ORIFICE PLATE
The orifice plate is one in a group known as head loss devices or
differential pressure flowmeters. In simple terms the pipeline fluid is
passed through a restriction, and the pressure differential is measured
across that restriction. Based
on the
work of Daniel Bernoulli in 1738 (see Tutorial 4.2), the relationship
between the velocity of fluid passing through the orifice is
proportional to the square root of the pressure loss across it. Other
flowmeters in the differential pressure group include venturis and
nozzles.
With an orifice plate flowmeter, the restriction is in the form of a plate which has a hole concentric with the pipeline. This is referred to as the primary element.
To measure the differential pressure when the fluid is flowing, connections are made from the upstream and downstream pressure tappings, to a secondary device known as a DP (Differential Pressure) cell.
From the DP cell, the information may be fed to a simple flow indicator, or to a flow computer along with temperature and/or pressure data, which enables the system to compensate for changes in fluid density.
In horizontal lines carrying vapours, water (or condensate) can build up against the upstream face of the orifice. To prevent this, a drain hole may be drilled in the plate at the bottom of the pipe. Clearly, the effect of this must be taken into account when the orifice plate dimensions are determined.
Correct sizing and installation of orifice plates is absolutely essential, and is well documented in the International Standard .
With an orifice plate flowmeter, the restriction is in the form of a plate which has a hole concentric with the pipeline. This is referred to as the primary element.
To measure the differential pressure when the fluid is flowing, connections are made from the upstream and downstream pressure tappings, to a secondary device known as a DP (Differential Pressure) cell.
From the DP cell, the information may be fed to a simple flow indicator, or to a flow computer along with temperature and/or pressure data, which enables the system to compensate for changes in fluid density.
In horizontal lines carrying vapours, water (or condensate) can build up against the upstream face of the orifice. To prevent this, a drain hole may be drilled in the plate at the bottom of the pipe. Clearly, the effect of this must be taken into account when the orifice plate dimensions are determined.
Correct sizing and installation of orifice plates is absolutely essential, and is well documented in the International Standard .
