LESER Type 811 High Efficiency Pilot-Operated Safety Valve

Overview

The LESER Type 811 is a High Efficiency pilot-operated safety valve (POSV) that departs from the direct spring-loaded architecture used across most of LESER’s range, instead using a small pilot valve to control a larger main valve for gas protection duty where operating margin and back-pressure tolerance matter as much as raw capacity. Sized from DN 25 to DN 200 (DIN EN 1092) or NPS 1 to NPS 8 (ASME B16.5), with set pressures from 2.5 to 255.5 bar (36.0 to 3,705.0 psig) and a temperature range of -162°C to 300°C, the Type 811 is engineered specifically for chemistry, oil and gas, petrochemical, energy, and LNG/LPG installations where systems must run close to their set pressure without nuisance relief.

Working closely with plant engineers in the region, Seven Star LLC proudly supplies the Type 811 to gas processing, LNG/LPG, and petrochemical projects across Oman and the wider GCC. Facilities in Muscat, Sohar, and Salalah handling high-value or safety-critical gas systems rely on Seven Star LLC for LESER pilot-operated hardware, correct pilot-configuration selection, and manufacturer documentation to support regulatory compliance.

Operating Principle

The Type 811 uses a pilot-operated “Pop Action” mechanism: a small pilot valve senses system pressure and, up to the set point, uses that same process pressure to hold the main valve’s larger piston or disc firmly closed against the seat – giving a tighter shutoff at pressures close to set point than a direct spring-loaded valve can achieve. When system pressure reaches the set point, the pilot vents the loading pressure from above the main valve piston, and the main valve snaps open abruptly to full capacity, discharging the excess gas until pressure falls and the pilot re-establishes the closing signal.

This pilot-controlled behaviour is what allows the Type 811 to operate efficiently up to 96% of set pressure without the risk of simmering or premature lift that a conventional spring valve can show as it approaches its set point, and to tolerate back pressure up to 70% of set pressure without adversely affecting the valve’s lift or reseating characteristics. Because the main valve is not held closed by a heavy spring but by process pressure itself acting through the pilot, larger orifice sizes are achievable in a more compact envelope than equivalent-capacity spring-loaded valve, while the pop-action opening still delivers the rapid, full-capacity discharge required for effective overpressure protection.

Engineering Design of the LESER Type 811

The LESER Type 811 main valve body is available in carbon steel (1.0619 / SA216 WCB) and stainless steel (1.4408 / SA351 CF8M), with Duplex, Monel, and Hastelloy variants available for sour, corrosive, or cryogenic services beyond standard carbon and stainless steel capability. Orifice designations run from D through T+, with the narrowest flow diameter at approximately 11 mm scaling up to 180 mm at the largest size, and connections are available to DIN EN 1092 or ASME B16.5 flange standards to suit the governing piping code.

The LESER Type 811 pilot assembly mounts external to the main valve body and is field-serviceable independent of the main valve, so pilot inspection, adjustment, or replacement does not require removing the main valve from the line in most configurations. Pilot configuration options support modulating or non-modulating (pop) behaviour, remote sensing where the pilot must respond to pressure at a point other than the main valve inlet, and back-flow preventer options for systems where reverse flow through the pilot sensing line would otherwise be a risk, giving engineers considerable flexibility to match the pilot system precisely to the protected process.

Key Features

The LESER Type 811 is the LESER platform of choice wherever plant efficiency and tight operating margins matter as much as relief capacity. Highlights include:

• Pop-action pilot-operated design that opens abruptly to full capacity once set pressure is reached.
• Operating efficiency up to 96% of set pressure, minimizing nuisance relief and lost process gas.
• Back-pressure tolerance up to 70% of set pressure without compromising lift or reseating performance.
• Size range from DN 25 to DN 200 (DIN EN 1092) or NPS 1 to NPS 8 (ASME B16.5).
• Set pressure range of 2.5 to 255.5 bar and temperature range of -162°C to 300°C, covering cryogenic LNG through elevated-temperature gas service.
• Body material options including carbon steel, stainless steel, Duplex, Monel, and Hastelloy for demanding or corrosive media.
• Orifice designations D through T+, with flow diameters from roughly 11 mm to 180 mm.
• Field-serviceable external pilot assembly, allowing pilot maintenance without removing the main valve in most installations.

Industrial Applications

The LESER Type 811 is specified for gas protection duty across chemistry, oil and gas, petrochemical, energy, and LNG/LPG facilities, including LNG storage and regasification systems, gas processing and compression trains, petrochemical reactor and separator protection, and high-value gas pipelines where minimizing product loss during near-set-pressure operation carries real commercial value. Its cryogenic-to-300°C temperature range and Duplex, Monel, and Hastelloy material options extend its reach into sour gas and corrosive process streams that would be beyond a standard carbon steel spring-loaded valve.

With fast quotation turnaround and technical support, Seven Star LLC supplies the Type 811 throughout Oman and the GCC, supporting LNG, LPG, and gas processing infrastructure in the Sohar and Salalah industrial and free zones as well as petrochemical and energy projects across Muscat and the wider Sultanate of Oman. Facilities specifying pilot-operated safety valves for high-value gas systems work directly with Seven Star LLC’s instrumentation division for pilot configuration, material selection, and supply.

Technical Specifications

Key parameters for the LESER Type 811 High Efficiency pilot-operated safety valve, the LESER Type 811, are summarized below for specifying engineers.

Request a Quote for LESER Type 811

Seven Star LLC’s instrumentation division is ready to prepare a formal RFQ for the LESER Type 811, with lead time confirmed at quotation for LNG, petrochemical, and gas processing project schedules. Technical datasheets, pilot-configuration guidance, and material certification are available on request, and as an experienced supply partner for LESER in Oman and the GCC, Seven Star LLC guarantees genuine product, full traceability, and manufacturer-backed warranty on every valve supplied. Contact our team today to specify the correct LESER Type 811 configuration for your gas protection application.

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