P&ID Symbols for AutoCAD — Free DWG Blocks for Tanks, Pumps, Valves and Instrument Loops

Open the two library pages and download what the drawing needs. Each symbol is its own small ZIP with one DWG and a README, so you do not carry the whole library around. Equipment and piping blocks start with PID_ (PID_TANK, PID_PUMP_CENTRIFUGAL, PID_VALVE_GATE, PID_CHECK_VALVE, PID_FLOW_ARROW), instrumentation blocks with ISA_ (ISA_DISCRETE_FIELD, ISA_DISCRETE_MAIN, ISA_ELEM_ORIFICE, ISA_CV_DIAPHRAGM, ISA_LINE_ELECTRIC, ISA_LINE_PNEUMATIC). For the example in this guide that is eleven blocks.

The sheet on each library page shows every symbol with its name, so you can find the right one before you download anything. Put the blocks you use in one folder and browse to it when you insert.

Use INSERT (or the Blocks palette) and click the position of each item. Equipment such as the tank and the pump is inserted at its centre; the pump is a 10 mm circle with its inlet on the left, so the suction line ends at the circle. Valves are 20 mm long and their insertion point is the inlet end of the valve on the centre line. Put a valve with its insertion point on the end of a pipe and start the next pipe 20 mm further on; the valve then sits exactly in the line.

Draw the process lines as polylines and give them a width, for example 0.8 mm with PEDIT (Width), on their own layer. A thick process line next to the thin symbol outlines is the usual look of a P&ID and lets you freeze or plot the piping on its own. The symbols are drawn in millimetres at 1:1, so a valve is 20 mm long on the sheet: insert at scale 1 on a sheet drawn in millimetres. Add a PID_FLOW_ARROW to show the flow direction.

The blocks carry attributes, so the tag stays with the symbol. A valve has VALVE_TAG, SIZE, RATING, BODY_MATERIAL and LINE_NO; a control valve adds FAIL_POSITION, CV and ACTUATOR. A pump has TAG, SERVICE, FLUID, FLOW_M3H, DIFF_HEAD_M, POWER_KW and DRIVER, and a tank has TAG, SERVICE, CONTENT, VOLUME_M3, DESIGN_PRESSURE and DESIGN_TEMP. Double-click a symbol to open the Enhanced Attribute Editor, click a row, type the value and finish with OK.

Only the tag and the size show next to the symbol; the rest stays in the block for the lists. If a tag lands on a process line, select the block and drag the grip of the text to a clear place. The attribute moves, the symbol does not. Use the same tag pattern throughout, for example HV-101 for hand valves and NRV-101 for non-return valves, so the lists sort the way people read them.

A flow control loop has four parts. The orifice plate FE-101 goes into the line: insert ISA_ELEM_ORIFICE on the centre line of the pipe. The transmitter FT-101 is a field instrument, so it uses the plain bubble ISA_DISCRETE_FIELD with no line through it, and the controller FIC-101 sits in the control room, so it uses ISA_DISCRETE_MAIN, the bubble with a line across it. In the bubble the letters come from TAG_FUNC (F for flow, I for indicating, C for controlling, T for transmitting) and the number from LOOP_NO.

Connect the parts with the signal lines: a thin line from the orifice up to the transmitter, a dashed ISA_LINE_ELECTRIC from the transmitter to the controller, and an ISA_LINE_PNEUMATIC from the controller down to the actuator of the control valve. The control valve is a single block, ISA_CV_DIAPHRAGM, with the diaphragm actuator drawn on top; its FAIL_POSITION attribute holds FC, FO or FL. Rotate the signal line blocks to any direction you need.

Look at the diagram the way a reviewer will. The flow reads from left to right and each line has an arrow. Every process line ends at a symbol and not just near it; zoom in on a few joints, or turn on the Endpoint object snap while you draw so that the line ends are exactly on the connection points. Every item has a tag, no tag sits on a line, and the instrument loop has one number everywhere: FE-101, FT-101, FIC-101 and FV-101 belong together.

Put the process lines, the signal lines and the symbols on separate layers. Then you can plot the instrument layer in a different colour or switch the signals off for a mechanical issue of the same sheet.

Run the COUNT command, accept the area and press Enter at the object prompt to list all blocks. The palette shows every block name with the number of copies, here three PID_VALVE_GATE, and Create Table puts the list into the drawing. COUNT only counts by block name, so for a valve list with tag, size and rating use DATAEXTRACTION: choose the blocks and the attributes VALVE_TAG, SIZE, RATING and LINE_NO and send the table to a drawing table or an Excel file.

The same works for the instrument index: extract TAG_FUNC, LOOP_NO, SERVICE and RANGE from the bubbles. Because the data lives in the blocks, the lists are right whenever the diagram is right.