Technical annex Movement and force at compensators

Before opting for a compensator type,it is important to decide on how achange in length of a pipe system is tobe compensated.

The choice of the compensator typedepends essentially on the securringexpansion, on the routing of the pip-ing system and on the space avail-able.

Pipe expansion can be absorbed byshift and deflection of a certain type ofcompensator.

Tolerable superposition of axial and lateral movement at rubber compensators

Tolerable superposition of axial and angular movement at rubber compensators

MovementWhen choosing a compensator thefollowing types of movement must beconsidered:

axial movement lateral movement angular movement

Rubber compensatorsIf both axial and lateral (superim-posed) movement are simultaneouslyintroduced into a rubber compen-sator, its maximum extension in theaxial direction and its ability to absorbthe highest rated movement are re-duced (see diagram ).

BL

BL

Ang

ular

win

kel

The interrelation of superimposed an-gular and axial movement is shown indiagram .Steel compensatorsIf axial and lateral movement are si-multaneously introduced into a steelcompensator (superimposed move-ment), the lateral share is convertedby an equation into an equivalent axi-al path and must not exceed 100 %when added. Please contact our Technical Consul-tation Service.

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late

ral t

rave

l

axial extensionaxial compression

axial extensionaxial compression

50 % of max. lateral movement

ang

ular

ang

le

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Force of axial and universal compensatorsAxial compression force FD referredto structural length (reaction force)Axial compression force is the longi-tudinal force resulting from internalpressure.

FD = axial compression force (N)A = effective bellows cross sectional

area (cm2) (see data sheet tables)p = internal pressure (bar)

FD = A p 10

Axial bellows moving force FaxThe axial bellows moving force is theforce required for the axial movementof the bellows. It results from the stiff-ness of the bellows together with themovement.

cax = axial bellows moving rate (N/mm)ax = axial travel (mm)

+ = sign for compression - = sign for extension

Fax = cax ax

Axial bellows total force FaxBAddition of axial compression forceand axial bellows moving forceFaxB = total axial force of the

bellows (N)+ = compression force on pipe - = tensile force on pipe

FaxB = FD + Fax

Lateral bellows moving force FlatBThe lateral bellows moving force is theforce required for the lateral move-ment of the bellows. It results from thestiffness of the bellows together withthe movement.

FlatB = lateral bellows moving force (N)

clat = lateral bellows spring rate(N/mm)

lat = lateral travel (mm)

FlatB = clat lat

force described for axial compen-sators. But this compression forcegenerates friction force at the tie rodhinges which must be overcome withthe lateral movement.The moving force of lateral compen-sators is calculated as follows:

Flat = total lateral moving force (N)Ffric = friction force from tie rod

hinges (N)

Flat = FlatB + Ffric

The moving force, introduced into thelateral compensators, is not as highas in unrestrained axial or universalcompensators, but is still transferredto the pipe and needs to be account-ed for when rating the fixed points.

Force of lateral compensators

Moment of angular compensatorsAngular bellows moving momentMangBThe angular bellows moving momentis the period required for the angularmovement of the bellows. It resultsfrom the stiffness of the bellows to-gether with the angular movement.

MangB = angular bellows moving moment (Nm)

cang = angular bellows moving rate(Nm/degrees)

ang = angular moving angle (degrees)

MangB = cang ang

Total angular moving moment MangSTENFLEX angular compensators areequipped with angular hinges. Thehinge restraints absorb axial com-pression force described for axialcompensators. But this compressionforce generates friction force at theangular hinges which must be over-come with the angular movement.The moving moment of restrained an-gular compensators is calculated asfollows:

Mang = total angular moving moment (Nm)

Mfric = friction moment in the hinges(Nm)

Mang = MangB + Mfric

Total lateral moving force FlatSTENFLEX lateral compensators areequipped with tie rod restraints. Thetie rods absorb axial compression

Effective bellows cross sectional ar-eas, moving rates and friction force ormoments are specific to the type ormanufacture, and depend on operat-ing conditions. Please inquire for fur-ther details.

Technical annex Movement and force at compensators

Pipe fixed points for compensators and pipe connectors

As a flexible pipe element, a compen-sator or pipe connector separates therigid system and de-stabilizes thepipe if there are no fixed points. Posi-tive internal pressure induces force in-to the pipe. Direction and degree ofthe force depend on the nominal di-ameter, pipe internal pressure, move-ment being absorbed and the piperouting. A lack of fixed points willcause the pipe to shift. The flexible el-ement would be stretched to its loadlimits and, eventually, this wouldcause the elastic connection to break.

In addition to the fixed points, func-tionally safe operation of compen-sators and pipe connections also re-quires flawless pipe routing.Guide bearings prevent the pipe frombuckling.

Fixed points are also necessary forunpressurized operation where vibra-tion must be compensated to relievethe pipe, or if several compensators orpipe connectors are fitted in a pipelinesystem.

Lack of fixed points

Pipe guide bearing with rollers

We differentiate between the follow-ing fixed points and guides:

HFP = main fixed pointZFP = intermediate fixed pointKFP = knee fixed pointFL = guide bearing (plain bearing)

Pipes with unrestrained compen-sators or pipe connectors must beequipped with robust fixed points andguides. The main fixed points mustabsorb FaxB and FReibFL force.

Special care must be given to correctrating and design of the fixed points.They must be robust enough to with-stand negative effect on supports(e.g., on building wall, ceiling or steelstructure), when pipe force is intro-duced.

Fixed point design

At pipe deflection points the main fixed points (HFP) and knee fixed points (KFP) absorb the full reaction force. The intermediate fixed points (ZFP) are practically relieved of pressure.

When rating fixed points, the followingforce must be taken into account:FD = axial compression force

(from positive inner pressurein the pipe)

FaxB = total axial force of the compensator

Flat = total lateral moving force ofthe compensator

Mang = total angular moving moment of the compensator

FfricFL = friction force at the guidebearings

Fcent = centrifugal force from pipediversions (at high flowspeeds)

In an unstable pipe system, a com-pensator or pipe connector cannotperform its function; pipe force cannotbe absorbed.

Pendulum-type pipe suspensions arenot fixed points

HFP

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Anordnung von Festpunkten und Fhrungslagern bei Axial- und Universal-KompensatorenL1 = distance between compen-

sator/pipe connector and fixedpoint or distance betweencompensator/pipe connectorand 1st guide bearing(L1 3 x DN)

L2 = distance between 1st guide

bearing and 2nd guide bearing(L2 = 0,5 x L3)

L3 = normal distance between 2guide bearings

L3 must be seen in the context of theweight and nominal diameter of thepipe together with the positive innerpressure (for indicative values see dia-gram).

The pipe must be guided exactlythrough the bearing. Guide bearingsmust be placed on both sides of thecompensator. A fixed point replaces aguide bearing. Internal guide sleevesare unsuitable as pipe guides.

3 3

HFP ZFPFL FL FL

Arrangement of a compensator beside a main fixed point

Arrangement of a compensator between two guide bearings

Dis

tanc

e be

twee

n gu

ide

bear

ings

L3

(m)

Anordnung von Festpunkten bei Lateral- und Angular-Kom-pensatoren

DN

Arrangement of fixed points for lateral and angular compensators

Arrangement of fixed pointsat pumps

Pump appliance in elastic mount, silenced pipe connection with rubbercompensators.

Distance between guide bearings

Arrangement of fixed points and guide bearings for axial compensators and pipe connectors

Appliances such as pumps are de-coupled from the pipe system bycompensators or pipe connectors.The pump housing is relieved of pres-sure and tension. The force is ab-sorbed by correctly positioned pipefixed points.

HFP HFP

L3 L3 L2 L1 L1 L2 L3 L3

FL FL FL FL FL FL

Pipes with lateral and angular com-pensators must also be equippedwith fixed points, even though axialcompression force FD is absorbed bythe restraint. Here only lateral moving force Flatresp. angular moving moment Mangneeds to be absorbed.

Compensation system with two an-gular compensators to compensatefor large pipe movement. Pipelinewith fixed points to absorb angularmoving moment.

As a rule only one compensation sys-tem may be placed between two fixedpoints. When several compensationsystems are fitted into the pipe sys-tem, fixed points must be providedbetween them.Hinged compensators have a givenrotation axis around which they canrevolve.When arranging a compensator sys-tem, the correct position of the rota-tion axes must be considered.

Technical annexPipe fixed points for compensators and pipe connec