I/P converter (current-to-pressure transducer)

01

Choose the operating principle and signals

ControlAir's technical paper Ins and Outs of I/P Transducers explains that I/Ps use an electrical signal to regulate gas pressure proportionally, and that "The most common application is in valve actuation". It states that "Most I/P’s utilize a flapper/nozzle design": a pilot chamber connected to a nozzle is throttled by a flapper, so the unit vents continuously; this "consumption rate" "typically ranges from 4-12 scfh" and varies by model, which matters because compressed air, or natural gas where used as the medium, is costly. The paper says the voice-coil design is "usually the lowest cost" but changes output with mounting orientation or vibration; piezoelectric actuators with an internal pressure sensor and feedback loop are more accurate and less sensitive to vibration and position, but cost more and consume more power. On the control signal the paper says "The most common is a 4-20 mA"; voltage-input versions are called E/Ps, and it states that "Most I/P’s are two wire devices." [1]

Marsh Bellofram's Type 1000 spec sheet describes an electro-pneumatic transducer converting the electrical input to a directly proportional output pressure, with zero and span set by front screws and thermistor temperature compensation; the 4–20 mA, 3–15 psig model can be recalibrated for 3–9 or 9–15 psig split ranging, and units are field-reversible by switching signal polarity and recalibrating. [2]

Editorial note: tell the supplier the signal type, output range, whether split ranging or reverse action is needed, and the vibration and mounting position at the valve.

Give the supplier the input signal (4–20 mA or voltage), output range, accuracy and repeatability needed, supply medium and pressure, required output flow or volume to fill, allowable air consumption, direct or reverse action and split range, electrical connection, enclosure and hazardous-area approvals, mounting (valve, pipe, panel), vibration, ambient temperature, and filtration available.

02

Set supply pressure, flow and air quality

The ControlAir paper notes that some I/Ps accept a maximum supply as low as 30 psig while others work on shop air of 80–100 psig or up to 150 psig, so supply pressure must be checked. [1] Bellofram's Type 1000 accepts supply from 3 psig (0.2 bar) above maximum output up to 100 psig (6.9 bar), and its integral volume booster gives flow up to 12 SCFM (339 slpm); extended-range models output from about 3–35 to 3–145 psig with supply up to 150 psig and flow up to 24 SCFM. It recommends instrument-quality air, clean, dry and oil-free, with filters in the supply. [2]

Editorial calculation: at the paper's 4–12 scfh (typ.) bleed, one I/P running all year consumes about 35,000–105,000 standard cubic feet (about 0.11–0.34 m³/h); multiply by the number of valves to see the air or gas cost. [1]

03

Read a metric I/P data sheet: range, capacity, consumption and accuracy

SAMSON's Type 6111 i/p converter data sheet (T 6111 EN, edition May 2026) converts a 4 to 20 mA input (0 to 20 mA on request, split-range 4–12 or 12–20 mA) into a proportional pneumatic output, with a maximum output pressure of 8 bar. The standard output range is 0.2 to 1 bar (3 to 15 psi), and wider ranges are set by installing different converter modules. Supply air must be at least 0.4 bar above the upper signal pressure range value, up to 10 bar, and the unit can run without an upstream pressure regulator. [4]

The data sheet states that the output is at least 100 mbar even at 0 mA input [4], and the ControlAir paper explains that flapper-nozzle I/Ps vent continuously [1]. Air consumption of 0.08–0.26 mn³/h on SAMSON's figures is the continuous bleed to compare between suppliers, and on natural gas a continuous vent is what EPA's NSPS bleed-rate limits address [3]. Ask each supplier for consumption at your supply pressure in one unit (m³/h or SCFH).

Bellofram's Type 1000 quotes up to 12 SCFM with its integral volume booster [2], while SAMSON quotes 8.5 m³/h at 5.0 bar output [4]. Check whether a quoted capacity is with or without a booster and at what output pressure and hose size: SAMSON's figures are measured with a 2 m hose of 4 mm inside diameter.

Editorial calculation: 8.5 m³/h is about 5.0 SCFM (8.5 × 35.31 ÷ 60); SAMSON's maximum consumption of 0.26 mn³/h is about 9.2 SCFH, inside ControlAir's 4–12 scfh (typ.) range; ≤1 % conformity on a 1 bar upper range value is ±10 mbar. [4] [1]

Values are from SAMSON data sheet T 6111 EN (edition May 2026), text extracted from the PDF.

04

Check the bleed-rate limit before running an I/P on natural gas

Where an I/P is supplied with natural gas instead of instrument air, its continuous vent becomes an emission. The US EPA rule 40 CFR 60.5390 (New Source Performance Standards, Subpart OOOO) sets bleed-rate limits for pneumatic controller affected facilities: each one at a natural gas processing plant "must have a bleed rate of zero", and each one constructed, modified or reconstructed on or after October 15, 2013 between the wellhead and a natural gas processing plant or the point of custody transfer to an oil pipeline "must have a bleed rate less than or equal to 6 standard cubic feet per hour." [3] ControlAir gives a consumption rate of 4–12 scfh for flapper-nozzle I/Ps [1], so a gas-driven unit at the upper end of that range would exceed the 6 scfh limit; ask the supplier for the measured bleed rate at your supply pressure.

The same section allows a controller with a higher bleed rate where it is required "based on functional needs, including but not limited to response time, safety and positive actuation", but the controller must then be tagged with the month and year of installation, reconstruction or modification and with identification that traces it to the records required under § 60.5420. [3] Editorial note: if the I/P will sit in an oil and gas installation, ask your environmental team whether the unit falls under this rule, and put the bleed-rate limit and any tagging requirement in the purchase specification.

05

Coil or piezo actuator, flapper-nozzle pilot, relay, booster, adjusters and enclosure

The first row is where ControlAir's designs part ways: voice-coil units shift output with mounting orientation or vibration, while piezo units with a feedback loop are more accurate but cost more and draw more power. [1]

06

Signal, output and supply ranges, hysteresis, air consumption and enclosure for an I/P

Bellofram supplies the signal, range and supply values and SAMSON the hysteresis, conformity and consumption figures; linearity, repeatability, response time and weight have no published value here. [2] [4]

07

Send the signal, air and site data together

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

Signal: [4–20 mA; voltage]
Output: [range; split range; action]
Accuracy: [linearity; hysteresis; repeatability]
Supply: [medium; pressure; filtration]
Flow: [actuator volume; booster]
Consumption: [allowable]
Site: [mounting; vibration; temperature; hazardous area]

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