AD-AO86 030 NAVY EXPERIMENTAL DIVING UNIT PANAMA CITY FL F/G 6/11IW 12 SSOS HELMET ADJUSTABLE EXHAUST VALVE ASSEMBLY EVALUATION. (U)MAR 80 M A COIJLOMBE

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NAVY EXPERIMENTAL DIVING UNIT REPORT

W 12 SSDS HELMET ADJUSTABLE EUAUST VALVE ASSEMBLY EVALUATION

By:M. A. COULONE, LT. (N), CP

24 MARCH 1980

Approved for public release; distribution unlimited.

Submitted b: Reviewed by: 'o

M. A. COULOdB. C.A. BIA/TMLT. (N), CF (CDR, USM CDR, USNProject Officer Senior Project Officer ComumndftS Officer

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UNCLASSIFIED419CUOUTY CLASSIFICATION Of TNIS PAGE (SMen Daw. Enored) __________________

REPORT DOCUMENTATION PAGE BEFORE____________Fowl

REPORT MU~g& 1. GOVT ACCESSION NO .2-RCCIPICNT'S CATALOG NMSRR

12B~E AJUSTABLE gXHUST VALVE EST:Cvg:

PERP ~ ~ ~ ~ ~ ~ ~ A PRORMING OGNZTONAEADARSSRalto RLENPRT. utAS

NAVYEXPRIMENTAL DIVING UNIT

PANAMA CITY, FLORIDA 324071CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

24 MARCH 1980

1MONITORING AGENCY NAME A ADDRESS(Ig diiforet he.o Cemavoilin this. reOii)

UNCLASSIFIEDIS. ASSI ICATONOOWNGRAING

1S. OISTRIIUUTION STATEMENT (of this Report

& $SIC*A Approved for public release;S distribution unlimited

17. OISTR6UTION STATEMENT (of the abstract entie In 11.4k 25. U E ese be.n *oO)

IS. SUPPLEMENTARY NOTES

1S. KEY WORDS (Continue an5 rOers s.ide It neceemp st and II by Week snkeiw)

EXHAUST VALVE HANDLE RETROFITSTOP DESIGN CHANGEADJUSTABLE EXHAUST VALVE COVERSTOP PIN

20. ASTRACT (Continue an reverse side Of no....mvy asd IdeneiF~ by Week sember)

tFILURE OF THE TEMPERED SPRING STOP PIN IN THE HELMET ADJUSTABLE EXHAUST14ALVE ASSEMBLY OF THEJK 12 SS HSRQIE FURTHER EVALUATION OF

EXISTING AND PROPOSED VXAS-AV COFIGURTIONS. ST RESULTSINDICATE THE ADOPTION OF RECOMMENDED RETROFIT AND DES IGN CHANGEPROPOSALS.

DOD 1473 rOtTiON oNOV Move IS OSSOLSTC UNCLASSIFIED

SECUITV CLAWSICATIOU OF THIS PAGE ~t m Owwe . -

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milufUS?? CLAaIPICA1o OF T441 PAOSEWAM 0 NOm

CONTENTS

Section Page

BACKGROUND 1STATEMENT OF PROBLEM ... . . . . . ............ 1TEST REQUIREMENTS .. .. . . . . . .............. 1STATIC TEST PROCEDURES .... . . . . ............. 4STATIC TEST RESULTS (TABLE 1) 5DYNAMIC TEST PROCEDURES 7.... ....... 7DYNAMIC TEST RESULTS (TABLE 2) •8.........8RETROFIT RECOMMENDATIONS 9DESIGN CHANGE RECOMMENDATIONS 9

LIST OF ILLUSTRATIONS

Figure Page

1. MK 12 SSDS HELMET ADJUSTABLE EXHAUST VALVE ASSEMBLYRETROFIT AND DESIGN CHANGE PARTS LOCATION . ... 2

2. PRIMARY FAILURE SITES ON MK 12 SSDS HELMET ADJUSTABLEEXHAUST VALVE ASSEMBLY .... . . . .......... 3

3. PROPOSED RETROFIT - 14K 12 SSDS HELMET ADJUSTABLEEXHAUST VALVE ASSEMBLY .... .. ......... 10

4. PROPOSED DESIGN CHANGE - MK 12 SSDS HELMET ADJUSTABLEEXHAUST VALVE ASSEMBLY .... ........... 11

LIST OF APPENDIX

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APPENDIX A ...... . . ................ A-1

ACCESSION for

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BACKGROUND

The stop pins on the helmet adjustable exhaust valve handles(PAl MS16562-211) of the MK 12 SSDS have failed on several occasionsboth during training and operational dives.

Although this failure will allow the handle to be removed from thevalve body, it should be noted that, with the handle removed, the exhaustvalve will operate in the ambient mode and no direct hazard to the diverexists.

Three stop pin failures were investigated by NSWC, Dahlgren. It wasreported that the failures were a result of intergranular fractures dueto the brittle characteristics of the stop pin material, which fracturedfrom the force of the stop pin impacting against the stop.

The results of these investigations are found in Appendix A, NCSCMemorandum dated 14 March 1980. Retrofit and design change recommendationspresented in this report (NEDU Test Report 80-11) supersede the recom-mendations presented in the above memorandum.

A summary of the findings outlined in the memorandum innicated thatmany of the existing stop pins had been plastically deformed dring valvehandle assembly. This condition is the result of inserting the temperedstop pin into a .004" to .006" undersized hole in the valve handle barrel.(See Figures 1 and 2).

STATEMENT OF PROBLEM

1. To develop appropriate retrofit procedures for existing MK 12 SSDShelmet adjustable exhaust valve assemblies to decrease the probability ofstop pin failure to an acceptable level.

2. To investigate alternate helmet adjustable exhaust valve assemblyconfigurations and submit design changes to be incorporated into newprocurements.

TEST REQUIREMENTS

To conduct both static and dynamic test procedures on different valveassembly configurations and to obtain comparable empir.ical data to be usedin determining appropriate retrofit and design change.

(Tables 1 and 2, Static Test Results and Dynamic Test Results, describeconfigurations utilized and results for each configuration). Configurationsthat include a new stop design are illustrated as Enclosures (1) and (2) ofAppendix A.

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DYNAMIC TEST PROCEDURES

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RETROFIT RECOMMENDATION

Based on the preceding test results and other available data, thefollowing Retrofit is recommended for existing MK 12 SSDS helmet ad-justable exhaust valve assemblies: (See Figure 3).

1. Machine unthreaded section of the valve handle barrel to .750 in.

2. Produce a ring of naval brass approximately 3/16 in. thick, ID.751 in. and OD 1.040 in., radially drilled with one 3/32 in. center hole.

3. Open the selected hole in the valve handle barrel to 3/32 in.

4. Position ring on barrel and secure with a solid stainless steelgroove pin, 3/8 in. long and 3/32 in. diameter, pressed in place.

5. Radially drill two additional center holes through the ring andbarrel 1/16 in. in diameter, and press solid stainless steel groove pins,1/4 in. long and 1/16 in. diameter in place. Position of new holes inring and barrel will be determined by available stock between existingholes.

DESIGN CHANGE RECOMMENDATION

The following design changes are recommended for new procurement:(See Figure 4).

1. Modify the valve handle barrel to be extended 1/16 in. in lengthand accept a full length 1-12 UNC-2A thread. (Length extension allowsmore material between the holes and the edge of the part).

2. Install the same 3/8 in. grooved pin described in the retrofit.

3. Move the stop .015 in. closer to the center of the exhaustvalve handle.

4. Rethread adjustable exhaust valve cover to accept the 1-12 UNC-2Bthread and relocate the stop hole .015 in. closer to the center of thecover.

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UINITI) SIAI:S OVEHNMENT NAVAL COASTAL UYNTJMS GUNTURMe ra du PANAMA O3WY. VPLMIDA 3 407Memorandum 14 Mac,980

From: A. F. Moeller, Code 753.1To: Lt M. Coulombe, Mark 12 SSDS, Project Manager, NEDU

Subj: Stop Pin Failure in MK 12 SSDS Exhaust Valves

1. Three reported failures of stop pins were investigated by NSWC (Dahlgren)personnel. They report that the failures were a result of intergranular fracturesdue to the brittle characteristic of the stop pin material which fractured fromthe force of the stop pin impacting the stop.

In reviewing the design and apparent mode of operation of this part, wesubmit the following:

a. The specified pin is a slotted tubular spring type (MS 16562-211) madeof Corrosion Resisting Steel 410/420 with a hardness of Rockwell C42-52.

b. This pin is installed in a selected hole in the exhaust valve handle(P/N 555) as detailed on Dwg 475 8552, Notes 2-C and 2-D.

c. The diamee 6 o0 f, the hole in which the pin is Inserted Is specified onDwg 555 as .090" ' We feel this diameter should have been .094" - .097"as recommended on AgoBwg 16562.

d. The valves that failed were manufactured by Morse Diving Company.Inspection of these parts shows that the diameter of the pin holes was .086"as opposed to the specified .090"/.092" on the drawing. This undersized holeputs an excessive stress concentration on a pin of this temper. It has beennoted that several of the valves, as received from the manufacturer, had thesepins split at assembly. It is apparent that if the pin is split at assembly,the ability of the pin to remain in its hole as well as resist bending orbreaking is considerably reduced.

e. It has also been noted upon inspection of seven exhaust valve assemblies,as received from the manufacturer, that five of these did not have the pins in-stalled in the proper hole as specified on Dwg. 475 8552, Note 2-C.

This improper assembly results in an Interference between the stop andpin that forces the pin to flex or the brass pin hole to be stressed beyond itselastic limits. This undue stress not only could contribute to the part failurebut it also conditions the operator to expect high resistance in normal operations.This could cause him to erroneously apply excessive force on the pin when it wasat the end of normal travel.

f. Examination of sonic of the failed valves indicated the possibility ofexcessively impacting the pin by freely spinning the valve handle into the pinstop. The design of the valve incorporates a friction drag to prevent this.Apparently the manufacturer did not properly assemble the units, as set forthon Dwg. 475 8552, Note 3-C. The user also did not excerclse the predive proceduresas set forth in the MK-12 O&M manual, Table 2-IA, step 1.2.1.k.

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2. Although it is indicated that correct manufacture (as per drawing package)and correct set up and predive procedures, as per the O&M manual, may have pre-vented most or all of the above noted failures, we consider that the possibilitiesof some of these recurring real enough to recommend the following:

a. A retrofit to existing valves in the nature of a redesign of the pinstop (see Encl. 1). The present pin and stop configuration sees a moment armon the pin of .242" and requires a force on the valve handle of approximately60" lbs. to faill. The proposed retrofit would reduce the moment arm to .08111and require a force of approximately 180" lbs. to fail. This retrofit wouldrequire a minimum effort, as it only requires that the existing pin stop be pressedout of the exhaust valve cover, the exisiting hole be reamed slightly larger;and the new pin stop pressed in. We feel that this change, with proper manufacturingand user technique, should be an acceptable solution to the problem in the existingvalves.

b. We would recommend a revision for future buys which would also be simpleto implement but would offer a considerable increase in strength over the retrofit.(See Encl. 2) This change would increase the .875" thread diameter to 1.000"diameter on the valve cover and handle. This would increase the available materialthickness from .125" to approximately .250" in the area of the pin engagement.With this added material, a solid pin may be used to replace the spring pin nowused. This design change also allows a reduction of pin moment arm to .015".This configuration would require a force in excess of 600" lbs. to cause failure.

The above change would require no change to the exisitng cover pattern,but a minor change to the pattern for the handle.

A. F. MOELLER

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ENCLOSURE I

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E14CLOSURI: 2.

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