Vessel or tank
A vessel, tank or drum: process equipment that holds liquid or gas. It is drawn as a tall rectangle with rounded ends.
How to read it
Tanks are among the major components that the DOE’s handbook on engineering prints names for every fluid system, with pumps, heat exchangers and fans. Kuphaldt’s Lessons In Industrial Instrumentation draws pressure vessels as rectangles with rounded ends, upright or lying on their side, and a jacketed vessel with a second outline around it. The DOE’s chart gives several shapes for a tank, including a rectangle with a peaked roof and a rectangle with rounded ends.
The name or number on the vessel says what it is. In the example process in Kuphaldt’s book, the knockout drum where vapour condenses has a level transmitter and a level valve on its bottom. The drawing shows how the vessel connects to the rest, not its size or place in the plant: the DOE’s handbook says P&IDs as a rule have no drawing scale.
Also searched as: drum symbol, tank symbol, vessel or tank p&id symbol, vessel or tank symbol.
This explains what a symbol represents on a diagram. Companies vary the symbols, and a diagram's own legend sheet takes precedence.
Look-alikes
A rounded rectangle with a zigzag inside it is one of the DOE’s alternatives for a heat exchanger, not a vessel.
Read next
- Next in P&ID symbolsField-mounted instrumentAn instrument mounted in the plant, out where the process is. It is drawn as a plain circle, the “bubble”, with the instrument’s tag inside.
- The same shape in Accessibility symbolsTTY symbolA telephone handset above a keyboard is the International Symbol of TTY. It marks a text telephone, a TTY, which lets people who are deaf, hard of hearing or speech impaired type a phone conversation.
More P&ID symbols
The same shape elsewhere
Browse symbols drawn with curves and waves or squares and rectangles.
Sources
- DOE Fundamentals Handbook: Engineering Symbology, Prints, and Drawings, Volume 1 of 2, DOE-HDBK-1016/1-93, January 1993, U.S. Department of Energy (University of Cambridge Engineering Department mirror), Module 2: Components (Figure 15); Fluid Power P&IDs
- Lessons In Industrial Instrumentation, Tony R. Kuphaldt, version 2.33, 2024 (CC BY 4.0), Tony R. Kuphaldt (ibiblio.org), 7.1 Process Flow Diagrams; 7.5.9 Process equipment
- P&ID General Information, Peter Woolf et al., Chemical Process Dynamics and Controls, section 4.1, Engineering LibreTexts, Section 4.1
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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