Roscoe Moss Company Memo

September, 1992
From: George Moss
To: RMC Technical, Marketing, and Sales personnel.

Well Screen Open Area

General Background

Continuous slot screen design originated in the early part of this century to overcome the problems of ground water development from distinctive aquifers characteristic of the north central United States. These aquifers were created from rock picked up, broken, and pulverized by advancing glaciers during the Ice Ages. Although glacial till is not well sorted, occasionally thin layers of fine-grained, uniform sands were washed from the original deposits. Such materials can be high yielding aquifers.

Prior to the advent of rotary well construction and the gravel envelope well design, it was difficult to produce the full capacity of sand free water from these aquifers. A well design, incorporating wire wrap screen, was successfully developed to meet these conditions. The characteristics of' the wire wrap screen are well suited for its original purpose.

The wire wrap screen design differs in many important respects from other types of water well screens. Wire wrap screen manufacturers particularly Johnson Filtration Corporation (Johnson) have for many years asserted a critical importance to wire wrap screen's distinguishing characteristic, high area of opening, using fallacious arguments and statements. This effort resulted in its unnecessary use in well designs other than that for which it was originally intended. This is especially true in the case of gravel envelope wells. Wire wrap screen has no inherent advantages over some other types of screen and some disadvantages.

The following is a discussion of the arguments Johnson has used in their three major publications since 1947 to advance the notion that higher area of opening provides advantages in all water wells. While these arguments and statements are unsupported on a scientific basis their constant repetition has earned them some acceptance in the industry. Regrettably this has resulted in well construction failures, premature well loss, and unnecessary extra cost. In this memorandum these arguments are analyzed scientifically and investigated to determine their real basis if any. The reader will be informed regarding the use of the entrance velocity criteria and its application to water well design.

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