Anderson Greenwood Series 400 Modulating Pilot Operated Relief Valve

Overview

The Anderson Greenwood Series 400 is a modulating pilot operated safety relief valve from Emerson that opens only as far as the relief demand requires. Instead of popping fully open, the main valve lifts in proportion to the flow that must be discharged, so the Anderson Greenwood Series 400 releases only the mass needed to keep process pressure inside the code allowance. Emerson states that under process conditions the main valve can be seat tight to as high as 98% of set pressure, and the published set pressure range runs from 15 to 1480 psig (1.03 to 102 barg) on ANSI Class 150 to 600 inlets.

Seven Star LLC supplies the Anderson Greenwood Series 400 to oil and gas producers, gas utilities, tank farms, desalination plants and petrochemical sites in the Sultanate of Oman and the wider GCC. Our engineers in Muscat help match the valve to the relief case and the fluid, and we offer sourcing and model selection support in Muscat for spares and soft goods.

How the Anderson Greenwood Series 400 Pilot Works

With no system pressure applied, the pilot inlet seat is open and the outlet seat is closed. As pressure enters the main valve inlet it passes a filter screen into the pilot, flows through passages in the feedback piston and past the inlet seat into the dome, holding the main valve piston closed. As system pressure approaches set, it acts upward on the sense element, a diaphragm or piston, and the feedback piston also rises to close the inlet seat. Dome pressure is now locked in because both seats are closed, and at any stable inlet pressure there is no pilot flow, which Emerson describes as zero leakage.

On the Anderson Greenwood Series 400, a small further rise in pressure opens the outlet seat and partially vents the dome. The reduced dome pressure acts on the unbalanced feedback piston, which moves to lock in the new dome pressure. Above set pressure the spool and feedback piston alternately raise and lower dome pressure so that the main valve piston sits at exactly the lift that holds system pressure constant at the required flow. Full lift, and therefore full capacity, is reached with relatively little overpressure. When pressure falls below set, the feedback piston opens the inlet seat, the dome refills and the main valve closes. The pilot exhaust is always discharged to the main valve outlet, not to atmosphere.

Why Modulating Action Matters

Emerson notes that the modulating action of the Anderson Greenwood Series 400 is strongly preferred for liquid relief because it minimises the destructive effects of liquid hammer. For gas service, proportional lift reduces product loss per relief event, cuts emissions and noise during normal system upsets, and avoids the instability that can follow when a valve is oversized for small upsets. Because only a small amount of fluid is discharged, the valve is also less sensitive to inlet pressure losses than a pop action design. Blowdown of the Anderson Greenwood Series 400 is minimal, with the valve reseating slightly below set pressure.

For natural gas DOT applications, the High Gain pilot option increases the effective gain of the pilot so the dome vents faster. Emerson states that this gives full main valve lift by 5% overpressure while still limiting product loss; the option is offered for natural gas transmission and supply applications from 15 to 1480 psig.

Key Features

Features of the Anderson Greenwood Series 400 listed in the Emerson datasheet include:

• Main valve seat tightness to 98% of set pressure, increasing system output without leakage.
• Balanced design, so lift is unaffected by back pressure and no bellows is needed.
• Set point indicator button and field test connection for in-service verification of set pressure without an isolation block valve.
• Non-flowing pilot with a feedback mechanism, independent of the primary sensing element, for smooth modulation in dirty or wet service.
• Soft seats that reseal bubble tight before and after relief cycles and avoid metal seat lapping.
• Single, accurate set pressure adjustment.
• ASME Section VIII and Section XIII (UV designator) code stamp for gas and liquid service, CE mark to PED 2014/68/EU, plus DOT and CSA compliance.
• Lettered orifices to API 526 dimensions, and API 526 direct spring center-to-face dimensions available for drop-in replacement.

Industrial Applications

Because it handles gas and liquid with the same pilot principle, the Anderson Greenwood Series 400 is widely used on pipeline pressure limiting stations, city gate and gas supply skids, compressor discharge lines, hydrocarbon liquid pumps and storage, and produced water and crude systems. In Oman, gas networks feeding power and desalination plants, refinery and petrochemical units around Sohar and Duqm, and oilfield facilities in the interior all have relief cases where low product loss and stable lift are important.

Seven Star LLC supplies the Anderson Greenwood Series 400 and its spare soft goods to plant owners and EPC contractors across Muscat, Sohar, Salalah and the GCC, helping customers keep relief systems compliant and minimise flaring.

Options and Materials

Optional accessories for the Anderson Greenwood Series 400 include a field test connection with indicator, backflow preventer, pilot supply filter, pressure spike snubber for gas, remote pressure sense connection, remote valve lift indicator, manual unloader, pilot lift lever, remote unloader, NACE trim to MR0175/ISO 15156:2015 and the High Gain pilot. For the Anderson Greenwood Series 400, main valve material codes cover CS body with SS trim, all stainless steel, low temperature CS, duplex and super duplex, with NACE compliant variants, and a full nozzle main valve is available.

Selection Notes (General)

This section is general engineering guidance, not manufacturer data. Confirm that the set pressure falls within the 15 to 1480 psig band and the inlet rating within Class 150 to 600; higher pressures call for the Series 800. Check the process temperature against the soft goods table, because continuous service temperature is limited by seat and seal materials. Calculate the Anderson Greenwood Series 400 orifice area for each relief case and specify whether the High Gain option or remote sensing is needed.

Technical Specifications

Data for the Anderson Greenwood Series 400 from Emerson datasheet VCTDS-00543:

How to Order

For a quotation on the Anderson Greenwood Series 400, send Seven Star LLC your relief case data: fluid, required capacity, set pressure, back pressure, temperature, inlet and outlet sizes and ratings, and material or NACE requirements. You can download the Emerson datasheet from this page. Related pressure relief products on our site include the Anderson Greenwood Series 90/9000 relief valve, the LESER Modulate Action series safety valves and the Crosby OMNI-TRIM Series 900 relief valves. Seven Star LLC provides model selection support from Muscat for customers across Oman and the GCC.