Valve Symbols on P&IDs: A Practical Guide for Buyers

Quick Answer

Valve symbols on a P&ID show the valve type, port arrangement and method of operation. They do not show size, pressure class, material, trim or end connection. Read the project legend and drawing revision first, then use the valve list and datasheet to complete the specification. GOWIN supplies ball, gate, globe, plug, butterfly, check and needle valves for that step.

Why Do Valve Symbols Matter to Buyers?

Because the drawing decides the valve type before anyone looks at a price.

On a typical project the facilities or process engineer builds the P&ID, the drawing is checked and approved, and it then goes to purchasing to obtain vendor quotes. By the time a buyer sees it, the valve type and function are fixed. What remains open is the specification behind the symbol, and that is the buyer’s work.

The symbol also fixes the commercial category. A ball symbol points to a quarter-turn isolation valve. A globe symbol points to a valve intended for throttling or frequent operation. A check symbol points to a non-return device. Each category has a different cost structure, lead-time pattern and option list. Reading the symbol correctly at the enquiry stage keeps the quotes comparable.

How Do You Read a Basic Valve Symbol?

Start with the legend, not with memory.

Every P&ID carries its own legend, and the same shape can be drawn slightly differently between organisations. The legend is the only reliable key for that drawing. Read it together with the revision number, because a symbol added on revision C may not appear in the legend printed on revision A.

Most valve symbols start from the same two-way base: two triangles pointing at each other, with the inner tips touching. Pipes connect to each side. The valve type appears as a shape at the centre where the tips meet. Flow direction is usually shown by an arrowhead on the line, including at right-angle turns.

Three details repay a second look:

• Ports. A three-way or four-way valve adds one triangle for each port or “way”. Three- and four-way ball valves may also show T-port or L-port drilling.
• De-energised path. Small arrows beside the symbol can show which way flow passes when the actuator is not energised.
• Fill. White symbols commonly mean normally open and solid black symbols mean normally closed. This is a convention, not a universal law, so confirm it in the legend.

Symbols are not to scale and are not dimensionally accurate. They do not show where the valve sits in the plant, so two valves drawn side by side may be far apart on site. Do not read spacing, orientation or elevation from the symbol.

How Are Gate, Globe, Ball, Plug and Butterfly Valves Shown?

The centre shape does the work. These are the five families a buyer meets most often.

Gate. The gate symbol belongs to the isolation family. A gate valve opens by lifting a gate out of the flow path, so it is used for on-off service rather than throttling. The symbol tells you the type, not the stem arrangement. Rising stem, non-rising stem, wedge design and back seat all belong in the datasheet. GOWIN lists its API 600 gate valve from 1 to 42 inches in Class 150 to 2500, with a back seat and graphite stem sealing, and the wider gate valve category covers the same isolation duty.

Globe. The globe symbol uses a smaller circle than the ball symbol. That circle shows the shape of the casing, not a ball inside the valve. A globe valve moves a plug against a stationary seat, which suits throttling and frequent operation. It is the body family behind many control valves. GOWIN builds the globe valve to BS 1873 from 1/2 to 24 inches in Class 150 to 2500, and the control valve range uses the same body style with electric or pneumatic actuation.

Ball. The ball symbol uses a larger circle, indicating the ball inside the valve. A quarter-turn ball valve is the usual choice for tight isolation and fast operation. The symbol does not tell you whether the ball is floating or trunnion-mounted, whether the bore is full or reduced, or whether the body is two-piece or three-piece. Those choices change cost and maintenance access. The ball valve category and the floating ball valve show the range: DN15 to 250, Class 150 to 300, full or reduced bore, with fire-safe, anti-static and anti-blowout construction listed.

Plug. The plug symbol marks a quarter-turn valve that uses a tapered or cylindrical plug rather than a ball. Plug valves suit dirty, viscous or fibrous media where a ball seat would be damaged, and they can be arranged for multi-port service. The symbol may show the port count but not the port pattern. GOWIN lists plug valves from 1/2 to 24 inches in Class 150 to 2500 with RF, RTJ, BW, THR or SW ends.

Butterfly. The butterfly symbol marks a rotating disc. On some drawings it appears as a damper symbol, because a damper is also a plate that regulates flow. The symbol does not distinguish wafer from lug body, centred from offset disc, or manual from actuated. GOWIN lists the wafer butterfly valve from 2 to 120 inches in Class 150 to 600 to API 609, with RF or RTJ ends, and the butterfly valve category covers the wider range.

Two more families appear often enough to name. A check symbol shows one-directional flow, but not whether the valve is swing, lift, dual-plate or damped. GOWIN’s cast steel check valve is a swing-disc design, and the check valve category covers the family. A needle symbol marks a small-bore valve for fine adjustment, and the needle valve range runs from 1/8 to 1 inch.

The table links the common valve symbols to the data the datasheet must confirm.

How Are Actuators and Normal Positions Shown?

Actuator notation is the part of valve symbols that changes a quote most, and it sits on top of the valve symbol. It tells you how the valve is driven. Common families are manual handwheel, pneumatic diaphragm, pneumatic rotary piston, electric motor, hydraulic, solenoid and balance. The shape identifies the family. It does not identify the model.

This matters commercially because actuation is often the largest variable in the price. A pneumatic diaphragm actuator and a double-acting rotary piston actuator are different products with different air consumption, failure behaviour and accessory lists. A solenoid pilot valve adds voltage, enclosure and certification questions. None of that is settled by the symbol.

Normal position is a separate layer. White fill usually means normally open; black fill usually means normally closed. The de-energised flow path arrows, where present, show what happens when the actuator loses signal. Read these with the note block, not instead of it.

The note block is where the drawing becomes useful to a buyer. A note such as 2″ 300 RF PB carries size, pressure class, facing and a valve descriptor in a few characters. Notes can also carry function, tag number and operator type. If a symbol has no note and no matching line on the valve list, the drawing is incomplete for purchasing purposes.

What Does a Valve Symbol Not Tell You?

Almost everything that determines the price and the delivery.

A valve symbol does not tell you:

• body, bonnet, trim or seat material;
• pressure class or pressure-temperature rating;
• nominal size and face-to-face dimension;
• end connection, facing or welding standard;
• bore, port pattern or flow coefficient;
• seat type, packing, gasket or fire-safe construction;
• test standard, inspection level or certificate scope;
• actuator model, spring range, voltage, enclosure or accessory set.

The limits of valve symbols are easiest to see in that list. It is not a criticism of the drawing: a P&ID is a process document. It shows what the system does, not how a supplier builds a component. The error is treating it as a specification.

Tags are a good example. A tag such as FIC045 identifies a flow indicating controller in loop 045. It tells you the instrument’s function and its loop. It does not tell you the valve size, the Cv, the body material or the fail position. Those live on the instrument datasheet and the valve list.

How Do You Reconcile the P&ID With the Valve List?

Use three documents in a fixed order, and record which one governs each field.

1. P&ID and legend. Confirms valve type, port arrangement, operator family and normal position. Read the revision.
2. Valve list. Carries tag, size, pressure class, body material, trim, end connection and quantity. This document turns a symbol into a purchasable line.
3. Datasheet and drawing. Confirms the model, face-to-face, actuator details, options and test requirements.

When the three disagree, do not choose the convenient one. The drawing revision governs the arrangement, the valve list governs the commercial scope, and the datasheet governs what is actually supplied. A mismatch is a query to the engineer, not an assumption by the buyer.

A worked example shows the gap. A drawing shows a butterfly symbol on line 12-B, tagged BV-1203, with the note 6″ 150 RF. The symbol tells you it is a butterfly valve. The valve list has to add wafer or lug body, body and disc material, seat material, shaft material and operator. If the line is to be isolated for maintenance, the lug versus wafer comparison is the relevant decision, because a wafer body relies on both neighbouring flanges for support. None of that is visible in the symbol.

The same test applies to a ball valve line. A ball symbol with a 3-inch note could be a two-piece or three-piece body, full or reduced bore, floating or trunnion ball. The difference between top-entry and side-entry ball valves matters for maintenance access, and the gate valve versus ball valve comparison explains why the process engineer may have chosen one symbol over the other.

API 600 Gate Valve

• Nominal diameter: 1″～42″（DN25~1050）
• Pressure: 150LB-2500LB 0.6Mpa-42.0Mpa
• End Connection: RF, RTJ, BW, THR, SW
• Temperature: -196℃-650℃

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What Should You Send With the RFQ?

Send the drawing and the specification together, and state which revision you are quoting. The pack should let a supplier check the valve symbols against the line, not guess what the symbols mean.

A workable enquiry pack contains:

• the P&ID extract with the relevant line and tag highlighted;
• the project legend page, or a clear statement that the standard legend applies;
• the valve list line with tag, size, class, material and end connection;
• the datasheet or data sheet template for the valve;
• service medium, design pressure, design temperature and flow requirement;
• actuation requirement, including fail action and available power;
• test, inspection and documentation requirements;
• the end-connection standard, which the end connection guide explains for flanged, threaded and welded joints.

If the drawing is marked “by vendor” or the note is incomplete, say so in the enquiry rather than filling the gap silently. A supplier who understands the open items can quote a compliant option and flag the rest. A supplier who receives an incomplete drawing usually quotes the cheapest interpretation, and the mismatch surfaces at inspection.

For actuated packages, the pneumatic valve types guide is a useful check on actuator and function before the enquiry goes out.

Which Valve Symbols Matter Most in a Quote Review?

Three checks catch most problems.

First, confirm that the symbol family matches the service. A gate symbol on a throttling line, or a butterfly symbol on a line that needs a tight metal seat at high temperature, deserves a conversation before the order.

Second, confirm the port count and flow path for multi-port and actuated valves. A three-way symbol with the wrong port pattern is a wrong valve, however good the price.

Third, confirm that every symbol on the enquiry has a matching valve list line. Orphan symbols are a common cause of a short shipment.

Where the line also carries isolation and non-return valves under a project standard, the API 6D overview explains how that standard frames the scope. That is a separate question from what the symbol shows.

Conclusion

Valve symbols are a fast, reliable way to read the process intent on a P&ID. They are a poor way to specify a valve. Use the legend and revision to read the symbol, the valve list to fix the commercial scope, and the datasheet to confirm what will be supplied.

GOWIN supplies ball, gate, globe, plug, butterfly, check and needle valves across the ranges linked above, and reviews enquiries against the drawing and datasheet rather than the symbol alone.

Send service media, size, pressure, temperature and the relevant drawing for a quotation.