Valve Replacement: Screw-On Butterfly to Ball Valve - Sizing, Measurements, and Identifying Marks

Hello. I need to replace the screw-on butterfly valve because it leaks, I note that it is without the so-called choke, i.e. nothing more can be done with it anymore. I want to replace it with a ball valve, ie with a red wajchą. The pipes are to be screwed into it, i.e. it has internal threads. My only problem is to determine the size.
Is, for example, 1/2 inch the inner or outer diameter of the pipe? I need to unscrew the valve first to check it?
How do you call plumbers, you just enter the room and you know what size it is?
Do you have any way to measure it?
Or maybe there are some markings on the valve itself, how many inches? Some valves have a number of 15 or 20.
Immediately I say that it is not possible to unscrew the valve, go to the store with him and buy the same, it will be hard to do without water at home. Thanks in advance to the expert.

https://www.plumbingsupply.com/pipethreadsizing.html
http://www.stpats.com/manuals/MEP%20manuals/corkerNewManuals/NPTSizing.pdf

They are often marked as 3/8, 1/2 or 3/4 (the most common sizes).
Cal is 25.4 mm or the diameter of the thread (internal or external does not matter).
And from this we have: 3/8 inch to 9.5mm (found as under-counter valves for washbasins)
1/2 inch is 12.7 (valves for sinks, cisterns)
3/4 inch is 19mm (main valves before and after counters).
Drop in to the market / store and pick up 3 nipples or 3/8 1/2 3/4 muffs compare and catch what a camel.

Cool luuuz - dude just wants to recognize the thread, do not write a doctorate.

Slavko252 wrote:

Do you have any way to measure it?
Or maybe there are some markings on the valve itself, how many inches? Some valves have a number of 15 or 20.

Some valves are marked as: DN (nominal diameter), e.g.
DN15 = 1/2 "
DN20 = 3/4 "
DN25 = 1 "
or mark in inches.
The "DN" marking is not to be confused with the nominal pressure, i.e. "PN"

If there is no sign on the valve, it is best to measure "something" that is screwed into this valve: pipe, nipple - outside diameter. Go to the hydraulic store and explain where we measured the diameter. It should be remembered that the same thread marked in inches, eg 1/2 "measured inside the valve will be smaller in millimeters than the 1/2" thread measured with a measuring tape or a vernier caliper outside the pipe or nipple.

Measure the total length of the valve so that you can have enough space later.

Slavko252 wrote:

Is, for example, 1/2 inch the inner or outer diameter of the pipe? I need to unscrew the valve first to check it?
How do you call plumbers, you just enter the room and you know what size it is?
Do you have any way to measure it?
Or maybe there are some markings on the valve itself, how many inches? Some valves have a number of 15 or 20.

As already written, this dimension in inches is the inner diameter of the pipe (approximately) and not the diameter of the thread. Valves always (or almost always) have a size designation, but they can be in inches or in millimeters. 15 is the size of 1/2 ", 20 is 3/4". You have to write down the name on the old valve.

In this case, my valve is 1/2 inch, because it has a casting number of 15, the diameter of the pipe screwed into the valve is about 21-22mm, and its length is 6.1 cm. Thanks for help, gentlemen.