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Brand: Flowserve
Flowserve Logix 520MD+ HART Digital Positioner
Description
Flowserve Logix 520MD+ HART digital valve positioner explained
The Flowserve Logix 520MD+ is a two-wire, loop-powered digital positioner that drives a pneumatic actuator from a 4-20 mA command and uses a piezo valve as its pilot stage. It is built for linear or rotary valves and carries HART communication with a built-in diagnostic engine. Seven Star LLC supplies the Logix 520MD+ and related positioner spares in Oman and the GCC as an independent supplier in Muscat; this page summarises the manufacturer data to help you prepare an enquiry.
The name encodes the diagnostic level. Per the manual, the family runs 510+, 520MD+, 521MD+ and 522MD+, which correspond to no extended diagnostics, Standard, Advanced and Pro. The Logix 520MD+ is the Standard version: it already includes position-based diagnostics and can be upgraded in the field to the Advanced level.
Logix 520MD+ technical specifications
| Parameter | Specification |
|---|---|
| Manufacturer / part number | Flowserve / Logix 520MD+ digital positioner |
| Input signal | Two-wire 4-20 mA, loop powered |
| Compliance voltage | 10.0 VDC at 20 mA (plus line losses) |
| Minimum operating current / shutdown | 3.8 mA / 3.6 mA |
| Communication | HART 6 as standard; HART 5 or 7 selectable by DIP switch |
| Air supply | 1.5 bar (22 psi) minimum; maximum 6.2 bar (90 psi) single-acting, 10.3 bar (150 psi) double-acting |
| Output air capacity | Single-acting 20.8 Nm³/h (12.2 SCFM) at 4.1 bar; double-acting 30.6 Nm³/h (18.0 SCFM) at 4.1 bar |
| Air consumption | Single-acting 0.082 Nm³/h at 4.1 bar; double-acting 0.637 Nm³/h at 4.1 bar |
| Performance | Resolution 0.25 %, linearity ±1.25 %, repeatability 0.25 %, hysteresis 1.0 %, deadband 0.3 % |
| Operating temperature | −52 to 85 °C (−61.6 to 185 °F) |
| Housing | Cast, powder-painted aluminium; fluorosilicone soft goods |
| Weight | 1.76 kg with single-acting relay; 1.88 kg with double-acting relay |
| Position feedback | Hall-effect sensor; shaft rotation 15 to 90 degrees (45 recommended for linear) |
| Hazardous area | Intrinsically safe: ATEX Ex ia IIC Ga, FM/CSA Class I Div 1 Groups A-D; non-incendive Class I Div 2 (check the label) |
How the Logix 520MD+ positions the valve
The positioner compares a command, which is the 4-20 mA signal or a digital HART value, with the stem position read by a temperature-compensated Hall-effect sensor. The command first passes through characterisation, linear, one of several equal-percent curves or a 21-point custom table, and through optional soft limits and tight shutoff. The result is the final command, and the difference between it and the actual position is the deviation the control loop must remove.
The output stage is where piezo technology is used. A piezo beam bender deflects as the inner-loop electronics apply voltage, throttling a nozzle and moving a spool or poppet relay that loads or vents the actuator. A second Hall sensor reports the relay position back to the inner loop. Because the positioner is fully powered by the 4-20 mA signal, there is no separate power wiring; start-up needs at least 3.8 mA.
Diagnostic levels on the Logix 520MD+ and its relatives
The Logix 520MD+ monitors the positioner, the relay and the electronics continuously and, together with ValveSight DTM software, can run off-line tests such as ramp, step and partial stroke tests. The Flowserve page quotes more than 130 warning alarms covering valve, actuator and positioner health.
| Model | Diagnostic level | Notes |
|---|---|---|
| 510+ | Limited diagnostics; cannot be upgraded | 4-20 mA positioner; HART is listed for the 520MD+ only |
| 520MD+ | Standard: complete safety and position-related data | HART, field-upgradeable to 521MD+ |
| 521MD+ | Advanced: adds pressure data | Upgradeable to 522MD+ |
| 522MD+ | Pro: adds force data, friction, data logging and system health | Fully upgraded |
Where the Logix 520MD+ fits in a control valve package
The manual provides mounting instructions for Valtek Mark One linear valves, FlowTop valves, standard Valtek rotary valves, MaxFlo rotary valves, rotary NAMUR (Automax) actuators and linear NAMUR pneumatic actuators. This makes the Logix 520MD+ a flexible retrofit choice when valves from several makers share one plant. A remote-mount option is also available, with cable and tube runs up to 30.5 m (100 ft).
Neighbouring models in the Flowserve line include the Logix 1500 compact single-acting positioner, the Logix 3800e and the Logix 3400MD fieldbus positioner. The 520MD+ is the choice when HART, a high diagnostic content and an LCD display are all wanted on a piezo platform.
Logix 520MD+ selection and ordering checklist
- Actuator type: single-acting spring return or double-acting, which sets the relay type and maximum supply pressure.
- Valve and actuator mounting: Mark One, FlowTop, rotary, NAMUR, and whether a remote mount is required.
- Diagnostic level wanted now (Standard, Advanced or Pro) and whether a field upgrade is likely.
- Hazardous area classification and the certification printed on the positioner, which must match the site requirement.
- Optional LCD, multi-function card with analog output, discrete output or discrete input, and limit switches.
- Air quality: the manual calls for ISA 7.0.01 clean, dry air, or air, nitrogen, CO2 or sweet natural gas; sour gas is not acceptable.
- Conduit and air port threads, and the supply pressure range available on site.
Installing and commissioning the Logix 520MD+
After mounting, tube the positioner to the actuator and connect a regulated, filtered air supply. Wire the loop in shielded cable, grounded at one end only, and check that the controller can deliver the 10 VDC compliance voltage required at 20 mA. For HART, observe the cable length and capacitance limits in the manual. Then run a stroke calibration, either with the one-button quick calibration or from the menu, and adjust gain if the response is too slow or too lively.
Maintenance is planned: the manual describes scheduled inspection, replacement of the relay and main board, and torque values for screws. Keep a spare relay assembly and main board for critical loops, and use Flowserve original spare parts only, as the manufacturer states.
Typical Logix 520MD+ applications in Oman and the GCC
Positioners of this type are used on control valves in gas processing, refineries, power plants, desalination and petrochemical units, where reliable HART-based valve health data reduces unplanned work. The wide ambient range, down to −52 °C and up to 85 °C, and the sealed aluminium housing suit outdoor installation in sun, dust and humid coastal air. Heat is the issue most relevant to the Gulf: mount the positioner so that it is shaded where possible, and check the temperature class marked on the label against the site hazardous-area drawing.
The Flowserve safety manual states that the 520MD+ is suitable for low-demand safety functions up to SIL 2 in a single (1oo1) configuration and SIL 3 in a redundant (1oo2) arrangement. The achieved SIL still has to be verified by a PFDavg calculation for the whole loop, including sensors and valves. The spool relay is stated to reach its fail-safe state in about 0.06 seconds under typical conditions, and more slowly at very low temperature.
Information to send with a Logix 520MD+ RFQ
- Quantity, and the model code or label data of an existing positioner if you are replacing one.
- Actuator make and size, single or double acting, and fail-safe direction.
- Linear or rotary mounting and the valve brand.
- Hazardous area zone, gas group, temperature class and required certification.
- Diagnostic level, LCD and any multi-function card or limit switches.
- Control system and HART host (for example AMS or a handheld) in use.
Documents and quotation
The Flowserve installation, operation and maintenance manual for the Logix 520MD+ and 510+ is attached to this page; it includes the specifications, hazardous-area certification tables and calibration procedures summarised above.
Send the positioner label data or your application details to Seven Star LLC and we will reply with a quotation for supply to Oman and the GCC.
Datasheets & Documents
- Manual Flowserve Logix 520MD+ and 510+ IOM Manual Download
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About brand
Flowserve is the American flow control company for pumps, valves, mechanical seals and valve automation, known through brands such as Durco, Worthington, Byron Jackson, Valtek, Limitorque, Worcester, Logix and Argus. It was formed on 22 July 1997 by the merger of equals of Durco International and BW/IP, whose heritage reaches back to Simpson & Thompson (1790) and Byron Jackson (1872). Flowserve Corporation is headquartered in Irving, Texas, and listed on the New York Stock Exchange.
Seven Star LLC sources and supplies Flowserve pumps, seals, control valves, ball valves, actuators and positioners for process plants in Oman, working from the nameplate data and the manufacturer's documentation.
Flowserve company profile
| Formed | 22 July 1997, merger of Durco International and BW/IP |
|---|---|
| Heritage companies | Simpson & Thompson, later Worthington Simpson (1790); Byron Jackson (1872); Duriron foundry, later Durco (1912) |
| Headquarters | Irving, Texas, USA |
| Ownership | Flowserve Corporation, public company (NYSE: FLS) |
| Product families | API and ANSI process pumps, Durco and Worcester ball and plug valves, Durco TX3 triple-offset and Valtek butterfly and globe control valves, Limitorque electric actuators, Logix positioners, mechanical seals |
Milestones
- 1790: Thomas Simpson founds Simpson & Thompson, a predecessor of Worthington Simpson pumps.
- 1872: Byron Jackson is founded, a root of BW/IP.
- 1912: The Duriron foundry, later Durco, is launched.
- 1997: Durco International and BW/IP merge on 22 July to form Flowserve, listed on the NYSE as FLS.
Flowserve product families listed here
Flowserve pumps on this page are the Durco Mark 3 ANSI process pump and the ECPJ vertical sump pump built to API 610 type VS4. Sealing products are the ISC2 cartridge mechanical seal to API 682 and DuraClear barrier fluid for dual seal systems. Flowserve valves include the Valtek Mark One globe control valve, Argus floating and trunnion-mounted ball valves (EK71, FK79, FK76M) and Durco Microfinish ball valves. Automation is covered by Limitorque MX and L120 multi-turn electric actuators, the Rotadisk RD and RDF pneumatic actuator and the Logix 3800 digital positioner.
Where Flowserve equipment is used
Mark 3 pumps handle acids, caustic, solvents and utilities in chemical and petrochemical units. VS4 sump pumps drain pits and collection tanks. Valtek control valves and Argus ball valves are found in refining, gas processing, power and desalination, and Limitorque actuators operate gate and globe valves on pipelines, tank farms and water networks across the GCC.
Flowserve products we list
Ordering Flowserve parts: what we need
The serial number on the nameplate is the key to Flowserve records for a pump, valve or actuator. Please add the following by product type:
- Pumps: size and model, impeller diameter, materials, seal arrangement, and the part name and item number from the sectional drawing
- Mechanical seals: seal type and size, drawing or part number, materials code, pumped fluid and flush plan
- Valves: size, pressure class, body and trim materials, end connections, and the actuator and positioner model
- Limitorque actuators: unit size, order and serial number, supply voltage, wiring diagram number
Facts checked against Flowserve's SEC filings and published company histories, October 2026.
Browse Flowserve products by category: Control Valves, Pumps, Valve Actuator, Valve Positioner.
FAQ
Questions about the Flowserve Logix 520MD+ HART Digital Positioner
Answers from our engineering team on installation, compatibility and integration.
01What does the Logix 520MD+ do?
It positions a pneumatic control valve from a 4-20 mA command. A piezo pilot stage and Hall-effect position sensor close the loop, and HART lets the positioner report diagnostics and be configured remotely.
02Does the Logix 520MD+ need a separate power supply?
No. It is loop powered by the 4-20 mA signal, with a compliance voltage of 10.0 VDC at 20 mA and a minimum operating current of 3.8 mA.
03Which HART versions are supported?
HART 6 is the factory default. The manual describes a DIP switch procedure to change the positioner to HART 5 or HART 7.
04What air supply does it need?
The manual gives 1.5 bar (22 psi) minimum and up to 6.2 bar (90 psi) for single-acting or 10.3 bar (150 psi) for double-acting relays. The air must meet ISA 7.0.01; sour gas is not acceptable.
05What is the difference between 520MD+, 521MD+ and 522MD+?
They are Standard, Advanced and Pro diagnostic levels. The 520MD+ has position-based diagnostics; 521MD+ adds pressure data; 522MD+ adds force data and on-line friction monitoring.
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