I just couldn't find my old school books about the orifice plates, so please help me with this topic, we have several orifice plates here at the mill, and when we took them of from the line, they were installed in different way each of them. What is the proper installation for a orifice plate? the orientation of the sharp side? (upstream or downstream), and the little hole in the plate, what is that use for? what is its right position, to the top or bottom of the pipe?
Normally the sharp edge is facing upstream. The holes are for draining or venting. Normally, if it is a gas, it is at the bottom and if it is a
liquid it is at the top.
William(Bill) L. Mostia, Jr. P.E.
Worldwide Excellence in Dependable Automation
These opinions are my own and are offered on the basis of Caveat Emptor.
The sharp-edge is always upstream (inlet to the orifice). the weep hole when at the bottem is to allow condensate to pass when the process fluid is wet gas or wet steam. The weep hole when in the top is to allow small quantities of entrained gas or air to pass when the process fluid is liquid.
Remember..these weep hole are typically added to the orifice plate when installed in horizontal lines.
Per Daniel, the weep hole is added to correct for the orifice diamieter. If they come with a weep hole, this causes velosity provile problems in gas measurement and thus changes the uncertinty (Error) of the installation. The company I work for will reject the weep hole. We have installed drain valves in the bottom of our Sr. Orifice fittings to remove liquids that accumulate.
Do we ask for the weep hole/vent hole when we order an orifice plate or do they come as part of a standard order even if customer didn't ask for it?
Orifice plates should have a data tag attached, and this tag should have the data stamped on to the upstrteam face.
The sharp edge goes upstream - unless you have a quadrant-edged plate for high viscosity, when the rounded edge goes upstream. The little hole allows vapour or gases (in liquids) or entrained liquids (in gas/vapour) to flow through the plate, and its orientation depends on the service - at the top for liquids where there may be some gas, and at the bottom for gases where there may be some liquids.
Normally for orifice plates sharp edge is always on the upstream side. However, if you use a Quarter circle or conical entrance orifice plate then the rounded edge or conical entrance should be at the upstream side. Quarter circle or conicale entrance type orifice plates are used for high viscous or low Reynold's no. applications.
The small hole in the plate is known as "weep hole". It is basically a drain/vent hole. For liquid applications in horizontal line you need a vent hole at the top of the pipe to pass away the entrapped gas in the fluid. For gas measurement application you need a drain hole at the bottom of the pipe to pass through condensate or liquid carried in the gas. If the pipeline is vertical then weephole is not needed.
I wrote a small post including original pictures from Foxboro Co. which shows the correct way to install an orifice plate depending on pipe position and kind of fluid.
Please, have a look!