IMI STI SL Exhaust Protection System with Check Valve

IMI STI SL exhaust protection system with integral check valve

The IMI STI SL is an exhaust protection system and silencer for large pneumatic actuators. It dissipates the energy of a high-volume exhaust through a labyrinth of cage elements, keeps back-pressure very low so that the actuator can still stroke quickly, and closes an internal check valve as soon as flow stops so that dust, sand and water cannot get back into the exhaust line. Seven Star LLC supplies the IMI STI SL in Oman and the GCC as an independent supplier in Muscat.

The SL is available in two sizes defined by the number of elements: a three-element version and a five-element version. The element count sets the maximum flow coefficient, the weight and the exhaust capacity, so it is the main selection decision for this product.

IMI STI SL technical specifications

How the SL labyrinth and check valve work

When a large actuator vents, the air leaves at high velocity and produces noise, and any restriction in the exhaust path slows down the valve. The SL spreads this flow through a cage labyrinth, which dissipates the energy of the jet with minimal resistance to the air. The brochure describes the design as self-cleaning, meaning that dirt carried in the exhaust is less likely to clog the passages than in a sintered or mesh silencer.

The integral check valve is the second key function. While the actuator exhausts, the check valve opens widely with very low back-pressure, so the valve can move at high dynamic speed. When exhaust flow stops, the check valve closes immediately. In that state the internal parts of the actuator and any accessories connected upstream are shielded from dust or other materials, which supports the IP65 protection rating and helps the actuator breathe cleanly in sandstorm conditions.

The labyrinth is designed for installation in any orientation and minimises the ingress or storage of water. This matters on offshore and coastal sites where the exhaust port may point sideways or down because of limited space.

Materials and ATEX-related construction of the SL

The SL combines a stainless steel 316 structure with an antistatic polymeric material. The brochure states that the polymeric material complies with ATEX directives for use in an explosive atmosphere, which is why an antistatic plastic can be used on a silencer in hazardous areas. If your project needs certificate numbers or a marking for a defined zone, request those documents with the enquiry so they can be checked for the exact version supplied.

Choosing between three and five elements for the SL

Choose the number of elements from the exhaust flow that the actuator and booster combination can produce, not from the actuator size alone. If the exhaust is throttled by an undersized silencer, the valve will close or open more slowly than the design stroking time, and a quick-exhaust or booster upstream will be wasted. When in doubt, send the actuator volume, supply pressure and required stroke time to Seven Star LLC.

Where the SL fits with other IMI STI accessories

The SL is used at the exhaust of a pneumatic circuit that may also include a positioner, a booster and a derivative unit. For instance, the IMI STI AV volume booster supplies air to the actuator, the UD derivative unit controls the speed of the exhaust, and the SL protects and quietens the final vent. In the same family, the BV and BW boosters are higher-capacity options for very large actuators, and the SL is a natural partner for them. For the positioner, see the FasTrak FTC digital model or the SR/CCK analog model.

Selection and ordering checklist for the SL

• Number of elements: 3 or 5, based on exhaust flow.
• Flange connection: confirm the flange dimensions and the pipe or port the SL will attach to.
• Actuator type and total air volume to be exhausted.
• Ambient temperature range, which must lie within -40°C to 85°C.
• Environment: offshore, sandstorm or copper-free service.
• Hazardous-area requirement and documents needed.

Installation and maintenance of the SL

Mount the SL on the flange at the exhaust point with a suitable gasket and secure it so that vibration cannot loosen it. Because it can be installed in any orientation, choose the position that is easiest to inspect and that keeps the exhaust path as short as practical. Do not add pipework or throttling after the SL unless the flow has been calculated, since added back-pressure reduces the valve speed.

During plant shutdowns, check that the labyrinth is free from debris, oil film or insect nests, and verify that the check valve closes freely. Stainless steel and antistatic polymeric parts need no routine lubrication. Keep a spare unit for critical valves, particularly those used in emergency depressurisation or shutdown duty.

Typical SL applications in Oman and the GCC

In the Gulf, exhaust protection is mainly about dust and humidity. Control and shutdown valves on desert wellpads, gas compression stations and power plants are exposed to fine sand that can enter an open exhaust port and damage soft seals. Offshore platforms and coastal desalination plants add salt-laden air. The SL is offered for standard, offshore and sandstorm conditions, so it is a suitable specification for large actuators on ESD valves, anti-surge valves and large-bore control valves in oil and gas, petrochemical and utility plants.

Information to send with an SL request

• Part name SL, number of elements and quantity.
• Actuator brand, size and volume.
• Supply pressure and required stroking time.
• Flange standard or drawing of the mounting point.
• Ambient temperature and environment.
• Hazardous-area marking or certificate requirement.

Documents and quotation

A brochure for the IMI STI SL is attached on this page, including the dimensional information for the three- and five-element versions.

Send the part number, element count and quantity to Seven Star LLC and we will confirm lead time and any further documents for the SL exhaust protection system.