Understanding PCS 7 APL Valve Block Icons: Rotating Behavior and Non-Rotating 'DC' Variants

In SIMATIC PCS 7 Advanced Process Library (APL), valve block icons utilize Enhanced Metafile (.emf) vector graphics designed to provide distinct visual feedback for operators, including accessibility for color-blind individuals. Standard APL valve icons rotate dynamically by 90 degrees depending on state (horizontal when closed, vertical when open). In contrast, the .emf files containing 'DC' in their filename—such as APL_Vlv_DC_Closed.emf—represent Direct Control / Non-Rotating (Direction Constant) variants. These icons maintain a fixed physical orientation regardless of state and display one or two extra thick border lines to clearly indicate the closed or closing condition without rotating the symbol on the piping diagram.

APL Visual Ergonomics and Accessibility Standards in PCS 7

In SIMATIC PCS 7 Advanced Process Library (APL), human-machine interface graphics adhere to strict visual ergonomics standards (such as NAMUR NE107, ISO 9241, and ISA-101). A core design requirement of APL is that process states must never be communicated solely through color coding (e.g., green for open, red for closed). Operators with red-green color vision deficiencies must be able to discern equipment status unambiguously through geometry, motion, and line weight.

In the WinCC @TemplateAPLV8.pdl and @TemplateAPLV9.pdl template pictures, valve block icons for two-way valves (VlvL), three-way valves (Vlv3WayL), and motorized valves (VlvMotL) utilize scalable vector graphics files (.emf) stored in the project's GraCS directory.

Rotating Valve Icons vs Non-Rotating 'DC' Variants

To satisfy diverse plant layout requirements, Siemens created two distinct graphical implementations for valve icons:

Standard Rotating Valve Icons:
- In standard icons, the valve symbol dynamically rotates by 90° between closed and open states.
- For a horizontal pipe run: closed state is horizontal (blocking the flow), while open state rotates to vertical (aligned with flow).
- This provides instant, unmistakable geometric feedback for all operators.
Non-Rotating 'DC' (Direction Constant) Icons:
- In dense piping and instrumentation diagrams (P&IDs) or complex 3D piping mimics, rotating a valve symbol can make pipe interconnections look broken, overlapping, or unnatural.
- The DC variants remain permanently stationary, preserving their drawn pipe alignment.
- To satisfy the color-blindness standard without rotation, the DC icons incorporate one or two prominent thick black lines across the valve body to symbolize the physical seating barrier when the valve is in the closed or closing state.

Comparison of APL Valve Icon Types and EMF File Naming Conventions

The following table compares standard and DC valve icon graphics across operating states:

Valve StateStandard Rotating File (.emf)Non-Rotating DC File (.emf)Visual Distinguishing FeatureClosedAPL_Vlv_Closed.emfAPL_Vlv_DC_Closed.emfDC has 2 thick black barrier lines across body; no rotationClosingAPL_Vlv_Closing.emfAPL_Vlv_DC_Closing.emfDC has 1 thick line indicating stroke travel; no rotationOpenAPL_Vlv_Opened.emfAPL_Vlv_DC_Opened.emfBoth show hollow body (full flow path); standard rotates 90°OpeningAPL_Vlv_Opening.emfAPL_Vlv_DC_Opening.emfDynamic color shading; DC maintains fixed orientationFault / InterlockAPL_Vlv_Fault.emfAPL_Vlv_DC_Fault.emfFlashing warning contour; DC maintains fixed orientation

Step-by-Step Procedure to Select and Configure Non-Rotating Valve Icons

Follow this procedure in WinCC Graphics Designer to configure non-rotating valve icons on a mimic:

Open Template Screen in Graphics Designer:
- In WinCC Explorer, open Graphics Designer.
- Open the template screen @TemplateAPLV9.pdl (or @TemplateAPLV8.pdl).
Locate the 'DC' Block Icon Variant:
- Locate the section for VlvL or VlvMotL block icons.
- Look for the icon variant labeled Type 2 or Type 3 (Direction Constant / Non-Rotating).
- Inspect the block icon properties: under General, parameter type is set to @VlvL/2 or @VlvL/3.
Assign the Variant to the CFC Chart:
- In the CFC Editor, open the technological chart containing VlvL.
- Right-click the VlvL block and select Object Properties.
- In the 'Block Icon' field, enter 2 (or the number corresponding to the DC variant in your template).
- Click OK.
Recompile OS and Generate Block Icons:
- In SIMATIC Manager Plant View, right-click the OS project and select Compile.
- Run the Create/Update Block Icons wizard (Options -> Plant Hierarchy -> Create/Update Block Icons).
- WinCC places the non-rotating DC icon on the target process graphic, linking all EMF files automatically.

Verification

Verify valve icon behavior in WinCC Runtime:
1. Open the process graphic in WinCC Runtime.
2. Command the valve to Close. Observe the block icon: verify that the valve orientation does not rotate, but two distinct thick black lines appear across the valve body.
3. Command the valve to Open. Verify that the barrier lines disappear, leaving the open hollow flow path.
4. Confirm that the icon maintains perfect geometric alignment with connected static process piping lines.

Limitations and Operational Precautions

Never Overwrite Standard EMF Files: Never replace standard .emf files in GraCS with customized images without renaming them. Running the OS Project Editor will overwrite modified files with factory templates.
Consistency Across Plant Areas: Maintain a consistent graphic philosophy throughout a plant unit. Mixing rotating and non-rotating valve icons on the same process screen creates operator confusion.
Three-Way Valve Orientation: For three-way valves (Vlv3WayL), DC variants are strongly recommended because rotating a three-way body misaligns common and bypass flow nozzles.

Engineer FAQ

What does 'DC' mean in APL valve icon filenames?

'DC' stands for Direction Constant (or Direct Control), indicating that the icon maintains a fixed, non-rotating physical orientation on the screen regardless of valve state.

Why do standard APL valve icons rotate?

Standard APL valve icons rotate 90 degrees between open and closed states to satisfy international accessibility guidelines (such as ISA-101 and NAMUR NE107), enabling color-blind operators to identify valve states without relying on color.

What are the thick black lines on DC valve icons?

The thick lines represent the closed mechanical seating barrier, providing clear visual proof that the valve is closed without needing to rotate the symbol.