Valve Interlocks

Valve Interlocks define which combinations of valve positions are physically permitted or forbidden within a plant. They protect against unsafe configurations — such as opening both an inlet and a drain simultaneously — and document the mechanical interlock requirements that operators and engineers rely on during production, cleaning, and maintenance.

Every interlock set ties together two or more valves and declares specific rules about how those valves may (or may not) be positioned at the same time.

🔒 Rule Types

Each interlock set operates under one of two rule types. A single set cannot mix rule types.

💡 When to use which:

• Use Forbidden when most configurations are acceptable but a handful are dangerous. You only need to list the dangerous ones.

• Use Only Allowed when the process is tightly controlled and only a few validated configurations should ever exist. Everything not explicitly listed is blocked.

⚙️ Creating Interlocks

There are two ways to create interlock sets.

Method 1 — From the Drawing (Quick-Create)

1. Run the DefineInterlock command.

2. Select two or more valves directly on the P&ID drawing.

3. AseptSoft identifies the selected valves and opens the quick-create dialog.

4. Choose the rule type: Forbidden or Only Allowed.

5. Set each valve's required state for the configuration (e.g., Open, Closed, Intermediate).

6. Click Save.

💡 If the exact group of valves already has an existing interlock set, the new configuration is appended to that set automatically rather than creating a duplicate.

Method 2 — From Module Data

1. Open the Data panel.

2. Navigate to Module Data → Interlocks tab.

3. Create and manage sets directly from the master-detail interface (described below).

📋 Managing Interlocks (Module Data Window)

The Interlocks tab uses a master-detail layout for full control over every interlock set and its configurations.

Left Panel — Interlock Set List

Each interlock set appears as a card showing:

Right Panel — Set Detail

When a set is selected, the right panel shows:

• Configuration grid — One row per configuration, with a column for each valve. Each cell contains a state dropdown (Open, Closed, etc.). Edit and delete controls appear per row.

• Valve management — Hover over a valve column header to reveal Replace and Remove icons. Click the "+" button to add another valve to the set.

• "Add Config" button — Appends a new configuration row to the grid.

Top Bar

🔄 Conditional Interlocks

Some interlock rules only apply under specific process conditions — for example, during a CIP cycle, when a temperature threshold is exceeded, or when a particular recipe phase is active.

How Conditions Work

• Each configuration row has a condition dropdown with these options: (none), any existing condition, an edit button, or "+ Create Condition".

• A configuration with no condition is unconditional — it is always enforced.

• A configuration tied to a condition is only enforced when that condition evaluates to true.

Conditions Panel

The right-side detail view includes a collapsible Conditions panel that lists all conditions defined for the set, each displayed with syntax-highlighted expressions for easy reading.

Creating and Editing Conditions

The InterlockConditionEditorWindow provides:

💡 Conditions are reusable — the same condition can be assigned to multiple configuration rows across the set.

⚠️ When a condition is deleted, all configuration rows that referenced it automatically become unconditional (always enforced).

👁️ Interlock Overlay

The overlay provides a quick visual check of which valves are interlocked on the P&ID.

1. Click the eye icon button in the Interlocks toolbar.

2. AseptSoft draws colored circles around each interlocked valve and connecting lines between valves that belong to the same set.

3. Each interlock set receives a unique color so overlapping sets are easy to distinguish.

4. The overlay clears automatically when the next command is executed.

🔍 Configuration Path Finder

The Path Finder helps answer the question: "How do I safely move from one valve configuration to another, changing only one valve at a time, without ever passing through a forbidden state?"

Using the Path Finder

1. Expand the "Configuration Path Finder" panel at the bottom of the Interlocks view.

2. Set the Initial Configuration — choose the current state of each valve from the dropdowns in the left column.

3. Set the Target Configuration — choose the desired end state in the right column.

4. Click "Find Path".

Results

The system uses a breadth-first search to find the shortest safe path:

• Each step is displayed as: ValveName: FromState → ToState

• Steps are numbered sequentially.

• Only one valve changes per step.

• No intermediate configuration is forbidden.

• If mechanical design data is available, each step is annotated with the required key movements.

⚠️ If no safe path exists, the Path Finder reports that the target configuration is unreachable from the initial configuration — indicating a potential design issue.

📊 Reachability Analysis

Reachability Analysis checks whether every legal configuration can reach every other legal configuration by changing one valve at a time without passing through a forbidden state.

Status Indicators

When Islands Are Found

• The analysis displays the distinct groups of mutually reachable configurations (islands).

• Process validation checks whether any defined process or algorithm requires transitions that cross island boundaries:

  • 🔴 Red error — A process requires moving between islands, meaning it cannot be executed safely with the current interlock rules.

  • Configurations used by a process that are themselves forbidden are also flagged.

• ⚠️ Warning triangles appear on the affected set cards in the left panel so issues are visible at a glance.

🔧 Mechanical Interlock Design

The Mechanical Interlock Design section documents the physical key-and-lock hardware that enforces interlock rules on the actual plant equipment.

Components

📁 Exporting Interlocks

Interlock data can be exported for documentation, review, and regulatory submissions.

Excel Export

Four export modes are available:

Sheet layout options:

• All in One — All interlock sets on a single sheet.

• Per Set — Each interlock set on its own sheet.

💡 Export preferences (mode and layout) are persisted so you don't have to reconfigure them each time.

Word Export

The same four modes (Raw, All Forbidden, All Allowed, Mechanical Design) are available as sub-checkboxes in the Word export dialog, allowing you to include any combination in a single document.

🏭 Pharma Example — CIP System Interlocks

Consider a Clean-in-Place (CIP) system with these valves:

Forbidden Rules — Preventing Unsafe Combinations

An interlock set with rule type Forbidden protects against dangerous states:

(A dash means any state is acceptable for that valve in this rule.)

Only Allowed Rules — Validated CIP Configurations

A separate interlock set with rule type Only Allowed restricts the CIP loop to validated configurations:

Everything other than these two configurations is forbidden for V-103 and V-104. Note the use of a condition: configuration 1 only applies when the "CIP Active" condition is true, while configuration 2 is unconditional.

Using the Path Finder

Suppose the plant is in production (V-101 Open, V-102 Closed, V-103 Closed, V-104 Closed) and you need to transition to CIP mode (V-101 Closed, V-102 Closed, V-103 Open, V-104 Open). The Path Finder calculates:

1. V-101: Open → Closed (stop product flow first)

2. V-103: Closed → Open (start CIP supply)

3. V-104: Closed → Open (start CIP return)

Each step is safe — no intermediate configuration is forbidden.

🔗 Related Pages

• Module Data — The data panel where interlocks are managed alongside other module-level configuration

• State — Valve states and how they integrate with interlock rules

• Equipment Module — How equipment modules reference and enforce interlocks

• Algorithm Design — Defining process sequences that respect interlock constraints

• Export to Word — Full documentation export including interlock data