Fisher Valve Sizing Rules
In the 1950s and 1960s the Fisher Governor Company (now Fisher Controls International LLC, a part of the Emerson Process Management division of Emerson) developed specialized slide rules to aid in the selection of control valves for either liquid, steam, or gas service. For gas use, the rules were primarily used to calculate the gas sizing coefficient "Cg" and the required valve size from known inlet and outlet pressures, specific gravity and flowing temperature, maximum flow rate and valve body style. The devices could also calculate the pressure drop across a specific valve given a known flow rate, inlet pressure, specific gravity and flowing temperature.
Gas Side Liquid Side
The 1954-copyrighted "Fisher Control Valve Sizing Rule" was a specialty slide rule manufactured by Pickett as their model number "N 1040". Made of aluminum, this slide rule is finished in Pickett's distinctive "Eye-Saver" yellow-green color. Based on the markings, this particular specimen was probably made in 1959 or 1960.
In 1967, Fisher introduced the "Fisher Universal Valve Sizing Rule" incorporating the Universal Gas Sizing Equation which uses the parameter C1 (the ratio of Cg/Cv) as one of the sizing parameters. Using C1 facilitates consideration of the geometry of the valve configuration, leading to accurate sizing of high pressure recovery valves having a C1 less than 35.
This aluminum slide rule was designated "N 1041-G" in the Pickett catalog. An unusual feature of this rule is its color; only one other Pickett-manufactured slide rule is known to have been green. Pickett slide rules were either "Traditional White" or "Eye- Saver" yellow-green.
This plastic Pickett-produced version of the N 1041-G (designated as the "N 1041-GP") probably dates from the early 1970s. Around this time, many slide rule manufacturers, facing increasing competition from electronic calculators, were switching to plastic to reduce material and manufacturing costs.
Some Universal Valve Sizing Rules were manufactured overseas. This unit was made by Blundell-Harling in Weymouth, England, probably in the mid to late 1970s. The slide rule had the same scales as the domestically-produced Pickett N 1041s and used "U.S. units" of measurement. These slide rules could have been replacements for the Pickett versions, as Pickett ceased slide rule production sometimes in the mid-1970s.