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Brand: LESER
LESER Type 821 Modulate Action Pilot-Operated Safety Valve
Description
API 526 pilot-operated safety valve that opens in proportion to overpressure
The LESER Type 821 is the modulate action version of the LESER High Efficiency pilot-operated safety valve (POSV). It combines the API 526 main valve with a Series 820 pilot that opens the valve gradually, in proportion to the overpressure, so that only as much mass flow is discharged as is needed to stop the pressure rise. This keeps product loss small and suits services where the medium should not be released to atmosphere in large quantities.
Unlike the pop action Type 811, which is limited to gas, LESER lists the modulate action design for steam, gases and liquids.
Technical specifications
| Parameter | Specification |
|---|---|
| Manufacturer | LESER GmbH & Co. KG |
| Type | 821, Series 820 modulate action pilot |
| Design standard | API 526 |
| Sizes | 1 in. x 2 in. to 8 in. x 10 in. (DN 25 to DN 200) |
| Orifices | API D to T; Extra Orifice 1 G 2 to 8 T+ 10 |
| Flange ratings | ASME B16.5 CL150 to CL2500; EN 1092-1 PN 10 to PN 400, depending on size (CL2500 / PN 400 marked as in preparation in the catalog) |
| Body materials | WCB / 1.0619, LCB, CF8M / 1.4408 |
| Full open | At max. 10 % overpressure |
| Blowdown | Max. 7 %, fixed |
| Media | Steam, gases and liquids |
| Back pressure | Up to 70 % of set pressure (main valve outlet rating permitting) |
| Tightness | Up to 97 % of set pressure |
| Pilot | Stainless steel pilot; tubing integrated in top plate; backflow preventer in manifold block as standard |
Why a pilot-operated valve
In a POSV the system pressure is led to the dome above the main valve piston. Because the dome area is larger than the seat area, the closing force rises as the pressure approaches set point, which is why LESER quotes tightness up to 97 % of set pressure. This allows plants to run closer to set pressure than with a spring-loaded valve. The set pressure is independent of superimposed or built-up back pressure within the operating limits, which matters on long flare headers in refineries and on offshore platforms.
Where inlet pressure loss exceeds 3 %, LESER refers to API 520 Part 2 and recommends remote sensing of the pilot.
Selection and related types
Size the valve with the required capacity, set pressure, back pressure and fluid; LESER provides its VALVESTAR sizing software for this. The modular design means pop action and modulate action pilots can be exchanged without changing the tubing, so a plant can standardise on one main valve. For gas service needing fast full lift, see the LESER Type 811 pilot-operated safety valve.
Typical uses named by LESER include gas compressor stations, where vibration can make spring-loaded valves simmer, and refinery units discharging into common flare headers with back pressure of 50 % of set pressure or more. On offshore platforms the compact size and tight shut-off help where weight and leakage are both limited. Integral cast support brackets on the main valve help absorb reaction forces at high pressures.
Documents and quotation
The attached LESER High Efficiency catalog covers Types 811 and 821 with materials, functional descriptions, article number tables and dimensions. Send the LESER article number, or size, orifice, flange ratings, set pressure, fluid, temperature and back pressure, for a quotation. Other valves are listed under Safety Relief Valves.
Datasheets & Documents
- Catalog LESER High Efficiency pilot-operated safety valves extended catalog, Types 811 and 821 (EN) Download
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About brand
Safety valves are the whole business at LESER, which traces its origins to Hamburg in 1818. The range runs from small threaded valves to API 526 flanged valves and pilot-operated designs. Seven Star LLC lists LESER safety relief valves across these product groups and sources them, with the manufacturer's documentation, for pressure equipment in Oman.
LESER safety valve product groups
LESER sorts its valves into named groups, and the type number identifies the design:
- API: Type 526 flanged safety relief valves to API 526 dimensions
- High Performance: Type 441/442 flanged valves, and Type 455/456 and 457/458 for high pressure
- Compact Performance: threaded Types 437, 459 and 462
- High Efficiency: pilot-operated safety valves such as the pop action Type 811
- Critical Service: Types 447 and 449 for corrosive media, the 447 with PTFE-lined wetted parts
- Clean Service: hygienic valves for food and pharmaceutical plants
Modulate Action valves and change-over valves, which let one of two safety valves be taken offline, complete the listing.
Where LESER safety valves are used
LESER safety valves protect pressure vessels, heat exchangers, boilers, compressors, pumps and piping against overpressure in oil and gas, refining, petrochemical, power, industrial gas, food and pharmaceutical plants throughout the GCC. Spring-loaded valves are the standard choice. Pilot-operated valves are selected where operating pressure runs close to set pressure or back pressure is high.
Ordering LESER valves: what we need
A safety valve is always built to a set pressure, so a type number alone cannot be quoted. Please send the nameplate data of the existing valve (type, article or job number, serial number, set pressure, orifice) or a full data sheet: medium and its state, set pressure, operating and relieving temperature, back pressure, required capacity, inlet and outlet size and rating, body and trim material, design code (ASME Section VIII or PED) and options such as bellows, lifting lever or sour service materials. We verify the selection against LESER documentation and supply the manufacturer's certificates on request.
Browse LESER products by category: Safety Relief Valves.
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Frequently Asked Questions
What is the difference between LESER Type 821 and Type 811?
Type 821 uses the Series 820 modulate action pilot and opens in proportion to overpressure; Type 811 uses the pop action pilot and opens fully at once.
Which media can the Type 821 handle?
LESER lists steam, gases and liquids for the modulate action design; the pop action Type 811 is for gas only.
Which sizes and orifices are available?
Sizes 1 in. x 2 in. to 8 in. x 10 in. (DN 25 to DN 200) with API orifices D to T, plus LESER Extra Orifices.
How much back pressure can a LESER POSV tolerate?
LESER states that its POSVs work with back pressure up to 70 % of set pressure, and the set pressure is not affected by back pressure within the limits.
Can a Type 821 be converted to pop action?
Yes. The catalog states that pop action and modulate action pilots can be exchanged without tubing modification.
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