Samson 3711 Quick Exhaust Valve for Actuators

Samson 3711 quick exhaust valve for faster actuator venting

The Samson 3711 is a compact quick exhaust valve that sits in the air line between a positioner or solenoid valve and a pneumatic actuator. Its single job is to let the actuator vent quickly when the control pressure falls, instead of forcing all the exhaust air to travel back through a small positioner or solenoid port. Behaviour is similar to a 3/2-way valve with an exhaust port. Seven Star LLC supplies the Samson 3711 in Oman and the GCC as an independent supplier in Muscat, for plants that need shorter valve stroke times on pneumatic control and on/off valves.

The datasheet lists one standard version, Type 3711-0, with an aluminum body and an adjustable restriction. A stainless steel body is available through the article code, which is relevant for offshore, coastal and washdown locations in the Gulf.

How the Samson 3711 works

Three ports are used: SIG receives the control pressure, OUT goes to the actuator and EXH is the exhaust port. When control pressure is applied at SIG, the diaphragm plate rests on its seat and closes the exhaust. Air passes through the check valve to the OUT port while pressure rises, and nothing is vented.

When the control pressure drops, the check valve closes. Once the pressure difference between actuator and control side reaches a certain value, the diaphragm plate lifts off the exhaust seat and the actuator air leaves directly through the large EXH port. The result is a much faster venting stroke than the positioner alone could achieve.

An adjustable restriction screw works in parallel. It stops the air from being exhausted quickly during normal modulating control and lets you set the venting characteristic. Access to the screw is secured with a cotter pin through a hole in the housing, so the setting cannot be changed by accident once commissioned.

Technical specifications of the 3711 quick exhaust valve

Decoding the 3711 article code

The ordering table of the datasheet builds the code Type 3711- from eight option positions followed by a final zero. The options that exist on this model are:

Because most positions have only one choice, the real decisions are body material and whether the silencer is supplied. If you give us the full code from an existing nameplate, we can match it directly.

Where the 3711 fits in the pneumatic circuit

The datasheet shows two hook-ups. In the standard hook-up the positioner output feeds the SIG port, a solenoid valve may sit in the line, and the 3711 OUT port connects to the actuator. In the second hook-up the quick exhaust valve is combined with purging of the actuator spring chamber, with a restriction and silencer added to the circuit. In both cases the valve should be mounted as close to the pneumatic actuator as possible, because the shorter the exhaust path, the faster the venting.

One restriction is stated clearly: the 3711 is not suitable for combination with a volume booster. If an actuator already has a booster in the line, the two should not be used together. Within the same Samson accessory family you may also meet related items such as the 4708 supply pressure regulator, the 3941 solenoid valve and the 4746 and 4747 limit switches, which are covered on separate pages.

Selection and ordering checklist for the 3711

• Confirm the actuator really needs faster venting; check the stroke-time requirement of the safety or process specification.
• Confirm supply and control pressure stay within 0 to 7 bar.
• Choose aluminum for general indoor and sheltered duty, stainless steel for marine, salt-laden or chemically aggressive air.
• Decide whether a silencer is required to reduce exhaust noise near operators; the datasheet recommends a silencer with adequate strength and flow rate.
• Check port sizes: G 3/8 on the control side and G 3/4 on both OUT and EXH.
• Check that instrument air meets the ISO 8573-1 classes given above, with dew point at least 10 K under the lowest ambient temperature.
• Confirm no volume booster is installed in the same line.

Installation, commissioning and maintenance of the 3711

Mount the valve close to the actuator port with the EXH port free to breathe. Where the exhaust air is routed away, keep the line short and wide, since restricting the exhaust defeats the purpose of the valve. Fit the silencer or an open fitting rather than a long small-bore tube.

For commissioning, start with the restriction screw in a middle position, run the valve through its stroke and then adjust until the venting behaviour suits the process. Remember that the supply-side flow coefficient changes between 1.3 with the screw closed and 1.9 with the screw open, so opening the screw also makes the fill stroke faster. Secure the setting with the cotter pin afterwards.

Maintenance is limited to keeping the air clean. Dust, oil carry-over or condensate are the usual causes of check valve leakage and sticking diaphragm plates. If hysteresis grows or the actuator drifts, inspect the VMQ diaphragm, check valve and seats, and check the upstream filter regulator.

Typical applications in Oman and the GCC

Quick exhaust valves are specified wherever a pneumatic valve must move to its fail-safe or shutdown position quickly. In oil and gas facilities this includes emergency shutdown and process isolation valves on spring-return actuators. In power and desalination plants they appear on cooling water, dosing and steam-side control valves where stroke time matters. High ambient temperatures in Gulf summers and dust are normal on these sites; the stated range of –40 to +80 °C and the corrosion-protected aluminum or stainless body suit that environment. For coastal installations Seven Star LLC would normally discuss the stainless steel body first.

Information to send with an RFQ for the 3711

• Full nameplate article code of the existing valve, or the required body material.
• Silencer required: yes or no.
• Actuator type, size and spring chamber volume if known.
• Operating pressure and instrument air quality.
• Required venting time or stroke time, if specified.
• Quantity and required delivery location in Oman or the GCC.

Documents and quotation

A Samson Type 3711 datasheet (T 8547 EN) is attached on this page and gives the data, article code and hook-up diagrams used above. Please confirm the details against it before ordering.

Send us the article code and quantity and Seven Star LLC will prepare a quotation for supply to Oman and the GCC.