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Origin of "Impulse Line"
What is the origin of the term - impulse line - in relation to head type sensors?

Please shed some light into the term - "impulse" line - in relation to head type sensors. Does it have do anything the term impulse which is related to force in physics? Else what was the reason to choose the term impulse? I am not a native English speaker.

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Origin of 'impulse line'

Yes, your connection impulse with physic's force is along the right path. I've actually wondered why and when the term was used too, and I'm a native English speaker. So I got out some old and older books to see when impulse line was used.

The 1989 edition of the Oxford English Dictionary has a full page of definitions for the word impulse. The closest reference is to an "impulse tube: a tube serving to expel a torpedo", aptly named because of the blast of compressed air used to launch it (or so my ex-naval colleagues say). But a carry over from navy? Not likely.

The Brown Instrument Co. book, dated 1941, Instrumentation and Automatic Control in the Oil Refining Industry, uses the term 'lead line' (page 21), "This means that methods of remote metering must be available for remote metering, inasmuch as it is quite impractical, if not impossible to bring the manometer proper into the control room in some of the larger units. In the first place, the installation of the mechanical or direct-connected meter on the control room board involves long lengths of lead lines from the orifice connections." (this reference to remote metering refers to what we call a pneumatic transmitter, early enough in use that the pneumatic range is stated as 0-15 psi, not the later convention of 3-15 psi. The pneumatic signal lines are referred to as 'transmission lines'.)

My copy of the 1961 Industrial Instruments and Control Piping for Steamfitter, Pipefitter Journeymen and Apprentices covers the installation of pneumatic process instruments. As far as I can tell, it does not contain the word "impulse". It's a paper-only copy (I doubt that it was ever converted to electronic formar-pdf) but my visual scans of the relevant sections (pressure instruments) find references to line(s), connecting lines, tubing, pipe, piping, or pipe runs. The term 'lead line' is used a multiple times.

The Ametek/US Gauge Pressure Gauge Handbook (1970) uses the term 'connection line' in its discussion of connection of the gauge to the measured medium (page 5-27).

John Hewson's book, Process Instrumentation Manifolds, Their Selection and Use (1981), uses the term impulse line, even including it in a glossary: the conduit that transfers the pressure signal from the process to the measuring instrument.

In North America, the word conduit is commonly used for electrical conduit. So the word conduit was not particularly useful in North America as a pressure conduit, particularly because fluid flows in a pipe.

I had two uncles from the WWII generation who worked in process instrumentation in the pneumatic and the early pre-uP electronic era but they've both been gone for over a decade. But if the adoption of the term impulse line was some time prior to 1981, then someone reading this forum probably knows when it gained common use. Hopefully they'll respond.

That is quiet a puzzle, it was not commonly used experience from the 70's on, though if not mistaken it may have been used in some of the pneumatic controls where both process and instrument tubing were commonly.

Did find a reference (2006)

"Impulse Line: The line, tubing or pipe, that connects the process to the primary measuring element of the instrument loop and is part of the process pressure boundary and containment. Sensing lines and impulse lines are the same."

Thank you David_2 for your detailed reply.

I did a basic Ngram search on Google ( and I think its results are almost agreeing with David_2's reply. however I have to do a detailed search.

So lets assume the word was popularised in early 80's, then, why the term 'impulse' and how it may be connected to Force?

Any help in this regard from senior members will be highly appreciated.

Remote gas pipe lines often used natural gas to power the pneumatic recorders and actuate the valving.

Most of that sort of thing is no longer done.

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I wish the ISA monthly magazines from the 1950's, 1960' and 1970's were digitized and on-line; I'd love to flip through them, admiring the technology from yesteryear. But they aren't, so access in using those to research this topic is limited.

I did find a book published in 1974 that uses the term "impulse line":

The 3rd Edition of Instrument Technology, Volume 1, Measurement of Pressure, Level, Flow and Temperature, by E.B Jones, (Butterworths 1974) uses the term "lead line", but "impulse line" appears in a discussion about orifice plate taps on page 198.

"In this case, the pressure taps were placed at a point diametrically opposite to the point where the hole coincides with the pipe, although in the latest practice it is found that this is not necessary, and they are placed to the side as air entrained in the liquid readily enters impulse lines at the top of the pipe."

According to the title page, the 1st edition was published in 1953, the 2nd edition in 1965, each with edition with multiple reprints. Maybe a British reader can locate a 1953 or 1965 copy and see if the reference to impulse lines was added in the 1974 or if it was in earlier editions (all used copies of this title on the Abe Books web site are in the UK).

Other publications not using the term "impulse line".

1) Don Gillum Industrial Pressure Measurement, a student text by ISA, 1982, pg 89, sec 7-3, uses the term, "Impulse Lines".

2) Fundamentals of Pressure and Temperature Instruments, published by Delmar in 1947, uses the term 'lead lines'.

Page 145: The pressure differential created at the primary device, for example, an orifice, must be conducted through tubes to the indicating, recording or controlling instrument where this differential pressure is measured. On industrial applications care must be taken to in the installation of these lead lines to make sure that false differential pressures are not introduced. Lead lines should be short, if possible, and should slope at least 1 in. per ft.

3) Douglas Considine's Process Instruments and Controls Handbook, 1957, uses the term "lead lines", pages 4-18, Piping Between Primary and Secondary Elements, or "piping", in the index: piping, flow meter, 4-28 to 4-21.

The term 'impulse' is listed 4 times in the index with none related to impulse tubing/lines.

The 2nd edition, dated 1974, uses the same text, same terms on page 4-16.

4) Grady Carroll's Industrial Instrument Servicing Handbook (1960), a comprehensive review of the pneumatic and early electronic instruments and controls of that era, uses the term 'gauge lines' in the troubleshooting tables for various manufacturer's DP measuring instruments (pages 2-5, 2-7, 2-10, 2-15, 2-23, etc.).

Ironically, his Industrial Process Measuring Instruments (1962) uses the term "connecting pipe or tube" (pg 433).

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The term Impulse line is rare, but did run across it in the 70's involving a large but self-contained hydraulic controls, that were quite sophisticated.

1. instrument tubing, lines, or leads for sensing or remote monitoring

2. hydraulic pressure lines to power the actuators

3. impulse lines referring to the hydraulic switching and control tubing for position control, etc. used within the hydraulic system.

each class had completely different installation practices and materials of construction. The term "impulse line" was specific to that one system and not used in the various project documentation for the plant.