Samson 4740 Electric Limit Switch with Optional Solenoid

Samson 4740 electric limit switch for small pneumatic valves

The Samson 4740 is an electric limit switch that reports when valve travel goes above or below an adjusted limit. The signal can drive a visible or audible alarm, or it can be wired into a central control or alarm system to confirm that a valve has reached its open or closed position. According to the datasheet it is mounted on the Type 3353 angle seat valve, the Type 3354 globe valve or the Type 3379 pneumatic actuator. Seven Star LLC supplies the Samson 4740 in Oman and the GCC as an independent supplier in Muscat.

Two contact versions exist: inductive proximity switches and mechanical microswitches, both with degree of protection IP 65. Either can optionally be supplied with an integrated 3/2-way solenoid valve, which turns the 4740 into a combined position-feedback and pneumatic control unit.

Technical specifications of the 4740 limit switch

Decoding the 4740 article code

The ordering table of the datasheet builds the code Type 4740- from fixed zeros and four meaningful options:

A limit switch without a solenoid valve needs no pneumatic connection, so those two positions are normally both zero.

Principle of operation of the 4740

As the valve stem or actuator moves, the proximity switches or microswitches react at the set limits and send a signal to the control or alarm system. The switching points can be changed anywhere within the 0 to 15 mm travel range, so the same unit can indicate end positions or an intermediate position.

When the integrated solenoid valve is energized, supply air goes to the actuator. When it is de-energized, the actuator is vented and the control valve travels to its fail-safe position. This combination is common for on/off process valves that need both a safe-state function and a position indication in one housing.

Electrical connection and signal handling for the 4740

The inductive version uses two-wire proximity sensors and is designed to work through isolating switch amplifiers to EN 60947-5-6; it is not meant to be wired straight into a plain digital input without the correct amplifier. The microswitch version is wired to terminals 41/42/43 and 51/52/53 and handles up to 250 V AC at 16 (6) A. The optional solenoid valve uses terminals 81 and 82. Use the M20x1.5 gland with a cable sized to give a proper seal, and close unused entries to keep the IP 65 rating.

Selection and ordering checklist for the 4740

• Confirm the host valve is a Type 3353, Type 3354 or Type 3379; the 4740 is intended for these.
• Confirm the total travel is within 0 to 15 mm.
• Choose inductive for connection through isolating amplifiers, microswitch for direct switching of mains-type loads.
• Decide on the 24 V DC solenoid valve option, with or without a pneumatic connection.
• Choose the correct mounting kit: 1400-9922 for the angle seat and globe valves, 1402-1067 for the Type 3379 actuator.
• Check the ambient temperature is between –20 and +65 °C and that no explosive atmosphere is present; the datasheet does not list an explosion-protection approval for this model.

Installation and maintenance of the 4740

Fit the correct mounting kit first, then adjust the limit contacts with the valve in each end position and check the signal at the control system. Test the solenoid function by removing power and verifying that the actuator vents and the valve reaches its fail-safe position. Keep the cover closed and the gland tight, particularly outdoors where dust and humidity are high. A periodic function test belongs in the plant preventive maintenance schedule, together with a check of the polyamide housing for cracks from UV exposure or impact.

Typical applications in Oman and the GCC

Small angle seat and globe valves with pneumatic actuators are common in utilities, steam and condensate lines, chemical dosing, food and beverage and water treatment. A compact limit switch like the 4740 provides open/closed feedback for the DCS or PLC without a separate positioner. Within its temperature limit, it fits process skids in desalination, power plants and general industrial plants across Oman and the GCC. For hazardous areas or higher ambient temperatures, other Samson limit switches such as the 4746 and 4747 should be reviewed instead.

Information to send with an RFQ for the 4740

• Full article code or the required options: sensor type, solenoid valve and pneumatic connection.
• Host valve or actuator type and travel.
• Control voltage and signal handling (amplifier or direct).
• Mounting kit needed.
• Quantity and delivery location.

Documents and quotation

A Samson Type 4740 datasheet (T 8357 EN) is attached on this page with the wiring diagrams, dimensions and article code.

Send the article code or the valve type and Seven Star LLC will confirm the details and prepare a quotation for Oman and the GCC.