Ball valve bore constriction

[RogerJolly]

Are the various ball valves makes similar in terms of the actual bore size you get - looks like you typically get a smaller hole through the ball - maybe (eg) 1 1/4 inches, rather than the full 1 1/2 ?

For the drain of a gravity holding tank, is it a factor? There doesn't seem to be much made of this issue, so maybe it's just me.

Many thanks.

 

[VicS]

You need a "full bore" valve.

Reduced bore valves also exist

For example

from ASAP's website

Maestrini ball valve constructed from de-zincification resistant CW602N CR brass. This ball valve is suitable for hot or cold water, steam, gasoline, fuel, oil, gas oil, kerosene and compressed air and can be used for sea water inlets and outlets. These ball valves are threaded 1½" BSP Female each end and have a lever handle on top which requires a 1/4 turn for on/off action. DZR CR ball valves are full bore meaning no restriction to flow when fully opened.
This ball valve features a CW602N DZR CR brass body and ball, as well as a stainless steel lever handle.

 

[Tranona]

Normal DZR valves are fine. Never had a problem with them on gravity tanks. If it is a dedicated drain - that is not taking the direct pumpout as well - then a 2" valve would be good. However, they are enormous and difficult to find space in a typical installation.