Let's say you have two pumps, one always running and the other in reserve. Maybe they're switched regularly, or maybe the other is only used when the first is broken/down for maintenance.

In a P&ID, drawn after ISO standards, will the reserve equiptment and/or the label of the reserve, equiptment be shown? I see a few different possibilities:

  1. Only one pump is shown, perhaps labelled with the label of the pump that was first installed. Nothing else.
  2. Only one pump is shown, but it is labeled "Pump x/x + 1/x + 2/..."
  3. All pumps are shown, with some kind of symbolization shown that the other pump(s) are not operating when one pump is operating. In the case of the reserve pumps only being used when the primary pump is down, this can easily be shown with normally-closed valves on the process lines going from the reserve pumps. In the case of periodic switching however, where there is no main pump, I have no idea how this is to be shown.
  • 1
    $\begingroup$ is it permanenty installed? I would expect all the piping (and pumps) to be shown. It's the P part. Parallel pumps are everywhere in industry, only 1 running at a time. $\endgroup$
    – Tiger Guy
    Jun 11, 2022 at 1:09
  • $\begingroup$ A drawing that does not reflect physical reality is useless. $\endgroup$ Jun 11, 2022 at 5:13
  • $\begingroup$ @StainlessSteelRat So that rules out no. 1? $\endgroup$
    – user110391
    Jun 11, 2022 at 14:29

2 Answers 2


From ISO 10628-1 Diagrams for the chemical and petrochemical industry — Part 1: Specification of diagrams

4.4 Piping and instrumentation diagrams (P&ID)

All equipment, valves, and fittings shall be represented in accordance with ISO 10628-2.

4.4.2 Basic information

The piping and instrumentation diagram shall contain at least the following information:

a) function and type of equipment and machinery, including drives, conveyors, and installed back-up/reserve equipment;

Essentially, P&ID are the most detailed. That document is a good read because it talks about different types of diagrams AND has examples.


A P&ID should reflect reality

A P&ID that doens't reflect the actual piping construction is a flowchart, not a P&ID. P&ID's are used to determine valve lockout and blind flange insertions for maintenance. I would consider this actionable against the creator if someone were injured because lockouts/blind flanges failed to protect a worker due to use of a mis-drawn P&ID. Here is the standard (ISO or not) that matters: show all pipes and valves. The lines matter more than the symbols.

A simplified P&ID would be terrible. Huge industries are put on these diagrams, they don't need to be simplified. They need to be accurate. Make more pages if it's too complex.

In summary, don't do this. If you do, don't consider it an engineering effort, it's graphic arts.


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