and descends through rings of packing, which often drags whatever product is in the pipe up with the stem. The valve’s 90 degree operation allows for ease of automation with either electric or pneumatic actuators. Ball valves also have an inherent low pressure drop and offer bubble-tight shutoff. While primarily considered as on/off valves, ball valves can be used in throttling service by using coated balls and hard seats. Ball valves are also considered to be downstream sealing, as they utilize the system pressure to push the ball into the downstream seat to achieve their shutoff. There are exceptions to this, but generally this is the case.
Basic Ball Valve Designs
There are three basic ball valve designs:
- One piece body. This is usually referred to as a throw-away or non-repairable valve and requires a valve union or break point to remove the valve when the time comes.
- Two piece body. This is considered a repairable valve, but it still needs a pipe union to facilitate the repair.
- Three piece valve. This is considered a fully repairable valve without removing the valve from the system. Removing three of the four valve body bolts and loosening the fourth allows for the valve body to swing out the line and the internal components to be replaced. These internal components would be the seats and seals available in Teflon, reinforced Teflon, Buna, Viton, carbon-filled Teflon, along with other composite seats or sintered metal seats, depending on the service.
All of the valves above are available in brass, carbon steel, various grades of stainless steel and other alloys. They are available in threaded connections, welded ends, flanged and specialty connections.
Ball Valve Cautions
Ball valves, by design, can trap pressure in the ball cavity while in the closed position, so care should be taken while disassembling a ball valve. This would include cycling the valve from closed to open before servicing, and in the case of the three piece valve, the ball needs to be in the open position to swing the center out.
The ball valve may not be the least expensive option at the initial price, but after factoring in its life cycle, pressure drop, dependability and easy maintenance, it is a very cost-effective choice. Contact your IPEG representative to see if the ball valve is the best solution for your application.