I understand the difference in regards to price (most homeowners are cheap), body size (a full port might not be viable in tight spaces), and physical design (inlet/outlet size difference) between a standard and full port ball valve but why do both exist?

If I am running a 3/4 inch plumbing trunk and put a standard ball valve on it then am I actually reducing the water pressure/volume/flow rate?

When is the right time to use one over the other?

Do the same considerations exist for both water and gas applications?

1 Answer 1


Full port valve provide a flow diameter that is the same as the inlet/outlet ports. So, for example a 3/4" full port will be 3/4" throughout.

A "standard" does NOT provide that and a 3/4" standard has a flow diameter restriction of something less than 3/4". Likely closer to 1/2".

Why use one over the other? Full port costs more and takes up more space and offers little benefit for many applications. So unless you have a specific need, chances are that the standard valve will be just fine.

If you have concerns about the flow or it's a relatively high-flow line then use a full port.

Generally the same principles apply to any fluid, water or gas, but gas is a compressible flow and is affected somewhat less. Gas, at least as used in homes, rarely flows at a rate comparable to water. But in some cases it may be needed to use full port.

Knowing when to use one vs. the other is not always obvious. This is why engineers go to college for 4 years or plumbers apprentice for several years.

  • You mentioned "So unless you have a specific need"; what is an example of a specific need? Becoming aware of what is a specific need is the entire premise of my question or at least how judge if my need is specific. Is it safe to say that for the average residential application a full port valve should be used as a main shutoff and standard everywhere else?
    – MonkeyZeus
    Sep 14, 2020 at 17:00
  • If you have a use for a higher than normal flow rate, that would be a "specific need". Only you know what you need here.
    – jwh20
    Sep 14, 2020 at 17:03
  • So if I want to be able to flush a toilet, wash my hands, and not interrupt the flow rate for someone washing dishes then a full-port would solve the issue?
    – MonkeyZeus
    Sep 14, 2020 at 17:11
  • ...that depends on where the pressure drop is coming from. If it's not the valve, won't make a bit of difference.
    – Ecnerwal
    Sep 14, 2020 at 23:33

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