INTRODUCTION 



Navy construction divers currently rely on oil hydraulic powered tools to perform various 

 underwater construction tasks. In today's growing awareness for environmental responsibility, 

 the Navy is actively pursuing technology that will minimize the risk of violating environmental 

 regulations. One focus for technology development has been improved hydraulic tools for safe 

 operation in and around environmentally protected waters. Commercial oil hydraulic powered 

 tools can be replaced by intrinsically safe seawater hydraulic powered tools developed at the 

 Naval Facilities Engineering Service Center (NFESC). 



Seawater has proven to be an effective and environmentally safe substitute for hydraulic 

 oil (Ref 1). The seawater hydraulic powered diver tool system, developed to satisfy the needs 

 of the underwater construction diver, includes a bandsaw, rotary disk tool, and rotary impact 

 tool. The system provides required capability without the hazards associated with using oil as 

 the hydraulic fluid. The fourth construction tool developed for the system, a seawater hydraulic 

 powered rock drill, has not been released because the linear impact mechanism was found to be 

 unreliable and subject to unexplained variations in performance (Ref 2). 



This task under the Navy Exploratory Development Technology Program Plan was funded 

 through the Office of Naval Research in fiscal year 1992 with the objective of identifying the 

 hydraulic and dynamic elements influencing impact mechanism operation. A goal of this 

 investigation was to determine whether or not computer modeling of the impact mechanism for 

 the seawater hydraulic rock drill would lead to an improved linear impact mechanism suitable 

 for a hand -held, diver-operated rock drill. This document is the final report on a 3-year effort 

 that has resulted in a better understanding of the single poppet-kicker port linear impact 

 mechanism and a technique for analyzing complex fluid power components. 



BACKGROUND 



The seawater rock drill performance problem was attributed to the operation of the single 

 poppet-kicker port linear impact mechanism. This mechanism provides cycle timing as well as 

 impact energy to the drill operation. During testing of the original rock drill, small changes to 

 component dimensions were found to produce wide variations in drill performance. The various 

 influences on linear impact mechanism performance were not understood. 



At the conclusion of the original seawater rock drill development, two recommendations 

 were presented. The first recommendation was to investigate alternate impact mechanism designs 

 in hopes of finding one more suited to development of a seawater hydraulic rock drill. The 

 second recommendation was for independent development of the single poppet-kicker port linear 

 impact mechanism. Computer modeling was recommended as a means to characterize 

 performance through parametric studies without the need for expensive hardware fabrications 

 (Ref 2). 



The results of the computer modeling effort are documented in this report. The pursuit 

 of the first recommendation lead to a separate parallel effort for the development and 

 demonstration of a water hammer cycle impact mechanism. A successful Phase I proof of 

 concept and an ongoing Phase II prototype demonstration water hammer drill have been funded 



1 



