This is another question that you might not have a lot of input into, but bears consideration in certain circumstances. Like thread size, the flow restrictions of many valves will be pre-determined by their function. That is especially true of control valves, which limit flow by design.
And although you may have the full, standard and reduced port options on other valve types, the most common place you will run into this is in ball valves. Since there aren’t really any twists and turns in most ball valve designs, ball valves have the potential for unobstructed flow.
That is only true with full port valves, however. That’s what full port – sometimes called “full bore” - means. The opening in a full port ball valve’s center is the same, or very nearly the same, as the pipe connection size. A good rule of thumb is that full port valves are a minimum of 90% full size.
You can compare that with standard port size – also known as “standard bore” - which reduces the center ball size by about one NPT pipe size. An informal survey of the industry shows that standard port valves are usually 75%-90% of full size.
Some manufacturers offer valves with an even smaller bore size, usually listed as “reduced port”. These valves can be less than 75% of full size and are used mostly as backups or secondary valves. They can serve well in those roles, but in instances like the ones outlined below, you really need to go with a full port valve.
Full port valves are usually more expensive than standard and reduced port valves, but they offer better flow rates and less potential for prohibitive chemical buildup along internal edges. Full port valves also minimize the chance for cavitation.
Cavitation happens when tiny bubbles, or “cavities,” form in the process material and then implode from the pressure inside the valve. That implosion causes a shockwave which can be noisy and cause major damage to the valve over time.
The bubbles are produced as a result of going from a higher speed flow area (such as the narrower area of a standard port valve) into an area of slower flow (when the valve opens back into the regular pipe size). Because full port valves do not have that internal change in flow rate, are less likely to cause cavitation.
However, in most applications where full flow is not a major concern, standard port valves work just as well. It depends on the material being transported and the flow rate. Dense, pure liquids with high surface tension and transported at higher speeds are more likely to produce cavitation. They would benefit from full flow, whereas less viscous liquids moving at a slower rate would be fine in a standard port or reduced port valve.