The lack of availability of this equipment commercially left me with no alternative other than to design and build in-house. In any event I had my own ideas and requirements.
This control unit manages a number of parameters in a readily visual way leaving aside the need for conversions.
The primary instrument is an 8½” dial Wallace & Tiernan Series 1500 high performance Absolute Pressure gauge, model 61A-1B-0031, with a range calibrated in inches Hg from 0 – 31.5” – accuracy is said to be < 0.03% across the range, a remarkable piece of mechanical engineering. This instrument can be used to calibrate, with very few exceptions, all the instruments that I work on. The imperial scale, of course, can be converted to other values, but happily most instruments show inches Hg. The primary pointer traverses the dial twice, indicating across a concentric scale. The point at which a reading should be taken is indicated in the small aperture, centre left of the dial.
Two smaller instruments with 3” dials are included: top left features an LP gauge with a scale from -5 to 25 Psi, a single rotation of the primary indicator showing a change of 1 Psi. The gauge, manufactured by Appleby & Ireland and designated for aviation, is of the highest possible quality. A&I were leaders in the field of high precision pressure sensing capsules and construction of barometric devices. This is a very useful instrument which can, by the use of various facia mounted valves, be used to measure and monitor a range of LP applications.
At top right is a basic encoding air altimeter by United Instruments Inc – I needed a good altimeter for the construction of this unit and it just happened to be at hand, with calibration to 20,000ft. The inclusion of this instrument is most useful in the calibration of other altimeters.
In all, this is an addition and a development of the Calibration & Flow Control Unit Mk1, the Mk1 giving a very open but limited scale. The various control knobs regulate the flow of air into and out of the vacuum chambers, enabling precise control of values to be created and measured. Leak off and trim valves are also included. Selection of chambers is also possible, along with vibrating devices.
The three units now provide a seamless and effective pressure management regime. All three are built specifically to reflect the great analogue age of the 1950s, 1960s and 1970s, the age of the “V” force. Almost all the hardware is repurposed military aircraft components.