Smith Flow Control and Netherlocks have merged. We are now Sofis.

Sequence control

Control complicated valve operating sequences with valve interlocks. Integrate manual valve operations in your process control.

Manage complex valve operation sequences with valve interlocks

Smith or Netherlocks interlocks assure a fixed operational sequence of valves or adjacent equipment. When you secure complex sequences with valve interlocks you require sequence control products to secure correct operation. These devices provide additional sequence guidance in the field.

Key interlocks for safe pigging operations
  • Sequence control for valve interlocks
  • Valve interlock key unit for controlling complex valve operations

Mechanical valve interock sequence control

The Sofis mechanically-programmed valve interlock key exchange unit controls complicated procedures like pig launching & receiving and filter regeneration. The unit functions as a mechanical PLC.

  • Reverse operation of valves in a non-reverse order of initial operation
  • Repeated use of a valve within a sequence
  • Valve opened and directly closed before proceeding to the next step

Optionally, the presence of keys inside the exchange control unit can be fed back to your DCS system. This provides field equipment status information to your control room.

Let us assist you with complex valve sequences

Integrate manual valves in your process control

Improve your process control by integrating manual valve operations. Our electronic sequence control products manage valve interlock key usage based on field device inputs. You include safety parameters, like measurements of contaminants or process conditions, in your interlocked valve operations. Thus you ensure opening and closure of equipment only under safe conditions.

  • Include safety parameters before opening or closing equipment
  • Change from one sequence to another, depending on signals or planned processes
  • Include interactive guidance through complex procedures.
  • Sequence control device for complex valve operation sequence
  • Operating sequence control system


Sequence control device for complex valve operation sequence

Single key release

Cabinet that releases valve interlock key based on permissive signals.

Control system for safe valve operations

Actuator panel

Switch panels for actuator operation, activated by valve interlock key insertion.

Control panel for complex pigging operations

Sequence control panel

Operating panels that integrate mechanical sequence control, actuator controls and permissive signals.

Engineering support

We have extensive application knowledge and over 30 years of experience and project management skills. Our global team of engineers is available to participate in HAZOP studies, assist with interlock sequence design and develop customized process safety products. They are committed to improve your valve operations and ultimately, your plant performance.

Apply for free advice and support