Annubar & OP Flowmeter


Thread Starter


Hi Everyone,
Do you have an experience with Annubar or Orifice Plate Flowmeters to measure steam line? Does this type of flowmeter be able to measure reverse flow and how about the accuracy...? My understanding was, when the reverse flow phenomena happen, the high pressure line connected to the LP line of flowmeter and vice versa and probably the result is minus DP on the flowmeter. Please share your experience

An orifice or Annubar can measure both direction.
The orifice has normally conical outlet, and will give a low reading with reverse flow.
But you can use an orifice without conical outlet, but then you will have reduced performance, but same in both directions. An Annubar on the other hand that has the diamond shape (model 585) is truly bi-directional.
In both cases though, you will need to have two dp-transmitters, one for each direction, because as you mention, with reverse flow the dp produced will be opposite/negative.
Just picking a nit. An "Annubar" refers to a proprietary product of Emerson Process Management. Not to disparage the fine people there, but the generic term "multiple port pitot tube flow meter" while longer and harder to say, accurately defines a flow meter type in a market where at least five companies make essentially similar devices. Almost all of them will give you essentially the same results.

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Rohit Chandak

The bi-directional capability of ANNUBAR or Averaging Pitot Tube is defined by their design. All Averaging Pitot Tube can't be bidirectional. Few vendors recommend using two sensors one to see one direction & other to see another direction this will give much better accuracy but at this point you should perfectly evaluate the money being spent & importance of the same in your measurement. Diamond II is a perfect bidirection ANNUBAR but I believe Dieterich (Emerson) has stopped manufacturing it & moved to 485 & 285 which are not bi-directional flow sensors.

As suggested one should use two DP Transmitter to see unidirectional flow metering & should have a program built on Flow Computer or DCS to cut off one transmitter to switch to other & vice versa based on the direction of flow. If the flow metering is not critical while one direction dominates other & your team understands that -ve values show opposite direction that holds good but not a good engineering practice.