Fixture Units don't Update

I read a post at RFO that said the value for Fixture Units added up along a pipe run were correct at the pipe (in properties) but that tags attached to those pipes did not report a matching value. My first thought was that the system's Calculations parameter was assigned to something other than Flow. So I mocked up a quick test (using version 18.1.1.18 - 20170907_2315(x64) - 2018.1.1). Three families, two with the same Fixture Units assigned and one rogue.

I changed the middle fixture to be the same as the outer two and the pipe properties responded, the tag didn't (2nd from left). I took a look at the Calculations parameter for the Sanitary Piping System. This is using a stock Imperial Plumbing template. It's already set to Flow.

I switched it to None, clicked Apply, and the tags responded with this (Performance does the same).

I changed it back to Flow, clicked Apply, and the tags responded again but now they report the correct values.

I thought that there might have been a subtle change within the Mechanical and/or Piping settings that I missed when Revit 2018 arrived. I don't think there is though.

If you're counting on Fixture Units being added up and reported correctly in tags, you'll need to keep an eye on this. I've been able to wake up the tags by toggling between Calculation Settings for the Pipe System.

Added: Temporarily adding a pipe or altering the connected pipes also cause the tags to wake up. Also, just to make things stranger, changing the fixtures again I find the information displayed in properties of the pipe does not respond either, nor does a schedule of Pipes. However, if I have a Piping Systems schedule that does update as changes to fixtures are made.

Revit 2016 - Piping Units Addition

Plumbing engineers must feel a bit like Rodney Dangerfield's "I'm tellin' you, I don't get no respect!". Here's one for them, subtle though it may be. We can specify Liters per minute (L/min) for piping project units. (woot)

One Minute with a Pipe Trap

Placing a pipe trap can be counter-intuitive or maybe just awkward until you "know how". The pipe trap family is built with the origin at the vertical or riser connection. That means you need to attach it to the bottom of a riser, the bottom of the pipe that is leaving a sink for example. Want to watch? It's just about a minute...

If you'd like to avoid placing pipe traps entirely you can consider incorporating them into plumbing fixture families that use them. Just do all the subtle plumbing work under the counter in the family and put the connectors at the wall face. I wrote a post that discusses the concept of rough-in families if you're interested. These are the links:

First mention of Rough-in Families
Follow Up Post