One, Two, or Three Piece Ball Valve?

Examples of one, two, and three piece ball valves.
Image courtesy Duravalve

Ball valves are employed throughout many commercial, institutional, and industrial venues where the need to isolate part of a system is necessary, or even just to regulate the on/off condition of system fluid flow. The product variants are almost uncountable, with a version to accommodate almost any application.

When selecting a ball valve, one facet of construction will be evident in your research. There are three common types of ball valve construction; one piece, two piece, and three piece. Here are some general considerations and differences among the three types.

• A one piece ball valve has a body and end connections formed from a single piece of material. This construction presents a comparatively reduced number of opportunities for leakage. The valve trim and seals are inserted through one of the end connections. This type of valve will not have a port size equal to the line size. The simplicity of the one piece body design tends to make their cost lower than the other versions. Once the valve is in place, it cannot be serviced without removing the entire valve assembly from the piping system.
• Two piece ball valves generally have one piece that includes an end connection and the body, plus a second piece that fits into the first that will hold the trim in place and provide the second end connection. The construction presents an additional leak potential where the two pieces are joined, but also allows disassembly of the valve for replacement of the internals. These valves can provide full port service and bidirectional flow shutoff.
• A three piece ball valve essentially separates the connection portions of the valve assembly from the body of the valve. These will be more expensive than either of the other two types, but their allowance for removing the valve body and trim from the piping system while leaving the connections in place may prove valuable for many applications. Full port and bidirectional shutoff can be provided by this construction.

Properly applied, all these valves will provide good service. Your selection depends on the demands of the application. Share your fluid measurement and control requirements and challenges with process control specialists, leveraging your own knowledge and experience with their product application expertise to develop effective solutions.

Understanding Instrument Valves

Gauge Root Valve, a type of
instrument valve
Courtesy Mac-Weld

Process measurement and control employs a wide array of gauges and instruments that may be permanently or temporarily connected to a piping system. Providing controlled isolation and connection of these instruments is the function of what are generically referred to as "instrument valves" or "gauge valves". These valves are generally small, with connection sizes ranging from 1/8" to 1", though there are specialty variants outside this range. The predominant valve type is a needle valve, but ball valves and some other types are also used. Certain attributes of particular applications may weight a selection decision toward a valve type. Widely used throughout the process industries, instrument valves are often designed to accommodate pressures as high as 6000 PSI and are intended for service with gaseous or liquid service.

When selecting an instrument valve, consider construction materials that are compatible with the process media. Additionally, operating temperature and pressure of the process must be well within the limits of the valve.

Instrument needle valves provide reliable function to throttle, regulate and isolate gaseous and aggressive non-viscous liquid services. Product offerings range from simple two-way isolation valves to multiport gauge root valves providing multifunction capability to isolate, calibrate and vent gauge, pressure switches and static instrument applications. Ball valves in this class do not provide the throttling accuracy of a needle valve, but may provide some advantage with the use of certain media. The ball valve design, with its full size port, enables easier cleaning and a lessened potential for clogging.

There are three basic configurations of instrument valves. The simplest is the isolation valve with a single inlet and outlet. It provides for selection of exposure or isolation of a connected gauge or other device to the operating process piping or vessel. Maintenance or replacement of the connected device can be effected without opening the contained process to the surrounding environment.

Schematic representation of isolation valve

A second variant of instrument valves performs the function of an isolation valve, but has an added port on the outlet side (the side where a gauge or instrument would be connected). The added function of the port is to provide connection access for service, calibration, sampling, purging, or a host of other tasks, all of which can be completed while the process remains in operation.

Schematic representation of block and bleed valve

The third form of instrument valve is a multi-port valve with a single inlet and three outlets. It is often called a "gauge root valve" and serves a number of purposes with its multiple outlet connections. Sometimes two of the ports will be plugged and the instrument or gauge connected to the port providing the most convenient or functional orientation of the connected gauge or the valve handle. This valve can also enable a wide variety of applications through connection of additional instruments, gauges, valves, or other equipment.

Schematic representation of gauge root valve

Share your process measurement and control instrumentation and gauge challenges with application experts and benefit from their expertise.