Samson TROVIS SAFE 3731-3 Ex d HART Valve Positioner

TROVIS SAFE 3731-3 flameproof Ex d positioner with HART

The Samson 3731-3, sold as the TROVIS SAFE 3731-3, is a single- or double-acting electropneumatic positioner built for control valves in explosive atmospheres. Its electronics are housed in a flameproof (Ex d) enclosure, the set point is a two-wire 4 to 20 mA signal and HART is used for remote parameterisation. Seven Star LLC supplies the 3731-3 in Oman and the GCC as an independent supplier based in Muscat.

The display and rotary pushbutton can be used without removing the cover, so operators can check and edit parameters while the area remains classified. Travel from 3.6 to 200 mm and opening angles from 24 to 100 degrees are listed on the front page of the data sheet, and the unit adapts itself to the valve and actuator it is mounted on.

Decoding the 3731-3 article code

The code reads Type 3731-3 followed by blocks of digits. The table lists the choices in the order the data sheet prints them.

3731-3 technical specifications

How the 3731-3 controls an actuator

A calibrated, gearless travel sensor measures stem position or shaft angle. A microcontroller compares this with the 4 to 20 mA set point and drives an analogue i/p module followed by an air capacity booster. When a deviation exists the actuator is filled with or vented of air. A pressure reducer keeps the i/p module on a constant upstream pressure, so supply pressure fluctuations have almost no influence, and a flow regulator maintains a steady air stream to atmosphere.

Software can limit the output pressure to protect the actuator and reduce the load on the valve seat. Other software features are a tight-closing function, continuous zero monitoring, an operating hours counter and a built-in temperature sensor. All parameters are stored in non-volatile EEPROM, and self-diagnostics are reported as NAMUR NE 107 messages, optionally also through the analogue position transmitter.

Fitting the 3731-3 in a flameproof loop

The Ex d enclosure means the cable entries must be fitted with Ex d certified glands or stopping plugs of the correct thread, so choose M20x1.5 or ½ NPT in the article code to match the plant standard. Compared with the Type 3766 and 3767 positioners, the 3731-3 uses a digital electronic travel loop with HART, while the Type 3766 with a Type 6116 i/p converter is an alternative flameproof arrangement for pneumatic positioning.

Mounting options are direct attachment to the Type 3277 actuator (120 to 700 cm²), NAMUR attachment to the yoke or rib, and rotary actuators per VDI/VDE 3845, including the Type 3278 rotary actuator. For double-acting actuators a pneumatic reversing amplifier is ordered with ISO 228/1-G ¼ or ¼-18 NPT connections. A pneumatic connecting rail and pressure gauges for signal pressure can be added.

Selection checklist for the 3731-3

• Area classification and the certificate set required by the site (ATEX, IECEx, FM/CSA, EAC, JIS and others appear in the table).
• Cable gland thread: M20x1.5 or ½ NPT.
• Optional functions: position transmitter, binary input, forced venting or binary output; only one option field is selectable.
• Safety function: whether emergency shutdown at 3.85 mA is required for the SIS design.
• Actuator: single or double acting, volume, and required stroking time against the 8.5 and 14.0 m³n/h air capacity.
• Mounting standard: Type 3277, NAMUR, or VDI/VDE 3845 with lever size.
• Diagnostics: EXPERTplus is a selectable code, so confirm it is included.

Commissioning and care of the 3731-3

Four initialisation modes are available, including a substitution mode that allows start-up while the plant keeps running and the valve stays in position. Parameters are preset, so only values that differ from the standard need to be changed. HART and the TROVIS-VIEW software give access to configuration and diagnostics, and the position of the unit can be anywhere except suspended. Check that the supply air is dry and oil-free, inspect the Ex d joints and seals when the cover is opened, and keep a spare unit of the same code for critical valves. Do not modify the flame path surfaces.

Typical 3731-3 applications in Oman and the GCC

Flameproof positioners are used on control valves in oil and gas gathering, gas processing, refineries, petrochemical units and fuel handling areas in Oman and the Gulf, where classified zones are common and ambient temperatures are high. The rating down to –40 and up to +80 °C, IP66 / NEMA 4X protection and a chromate and powder coated aluminium enclosure suit outdoor installations exposed to sun, dust and humidity near the coast. Compatible loops include emergency shutdown valves with SIL requirements.

Information to send with an RFQ for the 3731-3

• Complete 3731-3 article code or the required options
• Zone, gas group, temperature class and required certificates
• Valve and actuator data including stroke or angle and fail-safe action
• Thread type for cable entries and pneumatic connections
• HART host or asset-management system in use
• Quantity and any mounting kit, pressure gauges or reversing amplifier

Documents and quotation

The Samson datasheet for the 3731-3 is attached on this page and contains the certificate tables, dimensions and the complete article code. Always match the certificate of the delivered unit to the area classification in the project.

Send the 3731-3 article code and the area classification to Seven Star LLC for a quotation covering Oman and the GCC.