A cased large early and unusual lacquered brass Duplex Standard Pressure Hydraulic Gauge No 3850 by Bourdon for Negretti & Zambra c1880

Bourdon gauge having 6½” dial with off white ground, black painted annotation, calibrated in lbs per square inch, separated left and right with ranges from 0 – 2000 and divided down to 10. Twin japanned spring steel pointers, the upper part marked “Duplex Standard Gauge,” “E. Bourdon’s Patent,” the lower “Negretti & Zambra, Sole Agents” surmounting the Bourdon trademark logogram. Flat glass and heavy bezel.

The movement comprising twin concentric Bourdon tubes and autonomous chassis and gearing. Bright plated pressure port threaded ½” BSP. All contained in a heavy drum form case. Together with its original valve adaptor.

Presented in its original black leather over timber, purple velvet lined two tier clamshell case. Lock and key.

Condition: The dial crazed with minor losses at 12 o’clock, good colour and definition, the movement working though not tested for accuracy. The brass case with some marks, losses and minor abrasions. The leather case structurally sound with good external colour, the internal velvet lining also with good colour and in good condition. Working lock with key.

Comments: Anyone connected with science or indeed the measurement of pressure will know about Bourdon gauges – indeed the name has become a generic term for all such gauges, regardless of origin.

This hydraulic instrument is of particular interest since its design became a standard across the world. It is also testament to the close connection between Negretti & Zambra and Bourdon during the last quarter of the C20th and clear evidence of the business relationship. Negretti & Zambra’s Encyclopaedic Catalogue of 1887, pages of which are reproduced below, carries this ringing endorsement of quality: “Purchasers are desired to examine and compare M. Bourdon’s Gauges. They will find the works to be constructed and finished like a watch, whilst the majority of imitations are put together ROUGH FROM THE CASTINGS, consequently liable to adhere to give erroneous indications.”

The term “Duplex” usually implies two or double. Most people will associate Duplex gauges as instruments that may measure two pressure values, along with Differential gauges where the difference in two pressures may be determined. This gauge is designed to measure one value but does it twice – the reason for this being that in applications where great accuracy is required both readings may be compared – gauges fail or go out of calibration and if there is a difference the readings may not be relied upon.

The Bourdon Barometer, derived from the Bourdon gauge, is a much sought after instrument and examples can be seen here: https://vavasseur-antiques.com/bourdon-barometers