The Atlas fuel hydraulic transfer valve design is described. The design satisfies primary goals such as fuel and oil isolation before launch in order to use existing ground support and airborne hardware and procedures. The valve operates only after the vehicle has been committed to launch. Hydraulic system function is maintained if the valve fails to function. Valve operation is mechanical and interfaces only with the propulsion system

Ogman, M.

English

NASA Technical Reports Server

FUEL/HYDRAULIC TRANSFER VALVE IMPROVES
RELIABILITY OF ATLAS SPACE LAUNCH VEHICLE
M, Ogman
General Dynamics Corporation -- COnVairDivision
SUMMARY.
• ' The Atlas Fuel/HydrauUc transfer valve (FHV) desigJ_is enhancing the Atlas space vehicle launch
reliability without a major redesign. The concept representsa rational evolutionary design,change.
General Dynamics Convair Division has designed a fuel/hydrauliC transfervalve to permit comrolled
interfacing with the RP.I fuel supply. The design satisfies primarygoals such as fuel and oil isolation
before launch in order to use existing ground suppo_:tand.airborne hardware and.procedures. The
valve will operate only after the vehicle has been committed to launch. Hydraulicsystem function will
be maintained if the valve fails to function. Valve operation ismechanical and interfacesonly with the
propulsion system.
BACKGROUND
the Atlas vehtcle has two independent hydraulic systems, one for each stage, used to provide
power for thrust vector control and to the engine propellant utilization system. As a first generation
miSSiledesigned primarily as a high priorityweapons deliverysystem, no consideration was given for
designingredundancy features into the hydraulic system. As a weapon systemvehicle, its development
and operational flight record was tarnished, by occasiortaIhydraul_ system failures attributed to
system leakage.
The changeover from a weapons system to a space launch vehicle placed greater emphasis o_l
vehicle reliability. The hydraulic system.reliability was improved by critical analysis, design ira-
: provements, gerleroustesting, and tender loving care_
The Atlas vehicle carries at liftoff approximately47.3 cubic meters (i2,500 gallons) of Ri_-I fuel
and the hydraulic systems carry 0.0011 cubic meters (0.3 gallons)of reserve hydraulic fluid. Leakage
of the hydraulic fluid in flight in excess of reservecapacity could result in a costly mission failure. The
concept of tapping the RP-I fluid as an 'qn,firtite"reservoir for the hydraulic system became attrac-
tive. System reliabilitycan be increased to permit the hydraulic system to become leak-tolerant. An
estimated 50070of the previous hydraulic system flight failures (and mission losses) would have been
prevented if the concept had been utilized.
CONCEPT
The fuel/hydraulic transferca!re design uses a diaphragmto isolate hydraulicand RP-I fluids. A
ram is used tOrupturethediaphragm. This event can only occur when the engines are ignitedano high-
pressureRP-1 fluid is generated. The high-pressureRP-1 fluid is portedto the ram which then ruptures
the diaphragm. The subsequent interface attainment between low pressureRP-I and hydraulic fluid
thu_ makes the "iilfinite" supply of RP-I available to the hydraulic system. With zero systeminflight
leakage, the hydraulic system functiot_s on a low mixture of RP-I in hydraulic fluid. If a leak is
manifested, system function will continue as RP-I flows into the hydraulic system.
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PRI_VIOUSDEVELOPMENT
Air FOrceful_dSwere made av_ilabl_ in 196"}-68to des_n ariddevelop a similar interface valve to
the stibject _Ive. II_ ma_ordifference between the two designs was that the earlier version had a
design feature thatwot_ldnot al,low lntlight i,ate_faCingof RP-! fu_l with hydrauliCfluid u_derany clr-
cu_tancos except when a system,leak d_veloped. The valve would ftmctlon by sensing aJ_inflight
preasurelossit_.the_eturnorlowpr0ssuresystemcit'cuit.
A valvewas desisted,developed,and f_stedtodemonstratetheconceptfeasibility.The
diaphragm.design configuration was the major hurdle to overcome. After starting with no experience,
a satisfactory diaph1'agmconfig_tration was-attained. System tests using surplus fligllt Itardware
detaonstrated all program objectives, but the program was cancelled without implementation. FOr-
ttmatel-y,the data was used to design the c_rent valve now in f_ightservice.
HYDRAULICSYSTEMDATA
*. Number of independent systems: two .(one for each stage)
* Operating pressures (nominal)
High pressure: 205 ATM (3,015 psia)
Return or low pressure: 5.3 ATM (80 psia)
Hydraulic pump flow (variable, engine driven):
Booster: 0.1.45 x 10-3 m3/sec (0-23 gpm)
Sustainer: 0-0.50 × 10-3 m3/sec (0-8 gpm)
o Hydraulic fluid: MIL-H-5606, 0iydrocarbon -- red color)
* Fuel" RP-I per MIL-R-25576
• Function:
Booster system: Provide power to engine nozzle thrust vector servoactuators
Sustainer system: Provide power to engine nozzle thrust vector servoactuators and
engine propeiian_control System
OILIECTIYESAND CONSTRAINTS
The task objective was to design, test, and integratea valve into three existing Atlas vehicle con-
figurations requiring three different installation versions. Fortunately, the three vehicle hydraulic
systems used common hardwareand functioned identically. This allowed the designerto createa com-
mon valve design and envelope with port fitting configuration.differences to accommodate-unique in-
stallation requirements.
The Atlas SLV-3D model is manufactured for NASA under a Lewis Research Center managed
contract, The Atlas SLV-3A and E/F models were manufactured and subsequently modified for the
U,S, Air ForceSpace Division use, The U.S, Air Force Space Division and NASA jointly providedthe
design and testing funds for the valve basicdesign. All agencies participatedin preliminaryand critical
designreviews.
The prime tecl_riicalobjectives were:
I. To increase booster and sustalner hydraulic system reliability by utilizing RP-I fuel aS a
ready reserve fluid in the event of a hydraulic system leak to maintain system function:
A. With any size return system leak.
B. With a limited leak in the pressuresystem.
2. To maintain hydraulic system function if the FHV valve does not activate.
lSfi
O0000006-TSF04
3. To achievepcosrameconomybytitilizinga wholly mechanicalsystemahdavoidinga more
costlyek_etrlca[system.
Desisa Objectives Achieved:
A. Systemr-eWabilityhasbeeni_reased.
B. No pyrotechnicdevicesot electricalinterfaceswereused,.
C. The FHV ValVeuses high-pressure fuel to activat_ the valve. Valve integration
between hydraulic and propulsion systems is not affecting either system
performance.
D. Prior to vehicle launch, there is zero leakage of hydraulic or RP-I fluids into
_ thealien system.
E. Interface of RP-! fuel and hydraulic fluid occurs only when the vehicle is corn-
: mitred tolaunch. This occur_ for:
1. Atlas E/F vehicles: at initiation of "Engine Start:' sequence.
2. Atlas SLV vehicles: at vehicle release (Post-Engine start).
F. Valve design makes maximum use of design features of the "emergency fuel_
valve" design developed in 196.7-58.
In Design Objectl_,e E.l above, the E/F vehtcl_ is a nonrestrained launch concept. The
:= vehicle will liftoff when engine thrust exceeds vehicle weight. No launch abort is possible. The SLV
vehicle, being of an earlierdesign, is restrained to the.launcher until engine thrust has increased to a
steady state level. The vehicle is then automatically released for flight after satisfying all.launCh.control
monLtor functions. During the interim period between engine start and "laUnch release" an abort
capability exists. The problem pl_esentedhere is twofold: (t) how to delay valve operation past the
_ engine starttransient for E/F and $LV vehicles, and (2) how to allow an abort event for SLV vehicles
: without activating the valve.
In Design Objective E.2, +.heuse of a pyrotechnic device to trigger the FHV valve with high
,_. pressure fuel would have been ideat, but this introduces an electrical interface. This concept was drop-
pod because the E/F vehicle would have requiredan electrical relay box to fire the pyrotechnic squib.
_, The qualification cost of the relay box and lot control costs of the squibs would have exceeded
allocated funds.
":/ HOWTHE FHV VALVEFUNCTIONS'
_. See Figure 1. A diaphragm is used to i_olate gP-I fuel from hydraulic fluid. The diaphragm is
_ rupturedby high pressure RP-I that is only available upon engine ignition. When the diaphragm rup-
tures, low pressureRP-I and hydraulic fluid interface. The RP-I pressureis greater than the hydraulic
return pressure by the amount of the RP-I head pressure in the vehicle tank (about 0.4 atm, 6 psid).
With no hydraulic system leakage, the hydraulic return pressure will rise to equalize with RP-I
pressure.The small extra volume of RP.I is accommodated by the airbornehydraulic reservoirand nofurther mixing occurs, in case of an external leak in the hydraulic system, RP.I fuel will flow into the
,-.' hydraulicsystem and be directedto hydraulicpump inlet to maintain systempressute and flow. System
:_ function will be maifttalnedwith any size leak in the return portion of the circuit upstreamof the FHV
:: valve and a limited leak in the pressurecircuit.
_ In the event the diaphragm inadvertently does not rupture at lift off, the hydraulic system will
function as if the FHV valve does not exist. The airborne reset¢oir will maintain sufficient pump inlet
: pressuretOfeed the pump fluid.
in order tosatisfy the requirement to actuate the FHV valve after the engine transient phase, a
timing restrictor is installed in the high-pressure RP-I line at the engine thrust chamber. This line nor-
_ maliy contains/lo fluid arid is at atmospheric pressure. At engine start, RP-I is metered into the line
15'l
i ,
• . ?
and pressureb_lld_ up thermodynamically untilthe ram Overcomesdiaphra$m-ruptur¢ resistance. The
metering creates sufficient time delay for the engine start transient tO be completed before the
diaphragm will rupture, lmposinl_ a time delay prior to diaphragm rupture is more critical for SLV
vvhiclcs which have abOrtcap_bilities_The diaphragm must not break prio¢to tun out of time allotted
for an abort period while at the same time minimizing the tln_ewherein the FHV valve is not activated
while aik:borne.See Figure 2. Becaase of the many variables involved in calculation of the thormo_
dy_mic pressure rise in the timing circait coupled wi_hno meaningful data associated with some of !
those variables, the slz¢ of the timing res_rictorwas determined by making reasonable assumptions for
calculation purposes.
Flight data revealedthat the valve was activated early, but still within acceptable limits. What had
transpired, was a race o¢tween the run out of the abort timer and the diaphragm rupture event, fly
design, the abort timer was to run out a fraction of a second prior to the diaphragm rupture. Any abort
during the abort period would maintain the diaphragm structurally intact andthereby maintain isola.
tion between propulsion and hydraulic systems. In reality, a photo finish occurred.
FRY VALVE DESIGN FEATURES
The valve detail elements are shown in Figure 3_The simplicity of the valve design contributed to
its successful performance. A short stroke ram is the only moving part. Dual seals with an in-between
vent in the body assure no intermixing of fuel or hydraulic fluid because of seal leakage. The same
dual seal.is also employed on the diaphragm.
A filter is located ir_the hydraulic section whicl_allows hydraulicfluid to pass through its core
without filtration. RP-I fuel allowable contamination content is greater than that allowed for the
bd,draulic system. Consequently all RP-1 entering the hydraulic system is filtered.
Between.the low-pressurefuel port and the diaphragm is installed a fine mesh screen. Its function
, is-to prevent particles, generated when the diaphragm r_ptures, from entering the fuel system.
The diaphragm design is basically a V.groove cut 360 degrees in the interior wall end of cup
• design. The "shear" thickness of the V-groove is controlled dimensionally. This control consists of
physical dimensions, surface finish condition and anodize thickness. The choice of 5059H116
aluminum materialwas primarily based on its excellent corrosion characteristics. All diaphragms are
: leak checked with helium. Lot test consists of 2 out of 10 utiits being subjected to rupturetests. The
allowable rupture force is 5,782 N (1,300 lb) to 7,606 N (1,710 lb).
The original diaphragm rupture force tolerance requirementswere not met. This was anticipated
and our design concept allowed us to open the tolerance in eitherdirection. One lot of diaphragms fail-
ed rupturetolerance limits. This was baffling since all machining toleranceswere satisfied. A metallur-
gical analysis of the V-groove revealeddifferences between thin coat anodize thicknesses of the failed
and acceptable lots. This was a surpriseas it was assumed that the anodized strengthcapabilitywas in-
significant. ASa consequence, anodized thickness was subsequently controlled.
Diaphragm seal and structuralintegrity loss by accidental or ul_recognizedmeans was addressed
during the design reviewphase. The problem was not so much a gross diaphragm rupture, but rather
detection of a small leak. A gross ruptureby pressure was remote as it would requireapproximately
i 15.6 atm (1,700 psid) to rupture the unit. Neither the low-pressure fuel or hydraulic return systems
during factory or site checkout or in launch status are capable of such pressuremagnitudes.
In order to detect a potential smallleak, a port was designed into the low pressurefuel section to
allow for leak inspection. With no fuel tanked, it was simple to open the port cap and inspecl for
hydraulic fluid. With fuel tanged, it was difficL:Itto detect hydraulic fluid in fuel, since both fluids are
hydrocarbons and red in color. This was resolved by using infrared spectrophotometer analysis to
detect hydraulic oil in RP-I fluid. Hydraulicoil has a viscosity improvercompound and hydraulic fluid
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O0000006-TSF06
!:
' is detectabl.eas Lowas a half-percent in fuel Fluidsamples were taken on abot_t20 installed valves until....
sufficient confidence was g_ined to eliminate sample tests.
The cver-ptesem potential of human error did occur at the component level, A technician failed to
:,_ follow prescribed testing i__roceduresand managed to burst a diaphragm. Thi_ has b_en4he only
adverse incident to date.
_[ The resttictor check valve funCtiOn,is to minimize the back flow of RP-I fluid in the event an ox.ternal l ak occt_rsin the return system upstream of tile valve,
1 As instatled ia the system, the FHV valve is located as close to the hydraulic pumps as existing
, vehicle hardwarewould permit ia order to reducethe amount and length of tubes connecting between
!,i theFHV valveandthepump.ThelowpressurelIP.lconnectiontotheFHV vatvei_selfbleedingwith
I the vehicle erected in the vertical position.
FLIGHTEXPERIENCE
Ii The inflight performanceof the hydraulic systems is monitored by low pressure (return) and high
[ pressuretransducersvia telemetry. Any gross leak manifestation would be revealedby a.pressureloss.
i To date, 14 vehicles or 28 valves have been flown.. All valves have activated properly and all
hydraulic system functions were satisfaCtOry.We l_ave experienced no gross hydraulic system leaks
darJag inflight operation.
159
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?igure i.- System schematic with FHV valve.
Q I'--
_NIIINE
NOZZI.E._ viii _. TlllgiO ltTORESTRICT(IR 8tS
81.S -- lEO0 ,
I I
00.G- -- 1000 ' k-- - 0P.1 LlllltS
NiIiNE A.AT _ ] -- (Os) ..... :
J OtNltlON CAPAmUTV _i_._ lJ START ZONE.... l "__60,el ATM(E00PIIIA)
ifUfLI itlli_/_ il 1 --_'__- I
inui'illnEIJ_l--t_/-/AIF i I
I IlINE "-"T i i_ I.__ 31,O'lilt (480 Pill)
_'_ Ij/i/
i 0 = Ilia AiM
-, oJ- o !......
.ikO "340 "RiO " I 0 0 0 1.0 RiO Ik 0 4.0 Jr _.0
LWTOil
Illiil 6fC
Figure 2.- FIIVvalve timing curve.
OR|G_AL PAGE IS
00000006-TSF08
RODY
RtSlimTOp, 7076T756|ALUM FILT|R
CHECKVALVE (HARDANOL_ZED),
XYORAULIC OUt,LET.IXLET
LOW _ _ HIOHPnE$$UREPRESSURE ,%
FNL _..
CAP
A286
• ,,r_....$EAL8
(VITON)
NT _RAPHRAGM
BLEE_R 6051iHI|G 2D74T_51 20|4 1061
CAF ALUM ALUM (HARDANODIZED)
tcRtt, OH.
Figure 3.- FHV design details.
161
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Fuel/hydraulic transfer valve improves reliability of Atlas space launch vehicle

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