Flow Forces and the Tilting of Spring Loaded Valve Plates - Part

8/12/2019 Flow Forces and the Tilting of Spring Loaded Valve Plates - Part

1/6

Purdue University

Purdue e-Pubs

International Compressor Engineering Conference School of Mechanical Engineering

1980

Flow Forces and the Tilting of Spring Loaded ValvePlates - Part III

L. Boswirth

Follow this and additional works at: hp://docs.lib.purdue.edu/icec

is document has been made available through Purdue e-Pubs, a ser vice of the Purdue University Libraries. Please contact [email protected] for

additional information.

Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at hps://engineering.purdue.edu/

Herrick/Events/orderlit.html

Boswirth, L., "Flow Forces and the Tilting of Spring Loaded Valve Plates - Part III" (1980).International Compressor EngineeringConference. Paper 331.hp://docs.lib.purdue.edu/icec/331
http://docs.lib.purdue.edu/?utm_source=docs.lib.purdue.edu%2Ficec%2F331&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://docs.lib.purdue.edu/icec?utm_source=docs.lib.purdue.edu%2Ficec%2F331&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://docs.lib.purdue.edu/me?utm_source=docs.lib.purdue.edu%2Ficec%2F331&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://docs.lib.purdue.edu/icec?utm_source=docs.lib.purdue.edu%2Ficec%2F331&utm_medium=PDF&utm_campaign=PDFCoverPageshttps://engineering.purdue.edu/Herrick/Events/orderlit.htmlhttps://engineering.purdue.edu/Herrick/Events/orderlit.htmlhttps://engineering.purdue.edu/Herrick/Events/orderlit.htmlhttps://engineering.purdue.edu/Herrick/Events/orderlit.htmlhttp://docs.lib.purdue.edu/icec?utm_source=docs.lib.purdue.edu%2Ficec%2F331&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://docs.lib.purdue.edu/me?utm_source=docs.lib.purdue.edu%2Ficec%2F331&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://docs.lib.purdue.edu/icec?utm_source=docs.lib.purdue.edu%2Ficec%2F331&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://docs.lib.purdue.edu/?utm_source=docs.lib.purdue.edu%2Ficec%2F331&utm_medium=PDF&utm_campaign=PDFCoverPages


2/6

FLOWFORCES NDTHE TILTING OF SPRING LOADED VALVE PLATESPart II

L.Boswirth,Prof.,Hohere TechniacheBundes-Lehr- und VersucheanstaltMBdling{Federal TechnicalColl:ze at Moedling) A-2340 Moedling[ ustria

ABSTRACTUsing the basic relations from Part I theinvestigationof s tab il i ty of seat parallelmotion i s extended from l ine loads tosprings acting as point loads. Correctionfactors are givenwhich take into account geometr ic arrangement of springs.Stabili ty of motion for real conditionsduring opening and closure is discussed. Aball-groove model is givenfor a betterunde rst anding of t i l ted mot ion. Measuremen ts of t i l ted mot ionpublishedbyMacLaren are discussedand found to supportauthor's reasoning. Recomandat iona aregiven for preventing instabiltyand forestimating s tab il i ty from steady s ta te flowtes ts .SPRINGS ACTING AS P i h ~ LOADSUp to now we have assumed spring load tobe distributed along the center l ine ofthe channel length. Now we consider springsacting as discrete forces at givenpoints.As a simple example we take the s tr ip valveplate of fig.6,nowwith only 2 springs acting symmetrically . A t i l t ing disturbanceshifts the acting l ineof the resultingspring force F outside the center l ine .aprThe same is true for the impuls ive force,fig .12.Valve motion obviously remains stable, i f Fapr is shif ted more thanFi' i . e .

(14)HereMapr stands for themoment resultingfrom spring forces and M. for themomentresulting from impuls ive 1 forces. For small inclinationangles o both thesemoments are proportional to0 . Thereforethe amount ofo does not affect stab il i ty .For themomen ts we canwrite

193

nMspr = ~ sp ri .z i spr" Yi .z i

lc (15)n apr 4- 1LIn th is equationcspr is the stiffness ofan individual springand cspr is the overa l l stiffness n deno tes the number ofspring f o r e s ~ i n d e x i for the 1-thspring).For the moment resulting from the impu lsive forces we get

~ j dFi 1/ay) .o(z.ds.z. Yo=o oF.; 1/ay) J z 2.ds (16)..., Yo

(oFi 1/0,y)Y denotes the gradient of the0

IJ-_.

f----- z., FIGURE 12 Springs acting as point loads


3/6

impulsive forceperunit length of channel)with respect to valve l i f ty, taken forthevalue y 0 , for w hich s tab ili tyisinvestigated. For the simple configurationfig.2, we findeee appendix,Part I)

aF 1 = o 78LlP c17>Oy Yo independent from l i f ty 0 )The quantit ie s z2 and [ z 2 ds are closely related to themoment of iner tiaindynam ics and the same transformationrulescanbe applied.I fmany springs are regularely distributedindistances ~ s eq 14) reduces to eq12).This can be easily s h o w n l = n . ~ s ) :

cspr z2 = cjpr \ 2b sn i n i == ~ c 1 jz 2 .ds 18)H aving th is inm ind , we canuse a lltheequations and procedures givenpreviouslyin connectionwith distributedspring

force, when c 1 overall spring s tiffnessforunit lengthof channel) i smultipliedby a correctionfactor f taking inaccountgeometr ic configurationofspring loads:

f z ds 19)The in tegralhas to be performedalong thee n t e ~ l ine of a l lchannels of the valve.From analogy to the theory of moments ofiner t iai t arises that a l l configurationswithmore than 2 axis of symmetry haveequal stab iltyirrespectiveofangula rpositionof t i l t ingaxis. Table 5 givessome values for simple cases. From th is table i t also arises that there i spracticallyno difference between discrete springload forvalves with 1 ring. For a typical3-ringplatevalve with springs acting in themedium ring, we find f=0.7 andhences tab il i tyisreducedwhen com pared with

spring load.

TABLE Correctio n factors f according to equation 19)

z

aa

spring

R ing with 6 springsz

X

f=1

Ring with 3 Springs

z

X

z

X

:j.94

Ring with 4 springs

z

X

f =1 f =1

X

3-ringplatevalveRamedium Radius of outer ring

Rm=075 R8 (springs)Ri = 05Ra

f=07


4/6


5/6


6/6

Flow Forces and the Tilting of Spring Loaded Valve Plates - Part

Documents

Transcript of Flow Forces and the Tilting of Spring Loaded Valve Plates - Part