Slide Rule for Control Valve Sizing

[on Side A]
Fisher
Fisher Control Valve Sizing Rule Mark VII
BHL Weymouth England
P2734
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[on Side B]
Fisher
GEC-Elliott Control Valves Limited
Rochester, England
Copyright 1967

Qty 2. The given dimensions are for one slide rule in its case. A slide rule without its case is: 328 x 11 x 50 mm & 79g.

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 specialist slide rules to aid in the selection of Control Valves for either liquid, steam or gas service.

This Fisher Control Valve Sizing Rule Mark VII was made by Blundell Harling (P2734) for GEC-Elliott Control Valves Ltd, Rochester, England, ©1967. This duplex plastic rule has 17 specialist scales for gases, steam and liquids from which the size parameters Cv, Cg or Cs can be determined given pressure drop, inlet pressure and flow rate, specific gravity (liquid) or inlet density (gas/vapour), temperature and degree of superheat (steam).

This imperial rule has a fabric backed PVC slip case. Several versions of the Fisher rule were made including one by Pickett for the American Fisher company.

Both the fixed and sliding parts are marked with either "Side A" or "Side B" to indicate the symmetrical sliding part has been inserted correctly (or not!).