mst offset analysis of bauer high-pressure rotary feeder valve

MST Corporation White Paper

Study—Offset Analysis of Bauer High-Pressure Rotary Feeder Valve (HPRFV):

Rotor Offset v Bore Profile v Alternatives v CenterSeal™ ©

of 13

1659 SW Baldwin Road Prineville, OR 97754

(541) 416-9000 www.mstcorp.com

1. WHY A ROTOR OFFSET WAS, OR IS, USED ON A BAUER HIGH-PRESSURE ROTARY FEEDER VALVE (HPRFV)?

2. WHAT IS THE TRUE REASON AN OFFSET ROTOR EVOLVED AS GENERAL PRACTICE

3. A HISTORICAL PERSPECTIVE

4. THE PHYSICS INVOLVED

5. BETTER ALTERNATIVES OR METHODS THAT CAN BE USED TO ENHANCE VALVE OPERATIONS BASED ON STUDY AND ANALYSIS OF THE HISTORY AND PHYSICS INVOLVED?

By MST Corporation

Table of Contents: Page

INTRODUCTION ........................................................................................................................................2

EXECUTIVE SUMMARY ............................................................................................................................2

STRAIN ENERGY ELASTICITY PHYSICS VERSUS DEFORMATION FOR A HPRFV .....................3

STRAIN ENERGY PHYSICS AS IT APPLIES TO A HPRFV .................................................................4

IS THE PREMISE FOR THE OFFSET CORRECT? ................................................................................5

SO WHY DOES A ROTOR-AXIS-OFFSET-DOWN SEEM TO WORK? ..............................................8

ATTACHMENTS ...................................................................................................................................... 11

MST Corporation White Paper

Study—Offset Analysis of Bauer High-Pressure Rotary Feeder Valve (HPRFV):

Rotor Offset v Bore Profile v Alternatives v CenterSeal™ ©

of 13

Introduction

The purpose here is to provide knowledge to Bauer high-pressure rotary feeder valve owners about offset

specifications; related problems and solution options for technological and operational improvements.

The analysis reported here demonstrates to Bauer valve owner-users that there are other ways of looking at

the operational and mechanical issues. Users are given a perspective that leads to important improvements

and cost savings in maintenance, environmental control and energy consumption.

Executive Summary

Bauer documents allege elastic deflection

(bending) of the drive shaft is the reason for the

odd offset, sets. For example, on high-pressure

size 18, the nominal offset is, 0.028” for the rotor

and 0.020” for the inner bearing seal bore. Bauer

assert, based on pressure forces, that the shaft re-

centered due to bending.

Quotes from Bauer et al documents important

to this thesis:

(1) “The effects of the bending or deflection [emphasis mine] of the

rotor is further controlled by the adjustment of the relative position of

the offset of the rotor in relation to the body to provide minimum

running clearances under the influence of pressures with minimum

pressure loss.” From: (United States Patent; by H. S. Messing [of

M&D], 1960/1964)

(2) “Eccentric bearing sleeves installed at the factory provide radial

bearing offset to compensate for elastic deformation [emphasis

mine] at operation conditions.” From: (Bauer Maintenance Manual

451 (18); Important Notes Section; Paragraph 2)

(3) “eccentric inserts . . . accommodate various conditions of

differential pressure to which the rotor may be exposed. . . . where

different portions of its rotor are exposed to different temperatures

and pressures the rotor will inherently center in its housing

[emphasis mine].” From: (United States Patent; By James R

Starret; Bauer Bros Company; 1971/1973)

(4) “Another object of the invention is to provide simple but improved

means to pre-set a rotor unit and precondition the bearing support

therefore so that in use the rotor will center in its housing and

operate .relatively free of friction and imbalance [emphasis

mine].” From: (United States Patent; By James R Starret; Bauer

Bros Company; 1971/1973)

There is not enough pressure force in a vessel to

cause the amount of bending/deflection claimed.

See the attached FEA analysis. We tested the

bending theory based on two FEA analyses; two

different software programs, same results.

However, if one arbitrarily programs the shaft to

deflect that much, then the fits; the seal, the

centerline et al tend to line up. Reverse

engineering analyses points to several factors that

are behind the bending theory circulated by the

Bauer people.

Here, we offer information that will help the

Bauer user to have a better understanding of the

physics involved. This will help users‟ develop a

healthier understanding of the effects that cause

valve operational problems in general

Owners of Bauer style HPRFV‟s can benefit by

reassessing the soundness of having the rotor and

shaft in an axis-offset-down1 position. The

forensic data does not support using it.

1 The endbell registers, in the body, are on the same centerline as the body bore

axis/centerline.

Axis-offset-down defines the situation where one is directed to use eccentric sleeves around

the outer bearing races to cause the rotor to be positioned in the body bore with the rotor axis

different from the end bell registers; different from the body bore centerline.

WHITE PAPER - THE NATURE OF USING AN OFFSET ROTOR FOR A BAUER HIGH PRESSURE ROTARY VALVE—ANALYSIS OF THE

TOPICS; PROMOTE BETTER ALTERNATIVES

of 13 © February 22, 2003 Issue 10-0207

By MST Corporation Page 3 of 13 Print Date: 3/2/2010

hprfv; bauer; offset; physics; strain energy

A faulty posture of speculation and conjecture

(belief) is the reason for the axis-offset-down rotor

status publicized for decades by Bauer. Heuristics

effectively demanded they (Bauer) devise a

rationale. The rationale‟s worth is seriously flawed

based on physics.

The heuristic justification Bauer derived and

publicized as fact is wrong. The theory behind

their belief was based on the idea that elastic

bending (force induced deflection) dominated the

subject matter.

The true problem was not deflection; it was shape

change from heat combined with the affects of

torsional friction versus available HP

(horsepower) at the valve drive stub connection.

The forensic evidence does support the use of a

slight change of the relationship of the rotor to the

surface profile of the body bore to aid the

operators on first startup of a new valve. This is

not the same thing as offsetting the drive shaft

relative to the head register fit.

The basis for HPRFV design and function hinges

on strain-energy physics as a property of metals

used.

In this paper, we will show that an axis-offset-

down rotor setting is not required when the

installation is correct and the HP is proper for the

application. Point of interest: it is better if the axis

offset is not used; instead profile the body bore

surface to accomplish the intended goal.

Presetting the rotor axis offset (axis-offset-down)

different from the primary bore axis is

counterproductive. It increases the wear-in cycle

time and it increases the time to form a quality

circumferential seal fit. That is, the seal fit, rotor

to body bore.

Removing the current rotor axis-offset-down, and

replacing it with a CAD (computer-aided design)

body bore surface profile—in the upper-body-

bore-quadrants—permits operating the rotor on

the correct natural centerline. This way, the right

relation to the stuffing box, bearing oil seal, and

etcetera, are protected.

Current Bauer specifications; for a typical high-

pressure application, calls for approximately

0.028” axis-offset-down of the rotor to bore center

and 0.020” offset for the bearing oil seal bore.

These fits belong on center. It lessens the wear-in

time, permits replaceable stainless steel stuffing

box conversions; SealRyt™ type packing systems,

and makes the startups and break-in period

friendlier; more operator friendly.

The valve does not know the difference if the rotor

axis is offset relative to the body-bore or if the

rotor and body axes are the same and the body-

bore is shaped so the rotor thinks it is offset for the

break-in cycle. The rotor does not know the

difference.

Placing a prescribed bore profile (CAD designed

shape) in the upper quadrant to help compensate

for the startup quirks does provide dimensional

tolerance for heat distortion effects.

An on-center shaft provides improvements in

sealing technologies; longer packing life,

simplifies maintenance and the lifecycle run-time

is improved.

Knowledge of how the valve truly works will

explain the ideas here and decrease typical startup

annoyances.

The object of CenterSeal™ technology is to

reconfigure the seal and packing relation so they

are true to the rotor-shaft axis; the natural

centerline of all components.

Keeping the natural centerline for both the rotor

and the rotor shaft allows for packing and stuffing

box upgrades. Example: upgrades like use of

enhanced packing systems. Oil seal reliability is

also improved.

Instead of a rotor axis-offset-down, the Bauer

valve works better when a specific surface profile

is placed into the upper quadrant of the body bore

itself.

Strain Energy Physics versus Deflection for a HPRFV






Strain (in the context here) is defined as elastic

deflection (shape change) caused by the pressure

forces. Heat causes shape change, but this is a

metallurgical property which is treated differently.

Two primary dynamics contribute to shape-change

in a HPRFV. They are heat caused metal growth

and pressure forces; elastic deflection, called

strain.

The elastic deflection side of the problem is easy

to deal with based on strain energy physics. That

is, when the cross-sectional thickness of the valve

components involved is increased then the

distortion and deflections, due to pressure, is

controlled.

In the beginning, Bauer assumed the effects of

thermal shape change observed was a result of

pressure forces. They state that in their historical

writings. Using an offset rotor, they believed,

compensated for their alleged deflection theory.

Bauer‟s premise about this is documented in the

Bauer maintenance manuals, patents and other

internal papers. These references infer the

deflection was multi-faceted and included the

endbells—the reason for the bizarre jacking bolt

arrangement found on the endbells.

Strain Energy Physics as it Applies to a HPRFV

Using strain energy physics in design means one

spreads the load over enough cross section so the

deflection (from pressure) is under control and

elastic deformation becomes a non-issue in a

rotary valve.

Strain energy physics involves working with the

slope of the curve for metals within their elastic

range. In general, for a typical HPRFV, the goal is

to keep the unit stress on the metal to about 2000

psi maximum. There is a functional relationship

between psi and deflection (strain) amount. In this

case, the maximum psi value effectively sets a

design limit for deflection.

The strain (elastic deflection) comes about in

proportion to stress (symbolized here as σ [Greek

letter sigma]) based on the elastic modulus

(symbolized as Ἓ [Greek letter epsilon]). The

deflection, i.e., strain is symbolized here as ἐ

[Greek small letter epsilon]. If one pulls a steel

test specimen to failure, the stress-strain curve

looks like Figure 1.

„F‟ symbolizes the Force (the resultant of applied

digester pressure in this case). Letting „A‟

symbolize area, then:F

σ=A

. By inspection, one

can see that as the area „A‟ increases and the force

„F‟ stays the same, the stress „σ‟ decreases. It is

the equivalent of moving the stress level down on

the vertical axis. See Figure 1.

Existing HPRFV‟s yield very little at their

connections, deflection is controlled based on

strain energy physics, as described. That said, per

the stress strain curve shown in Figure 1,

theoretically, the maximum elastic yield (in/in) of

the shaft-bearing and endbell connections would

be approximately the 0.0012”/in, pointed out. See

FEA report at the end of this document.

Competent designers would not design up to the

limit; therefore, the strain (deflection) value would

be significantly less. Strain is defined asL

, in

inches/inch. Where „δ‟ equals the change in length

and „L‟ equals the original length.

Based on the typical section strength design for a

HPRFV, the strain (elastic movement) would be

about seven-millionths (0.000007”) of an inch.

This is far below the rotor-axis-offset settings

used on a Bauer rotary feeder.






Most of the claims for deflection center on

bending of the shaft. Bending deflection is the

strain (deflection) affects of a moment due to an

applied load—pressure in this case.

To factor that variable in we contracted with JHI

Engineering to perform a finite elemental analysis

(FEA) to find out the maximum deflection under

the condition of 150-psi digester pressure. Near

the maximum digester pressure one would

normally encounter.

The maximum deflection—in bending—came in

at about 0.0012”. See the JHI report below. This

figure is a maximum because we negated the

resistance effect of the rotor-shaft combination;

the resistance effect of the rotor touching the body

bore and the resistance effect of the packing,

etcetera.

Let us round the 0.028” number to 0.030”for

simplicity. Per the FEA work, the pressure-

induced strain (deflection) affect, combined,

would be less than two-thousands (0.002”) of an

inch. This begs the question, how did they (Bauer)

come up with the roughly thirty-thousand inch that

is common, and why?

The people that do the FEA work agree the basic

thesis in this document is valid and the reason for

the much larger offset Bauer promoted all these

years is not related to deflection as Bauer claimed.

The information here points to several

considerations Bauer overlooked or analyzed

incorrectly, as follows:

1. The original idea (Bauer‟s justification for the

offset) was based on flawed assumptions.

2. Bauer failed to take into account the profile of

the valve based on heat distribution (profile)

at hot thermal equilibrium—hot versus cold—

after a prolonged stable runtime.

3. Non-equilibrium thermal conditions, in terms

of time (transients), are not accounted for in

their theory.

4. HP coupled with torsional friction, resisting

rotation, is a (key) factor that should have

been considered, but was not.

5. Improper startup procedures, and their affects,

are not accounted for using their stated

conclusions.

Is The Premise For The Offset Bauer

(Institutionalized all These Years) Correct?

Elastic deflection does not explain the use of an

axis-offset-down rotor. Only thermal affects on

metals; startup and torsional friction issues, can

explain the run problems that caused them (Bauer)

to construe the need for their offset theory.

One can calculate the strain-equivalent „ε‟ for a

section of each metal type based on the

temperature profile. That value can be introduced

into the stress-strain curve to find its force

equivalent on the curve.

Comparison and analysis about true deflection

from a force versus shape change, due to heat,

helps in understanding the ideas presented here.

For example, it only takes a temperature

differential of about 185 °F to change 1-inch of

the body material an amount equal to the 0.0012”

mark on the curve in Figure 1.

A typical size 18 valve body-bore can vary about

10 times that amount based on a normal stable

thermal profile. It may vary far more when

startups are rushed, like operational upsets and

transient events that imitate conditions as on a

startup.

Another variable: the stainless steel rotor has a

higher coefficient of expansion rate and a higher

equilibrium temperature by comparison. The

stainless steel can vary radially about 54 times the

amount above.

The point is: the different metal properties are

reacting simultaneously to the heat variations. The

combinations are complex, however, the forces

producing deflection due to steam pressure, on the

metal cross sections involved, cannot account for

the offset figures.






The original beliefs by the pioneers in this

technology lead to wrong thinking. Likely, they

based their theories on damage assessments and

sketchy field experiences that were not accurate.

Bauer references damage assessment factors in

their patent documents as grounds for “improving

[their] prior art.”

The offset engineering was reactionary

engineering based on operational problems in the

field. The real issue was—and is—how the

thermal profile versus dimensional relationship

variables (metallurgically speaking) affect how the

torsional friction and HP requirements factor into

the mix.

In real life, uniform heating of the rotor takes

place because it (the rotor) rotates over the heat

source. This is not the case for the housing.

The housing bolts to the heat source and therefore

is subject to a thermal profile (gradient) disparity,

bottom to top. During start-up and/or transient

conditions the thermal profile variations are

dynamic.

The housing bore will change from its (round)

close tolerance cold setting to a slight, complex,

egg-shape like form when heated. The rotor,

because of even rotational heating, will stay

round.

The included angle-rotor-to-housing relation will

change because the large end of the rotor grows

(from heat) a greater amount compared to the

small end.

The rotor carves out (wears-in) the bore to remove

the egg-shape and also wears-in to compensate for

the thermally induced different included angles;

rotor versus body-bore.

The included angle of the rotor taper versus body-

bore taper changes from heat and each change

differently with respect to each other because of

the metallurgy involved.

The body bore starts out life round at room

temperature; in the shop. The heat difference at

startup causes the body bore to take on an egg-

shape. As noted, the rotor stays round because it is

rotating over the heat source. Imagine what we

have just described:

We have described a condition whereby a new or

cold valve is trying to fit a round rotor into an egg-

shaped body bore; both conditions due to the

nature of the thermal effects on startup. It is the

round peg into a square hole allegory. In this case,

a round peg into an egg-shaped hole.

The offset was a tool (if you will) used to

compensate for that round peg into the egg-shaped

hole dilemma. In addition, this dilemma

effectively increased the power requirement as a

direct result of the high torsional friction load it

caused.

In sum, the offset was not needed because of

deflection, it was needed because the valves did

not have enough power to drive through the break-

in period. After about 8-hours of uninterrupted

operation the rotor and body become thermally

stabilized.2 Bauer does not deny the fact it takes

about 8-hours; they refer to it in their manuals, etc.

After stabilization has occurred, the body bore is

still egg-shaped because the body is static; not

rotating like the rotor; different temperature

bottom-to-top.

The offset rotor did not seal as well as one fully

worn to fit, but it got them by the fitful stalls

etcetera related to the torsional friction problem

for the duration of the time needed to wear into the

bore until it fit, creating an optimal seal, rotor to

body.

The full offset amount (nominally about 0.028” on

high pressure applications) requires the body-bore

to wear-in (become round at hot equilibrium

status) until the offset, in effect, disappears, or,

more correctly stated; until the egg shape

disappears at hot equilibrium operation.

Moving the rotor down 0.028” toward the bottom

doubles the clearance at the top,

2 0.028" 0.056"x , the true offset relative to the

body bore surface.

2 Thermally stabilized defines the status whereby the valve parts stay

at their normal temperature, and start-out shape (known as a hot

equilibrium state), for a prolonged period of time. Long enough to

reshape the body bore back to a round condition based on the rotor wearing to fit.






The taper ratio is 6 to 1 per side. The design for

the valve calls for the ability of the rotor to move

toward the small end 1-inch during a valve

lifecycle.

By design, the Bauer valve unit has a theoretical

lifecycle equal to the 1-inch of axial travel. The

rotor will fit the body bore all around (at hot

equilibrium) when the axial travel reaches about 3/8”, i.e.,6 0.056" 0.360"x .

The effect is the bore—in operation—moves

(because of wear) to the same axis of the rotor.

This occurs over time, as the rotor is moved

(wears-in) axially toward the small end; known as

the break-in period.

The break-in period varies depending on the skill

of operators in combination with the usable

horsepower at the drive shaft. Overcoming

torsional friction variables during the shaping

(rounding) time period is functionally realted to

these two chief variables.

The valve is designed for a lifecycle defined as 1-

inch total axial travel, then by definition, after the

0.056” top gap disapears; because the rotor

effectively laps itself into the body bore until it fits

all around.

At the point the 0.056” top gap is gone; and

because the rotor is fixed in the bearing centers,

the rotor and its shaft centerline become the same

as the lapped in bore. This leaves about ¾” of

axial lifecycle left.

One could ask: if the rotor being offset is a

requirement why the discrepancy; most of the

designed lifecycle of the valve takes place after the

offset is gone?

Assuming one has enough HP to overcome the

torsional friction, then that last approximately ¾”

of movement takes place without the existence of

any offset (radial difference), top, sides, or

bottom.

It is very important to recognize the part HP plays

in the successful (trouble free) operation of a

Bauer valve.

Horsepower is what determines if the users can

maintain a close (minimal radial clearance) rotor

to body seal fit. One can see there is a functional

relationship between; (1) radial clearance, (2) HP

and (3) amperage. These three factors can be

varied to improve opetations.

The power available at the drive is a controlling

factor as to how friendly the valve will seem to the

operators throughout the valve lifecycle. Higher

HP always will help make operations seem

friendlier during startups and/or transients.

In a metallurgical sense, it takes about eight hours

for a HPRFV to reach true thermal equilibrium.

When the startup is pushed too quickly or there is

operational thermal upsets. The bottom to top

thermal gradient causes shape change.

The thermal bore distortion increases and there is

a greater torsional frictional resistance. That is, a

greater demand for power to compensate for the

increased frictional resistance. The valve tends to

stall or act erratically.

Operationally, a taper plug rotary valve is all

about power (usable HP) because the rotor-to-

body clearance control is functionally regulated by

monitoring—and maintaining—the amperage

(friction) range for the drive.

The amperage range (by Bauer‟s definition of how

to operate) tells the operators when the taper rotor

is seated, based on amperage, functionally related

to an acceptable level of friction versus the

functional relation to motor size

There has been a tendency—over the years—to

increase horsepower to compensate for amperage

kick-outs compared with the original lower

horsepower units. Nothing is more frustrating to

an operator than to be saddled with an

underpowered valve or a valve that looses too

much power through the drive train, etcetera.

The higher HP helps, as the rotor-to-body seat

tightens up over time. However, reserve power is

what eases the burden on the operators and

operations.






The worn-in fit makes the better seal, but is more

sensitive to the increased friction loads related to

the thermal transients described. The transient

friction factors, in general, increases the HP

demand based on higher torsional friction.

The thermal issues outlined above (in combination

or individually) give rise (no pun intended) to

false speculations and analyses. The original

theory for the offset persists based on perpetuated

and mistaken conclusions first promulgated in the

1950‟s.

Using the knowledge condensed here, it is

possible to pre-shape the body bore to provide all

the benefits an offset may provide with the added

improvements available when all axial

relationships are coincident—the same.

Benefits like improved sealing and sealing

options. Longer life in the packing system; the

bearing seals and packing are truly on center;

simpler maintenance (no offset bearing sleeve

required) and etcetera.

So Why Does a Rotor &Shaft-Axis (Original Bauer)-Offset Seem to Work?

The exact events leading to the false conclusion

for the offset value are lost in the past. However,

based on forensic analysis and reverse engineering

work the following conclusions can be inferred:

The rotor is stainless steel and the body is

mild steel.

Originally they manufactured the rotor and the

body without an offset.

The coefficient of thermal expansion

between these two metals is a net difference

of:

63.5

[( )/ /deg

( )]

x Operating temp Roomtempin in F

x total inches

The greatest growth takes place with the

stainless steel.

The top side of the bore is less temperature

than the bottom side. Hence an inherent egg

shaped bore surface on a new or cold valve.

The real time reaction to too much friction

(high amp loads) is not quick enough because

it is fundamentally manually controlled and

the information feedback for the operators‟

places the operator at a disadvantage.

The rotor back-off (after touching) specification

for startup (see Bauer startup procedure) of the

valve is 3 to 4 seconds on the limit torque based

on amperage feedback (the touchdown indication).

This translates to about 0.003” axial movement;

about 5-ten thousands (0.0005”) increased radial

clearance. Note: based on the limits of amperage

(HP) the correct running clearance, by definition,

becomes the ongoing seated rotor control

reference.

Based on the differential growth of the body

versus the rotor and the uneven profile, bottom to

top of the body, these factors can lead to rubbing

contact severe enough to cause stalling problems.

Depending on the rate of heat-up (thermal shape

change) the interference at the top (rotor versus

body-bore) may range from a theoretical minimum

of 0.012” to a maximum of about 0.060” for the

high pressure units on new valve startups.

The actual values depend on warm-up rates and/or

rates of change initiated by transient events.

Originally, they (Bauer) misinterpreted the

difference as “deflection” of the rotor due to

pressure. In the case of steam there is a functional

relation between pressure and temperature. As

such, there is a quasi metallurgical relationship;

temperature versus pressure.

Different temperatures at different pressures (the

functional relationship) better explains the

historical offset range of 0.012” to 0.040” (0.024”

to 0.080” at the top) based on pressure and valve

size for all sizes of valves, as noted in the Bauer

documentation—tables.

The rotor stays round because it rotates over the

heat source (like a Bar-B-Q spit); heats uniformly

and is equal to the vessel temperature.






For the tapered rotor to seat, it is necessary to

wear-in the egg-shape body bore to fit the round

rotor and to rematch (wear-to-fit) the included

angle of both rotor and body-bore, over a steady

hot-equilibrium run-time period; the time is

functionally related to available power.

The perceived contact at the top of the bore—

because of thermal shape change—lead to the

view they (Bauer) needed to back off the rotor

axially. That is, move the rotor back, then down,3

which lead to the general rotor setting on a cold

valve assembly.

In the one sense they overlooked the thermal

dimensional changes described. However, in

another sense, by shifting the rotor to a rotor-axis-

offset-down—in a crude way—it dealt with the

thermal distortion problem—albeit a quasi do-it-

yourself (partial) solution.

At the same time they were closing the rotor to

body clearance on the pressure side of the rotor;

essentially, providing a quasi seal on the pressure

side long enough for the rotor to wear (round up)

the egg-shape bore profile.

Creating an axis-offset-down-rotor was an

indirect way to make operation friendlier,

specifically when the HP was inadequate for the

operational conditions. That is, when the valve

assembly distorts from uneven heating.

Some wear-in is always required, especially on

start-up and during the break-in period because of

heat distortions; noted. The Bauer offset is

effectively a crude built-in HP (amperage) control

mechanism when the body is moving around due

to uneven heating and initial wear-in is taking

place.

Summarized, the true effect of an offset rotor was

to provide room, mostly at the top and sides of

the body-bore to compensate for thermal

variations in shape of the body-bore, especially

on startup.

3 It is the taper that requires the rotor be moved back then down.

The 6 to 1 taper per side requires one to move the rotor back

axially six units for every one unit of offset desired. This is also the reason the clearance doubles at the top.

The “round” (heated) rotor will have to wear-in

(all) surface contacts until its axis matches a

mostly round bore when the valve is at thermal

equilibrium.

Most importantly, the offset helped lower the

torsional friction, or stated another way, helped

make it possible to operate based on the limited

HP available in those days.

Torsional friction effectively sets (defines) the HP

that needs to be available for the intrinsic radial

clearance established for a good operational seal.

When it comes to the HP versus torsional friction,

it is, metaphorically, the proverbial chicken or egg

problem. Generally, not enough attention is given

to the HP requirements versus operational

troubles.

What the data here demonstrates is the true rotor

to body fit is not a deflection problem per se. It is

a thermal profile problem in conjunction with the

limits placed on the operation of the valve related

to real-time torsional friction and the available HP

to overcome the friction.

Because it is a thermal profile issue, the better

course of action is to predefine the body bore

using an obround-like (shaped) bore. That is,

precondition the bore shape to deal with the

problem.

Using the rotor offset approach is a crude

alternative for dealing with heat variation. It leads

to other problems and interferes with important

improvements that make operation and

maintenance easier.

Shaping the bore surface profile allows a truer seal

at the bottom bore quadrant and near ideal seal on

the entire circumference of the rotor-to-bore fit.

In addition, as noted before, the packing and oil

seal fits can then operate on true center with the

rotor, allowing a number of changes that improve

the mechanical reliability of the valve units;

improve packing seal options; save on steam

consumption, to name a few.






The goal here is to make known information that

will help Bauer valve users see ways for Bauer

valve improvements that will advance technology

in this field and promote the advantages of having

the seal area, packing area and rotor to body

coaxial relationship.

The Better Method(s)- Reassessment-Time Tested MST-Bauer CenterSeal™ Design & Related Improvements:

Summing up, a controlled bore surface profile

method, i.e., CenterSeal™ design—coupled

with reassessment of one‟s HP and drive

limitations, etcetera—directly deals with the true

issue outlined here.

That is, the historical offset rotor method was

based on a flawed theory and is cause for

numerous operational problems to this day.

Ray Lackey

Go to attachments:






Attachments






BAUER SHAFT WIREFRAME SHOWING LOADING DISTRIBUTION JHI Engineering, Figure ‘1’






BAUER SHAFT DISPLACEMENT GRADIENT PLOT ‘Y’ DIRECTION JHI Engineering, Figure ‘2’

Appendix A

mst offset analysis of bauer high-pressure rotary feeder valve

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