ASCO 308 Tamper-Proof Manual Reset Solenoid Valve

ASCO 308 / EV8308 tamper-proof manual reset solenoid valve

The ASCO 308 series (sold in explosionproof form as the EV8308 and 8308 numbering) is a pilot-operated solenoid valve with a manual reset handle, designed so that the valve cannot be re-opened by hand unless the solenoid is energized and auxiliary air is available. It is a safety-shutdown style device: the process stays isolated after a trip until a person deliberately resets it.

Seven Star LLC supplies the ASCO 308 series in Oman and the GCC as an independent supplier in Muscat. The catalog numbers we checked in the manufacturer literature are EV8308G060, EV8308G360, EV8308G061 and EV8308G361. The “EV” prefix marks the ATEX/IECEx certified construction, the digits 060/061 and 360/361 separate AC from DC pilots and the two pipe sizes, as laid out in the table below.

How the catalog numbers differ

ASCO 308 technical specifications

How the ASCO 308 manual reset and no-voltage release work

The 308 is a three-way valve that uses a small solenoid pilot to control an air-operated main section. The reset handle sits on the operator and does not drive the process port directly. Lifting it only latches the operator up, and only when the pilot is energized and auxiliary air is present at the pilot.

If the solenoid is de-energized, the latch trips and the operator drops to its down position. Moving the handle while the valve is tripped does not shift the valve. This is the tamper-proof behavior: the valve stays shut even when someone holds the handle up. After a shutdown, power has to be restored to the solenoid first, and only then can the valve be reset by hand.

The catalog also notes that if the auxiliary air to the pilot is lost, the main valve shifts position. For that reason the supply air and its failure mode should be part of the safety design, not an afterthought.

Where the ASCO 308 fits in a plant

A manual reset valve belongs in the final-element part of a shutdown loop. A typical use is a fuel or gas supply to a burner, a heater skid or a compressor package, where an emergency shutdown must close the line and keep it closed until an operator has inspected the cause. The valve can also pilot a larger actuated shutdown valve, with the 308 venting or supplying the actuator air.

Because the catalog states SIL 3 capability per IEC 61508 with third-party certification, designers can use it in safety instrumented functions, but the final SIL claim always belongs to the complete loop calculation. For general-purpose automatic valves in the same ASCO range, other series are more suitable; the 308 is chosen when a deliberate manual reset is a requirement.

ASCO 308 selection and ordering checklist

• Pipe size: 1/4 in. (Cv 1.5) or 1/2 in. (Cv 4) according to the flow the shutdown line needs.
• Pilot type: AC (10.1 W, fluid to 82 °C) or DC (1.4 W, fluid to 60 °C). Low-power DC pilots suit loop-powered or battery-backed trip circuits.
• Coil voltage and frequency, since the catalog says voltage must be specified when ordering.
• Hazardous area classification of the site, so the EV certified construction and the right enclosure type are chosen.
• Auxiliary air supply: pressure must stay within the 25 to 125 psi pilot differential, and the main valve is limited to 150 psi.
• Ambient temperature at the installation point against the 52 °C (AC) or 60 °C (DC) limits.
• Optional position indicator switch (suffix SP); the manufacturer asks for factory contact on ordering details.

Installation, commissioning and maintenance of the ASCO 308

Mount the valve with the pilot accessible and the reset handle free to move through its full travel. Pipe the auxiliary air through a clean, dry supply; filtering and drying the air protects the small pilot passages. After wiring, energize the solenoid, supply air, lift the handle and confirm that it latches. Then remove power and check that the operator drops and the process port isolates. Repeat with the handle held up to prove the tamper-proof action.

Record the trip test in the plant proof-test log. Spare coils should be kept: the catalog lists coil part numbers 238610 (AC general purpose), 238710 (DC general purpose), 238614 (AC explosionproof) and 238714 (DC explosionproof), and a spare DC coil 274714-902-D for 24 VDC. Replace seals according to the manufacturer rebuild kit for the exact catalog number rather than guessing.

Typical applications in Oman and the GCC

Gas processing plants, wellhead and flowline skids, burner management systems on heaters and boilers, and fuel gas trains on turbine packages all use manual reset shutdown valves. Coastal sites such as desalination and power stations value the stainless construction and the anodized, coated aluminum parts against salt-laden air. In hot desert installations the ambient limits in the specification table need to be checked against enclosure surface temperature under direct sun.

The explosionproof enclosure options are relevant for Zone 1 and Zone 2 areas in refineries and petrochemical units. For dusty locations the NEMA 4, 4X and 6 ratings help keep sand and humidity out of the solenoid housing.

Information to send with an ASCO 308 RFQ

• Full catalog number from the nameplate (for example EV8308G061) or the process data if you only know the function.
• Coil voltage, frequency and AC or DC.
• Pipe size, process medium, operating pressure and temperature.
• Area classification and certification required (ATEX, IECEx or other).
• Quantity of valves and spare coils or rebuild kits.
• Photo of the nameplate when replacing an existing valve.

Documents and quotation

Send the ASCO 308 catalog number and your required voltage and we will confirm the available documents before quotation.

Seven Star LLC quotes against the exact catalog number so that voltage, pilot type and certification match your safety design. Contact our Muscat office with the details above to start an RFQ.