Three process connections out of One Ventury Tube?

[pkera]

Three process connections out of One Ventury Tube?

I have to use a 2oo3 implementation for flow measurement from a ventury tube.
So three transmitters have to be somehow process-connected to the ventury tube.
So long I have seen double-tapped orifices with two available process connection. The way 2oo3 was implemented was one process conn. to one transmitter, and the other one splitted to the two others. I'm not quite sure if this is a proper 2oo3 implementation but anyway:

A. Are there any options so that ventury tubes can have more than one process connection?
B. If not, is it ok to split one process connection to three transmitters for 2oo3?

Thanks

[LostTrolley]

For high accuracy and high integrity applications it is common practice to connect multiple transmitters to a single pair of DP tappings. In the case of high accuracy, DP transmitters with different ranges may be connected to provide accurate indication over a wide range of flow. In the case of high integrity, multiple transmitters with the same range may be connected. It is also usual for a pressure transmitter, if present, to share one of the tappings, and in high-end applications the downstream tapping may also form part of the density loop. In a high-integrity application, you will probably want to fit valve manifolds to enable the transmitters to be tested periodically in order to maintain integrity. It is part of the 2oo3 concept that one device can be tested without tripping the safety loop, so each transmitter should have its own manifold.

You are right that orifice carriers for high-end applications usually come with dual pressure tappings, one to either side of the horizontal. Given that the tappings must be the proper distance from the plate measured along the tube, this is the maximum number possible within the constraint that they should to the sides. However, these double tappings are provided for the convenience of being able to install instruments on the side that gives best maintenance access, not to enable instruments to be installed on both sides. The unused tappings are blanked.

[pkera]

Let's say you're right about gases and clean liquids. But what about slurry and dirty services? If you have three Txs process connections out of one set of taps (orifice or Ventury in my case) then what if the tap stucks? Then you lose all of your transmitters and the 2oo3 is useless.

In that sense using both set of taps in an orifice seems a good practice.

Any thoughts?

[LostTrolley]

Let's say you're right about gases and clean liquids. But what about slurry and dirty services? If you have three Txs process connections out of one set of taps (orifice or Ventury in my case) then what if the tap stucks? Then you lose all of your transmitters and the 2oo3 is useless.

In that sense using both set of taps in an orifice seems a good practice.

Any thoughts?

If there is enough solid content to plug one tapping there will be enough to plug all of them. So I think answer in your case is that a Venturi or any other kind of meter that has tappings that can plug is the wrong choice. However, perhaps your choice is driven by difficulties in finding a more suitable flow meter that has any kind of SIL rating. Did you try??

A clamp-on ultrasonic meter would be the most obvious kind for this kind of application in general applications if you are not looking for great accuracy. A Coriolis meter would be more accurate, but very expensive if the line size is large. For something that is not much more than a flow switch, you could consider a target meter - or more than one - and this kind is simple enough to stand a chance of getting a SIL rating.