Process equipment symbols
A compressor is a trapezoid that narrows from suction to discharge. A heat exchanger is a circle with a zigzag through it. A filter is a body with a hatched or dashed line across the flow, a cyclone is a body with a cone and a tangential inlet, and an electric heater is a rectangle with a resistor zigzag inside. On an HMI the ones with a motor get running states; the passive ones show a measurement and an alarm badge.
In short
- Compressor: narrowing trapezoid + motor. Tag
C-101orK-101. Has running states. - Heat exchanger: circle + zigzag, or capsule + straight line. Tag
E-101. Passive, shows temperatures. - Filter: body + dashed line across the flow. Tag
F-101. Passive, shows differential pressure. - Cyclone: cone body + tangential inlet. Passive, discharges to a rotary valve.
- Mixer: vessel + shaft and paddle, or an in-line box with an X. Has running states.
- Heater: rectangle + resistor zigzag. On/off or modulating, alarm on over-temperature.
The common process equipment symbols
These are the pieces of equipment on a P&ID that are neither a pump, a valve nor a vessel. Each has an outline that says what it does to the fluid or the solid passing through:
Relatives of these: an air cooler is a rectangle with a fan circle on top, a plate exchanger is a rectangle with several vertical lines, a dryer is a horizontal cylinder with an inclined line for the drum, a screen is an inclined rectangle with a mesh, and a crusher is a trapezoid pointing down with jagged lines inside. Fans and blowers are covered in the pump guide, because they are drawn and behave like pumps for gas.
Reading each outline
Compressor
The trapezoid narrows in the direction of flow: gas comes in at the wide end and leaves at the narrow end at higher pressure. Reciprocating compressors are sometimes drawn as a cylinder with a piston bar instead. The driver sits next to it as a motor circle marked M, or as a turbine symbol on large machines. Around it you will find the air receiver (a horizontal vessel), an aftercooler (an exchanger) and a dryer. Tags are C-101 or K-101; the K comes from the German Kompressor and is common in petrochemical legends.
Heat exchanger
The generic circle-and-zigzag says "two fluids exchange heat here" without saying how. The shell-and-tube form is more literal: the capsule is the shell, the line through it is the tube bundle, and the two pairs of nozzles are the shell side and the tube side. Tags are E-101 or HX-101. The exchanger itself has no state; what the HMI shows is the four temperatures around it and the valve that controls one of the flows.
Filters, cyclones and dust collectors
A filter is a body with the element drawn across the flow, as a dashed, hatched or zigzag line. The only thing an operator needs from it is the differential pressure, PDT-101 or PDSH-101, which says how clogged it is. A bag filter adds vertical lines for the bags and usually a pulse-jet cleaning sequence driven by the PLC, which is a set of solenoid valves the HMI shows as a small row of indicators. A cyclone has no moving parts: gas enters tangentially, spins, drops the solids into the cone, and leaves through the top. Under the cone there is always a rotary valve or a gate, from the gate guide.
Mixers and heaters
A mixer in a vessel is a shaft with a paddle in an open tank, covered in the tank guide. An in-line mixer is a box with an X, static or motorised. An electric heater is a rectangle with a resistor zigzag; it is switched on and off by a contactor or modulated by a thyristor unit, and the thing that matters on the screen is the over-temperature trip, TSHH-101.
From P&ID glyph to live HMI object
Split the equipment into two groups and treat them differently on the screen:
| Group | Equipment | What the HMI object shows |
|---|---|---|
| Has a motor | Compressor, mixer, agitator, crusher, screen, fan | The motor states: stopped, running, no feedback, manual, fault. Plus load or speed as a number. |
| Passive | Heat exchanger, filter, cyclone, static mixer | Neutral gray outline that never changes. The values around it (temperatures, differential pressure) as numbers, and the alarm as a priority badge on the outline. |
| Heater | Electric or steam heater | On/off as a two-state object, or the control output as a percentage. Over-temperature as a badge. |
The temptation with passive equipment is to invent a state for it: a filter that turns orange when it is "dirty", an exchanger that turns blue when it is "cold". Resist it. The filter is not dirty, its differential pressure is high, and that is a rationalised alarm with a priority, shown in the badge. The outline stays gray and the calm palette survives.
Geometry varies by project legend
ISA-5.1 does not define equipment outlines. ISO 10628 gives the basic shapes above, and every engineering company adds detail in its legend sheet: the number of nozzles on an exchanger, whether a compressor is a trapezoid or a cylinder, how a filter element is hatched. Read the legend of the drawing set first, and treat these as the common, recognisable conventions.
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Open the builder → Browse community equipment symbols →Frequently asked questions
What is the P&ID symbol for a compressor?
A trapezoid that narrows from the suction side to the discharge side, showing the gas squeezed into a smaller volume, with a motor circle marked M beside it. Tagged C-101 or K-101.
What is the P&ID symbol for a heat exchanger?
The generic form is a circle with a zigzag through it for the tube bundle. A shell-and-tube exchanger is a horizontal capsule with a straight line through it and two nozzles per side; a plate exchanger is a rectangle with vertical lines. Tagged E-101 or HX-101.
What is the symbol for a cyclone?
A body with a cone at the bottom, the inlet entering tangentially at the top of the body and the clean gas leaving through a pipe on the top. The solids fall out of the cone into a rotary valve or a hopper.
Which process equipment gets running states on an HMI?
Anything with a motor: compressors, mixers, agitators, crushers and fans follow the motor state list. Exchangers, filters and cyclones are passive: they show a measurement, such as differential pressure or outlet temperature, with the alarm as a badge on a gray outline.
Where can I download process equipment symbols?
Browse the community library (Process) and download PNG or SVG with a free account, or draw the equipment in the Symbol Builder.
Keep reading
- P&ID pump symbols — pumps, fans and blowers, the compressor's relatives.
- Tank, silo and hopper symbols — the vessels around an exchanger or a cyclone.
- Gate, diverter and damper symbols — the rotary valve under a cyclone.
- Alarm management — why a dirty filter is an alarm, not a colour.
- Build your own symbols — free online editor.
- Ask the community — a piece of equipment your legend draws differently.