Foxboro Sizing Rules

The Foxboro Company developed a series of slide rules to assist gas engineers in sizing control valves and in performing calculations relating to orifice meters. These devices were not widely used in gas distribution except for the design of those city gate stations using orifice meter runs to measure the flow of gas.

 These Valve and Meter Slide Rules date from 1970. Sizing control valves usually involved solving for the valve's Cv based on flow rate, flowing temperature, specific gravity, and upstream and downstream pressures. The most common orifice meter calculation involved solving for the "beta ratio" or "beta" (the ratio between the diameter of the orifice and the inside diameter of the meter run pipe, or "d/D") given the maximum flow, flowing temperature, specific gravity of the gas, static pressure and line size of the run.

Given the small size of the slide rules, these devices were intended to be more portable than precise. If more accurate answers were required, the user was referred to the companion book "Principles and Practice of Flow Meter Engineering" by L. K. Spink.

The image aboves shows versions for both English (red or maroon) and Metric (blue) units.

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This colorful and well made plastic slide rule was manufactured in the late 1960s through the mid 1970s by the Japanese slide rule maker Hemmi (which also produce the majority of Post slide rules sold in the United States). This device was basically used much in the same way as the pocket models described above, except with improved accuracy due to its larger size.