Tank, vessel, silo and hopper symbols
An atmospheric tank is a plain rectangle. A pressure vessel has rounded ends, vertical for a column or drum, horizontal for a bullet or separator. A silo or hopper is a body with a cone at the bottom. On a P&ID the outline is static; on an HMI the same outline holds a level bar that follows the transmitter, with the alarm shown as a badge, never as a colour change of the liquid.
In short
- Tank: rectangle, flat or domed roof. Tag
T-101orTK-101. - Vessel: capsule with rounded ends, vertical or horizontal. Tag
V-101orD-101. - Silo / hopper: body with a cone bottom, gate or feeder at the outlet.
- HMI: neutral level bar + numeric value + tick marks for the limits; alarm as a badge.
- Instruments:
LT,LSH,LSL,LSHH;PTandPSVon pressure vessels.
The common tank and vessel symbols
Vessels are the largest glyphs on a drawing and the ones operators look at most, because the level in them is what the plant is really doing. Each type is recognised by its outline:
Other vessels reuse these bodies with a detail: a jacketed vessel has a second outline around the lower half, a column is a tall capsule with horizontal tray lines, a bag filter or cyclone is a body with a cone but belongs with the process equipment, and a sump is a rectangle drawn below the ground line.
Reading a vessel symbol
Square corners mean atmospheric: the vessel is vented and holds no pressure, so the wall does not need to be curved. Rounded ends mean pressure: the dished heads that hold pressure are drawn as they are built. A cone at the bottom means the contents are a solid that has to flow out by gravity. Nozzles are short lines leaving the outline; the inlet is usually at the top, the outlet at the bottom, and an overflow near the top edge. Tag letters follow the plant convention rather than ISA-5.1: T or TK for tanks, V or D (drum) for vessels, S for silos, H for hoppers, R for reactors.
Instruments around a tank
The vessel itself is passive; the ISA-5.1 bubbles around it are what the HMI actually displays:
LT-101: level transmitter, the continuous value the bar follows. Radar, ultrasonic, hydrostatic or load cells on a silo.LSH-101/LSL-101: level switches, high and low. The alarm limits.LSHH-101: high-high switch, the independent overfill trip that stops the inlet pump.TT-101: temperature, on heated or jacketed tanks.PT-101andPSV-101: pressure transmitter and safety valve, on any pressure vessel, drawn on the top head.WT-101: weight, when a silo sits on load cells instead of using a level probe.
From P&ID glyph to live HMI object
A tank has no motor, so it has no running state. What it shows is a quantity, and the ISA-101 way to show a quantity is a bar with context, not a colour:
| Element | How to draw it | Why |
|---|---|---|
| Level bar | Light gray or a muted blue inside the outline | Neutral fill keeps the screen calm; height carries the information. |
| Numeric value | 62.4 % or 1 250 L next to the bar | The bar shows trend at a glance, the number gives the exact value. |
| Limit ticks | Thin marks at the LSH and LSL heights | The operator sees how far from the alarm the level is, before it trips. |
| Alarm | Priority badge on the outline | Colour appears only when something is wrong, and says how urgent. |
| Bad quality | Bar hatched or hidden, value replaced by ??? | A frozen bar looks like a valid reading; a broken transmitter must look broken. |
Two habits to avoid. First, painting the liquid in its "real" colour: blue water, brown sludge, yellow oil. It looks pretty in the demo and turns the screen into a colouring book where the one red thing that matters gets lost. Second, changing the bar to red when the level is high: the alarm belongs in the badge, the bar keeps its neutral tone. In the Symbol Builder the badge is a separate element that shows only in the alarm states, so the tank outline stays the same in every state.
Silos and hoppers on the screen
For solids the level is often a set of point switches rather than a continuous transmitter: LSH full, LSL empty, sometimes a middle one. Show them as three discrete marks on the silo outline that fill when made, and add the weight from the load cells if there are any. The gate or feeder at the cone is its own object, with the states from the gate guide.
Geometry varies by project legend
ISA-5.1 does not define vessels, so the outlines come from ISO 10628 and the company legend sheet. Some legends draw every tank as a rectangle, some add the roof shape, some draw silos as cylinders with an elliptical top. Read the legend of the drawing set first and match its proportions when you draw your own.
Browse by category
Jump into the community library for the families on this page, or draw the set yourself:
Get tank symbols as PNG / SVG
Browse the tank and silo symbols published in the community library (CC BY 4.0) and download with a free account, 5 a month on Free, or draw a tank with a level bar and alarm badge in the builder. The builder is free to use, no account needed.
Open the builder → Browse community tank symbols →Frequently asked questions
What is the P&ID symbol for a tank?
An atmospheric tank is a plain rectangle, sometimes with a flat or domed roof line. A pressure vessel has rounded ends, vertical for a column or drum and horizontal for a bullet or separator. A silo or hopper has a cone at the bottom. Tags are T-101 for a tank, V-101 for a vessel, S-101 or H-101 for a silo or hopper.
How do you show tank level on an HMI?
A vertical bar inside the outline whose height follows the level transmitter, in a neutral tone, with the numeric value and unit next to it. The high and low limits are thin tick marks on the bar; the alarm itself is a priority-coloured badge on the tank, not a colour change of the liquid.
What is the difference between a silo and a hopper symbol?
Both have a cone at the bottom. A silo is drawn taller than it is wide and stores material for hours or days. A hopper is wider than it is tall and holds material briefly before a feeder or a gate.
Which instruments go on a tank?
LT for the continuous level, LSH and LSL for the high and low alarms, LSHH for the overfill trip, often TT for temperature. Pressure vessels add PT and a PSV on the top head. See the instrument symbols guide.
Where can I download tank symbols?
Browse the community library (Tanks) and download PNG or SVG with a free account, or draw one with a level bar in the Symbol Builder.
Keep reading
- Instrument symbols — the LT, LSH and PSV bubbles on a vessel.
- Gate, diverter and damper symbols — what discharges a silo.
- Process equipment symbols — heat exchangers, filters, cyclones and compressors.
- The calm HMI colour palette — why the level bar is gray.
- Build your own symbols — free online editor.
- Ask the community — a vessel your legend draws differently.