LESER High Pressure Series – Type 455/456 and 457/458 Safety Valves

Overview

The LESER High Pressure Series groups together LESER’s full-nozzle safety valve types built specifically for the upper end of the pressure spectrum within the wider High Performance product platform: the Type 455/456 and the Type 457/458. Where the standard rolled-in-seat Type 441/442 line is optimized for general industrial pressure ranges, these two types share a full-nozzle, welded-in-seat construction engineered to hold set-pressure accuracy and seat integrity at pressures up to 300 bar — a critical distinction for process engineers specifying safety relief on high-pressure separators, gas compression trains, and steam generation equipment.

With regional stock and engineering support in Muscat, Seven Star LLC proudly supplies the High Pressure line to refineries, gas processing plants, and power generation facilities throughout Oman and the wider GCC, backed by genuine manufacturer documentation, warranty support, and local technical guidance.

Operating Principle

Both types in this line are direct-acting, spring-loaded, full-lift safety valves with a nozzle-type seat rather than the rolled-in seat used on the standard-pressure Type 441/442 line. In a full-nozzle design, the seat ring is machined into (or permanently fitted within) a separate nozzle insert that is isolated from the body casting, so the seating surface is not subject to the same thermal and mechanical stress the body itself experiences under high system pressure. This isolation is what allows the Type 455/456 and Type 457/458 to hold tight, repeatable set-pressure tolerances at pressures where a standard rolled-in-seat design would be more prone to seat drift over repeated lift cycles.

Once system pressure exceeds the calibrated spring force, the disc lifts fully off the nozzle seat and discharges through the valve outlet, and the design gives a stable full-lift characteristic rather than a partial “simmer” lift, which matters directly for capacity-critical high-pressure relief scenarios where the full rated flow needs to be reached quickly and predictably. Both types are available with a metallic seat and sealing-plate or O-ring secondary seal options depending on the tightness requirement of the protected system.

Engineering Design of the LESER High Pressure Series

The Type 455/456 covers DN 25 to DN 100 (or NPS 1 to NPS 4 on ASME B16.5 flanges) with a set-pressure range of 2.5 to 100 bar and a temperature range of –85°C to 550°C on CE-certified units (–29°C to 538°C on ASME units), in orifice sizes F+ to N+. The Type 457/458 extends the same full-nozzle body concept to a wider DN 25 to DN 150 (NPS 1 to NPS 6) size range and a higher 2.5 to 300 bar set-pressure ceiling across the same temperature envelope, with orifice sizes E through Q. Both types are supplied in carbon steel (1.0619), high-temperature carbon steel (1.7357), and cast stainless steel (1.4581) body materials, with stainless steel bellows available where back-pressure compensation is required.

Because both types share the same full-nozzle architecture and body material options, a plant standardizing on the LESER High Pressure line can move between the Type 455/456 and Type 457/458 purely on the basis of required set pressure and flow capacity, without changing bellows configuration, seat material logic, or spare-parts strategy. This shared design lineage keeps maintenance procedures and technician training consistent across a plant’s full population of high-pressure safety valves.

Key Features

The LESER High Pressure line delivers the following strengths for demanding process safety applications:

• Full-nozzle seat design isolates the seating surface from body stress, holding tighter set-pressure accuracy at high pressure than a rolled-in-seat design.
• Type 457/458 reaches set pressures up to 300 bar, covering the most demanding relief duties within the High Performance product platform.
• Wide temperature capability from –85°C to 550°C (CE) suits both cryogenic and high-temperature steam or process gas service.
• DN 25–150 / NPS 1–6 size range on Type 457/458 covers everything from small high-pressure separators to larger process vessels.
• Stainless steel bellows options are available on both types for services with variable or superimposed back pressure.
• Body material choices spanning carbon steel, high-temperature carbon steel, and cast stainless steel match the valve to the protected system’s temperature and corrosivity.
• Metallic seat with sealing-plate or O-ring secondary seal options let engineers tune tightness to the specific application.
• Full-lift, stable-flow characteristic ensures rated capacity is reached predictably during a genuine overpressure event.

Industrial Applications

The LESER High Pressure Series is specified wherever process conditions exceed what a standard rolled-in-seat safety valve is designed to hold reliably — high-pressure gas compression trains, deep-well injection and gas-lift systems, steam generation packages, and high-pressure separator vessels found across upstream oil and gas facilities, gas processing plants, and refineries. These duties are common across Oman’s upstream and midstream oil and gas sector and the wider GCC’s petrochemical corridor.

Backed by genuine manufacturer documentation, Seven Star LLC distributes the High Pressure line to EPC contractors, plant reliability teams, and process equipment fabricators across Muscat, the Sohar Freezone and industrial port, the Salalah Free Zone, and the wider Sultanate of Oman and GCC, ensuring every valve supplied carries full manufacturer traceability, certification, and after-sales technical support from a locally based team.

Technical Specifications

The comparison below sets the two High Pressure types against each other by verified size, pressure, and temperature range:

Call To Action

Seven Star LLC invites process engineers, EPC contractors, and procurement teams across Oman and the GCC to submit a formal RFQ for the LESER High Pressure Series, covering Type 455/456 and Type 457/458. Regional warehouse stock, full technical datasheets, and direct access to the Seven Star LLC instrumentation and valve division are available on request. Working closely with plant engineers in the region, Seven Star LLC guarantees genuine product, complete documentation, and factory-backed warranty on every unit supplied.