Migrating Legacy Valve Blocks to APL: Mapping TE_VALVE to VlvL vs VlvMotL in PCS 7

When migrating legacy PCS 7 valve blocks (such as TE_VALVE from the PTE library) to the Advanced Process Library (APL), connecting a legacy 'STOP' command to the APL block VlvL input 'CloseForce' is technically incorrect and hazardous. VlvL is engineered strictly for binary (2-state open/close) valves and possesses no intermediate stop state; 'CloseForce' is an emergency force-tracking input that bypasses safety interlocks. If the physical valve requires stopping in intermediate positions, the correct APL replacement is VlvMotL (motor-driven valve), which natively provides a 'StopAut' command input.

Architectural Evolution: Legacy PTE Blocks vs Advanced Process Library (APL)

During modernization of SIMATIC PCS 7 systems, migrating legacy block libraries—such as the PTE (Process Technological Elements) library or early PCS 7 Standard Library V7.1—to the modern Advanced Process Library (APL) is a foundational milestone:

Legacy Design Philosophy:
Early libraries utilized monolithic, multi-purpose function blocks with generic input pins attempting to accommodate multiple physical actuator types within a single block definition (e.g., TE_VALVE).
The APL Specialization Standard:
The Advanced Process Library strictly differentiates between distinct physical actuator mechanics:
VlvL (FB 1899): Engineered exclusively for binary, 2-state valves (solenoid valves, pneumatic on/off valves).
Vlv2WayL (FB 1897): Engineered for two-way directional valves.
VlvMotL (FB 1898): Engineered for motor-driven valves with intermediate positioning (AUMA, Rotork, or motorized dampers).
VlvAnL (FB 1896): Engineered for analog modulating control valves (4..20 mA positioners).

Functional Analysis of TE_VALVE: Two-State vs Intermediate Positioning

In legacy PTE projects, the block TE_VALVE possessed an input named STOP:

Legacy Functionality:
In TE_VALVE, activating STOP immediately de-asserted both the Open and Close control outputs.
The Migration Misinterpretation:
Engineers migrating to VlvL observe that VlvL has only OpenAut and CloseAut (or automatic open/close commands), but no StopAut pin.
Looking at the APL manual, they note that CloseForce forces the valve closed and assume wiring the legacy STOP signal to CloseForce accomplishes the same function. This assumption introduces severe operational and functional safety violations.

Why VlvL Cannot Support a Stop Command (Binary Actuator Mechanics)

A standard binary valve driven by VlvL operates on a single binary output (Ctrl):

Physical Solenoid Actuation:
Output Ctrl = 1: Energizes the solenoid coil, moving the valve to the OPEN position (against spring return).
Output Ctrl = 0: De-energizes the solenoid coil, allowing the mechanical spring to return the valve to the CLOSED position.
No Mid-Stroke Intermediate State:
Electrically and mechanically, a single-acting pneumatic valve cannot "stop" halfway. It is either traveling open or spring-closing. Therefore, providing a "STOP" command on VlvL is physically impossible for binary valves. The only valid automated commands are OpenAut (1) and CloseAut (0).

The Operational Dangers of Misusing the CloseForce Input

Wiring a routine automated stop command to CloseForce on VlvL creates extreme operational hazards:

Command Priority Hierarchy in APL:
APL blocks enforce a strict command priority:
1. Force Commands (OpenForce, CloseForce) [Highest Priority]
2. Interlock Protection (Protect, Intlock)
3. Manual Operator Commands
4. Automatic Commands (OpenAut, CloseAut) [Lowest Priority]
Bypassing Interlocks:
CloseForce is intended exclusively for emergency override or simulation tracking. If an engineer wires routine automated logic to CloseForce:
If the plant safety interlock (Protect = 0) commands the valve to a fail-safe state, CloseForce can override or corrupt the interlock state machine depending on tracking configurations.
In WinCC faceplates, an active CloseForce locks out the human operator, displaying an intrusive purple "Forced" status banner that alarms control room operators.

Selecting VlvMotL for Intermediate Positioning and Multi-Command Valves

If the field valve possesses a physical actuator capable of stopping mid-stroke (e.g., a motorized actuator with separate Open and Close limit switches and intermediate stopping capability):

The Correct Block Choice is VlvMotL (FB 1898):
VlvMotL is purpose-built for motor-driven valves. It provides:
Dedicated automatic inputs: OpenAut, CloseAut, and StopAut.
Dedicated control outputs: Open, Close, and Stop (or pulse outputs).
Limit switch feedback: FbkOpen, FbkClose, and torque fault monitoring (Trip, TorqOpen, TorqClose).
Mid-position visualization: The WinCC APL block icon and faceplate accurately render the valve in the intermediate running or stopped state.

Comparison Table: TE_VALVE vs APL VlvL vs APL VlvMotL

The following table details the functional mapping between legacy TE_VALVE and modern APL valve blocks:

Parameter / FeatureLegacy PTE TE_VALVEModern APL VlvLModern APL VlvMotLTarget Valve TypeGeneric multi-purpose valveBinary On/Off (Solenoid)Motorized / Actuator ValveOpen CommandOPENOpenAutOpenAutClose CommandCLOSECloseAutCloseAutStop CommandSTOPNone (Not applicable)StopAut (Natively supported)Intermediate StateSupported in softwareStrictly binary (Open/Close)Fully supported with travel timersForce OverrideNoneOpenForce / CloseForceOpenForce / CloseForceInterlock PriorityBasic interlockingStrict NAMUR NE 107 hierarchyStrict NAMUR NE 107 hierarchyRecommended Use CaseObsolete; Do Not Deploy2-position spring-return valvesActuators with stop capability

Step-by-Step Procedure to Migrate Legacy Valves to APL

Follow this verified engineering procedure to migrate legacy valve instances to APL:

Audit Physical Field Valve Characteristics:
* Inspect the equipment schedule / P&ID.
* If the valve is a 2-state solenoid valve: Select VlvL.
* If the valve is a motorized actuator with intermediate stop capability: Select VlvMotL.
Migration to VlvL (Binary Valves):
* Replace TE_VALVE with VlvL in the CFC chart.
* Connect automated open commands to OpenAut.
* For the closing condition, invert or reset OpenAut, or pulse CloseAut.
* Disconnect the legacy STOP signal. Never connect operational logic to CloseForce.
Migration to VlvMotL (Motorized Valves):
* Replace TE_VALVE with VlvMotL in the CFC chart.
* Connect automated open to OpenAut.
* Connect automated close to CloseAut.
* Connect the legacy stop signal directly to StopAut.
* Wire limit switch feedbacks to FbkOpen and FbkClose.
Compile and Update Block Types:
* In SIMATIC Manager, run Options > Charts > Update Block Types.
* Perform CFC compilation and OS compilation.
* Update WinCC block icons to modern APL typicals (@VlvL/1 or @VlvMotL/1).

Verification

Verify that migrated valve logic operates safely:
1. In CFC Test Mode, test the automated sequence; verify that pulsing OpenAut moves the valve to Open and pulsing CloseAut closes the valve.
2. If using VlvMotL, pulse StopAut while the valve is in transit; confirm that outputs de-energize and the faceplate displays "Stopped in intermediate position".
3. Verify that CloseForce and OpenForce inputs remain disconnected (0), confirming that the faceplate does not display an active force override symbol.
4. Test interlock protection by forcing Protect = 0; verify that the valve immediately transitions to its configured safe state, overriding automated commands.

Limitations and Operational Precautions

Never Misuse Force Inputs: In APL, OpenForce and CloseForce are strictly designated for high-level simulation, maintenance override, or SIS trip actions. Using them for regular batch sequencing invalidates standard interlocking.
Torque and Travel Timeouts: VlvMotL includes integrated monitoring timers (Monitor, MonTiDynamic). Parameterize these timers to match the physical travel time of the actuator to prevent nuisance runtime discrepancy alarms.
Safe Position Configuration: On VlvL, configure SafePos (0 = Closed, 1 = Open) to match the physical spring-return fail-safe state of the pneumatic actuator.
Commercial Accuracy: Advanced Process Library blocks (6ES7658-2CX58-0YB5) are included with standard PCS 7 engineering packages. Validate license allocations with an authorized Siemens distributor quotation.

Engineer FAQ

Can VlvL be configured to stop a valve halfway by setting OpenAut = 0 and CloseAut = 0?

No. Setting OpenAut = 0 commands VlvL to transition to the closed position. A binary solenoid valve has no mechanism to freeze in mid-travel when de-energized.

Why does APL give Force inputs higher priority than Interlocks?

Force inputs represent manual emergency plant interventions (e.g., a safety commissioner forcing a damper open during an emergency smoke purge). Because they represent ultimate human override, they supersede normal interlocking.

What is the difference between VlvL and Vlv2WayL?

VlvL controls a single valve with one control output. Vlv2WayL controls a two-way diverter valve directing flow between two alternative process paths using complementary outputs.