1. The orifice plate can easily be changed to accomodate
widely different flow rates, whereas the throat diameter of
a venturi is fixed, so that its range of flow rates is
circumscribed by the practical limits of Dp.
2. The orifice meter has a large permanent loss of
pressure because of the presence of eddies on the downstream
side of the orifice-plate; the shape of the venturi meter
prevents the formation os these eddies and greatly reduces
the permanent loss.
3. The orifice is cheap and easy to install. The venturi
meter is expensive, as it must be carefully proportioned and
fabricated. A home made orifice is often entirely
satisfactory, whereas a venturi meter is practically always
purchased from an instrument dealer.
4. On the other hand, the head lost in the orifice for
the same conditions as in the venturi is many times greater.
The power lost is proportionally greater, and, when an
orifice is inserted in a line carrying fluid continuously
over long periods of time, the cost of the power may be out
of all proportion to the saving in first cost. Orifices are
therefore best used for testing purposes or other cases
where the power lost is not a factor, as in steam lines.
5. However, in spite of considerations of power loss,
orifices are widely used, partly because of their greater
flexibility, because installing a new orifice plate with a
different opening is a simpler matter. The venturi meter can
not be so altered. Venturi meters are used only for
6. It should be noted that for a given pipe diameter and
a given diameter of orifice opening or venturi throat, the
reading of the venturi meter for a given velocity is to the
reading of the orifice as (0.61/0.98)2, or 1:2.58.(i.e.
orifice meter will show higher manometer reading for a given
velocity than venturi meter).
1.The major difference between venturi and orifice meter is the time taken for water collection in measuring tank (size of tank minimum 60 ltrs )is more in venturimeter when compared with orificemeter.
2.The cost of venturimeter is very high compared with orificemeter.
3.The cofficient of discharge is more in venturi than in orificemeter.
AN VENTURIMETER IS AN ONE IN WHICH CONSISTING
OF DIVERGENT&CONVERGENT PORTION IN THE INLET & OUTLET
WHEREAS AN ORIFICE VENTURIMETER IS AN ONE IN
WHICH CONSISTING OF INLET&OUTLET TO BE SAME WITH
CIRCULAR THROAT AT THE CENTER
THE DISCHARGE OF AN ORIFICEMETER IS ALWAYS HIGHER
THAN THE VENTURIMETER