P&ID symbols explained
A Piping & Instrumentation Diagram (P&ID) is the detailed engineering drawing of a process: every vessel, pump, valve, instrument, line and control loop, drawn with a shared set of symbols. This guide walks through the main symbol families — what they mean, the standards behind them, and how to download or build them as PNG/SVG for your HMI.
The standards behind P&ID symbols
There is no single universal standard — a P&ID combines several:
- ANSI/ISA-5.1 — instrumentation symbols and identification: the instrument bubbles, tag letters and function blocks. This is the one HMI and control engineers reference most.
- ASME Y32.11 — graphic symbols for process flow diagrams (equipment and piping).
- ISO 10628 / ISO 14617 — the international equivalents for flow diagrams and graphical symbols.
In practice every project publishes a legend sheet that fixes which variant of each symbol the drawings use. The symbols in the HMI Library catalog follow the ISA-101 calm palette and ISA-5.1 conventions so they read consistently on an operator screen.
Equipment symbols
The big process items. On a P&ID these are simplified outlines; on an HMI they become multi-state objects (running, stopped, fault…).
- Pumps — a circle with a triangle/volute for centrifugal pumps; positive-displacement, vacuum, progressive-cavity and sump variants have their own outlines.
- Compressors & blowers — trapezoidal or circular bodies depending on type (centrifugal, reciprocating, rotary lobe).
- Motors & drives — a circle marked
M, often paired with a VFD block; reversible drives add direction arrows. - Tanks & vessels — rectangles, cylinders or spheres for atmospheric tanks, pressure vessels and bullets.
- Heat exchangers, columns, dryers, cyclones — process equipment with distinctive outlines.
Valve symbols
Valves are the most varied family on a P&ID. The body shows the valve type and the top shows the actuator:
- Gate, globe, ball, butterfly, needle valves — each has a distinct body symbol (the classic "bow-tie" with variations).
- Check valves — show flow direction; non-return.
- Control valves — a valve body topped by an actuator (diaphragm, piston, motor) and usually tagged
FCV,PCV,TCV… - Relief & safety valves (PSV/PRV) — spring-loaded outline; part of the safety family.
- 3-way and on/off valves for routing and isolation.
For a deeper look — every body type, actuators, fail-safe positions and tags — see the dedicated P&ID valve symbols guide.
Instrument symbols (ISA-5.1)
Instruments are drawn as a bubble (circle) carrying a tag. The bubble outline shows where the function lives:
| Bubble | Meaning |
|---|---|
| Plain circle | Field-mounted (local) instrument |
| Circle with a horizontal line | DCS / shared display, control room |
| Circle in a square (or diamond) | PLC / programmable logic function |
| Circle with a double line | Shared / auxiliary location |
The tag inside follows the XX-NNN format — first letter = measured variable, following letters = function, NNN = loop number. For the full letter-code table see our ISA-5.1 instrumentation symbols reference.
Line & connection symbols
Lines tie everything together, and their style encodes what flows:
- Process / pipe — solid line, the main material flow.
- Electrical — dashed line.
- Pneumatic signal — line with cross-hatches.
- Instrument / data signal — dotted or special-marked line.
- Capillary, hydraulic — their own conventions.
You can draw all of these — pipes, signal lines and flow arrows — directly in the Symbol Builder.
How to get P&ID symbols
Two practical options, both vendor-neutral (PNG + scalable SVG, ready for Weintek, WinCC, FactoryTalk, Ignition, Citect and AVEVA):
- Browse the catalog — 900+ ready-made ISA-compliant symbols. Filter by category, tweak the palette live, and export.
- Build your own — compose a symbol from shapes and catalog parts in the free online Symbol Builder.
Get P&ID symbols as PNG / SVG
Browse 900+ ISA-101 / ISA-5.1 symbols, or compose your own — free, no account.
Open the catalog → Open the builder →Frequently asked questions
What standard defines P&ID symbols?
Instrument and function symbols come from ISA-5.1. Equipment and piping symbols draw on ASME Y32.11, ISO 10628 and ISO 14617. Most plants combine them into a project legend sheet.
What is the difference between a P&ID and a PFD?
A PFD shows major equipment and main streams. A P&ID adds every valve, instrument, line size, tag and control loop — the detailed drawing used for construction and operation.
Where can I download P&ID symbols?
Browse and download 900+ ISA-compliant symbols as PNG or SVG from the HMI Library catalog, or compose your own in the Symbol Builder.
How do you read an instrument tag?
An ISA-5.1 tag is XX-NNN: first letter = measured variable (F, T, P, L…), following letters = function (I, C, T…), NNN = loop number. FCV-104 is a flow control valve on loop 104.
Keep reading
- ISA-5.1 instrumentation symbols reference — tag letters, modifiers, mounting bubbles.
- ISA-101 HMI design standard — calm color, alarm priorities, hierarchy.
- The 9 motor states every HMI should show.
- HMI / SCADA / P&ID glossary.