Originally Posted by toolmaker03
yes, but he is not using a impeller type of mechanical flow meter, the style he is using is the weighted style, and they react a little more differently than the rotary style of flow meter, when it comes to what kind of build they require to be piped to them.
that is why one can get this style of flow meter made for all of the different sizes in tubing, so that one can get the correct mechanical flow meter, for the type of build that it will be functioning within.
These are called a rotameter.
They are actually not that fussy on what tubing size is run up to them.
How they work is that the conical taper inside the meter is of a known entity. the float itself is designed for a fluid with a known specific gravity (usually they are calibrated at SG=1 which is the same for distilled water).
The float will move upwards a certain amount for a given flow rate irrespective of pressure and whatever is connected to it. All the fluid volume must traverse through the flow meter similar to the rotary mech type [ie. all the fluid must pass through the all important measuring section]. As we know the internal conical taper dimensions we can then scale it accordingly.
It will not matter whether you have a 1" or 1/4" inlet as the flow is measured internally by the device [conical tapered section is obviously the measuring bit] everything past the conical section is sort of superfluous.
Rotameters also have excellent linearity. One advantage of a rotameter is that their restriction is extremely low and the best part is that as the fluid flow rate increases their restriction stays fairly constant (unlike most other flow meters) as the gap between the float and the conical taper walls increases at the same time.
Here is one of mine which I use - has an inbuilt valve which can be handy simulating restrictions or simply to restrict flow etc.....Edited by Costas - 1/25/16 at 1:37am