7.02-2: Mercoid 1928 Automatic Pressure Control

HHCC Accession No. 2006.032HHCC Classification Code: 7.02-2

An early automatic low side pressure control for commercial refrigeration applications, made in the form of the then familiar Bourdon tube actuated pressure gauge; equipped with line-voltage, tilting mercury bulb switch, with glass viewing window, Mercoid Switch, Federal Gauge Chicago, Ill., Circa 1928

Image Gallery (2 Images)

7.02 Refrigerating and Air Conditioning Pressure and Temperature Controls - Commercial


Mercoid Switch


Mercoid Switch, Chicago, Federal Gauge Chicago, Ill. See Note 1


Type H, Reset

Serial No.:



6’ round x 4’ deep






Exhibit, education, and research quality, illustrating the design, engineering and manufacture of early refrigeration pressure controls commercially available in Canada

Patent Date/Number:

From York County (York Region) Ontario, once a rich agricultural hinterlands, attracting early settlement in the last years of the 18th century. Located on the north slopes of the Oak Ridges Moraine, within 20 miles of Toronto, the County would also attract early ex-urban development, to be come a wealthy market place for the emerging household and consumer technologies of the early and mid 20th century.

This artifact was discovered in the 1950’s in the used stock of T. H. Oliver, Refrigeration and Electric Sales and Service, Aurora, Ontario, an early worker in the field of agricultural, industrial and consumer technology.

Type and Design:

Bourdon tube actuated


Heavy bronze Bourdon tube with strip brass linkages
deep dish cast steel enclosure with formed, sheet steel cover in mat black, with glass inset

Special Features:

rear mounted manual adjustments, executed in brass see below Beautifully etched name plate in sheet broass

Performance Characteristics:

7 ‘ psi to 5 inches vacuum

Control and Regulation:

Employing a large Bourdon tube to reposition a mercury bulb switch in response to small pressure changes on the low side of the refrigeration system.

Targeted Market Segment:

Commercial and industrial

Consumer Acceptance:
Market Price:
Technological Significance:

An example of early pressure gauge design and construction based on the use of a relatively crude Bourdon tube-actuating device, found prior to the wide spread introduction of hydraulic bellows and extended capillary line actuators ‘ See ID # 151-154

See also notes on significance, ID # 151

Mercoid Division , Dwyer Instruments Inc, Michican City Ind. Currently show in their catalogue listings a range of Bourdon tube pressure switches of very similar construction and operation, indicating something of the precision and reliability to be expected of this genre of commercial and industrial controller technology. See note 1

Industrial Significance:

The development of early automatic pressure controls started with the materials and understandings of the day. In the early 1920’s these included the Bourdon pressure tube and the mercury bulb switch. The circular Bourdon tube is designed to responds to changes in internal pressure by changing its curvature, used here to move a mercury bulb switch through a simple and elegant brass linkage. The control has a manual set knob on the back, as well as a means of repositioning the bulb, so as to re-set its control point. The control is designed to operate over the commercial, So2 pressure/temperature range of 7-1/2 lbs. pressure to 5 inch of vacuum, requiring a large tube to respond to these low pressures. A crude device, when compared with even mid-20th century practices, it provided the essential beginnings for the development of fully automated refrigeration equipment.

Socio-economic Significance:

The results of automatic control research and development work, started here, have helped to make possible the vast array of low and commercial temperature equipment, as well as air conditioning applications, which have since altered almost every corner of Canadian life.

Socio-cultural Significance:

G. Leslie Oliver, The T. H. Oliver HVACR Collection

HHCC Storage Location:
Bibliographic References:
  1. A Google Search of Mercoid, Jan. 2005 indicates that the company name is still associated with the field, now as a division of the Dwyer Instruments Inc. Michigan City Ind.
  • See CMX02 and 04 catalogues, item R18

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