Instrumentation Valve Symbols: P&ID & ISA 5.1 Reference Guide

Instrumentation valve symbols are the standardized graphics on Piping & Instrumentation Diagrams (P&IDs) that show a valve's type, actuation and fail state. Most trace back to a common valve body, two triangles meeting at a point, modified to identify a needle, ball, check, relief, diaphragm or manifold valve. This guide reads each P&ID valve symbol, explains what it means, and shows how open/closed states and actuation get marked. It also pairs every symbol with the real instrumentation valve it represents.

On this page, "needle valve" refers to an instrumentation needle valve used for flow metering and isolation on gauge, sampling and impulse lines. It isn't a carburetor needle. "Ball valve" means an instrumentation ball valve, not a plumbing valve. And "manifold" refers to a 2, 3 or 5-valve instrument manifold, not an exhaust manifold or a PEX manifold. The symbol descriptions below track the published ISA-5.1 / P&ID convention, cited here as a reference standard.

Reviewed by the Crestflo Engineering Team

Also Known As: P&ID Valve Symbols, Instrument Symbols & Valve Legend Designations

These graphics go by a lot of different names on drawings and in standards. People call instrumentation valve symbols P&ID valve symbols, PID valve symbols, process valve symbols, instrument valve symbols, valve schematic symbols, a valve legend, or a valve symbol chart. They fall under the broader umbrella of piping symbols, instrument symbols, and P&ID symbols. ISA-5.1, ISA S5.1, and ANSI/ISA-5.1-2009 ("Instrumentation Symbols and Identification") set the governing rules here, and ISO 14617 and ISO 10628 serve as their international counterparts for diagram symbols. Hydraulic and pneumatic power schematics follow a separate standard, ISO 1219. Its valve symbols aren't the same as P&ID symbols, a distinction worth unpacking below.

What Is a P&ID Valve Symbol?

A P&ID valve symbol is a standardized graphic that identifies a valve on a piping and instrumentation diagram, its type, its actuator, and its fail or normal state. It doesn't convey size, material, or exact rating; those live on the line list and datasheets instead. Most valve symbols start from a common two-triangle valve body, often called a "bowtie." A small modifier at the center or on the stem tells you whether it's a needle, ball, check, globe, gate, or diaphragm valve, while symbols attached above the body describe the actuator. A P&ID uses these symbols to show the process and its control scheme. A Process Flow Diagram (PFD), by contrast, shows fewer valves at a higher level. And a hydraulic schematic uses ISO 1219 envelope-and-port symbols that look nothing like the P&ID set. Reading a valve symbol means reading three things at once: the body, which gives the valve type; the modifier, which gives port count or trim; and the actuator with its fail action. Always check these against the drawing's own legend.

Master Valve-Symbol Chart: Needle, Ball, Check, Relief, Manifold & More

Use the chart below as your main reference. Each row lists the ISA-5.1 / P&ID symbol description, explains what that symbol means in instrumentation service, and links to the actual Crestflo valve it stands for. Find your valve type, read the symbol description, then click through to the matching valve.

These symbol descriptions follow the published ISA-5.1 / P&ID convention. Not every drawing sticks to it exactly, though, so check the legend sheet on the specific drawing before you rely on anything here.

Need a copy for your files? The engineering team can send a printable, downloadable ISA-5.1 valve symbols chart in PDF form on request. Just ask us for the valve symbols chart PDF, or request a link to download the valve symbols reference, using the contact block below.

Needle Valve Symbol on a P&ID: What It Means

The needle valve symbol depicts a globe-type valve body: two triangles meeting at a point. A fine needle or dart stem indicator runs through the center, marking the slender tapered stem that seats into a small orifice. This design is meant for throttling and fine flow control, not for tight on/off duty. That's exactly why it serves as the standard isolation and metering symbol on gauge lines, pressure-transmitter impulse lines, and sampling connections. The gauge root valve symbol relies on this same body; it's simply a needle valve drawn at the process tap. So does the metering valve symbol, which uses a needle body with a finer-taper stem. Both belong to the needle-valve family. One point worth flagging: a needle valve in a hydraulic power schematic follows ISO 1219 and uses a different envelope entirely. A "needle valve symbol hydraulic" isn't the same graphic as the one found on a P&ID. For the physical valve behind this symbol, see the instrumentation needle valve. For the isolation-versus-throttling decision, check the needle vs ball valve selection guide.

Ball Valve Symbol, Including 3-Way, L-Port & T-Port

Picture the ball valve symbol: a two-triangle body with a circle at its center, standing in for the ball itself. That combination marks a quarter-turn valve built for on/off isolation, one that pushes fluid through a full bore with little restriction. Add a third port and an L- or T-shaped flow-path line, and you get a three-way ball valve; that extra mark shows whether the bore diverts flow or simply selects between paths. Multi-port variants stretch the same logic further, covering two-way, four-way and five-way directional service. What actually carries the routing information isn't the ball. It's the number of ports and the flow-path letter.

For the products themselves, see the instrumentation ball valve, the 3-way ball valve and its L-port and T-port bore configurations.

Check Valve & NRV Symbol: One-Way Flow

Crestflo shows check valves, sometimes called non-return valves (NRV) or one-way valves, as a valve body with a ball or disc pressed against a seat, plus an arrow marking the one direction flow is allowed to go. Flow moving the other way shuts the element. That arrow matters a lot: install the valve backwards and you've built yourself a blockage, nothing more. Swing-check and lift-check types carry the same one-way meaning; rather than getting their own symbols, they're usually just called out in a note. For the valve itself, see the check valve and NRV pages.

Relief & Safety Valve Symbol: Spring and Angle Body

The relief valve symbol, sometimes called the pressure relief valve symbol, used for safety and PSV/PRV service, shows an angle-body valve with a spring (drawn as a zig-zag or coil) sitting on top and an angled outlet. It represents a valve that lifts at a set over-pressure to protect equipment. That spring stands for the set-pressure mechanism. Pilot-operated versions just add a pilot line to the same body. Set pressure and orifice size get stated on the drawing and datasheet, never in the symbol itself. See the relief valve product page from Crestflo.

Diaphragm, Bellows & Plug Valve Symbols

The diaphragm valve symbol shows a valve body with a diaphragm, a dome or arc, sitting across the top. It marks a valve whose flexible membrane keeps the stem separate from the process, which matters for high-purity, corrosive, or leak-tight duty. This same glyph covers both the weir-type and the straight-through diaphragm valve symbol. The weir diaphragm symbol is what you'll see most often in instrument service, and a drawing note spells out which type is meant when the distinction actually matters. The bellows or packless valve symbol looks different: an accordion-shaped bellows sits on the stem, signaling a hermetic stem seal built for fugitive-emission and vacuum service. Then there's the plug valve symbol, drawn as a two-triangle body with a rectangle, the plug, at its center, representing quarter-turn isolation. Each of these ties back to an actual product: the diaphragm valve, the bellows valve, and the plug valve.

Manifold, DBB & Monoflange Symbols on Instrument Hook-Ups

Instrument manifolds show up as a grouped assembly of individual valve symbols, not a single glyph. A 2-valve manifold shows a block plus a vent. A 3-valve manifold shows two blocks plus an equalize valve for differential-pressure transmitter hook-ups, and a 5-valve manifold adds two more vents. A double block & bleed (DBB) symbol combines two block valves and a bleed valve in one assembly, giving positive isolation with a bleed you can actually verify. A monoflange, by contrast, packages isolate-and-vent into a single flanged body right at the instrument. Crestflo double block & bleed valves are designed per ASME B16.34, and manifolds and DBB assemblies get seat- and shell-leak tested to the applicable valve standard. See the 2-valve, 3-valve and 5-valve manifolds, the DBB valve and monoflange valve, plus the 2 vs 3 vs 5-valve manifold guide and DBB vs monoflange comparisons.

Pressure Regulator, Bleed, Purge & Toggle Valve Symbols

A pressure regulator symbol, whether PCV, self-contained, or back-pressure, shows a valve body fitted with a spring and a diaphragm dome plus an adjustment arrow. It represents a valve that holds a set downstream or upstream pressure, rather than one that simply opens and closes. A bleed, vent, drain, or purge valve symbol looks different: a small needle or globe body venting to an open outlet, used to depressurize or purge a trapped cavity. The toggle valve symbol is simpler still: a small two-way body marked with a lever or toggle actuator, meant for quick manual shut-off on panels and analyzer racks.

See the regulators range and the back-pressure regulator, plus the bleed valve, purge valve and toggle valve.

Adjacent Valve Symbols: Gate, Globe & Butterfly

For completeness, three common line-service valve symbols sit next to the instrumentation set. The gate valve symbol is the bowtie body with a rising wedge or gate (parallel lines), used for full-open/close isolation. The globe valve symbol is two triangles meeting at a filled circle, meant for throttling. And the butterfly valve symbol is a circle with a disc or line across its diameter, used for large-bore isolation. These are line valves, not instrumentation valves. They're shown here to help read a full P&ID, not offered as Crestflo instrumentation products. Crestflo's scope is the instrumentation valve set above.

Actuator & Fail-Action Modifiers: Manual, Pneumatic, Solenoid, FO/FC

An actuator symbol sits above the valve body. It tells you how the valve moves and how it fails when something goes wrong. The same modifiers apply to any body symbol you'll find in the master chart.

Read against the searched actuator names, these modifiers point to specific glyphs. The solenoid valve symbol is a box with a diagonal line, an "S," sitting above the body; it marks an electrically actuated pilot. The pneumatic valve symbol shows a diaphragm-actuator dome, or sometimes a piston/cylinder rectangle, above the body, marking air operation. A control valve symbol can be any valve body carrying a pneumatic or motor actuator together with fail-action letters, since a control valve is by definition a modulating, actuated body. And the manual valve symbol is simple: a tee handle or lever on the stem, with no automatic actuator in sight.

Fail-action and normal-state letters aren't just labels tacked onto the actuator call-out. They're the safety-critical piece, since they spell out exactly where the valve moves if signal or air pressure drops away. Values and letters follow the drawing legend, in line with ISA-5.1 convention.

The pneumatic actuation loop itself may carry a quick exhaust valve symbol. This is a fluid-power (ISO 1219) symbol marking a valve that rapidly vents actuator air to speed up a stroke. It sits on the air supply line, not the process line, so it's drawn under ISO 1219 next to the actuator rather than as a P&ID process-valve body.

How to Read a Valve Symbol: Open vs Closed & End Connections

The base valve symbol tells you the valve's type, not whether it's open or closed. For that, check the legend, not the shape of the body. Many drawings use a filled, solid body to mean closed and an unfilled one to mean open, but that convention isn't universal: it shifts from project to project, so the legend sheet has the final word. Valve state also shows up explicitly through a "NO" or "NC" note, and on control valves, through the fail-action letters. End connections get marked at the ends of the valve's lines: flanged (two short perpendicular bars), threaded/NPT, socket-weld, butt-weld, or tube-fitting. The same needle or ball valve, then, can appear with completely different end marks depending on the drawing. When a symbol and a note disagree, trust the note and the legend. One symbol worth keeping separate from all this is the instrument bubble, sometimes called an instrument tag or balloon: the circle-and-tag-number graphic used to identify a transmitter, gauge, or controller. The bubble names an instrument and its loop number; every valve symbol on this page, by contrast, names a valve body. To turn a symbol you've read into an actual specification, see how to specify instrumentation fittings and valves.

ISA 5.1 & Related Standards: ISO 14617, ISO 10628 & ISO 1219

Instrumentation valve symbols fall mainly under ANSI/ISA-5.1 ("Instrumentation Symbols and Identification"). ISO 14617 and ISO 10628 add internationally harmonized diagram symbols on top of that. One mistake shows up again and again: pulling hydraulic-schematic symbols into a P&ID. Hydraulic and pneumatic power circuits follow ISO 1219 instead, and its valve symbols rely on envelope-and-port boxes, quite different from the P&ID valve set. The table below maps out each standard's scope.

These symbols mark valves qualified to valve standards, not fitting standards. Crestflo instrumentation valves are built and qualified to the applicable ASME B16.34 and API valve standards; that's API 598 inspection and testing, and API 6D where it applies. Each one ships with EN 10204 3.1 material certificates. Full heat-number traceability included.

Why Crestflo: The Maker Behind Every Symbol

Most pages showing valve symbols come from drawing-software vendors or blogs, and none of them actually make the valves. This one is different: the manufacturer of the instrumentation valves behind each symbol wrote it, so every symbol links to a real, buildable product with a direct path to specify and quote it. Crestflo builds the needle, ball, 3-way, check/NRV, diaphragm, bellows, relief, plug, bleed, toggle, metering, gauge-root, 2/3/5-valve manifold, DBB and monoflange valves covered in this guide, in 316/316L stainless plus high-nickel and corrosion-resistant alloys. DBB valves are designed to ASME B16.34. Manifolds go through seat- and shell-leak testing, and every part ships with EN 10204 3.1 material test certificates (3.2 on request) and heat-number traceability from start to finish. Crestflo holds ISO 9001, 14001 and 45001 certification, plus PED, and is the instrumentation division of an export house that's been running for four decades, recognized by the Government of India, with a proven delivery record across the Middle East. We Engineer Confidence.

Get the Instrumentation Valves Behind These Symbols

Every symbol in this guide points to a valve Crestflo actually builds. Specify from the symbol, and quote it in one place. End users, EPC contractors, panel fabricators and OEMs all order the full instrumentation valve range direct.

• Availability: Ready stock for standard items · made-to-order for specials · 6–8 week delivery.
• Origin: Indian origin; US / European melt available on request, with full material traceability.
• Contact: sales@crestflousa.com · +1 346 594 9005 · Houston, TX.

Customers can request datasheets and CAD files directly. Take a look at the full instrumentation valves range, then request a quote or request a sample. If you're trying to match a valve on an existing drawing to a Crestflo equivalent, don't rely on a published part chart, instead, request your cross-reference from the engineering team. From there, talk to an engineer about a hook-up. Distributors and OEMs, meanwhile, can look into the private-label program.

Frequently Asked Questions: Instrumentation Valve Symbols

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• DBB vs monoflange
• How to specify instrumentation fittings & valves
• ASME B16.34 valve standard
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