Valve controller (valve positioner)

01

Match the signal, air supply and mounting

Samson's Type 3730-0 positioner compares the control system's DC signal with the valve travel and changes the output pressure to the pneumatic actuator through an i/p converter and air booster. It accepts 4–20 mA, 4–12 mA or 12–20 mA set points selected by DIP switch for split-range operation, with a minimum current of 3.6 mA and a load below 6 V (300 Ω at 20 mA) on a two-wire loop. It needs 1.4 to 7 bar (20 to 105 psi) supply air meeting ISO 8573-1 class 4 particles, class 3 oil and a dew point of class 3 or at least 10 K below the lowest ambient, and gives output from 0 bar to supply pressure, limitable to about 2.4 bar. [1]

It suits single- or double-acting actuators, with travel from 5.3 to 30 mm on direct attachment, 5.3 to 15 mm on a micro-flow valve and 5.3 to 200 mm on NAMUR (IEC 60534-6) rib mounting, also VDI/VDE 3847, and travel can be restricted to one fifth of the initialised range. [1]

Editorial calculation: 110 ln/h of air is about 1.8 l/min; the 4–12 mA and 12–20 mA split ranges each cover 8 mA, half of the 16 mA span of a 4–20 mA signal. [1]

Give the supplier the valve and actuator (linear or rotary, single- or double-acting, size, travel or rotation), mounting interface (direct, NAMUR, VDI/VDE 3847), input signal and protocol (4–20 mA, HART, fieldbus), split range, air supply pressure and quality, fail action and tight-shut function, feedback and limit switches, diagnostics, hazardous-area approval, SIL requirement, housing material and IP rating, ambient temperature, and quantity.

02

Check accuracy, diagnostics and approvals

The 3730-0 states a linear characteristic with deviation ≤1%, hysteresis ≤1%, sensitivity ≤0.1%, temperature influence ≤0.15% per 10 K, vibration influence ≤0.25% up to 2,000 Hz and 4 g, and air consumption of about 110 ln/h at 4 bar independent of supply; it operates from −20 to 80 °C (−45 °C with metal cable gland), is IP66/NEMA 4X in die-cast aluminium or stainless steel, weighs 1.0 kg, holds ATEX, CSA, FM and other Ex ia certificates, and can be used up to SIL 2 as a single device or SIL 3 redundant for emergency venting under IEC 61508/61511. [1]

Emerson describes its Fisher FIELDVUE DVC6200 digital valve controller as using linkage-less feedback with no physical contact to avoid wear, fully encapsulated electronics against vibration, temperature and corrosion, HART communication so valve information can be read anywhere along the loop, a modular design that allows working parts to be replaced without removing wiring or tubing, and performance diagnostics that monitor valve health online. [2]

03

Compare air delivery, air consumption and instrument-air quality

ABB's TZIDC digital positioner data sheet (DS/TZIDC-EN Rev. I, 02.2025) gives a 4–20 mA set point with HART, supply pressure of 1.4–6 bar (20–90 psi) in the standard design, air capacity above 5 kg/h (3.9 Nm³/h) at 1.4 bar and above 13 kg/h (10 Nm³/h) at 6 bar, and steady-state air consumption below 0.03 kg/h independent of supply pressure. It states deviation ≤0.5%, an adjustable dead zone of 0.1–10%, resolution above 16,000 steps, 20 ms sampling, ambient temperature effect ≤0.5% per 10 K and vibration influence ≤1% up to 10 g and 80 Hz, over −40 to 85 °C. [3]

The data sheet adds characteristic curves (linear, equal percentage 1:25 or 1:50, or a free curve with 20 points), seismic vibration to DIN/IEC 60068-3-3 Class III, noise up to 100 dB(A) (85 dB(A) noise-reduced), and lets nitrogen be used as supply gas. [3] Compare with the 3730-0 figures and the DVC6200 diagnostics above. [1] [2]

Editorial calculation: 0.03 kg/h of air is about 23 l/h at standard conditions, about one-fifth of the 110 ln/h Samson states for the 3730-0 at 4 bar; the two makers state consumption under different conditions, so compare at your supply pressure. A 9.7 V load at 20 mA means the loop must leave at least 9.7 V for the positioner.

Flowserve's Logix 3800 page gives air figures for single- and double-acting versions at 4.1 bar (60 psi): single-acting air capacity of 20.4 Nm³/h with consumption below 0.25 Nm³/h over −40 to 85 °C, and double-acting capacity of 30.6 Nm³/h with consumption of 0.082 to 0.637 Nm³/h over −52 to 85 °C. Flowserve lists a shielded dual-element non-contact magneto-resistive position sensor, five onboard pressure sensors for diagnostics, IP66 construction in copper-free aluminium or stainless steel, analog, HART, Foundation Fieldbus and discrete I/O options, one-button calibration of zero, span and gain in under 60 seconds, ATEX/IECEx Ex db and Ex ia approvals, and SIL 3 capability for the double-acting version; a zero-bleed variant (Logix 3800zb) is offered for zero steady-state emissions. [4]

Editorial calculation: taking air at about 1.29 kg/Nm³, the TZIDC's steady-state consumption below 0.03 kg/h is roughly 0.023 Nm³/h, against below 0.25 Nm³/h for the single-acting Logix 3800 and about 0.11 Nm³/h (110 ln/h at 4 bar) for the Samson 3730-0; over 8,760 hours a year, 0.25 Nm³/h is about 2,190 Nm³ of instrument air per positioner, so state the number of positioners when sizing the compressor. [4] [3] [1]

Ask each maker for steady-state air consumption and air delivery at your supply pressure, the load voltage it takes from the 4–20 mA loop, and the instrument-air class it requires.

04

Compare what suppliers offer

Suppliers linked to this page list valve positioners; each card links to the page reviewed.

Listings include smart and electropneumatic positioners, flameproof (Ex d) positioners, intelligent positioners with actuators, and control valves supplied with positioners; ask each for hysteresis and sensitivity, air consumption, supported protocols, mounting kits and approval certificates.

05

Trace the positioner construction

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your valves

A valve controller quotation needs values for your loops. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the valve, signal and approvals together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Valve: [linear/rotary; actuator; single/double acting; travel]
Mounting: [direct; NAMUR; VDI/VDE 3847]
Signal: [4–20 mA; HART; split range]
Air: [supply pressure; quality]
Performance: [hysteresis; diagnostics; feedback]
Approvals: [Ex type; SIL]
Housing: [material; IP; temperature]

See manufacturer records Send an enquiry through CNFX