Capillary compensated hydrostatic thrust pad bearing report

1. Capillary compensated hydrostatic thrust pad bearing
Commonlyusedcompensating devices(Flowrestrictor)
1. Capillary(Flowisproportional topressure drop)
2. Sharp edge orifice (flowisproportional tosquare rootof pressure drop.)
3. Flowcontrol valve (constantflow)
4. Pressure sensingvalve (mostaccurate)
Requirementof using capillarycontrol device:
The bearingstiffnessdependsmainlyonthe nature of the flow control stiffness.Indiscussing
circuitdesign,itwillbe therefore necessarytoconsider the relatedeffectsonbearingstiffnessaswell
as the more practical aspects of control valve.
A simple wayto control the flow of fluidflow to bearingis to introduce a resistance intothe
supply line. For example a capillary may be used which produces a pressure drop proportional to
follow.
A fixeddisplacementpumpdrawsliquidfromatankthroughastraineranddeliversitthrough
a line filter to the capillary at a pressure Ps, determined by a pressure relief valve. It is importantto
take care that no blockage occur inthe capillarywhichmayleadto a bearingfailure.If the capillaryis
easily removable, this will make occasional cleaning convenient.
Fig. Capillary compensated hydrostatic thrust pad bearing
Four possible methodof manufacturingcapillary restrictor:-
1. Hypodermictubing(commerciallyavailable)
2. Glasscapillary(Commerciallyavailable)
3. Drilling
4. Spark machining

2. Flowrate and pressure characteristic for various compensatingdevices
Fig.Flowrate vs pressure characteristic
Fig.Stiffnessfactorvs.Ratioof supplypressure torecesspressure
Advantages of Usingcapillary:-
 The major advantage of laminarflow restrictorsuchas capillariesisthattheyendow the
bearingwiththe greatesttolerance tomanufacturingvariationonbearingclearance.
 Capillaryrestrictorismade bycuttinga tube of knownbore toa suitable length. Sothere is
manufacturingsimplicity.

3. Limitationof capillary:-
 Capillariesgivesleaststiffnessandpressure sensingvalvegiveshigheststiffness.
 Highstiffnesscanonlyachievedbyprovidingmoderatepressureandbearingarea.
Hydrostatic thrust pad bearing:-
 Designedtoprovide axial loadsupport
 PressurizedFluidfilmisgeneratedtobalance the appliedthrustloadwithsufficient
separationof stationary(thrustpad) androtatingsurface (Shaftmachinedcollar) toavoid
wear,to provide lowfrictioncoefficientandtoavoidexcessive temperature.
Mathematical expressionforcapillarycompensatedHydrostatic thrust pad bearing:-
Stiffnessof capillarycompensatedhydrostaticthrustpadbearing:-