NASA-CR-193136

MOOG;

.,3S/

STUDY OF HYDRAULIC ACTUATION SYSTEM

FOR

SPACE SHUTTLE MAIN ENGINEPROPELLANT VALVES

(NASA-CR-I93136) STUOY OF

MYDRAULIC ACTUATION SYSTEM FOR

SPACE SHUTTLE MAIN ENGINE

PROPELLANT VALVES Final Report,

i3ec. i992 - 3i May i993 (Moog)

71 pG]/3T

N93-27II2

Uric|as

0167881

June 1,1993

-1-

https://ntrs.nasa.gov/search.jsp?R=19930017923 2020-03-28T07:01:56+00:00Z

TABLE OF CONTENTS

Section Title

Introduction

Page

3

2.0 Background 3

3.0 Objective 3

4.0 Analysis Summary

5.0 Test Results 6

6.0 Recommendations 12

Appendix A Test Data 13

-2-

SPACE SHUTTLE MAIN ENGINE PROPELLANT VALVE ACTUATOR

ASSEMBLY STUDY REPORT

1.0- INTRODUCTION

This report was prepared to document the analysis and tests conducted in response

to Attachment J-1 of Contract NAS8-39711 issued by Marshall Space Flight Center,

NASA. The report was a requirement of Attachment J°2 of the contract.

2.0 BACKGROUND

The Space Shuttle Main Engine Propellant VaNe Actuator assemblies have been the

source of recurring problems since their inception. The troublesome areas have

been studied and design and process improvements have been made to eliminate

the problems. However there have been recent performance concerns with the

operation of a bypass valve which is located within the actuator assembly. These

concerns led to a request for an independent assessment and study of the Propellant

Valve Actuator assemblies.

Moog Inc. responded to this request with a proposal and received a contract to study

the system.

3.0 OBJECTIVE

The main objectives of the study were to recommend changes to improve the system

reliability and decrease maintenance costs while preserving the present interfacing

with other Shuttle hardware and software. The system performance requirements

were to remain as presently specified.

4.0 ANALYSIS SUMMARY

The Propellant Valve Actuation System was studied and the requirements were

reviewed to obtain a good understanding of the functions and operation of the

system.

-3-

The system employs technologies that were current in the late 1960's and early

1970'swhen the design was first conceived. The design is basically sound but could

be changed to take advantage of modern improvements that are presently available

for hydraulic systems.

Contamination

The servovalve pilot stage orifices are extremely small and therefore subject to

plugging from small contaminants. The small orifices are required to comply with

the low allowable leakage requirements. Two stage valves are also used as switches

in the failure detection and correction part of the actuation system, probably for

commonality with the two servovalves. Solenoid valves with essentially zero leakage

could be used for this function. This would allow a redistribution of the tare leakage

loses and permit larger servovalve orifices to be used. Single inlet servovalves such as

deflector jet or jet pipe types would offer the advantages of minimizing hard-over

failures and reduced contamination sensitivity.

The actuator housing contains several blind or dead ended passageways which are

very difficult to clean. A design without stagnant fluid in blind passages would be

preferred. The sleeves or bushings that house the spools for the servovalves, bypass

valve and switching valve use elastomeric seals to separate fluid from adjoining

areas. Laminar metallic sealing lands could be used to isolate fluids of different

pressures and eliminate many elastomeric seals. This technique would eliminate

temperature sensitive materials and reduce another source of contamination.

Contaminants are often introduced when hydraulic lines and fittings are installed or

changed. The present system has a filter located upstream of the interfaces between

the hydraulic lines and actuators with no provision for filtering particles that might

be generated as the lines are installed. This situation could be alleviated by

installing filters within the actuators and adding a flushing/bypass valve to each

actuator. The lines could then be flushed after installation without the danger of

adding contaminants to the sensitive actuator components.

Bypass Valve

A majority of the study effort was focused on the bypass valve section of the

actuator assemblies. Detailed finite element models of the sleeve and spool had

-4-

been created by engineers from Marshall Space Flight Center and by the actuator

supplier. The conclusions reached from the modeling and analysis indicated the

possibility of interference between the sleeve and spool. Moog engineers verified

that the clearance between certain sections of the sleeve/spool assembly could

indeed decrease significantly during switching transients. We believe that this

decrease in the inside diameter of the sleeve could be one of the contributors to a

tendency for the spool and sleeve to bind as the spool moves with respect to the

sleeve or bushing.

Since the bypass valve is inactive during normal operation, a collection of very fine

contaminants will be deposited on the spool lands where low levels of leakage flow

exists. This action is commonly referred to as silting. Silting occurs even in very clean

systems with low micron filtering. When spool motion is commanded, these fine

particles can wedge between the two parts that have motion relative to one

another. The very small or non-existent clearance between the parts, coupled with

the wedging action of the contaminants which drives the parts eccentric to one

another, can cause severe galling. This results in an inoperative valve. Because the

spool and sleeve are manufactured from the same material, which they should be to

allow for thermal considerations, the parts are very susceptible to galling problems.

Also any minute manufacturing defects can amplify the tendency of the parts to gall,

upset surface metal and quickly seize.

Larger drive areas which increase the force available to drive the spool, are effective

for chip shearing capability, but have little value once the metal is upset by the

rubbing action between the two parts.

Increasing the clearance between the spool and sleeve is not recommended for two

reasons. Primarily, in this type of application, increased diametrical clearance can

allow larger particles to wedge between the parts resulting in an even greater

susceptibility for seizure. The other disadvantage to larger clearance is the creation

of a greater leakage path between sections of the spool that are now isolated by the

laminar clearance and limit the fluid flow. The increased leakage could affect the

functionality of the assembly and certainly would create an additional fluid power

drain.

-5-

Based on the information given above, the main thrust of the study was

concentrated toward solving the suspected design problem. The objectives were

twofold. First, to eliminate the clamp down action of the sleeve that occurs during

switching between operational modes. The second objective was to maintain

inte-rchangeability between any modified parts and those being replaced. The

proposed solution is shown in Figure 1. The design of the sleeve and spool assembly

could be simplified if the interchangeability criterion was not used.

The proposed design permits the use of all of the ancillary piece parts that are

contained in the present assembly including springs, seats, spacers, pivots, seals and

end caps. The new approach does, however, eliminate the differential pressure

across the sleeve that is believed to be a major source of the present problem.

An additional change was incorporated to alleviate the concern over the complexity

of the filtered timing orifice. This orifice is used to control the actuator rate when

the bypass valve moves to the actuator bypass position and to control the valve

closing sequence and timing. The low allowable rate precipitated the use of a small

orifice between one actuator cylinder cavity and the return fluid port. This small

orifice is subject to plugging and is therefore protected by a filter which is built into

the bypass valve assembly.

The suggested solution takes advantage of a reduced diameter on a section of the

spool. Flow through the curtain area formed by this reduced section of the spool

and a hole that exits to the return port, creates the necessary pressure drop to

control the actuator rate in the bypass mode. This design creates a self cleansing

action that eliminates the need for the orifice filter. This feature is shown in Figure

o

5.0 TEST RESULTS

The early analyses and suggestions are presented to Marshall Space Flight Center

personnel at a program status review meeting. This meeting was held

approximately one month after the study was initiated. It was agreed at the

meeting that a sleeve and spool assembly which represented the proposed solution

should be designed, fabricated and tested as part of the study program. Three sets

of proof of concept hardware were built and tested at Moog and shipped to the

-6-

FIGURE 1

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FIGURE 4

-10-

servoactuator production vendor. The ancillary centerline parts used to

demonstrate functionality were supplied by the production vendor from production

stock.

All testing was conducted at fluid temperature between 70 and 100 deg. F. using

MIL-H-83282 as the test fluid.

The assemblies were tested in the test block shown in Drawing BT00353. Initially,

cross port leakage and basic functionality were checked. Plots were generated from

flow versus switching pressure to demonstrate switching pressure levels and spool

threshold or friction. Bypass flow and required pressure to move the spool to the

bypass position were recorded to demonstrate the effectiveness of the revised

orifice configuration. The assemblies were operated with control pressures from 500

psi to 3000 psi to demonstrate consistency over sleeve pressure extremes. The units

were cycled after sitting pressurized for extended periods of time in an attempt to

introduce problems caused by silting at the spool lands. Test results are included

with this report as Appendix A.

The assemblies operated as expected throughout the test sequence. No anomalous

behavior was observed. The tests were conducted to demonstrate functionality

which was the main goal. We recommend further testing at the servoactuator level.

Tests at temperature extremes and under vibration loads are recommended as

additional proof of concept.

S/N 001 TEST SUMMARY

Operate to Lockup

Lockup to Operate

Friction

Lockup to Bypass

Bypass flow thru orifice

Leakage in locked mode at 3000 psid

ClPto ClV

ClPto Return

ClPto C2P

C2P to C2V

C2P to Return

C2P to C 1P

approximately 1050 psid

approximately 1050 psid

less than 4 pounds

250 to 300 psid

0.5 cis at 500 psid

2.7 cc/min

2 drops/min

11 drops/rain

7 drops/rain

4cc/min

12 drops/min

-11-

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6.0 RECOMMENDATIONS

It is probably not sensible to embark on a complete redesign of the servoactuators.

The design is mature and well understood and the manufacturing processes are well

past development. Any start up problems have been eliminated and early

performance difficulties have been addressed. There are no problems known to

exist with the exception of the bypass spool jamming. However, if the scope of the

Space Shuttle Program were to drastically increase, some of the basic design features

could be improved. Three areas that are candidates for change are:

1. The filtration scheme that was discussed in the analysis section.

2. The use of more contamination tolerant servovalve designs.

3. Use of solenoid type valves for failure correction switches.

All of these changes would require modifications to the actuator interfaces and

requirements which is probably not practical at this time.

We do recommend changing the Bypass Valve to a design that is less subject to

interference between the spool and sleeve. We also recommend a change to the

method presently used to protect the timing orifice from contaminants. The design

used to "prove the concept" operated well during laboratory testing and should be

considered as a replacement for the existing design. The interchangeability features

should make this effort relatively painless. A substantial amount of testing should

be done on the complete servoactuator assembly before the change is incorporated.

Environmental testing at extremes of temperature and vibration are recommended

asa minimum.

-12-

APPENDIX A

TEST DATA

-13-

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PART 53---FORMS 53.301.298

° ,-.

1,.

_

, i ,

REPORT DOCUMENTATION PAGE o,,,,sNo.,_'o,,-o,a8

_am4_mm_.t_q m_m tot met ¢_;_-l-.o_of w_uoe) .b e_umattQ ZO,h_W;We _ _ g_'re,momm, m(Su_e,q t/xt ner_ for _ m, tul/¢_*_ _,eo_:_m/txmveq _ _

Ow_ _m..me. _qe 1204, AawWfo_. VA 222_I'4M2. _ _ me Office De M_ _ =_d_r_ _ _m_mm/yore2 (Q7044 !IMIL wm_._xFon. 0C 20_1$.

I. AGENCY USE ONLY (Leave _anJ¢) 12. REPORT DI4TE ' 13. AEPORTTYPE ANOOATESCOVEREO6/]./9._ Final Dec.. 92 - 31 May 93TITU[ AN0 SUBTITU[ S. FUNDING NUMBERS

Study of Hydraulic Actuation System for C-NAS 8-39711

Spac e Shuttle N.aLn Engine Propellant Valves

6, AUTHOR(S)

Bob Ewel, Editor and Omupiler

7. eeeeOmiHG ORGA._._ON NAME(S) ANO AOOeESS_[Sj'

Moog Inc.

Missile Systems Division

Jamison Road, Plant 20; East Aurora, NY 14052

_.M_ONSOmNG/MONITOR_NGAGENCYNAME(S}ANO AOORES_ES) .....

National Aeronautics & Space Administration

11. SUPIIq.I[MENTARYNOTES

8. PERFORMING ORGANIZATION

R[F_RT NUMBER

_0.'S_ONSOmNG/_ONI÷O_UN_ ....AGENCY REPORT NUMBER

12a. DISTRIBUTION/AVAILABILITY STATEMENT

1_. ABSTRACT (Maximum 200 wo,',_)

12b,

OISTRIBUI_ON CODE

Recent performance concerns involving the Space Shuttle Main Engine

Propellant Valve Actuator assemblies prompted the NASAMarshall Space

Flight Center to request an independent design assessment. M_Dg Inc.

responded to this request and received a study contract with objectives

of increasing valve reliability, decreasing maintenance costs while

preserving the existing design interfaces. The results of the

Propellant Valve Actuation System review focus on contamination control

and the Bypass Valve design. Three proof of concept Bypass Valves

employing design changes were built and successfully tested. Test

results are presented.

14. SUBJECT TERMS

Contamination Control_Bypass Valve

t7. SECU""""NTY(3.ASSiFI4C.ATIONT1E,SECURITYCLASSIFICATION lg. SECURITYCLASSIFICATIONOP REPORT I OF THIS PAGE ] Oe ABSTRACT

Unclassified Unclassified Unclassified

1_. NUMBER OP PAGES

70

O. UMITATION OF ABSTRACT

Standard Form 298 (Rev. 2-89)

_ AN_ fktd. _J_ll

_91ktQ2

53.