1. DESCRIPTION 1.1. GENERAL The pressure fluctations occurring in hydraulic systems can be periodical or one-off problems due to: flow rate fluctuations from displacement pumps actuation of shut-off and control valves with short opening and closing times switching pumps on and off sudden linking of spaces with different pressure levels HYDAC hydraulic dampers are particularly suitable for damping such pressure fluctuations. Selecting the most suitable hydraulic damper for each system ensures that vibrations caused by pipes, valves, couplings etc. are minimised and resulting pipe and valve damage is prevented measuring instruments are protected and their performance is no longer impaired the noise level in hydraulic systems is reduced the performance of machine tools is improved interconnection of several pumps in one line is possible a pump rpm and feed pressure increase is possible the maintenance and servicing costs can be reduced the service life of a system is increased Hydraulic Dampers E 3.701.10/09.04
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1. DESCRIPTION1.1. GENERAL
The pressure fluctationsoccurring in hydraulic systemscan be periodical or one-offproblems due to:flow rate fluctuations fromdisplacement pumpsactuation of shut-off and controlvalves with short opening andclosing timesswitching pumps on and offsudden linking of spaces withdifferent pressure levels
HYDAC hydraulic dampers areparticularly suitable for dampingsuch pressure fluctuations.Selecting the most suitablehydraulic damper for eachsystem ensures thatvibrations caused by pipes,valves, couplings etc. areminimised and resulting pipe andvalve damage is preventedmeasuring instruments areprotected and their performanceis no longer impairedthe noise level in hydraulicsystems is reducedthe performance of machine toolsis improvedinterconnection of several pumpsin one line is possiblea pump rpm and feed pressureincrease is possiblethe maintenance and servicingcosts can be reducedthe service life of a system isincreased
HydraulicDampers
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2. TYPES OF CONSTRUCTION2.1. PULSATION DAMPER TYPE SB ... P
pres
sure
pres
sure
pres
sure
pres
sure
pres
sure
pres
sure
2.2. SUCTION FLOWSTABILISER TYPE SB ... S
without damper
time
with bladder accumulator
time
with pulsation damper
time
2.1.1 GeneralThe HYDAC pulsation damperprevents pipe breaks caused by material fatigue, pipeoscillations and irregular flow rates;protects valves, control devices and other instruments;improves noise level damping.
2.1.2 ApplicationsThe pulsation damper is particularly suited for:hydraulic systems, displacement pumps of all types,sensitive measurement and control instruments andmanifolds in process circuits in the chemical industry.
2.1.3 Mode of operationThe pulsation damper has two fluid connections andcan therefore be fitted directly inline.The volume flow is directed straight at the bladder ordiaphragm by diverting it in the fluid valve. This causesdirect contact of the volume flow with the bladder ordiaphragm which, in an almost inertialess operation,balances the flow rate fluctuations via the gas volume.It particularly compensates for higher frequencypressure oscillations. The pre-charge pressure isadjusted to individual operating conditions.
2.1.4 ConstructionThe HYDAC pulsation damper consists of:the welded or forged pressure vessel in carbon steel;for chemically aggressive fluids with internal coating orin stainless steel;the special fluid valve with inline connection, whichguides the flow into the vessel (threaded or flangeconnection);the bladder or diaphragm in various compounds asshown under point 5.1.
2.1.5 InstallationAs close as possible to the pulsation source. Mountingposition preferably vertical (gas valve pointingupwards).
without damper
time
with bladder accumulator
time
with suction flow stabiliser
time
2.2.1 GeneralThe HYDAC suction flow stabiliserimproves the NPSH value of the system;avoids cavitation of the pump;prevents pipe oscillations.
2.2.2 ApplicationsMain application areas are piston and diaphragmpumps in public utility plants, reactor construction andthe chemical industry.
2.2.3 Mode of operationTrouble-free pump operation is only possible if nocavitation occurs in the pump suction and pipeoscillations are avoided.A relatively high fluid volume in the suction flowstabiliser in relation to the displacement volume of thepump reduces the acceleration effects of the fluidcolumn in the suction line. Also, an air separation isachieved due to the extremely low flow rate in thesuction flow stabiliser and the deflection on a baffle.By adjusting the charging pressure of the bladder tothe operating conditions, the best possible pulsationdamping is achieved.
2.2.4 ConstructionThe HYDAC suction flow stabiliser consists of a weldedvessel in steel or stainless steel. Inlet and outlet are onopposite sides and are separated by a baffle. The upperpart houses the encapsulated bladder. In addition, thereis a vent screw in the cover plate and a drainage facilityon the bottom.
2.2.5 InstallationAs close as possible to the suction inlet of the pump.Mounting position vertical (gas valve pointing upwards).
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2.3. SHOCK ABSORBERTYPE SB ... A
2.4. FLUID SILENCERTYPE SD ...
without silencer– with silencer
pres
sure
time
2.4.1 GeneralAll displacement pumps such as axial and radial pistonpumps, vane, gear or screw pumps produce volumeand pressure fluctuations which show up as vibrationsand noises. Noises are not only produced andtransmitted by the pump but they are also the result ofmechanical vibrations and vibrations caused by the fluidpulsations, which are amplified when transmitted tolarger areas. Insulation, the use of flexible hoses andsilencer covers can only provide partial solutions to theproblem as they do not prevent transmission to otherareas.
2.4.2 ApplicationsVehicles, machine tools, plastics machinery,aeroplanes, ships, hydraulic power stations and othersystems with a large "surface" are all applicationswhere the noise level can be reduced.
2.4.3 Mode of operationThe HYDAC fluid silencer is based on the principle ofan expansion chamber with interference line.By reflection of the oscillations within the silencer themajority of the oscillations is damped across a widefrequency spectrum.
2.4.4 ConstructionThe HYDAC fluid silencer consists of a welded orforged external housing, an internal tube and two pipeconnections on opposite sides.The silencer has no moving parts and no gas chargeand is therefore absolutely maintenance free.The HYDAC fluid silencer can be used for mineral oils,phosphate ester and water glycol. A stainless steelmodel is available for other fluids.
2.4.5 InstallationIt is recommended that one connection side is joinedvia a flexible hose in order to reduce the transmission ofmechanical vibrations.The mounting position of the damper is optional,whereby the flow direction has to be taken into account.
2.3.1 GeneralThe HYDAC shock absorberreduces pressure surges;protects pipe lines and valves from destruction.
2.3.2 ApplicationsThe accumulators are particularly suited for use in pipelines with quick-acting valves or flaps and duringswitching on and switching off of pumps. They are alsosuitable for energy storage in low pressure applications.
2.3.3 Mode of operationSudden changes in pipe line flow, such as those causedby pump failure or the closing or opening of valves, cancause pressures which are many times higher than thenormal values.The shock absorber prevents this by convertingpotential into kinetic energy and vice versa. Thisprevents pressure surges and protects pipe lines,valves, control instruments and other devices fromdestruction.
2.3.4 ConstructionThe HYDAC shock absorber consists of:the welded pressure vessel in carbon steel with orwithout corrosion protection or in stainless steel;the connection with perforated disc which prevents theflexible bladder from extruding from the vessel, and theflange;the bladder in various compounds as shown under point5.1. with built-in gas valve, which is used for chargingpressure p0 and for possible monitoring activities.
2.3.5 InstallationAs close as possible to the source of the erraticcondition. Mounting position vertical (gas valve pointingupwards).
without damper
pres
sure
pres
sure
time
with shock absorber
time
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3. APPROVALSPECIFICATIONS
3.1. EUROPEAN PRESSUREEQUIPMENT DIRECTIVEPED (DGRL/DEP)On 29 November 1999 thedirective 97/23/EC (PressureEquipment Directive) came intoforce and has been operativesince 29 May 2002.This Directive applies to thedesign, manufacture, conformityassessment and circulation ofpressure equipment andassemblies with a maximumpermissible pressure of over0.5 bar. It guarantees the freemovement of goods within theEuropean Community.EU member states must notprohibit, restrict or obstruct thecirculation and commissioning ofpressure equipment on account ofpressure-related hazards, if theequipment complies with therequirements of the pressureequipment directive and has theCE mark, and is subject to aconformity assessment.According to Article 3 Paragraph3, hydraulic accumulators with acapacity V ≤≤≤≤≤ 1 litre, a maximumpermissible pressurePS ≤≤≤≤≤ 1000 bar and a pressurecapacity PS • V ≤≤≤≤≤ 50 bar • litrefor gases of fluid group 2(non-hazardous fluids) do notreceive a CE mark.Inspection of the equipment andinstallation, operational safety andrepeat testing are controlled asbefore by national laws.The equipment relating to safetyis described in AD2000, ISO 4126and EN 14359.The repeat testing intervals arestipulated in the new operatingsafety regulations.
3.2. OVERSEASPressure accumulators which areinstalled overseas (outside theEU) are supplied with the relevanttest certificates required in thecountry of installation. Thecountry of installation must bestated at the time of ordering.HYDAC pressure vessels can besupplied with virtually any testcertificate. In some of these thepermissible operating pressurecan differ from the nominalpressure. Depending on theauthority, the different materialrequirements must be observed.The following table contains thecodes used in the model code fordifferent countries of installation(See Page 13).
Country Certificate codeAlgeria U 3)
Argentina U 3)
Australia F 1)
Bahamas EBarbados U 3)
Bermuda U 3)
Bolivia U 3)
Brazil U 3)
Canada S1 2)
Chile U 3)
China A9Costa Rica E 3)
Czech Republic UEcuador U 3)
Egypt UHong Kong A9Hungary U 3)
Iceland U 3)
India U 3)
Indonesia U 3)
Iran UIraq U 3)
Israel U 3)
Japan PJordan U 3)
Korea UKuwait U 3)
Lebanon U 3)
Libya U 3)
Malaysia U 3)
Mexico U 3)
New Zealand TNigeria U 3)
Norway U 3)
Pakistan U 3)
Peru U 3)
Philippines U 3)
Poland UPuerto Rico E 3)
Romania URussia (CIS) A6Saudi Arabia U 3)
Singapore USlovakia USouth Africa U 3)
Sudan U 3)
Switzerland USyria UTaiwan U 3)
Thailand U 3)
Tunisia U 3)
Turkey UUSA SYugoslavia U1) = approval required in the individual territories2) = approval required in the individual provinces3) = alternative certificates possible
3.3. CERTIFICATE CODE = S(U stamp)HYDAC Technology GmbH inD-66280 Sulzbach/Saar isauthorised (with effect from 21August 1985) by the "NationalBoard of Boiler and PressureVessel Inspectors", in conformitywith the appropriate specificationsof the American Society ofMechanical Engineers (ASME),to use the Code Symbol
as a stamp and for registrationpurposes.
3.4. CERTIFICATE CODE = P(KHK certificate)For the Japanese market,HYDAC Technology GmbH isapproved as a "self inspectingmanufacturer". Therefore HYDACis authorised to manufacture, testand import accumulators fromoutside Japan.
3.5. CERTIFICATE CODE = A9(Self quality licence for China)HYDAC Technology GmbH isrecognised as an importer ofbladder, diaphragm and pistonaccumulators since 30.03.1998.
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4. SIZING4.1. DEFINITION
OF VARIABLESThe compression and expansionprocesses are governed by thelaws of polytropic change in stateof ideal gasesp • Vn = constant,where time is taken into accountby the polytropic power "n" (ratioof specific heat capacity cp/cv).p0 • V0
n = p1 • V1n = p2 • V2
n
Slow expansion or compressionprocesses occur almostisothermally, the polytropicpower can be set at n = 1.For rapid processes theisentropic (adiabatic) change instate applies with an isentropicexponent κ which is dependent onpressure and temperature (forgraph, see Point 4.3.).
With the aid of the followingformulae the required gas volumeV0 can be calculated for variousapplications. In the formulaepressures always have to be usedas absolute values.p0 = gas pre-charge pressurep1 = minimum working pressurep2 = maximum working pressurepm = working pressureV0 = effective gas volumeV1 = gas volume at p1
V2 = gas volume at p2
t0 = gas pre-charge temperaturetmax = max. working temperature
The bladder (diaphragm) is pre-charged with nitrogen. The fluidvalve is closed and stops thebladder (diaphragm) extrudingfrom the shell.When the minimum workingpressure is reached, there shouldbe a small amount of fluidbetween bladder (diaphragm) andcheck valve (approx. 10 % of thenominal accumulator volume) sothat the bladder (diaphragm) doesnot hit the valve every time itexpands, as this could causedamage.Accumulator at maximum workingpressure. The volume changebetween the minimum andmaximum working pressurecorresponds to the effective fluidvolume:ΔV = V1 - V2
4.2. SELECTION OF GASPRE-CHARGEPRESSURESThe selection of and adherence tothe gas pre-charge pressure hasa considerable influence on theperformance of the damper andthe life expectancy of the bladder/diaphragm.
4.2.1 Recommended valuesDepending on the individualapplication, the following gas pre-charge pressure is set atmaximum working temperature:for pulsation damping:p0, tmax = 0.6 ÷ 0.8 • pm
for 1 piston pump:p0, tmax = 0.6 • pm
for 3 or more piston pumps:p0, tmax = 0.7 • pm
for working pressure range:p0, tmax = 0.8 • p1
for suction flow stabilisation:p0, tmax = 0.6 ÷ 0.7 x • pm
with a permissible pressureratio of p2/p0 ≤ 4 : 1Shock absorber:p0 max = 10 barHydraulic damper withdiaphragmp0,tmax ≤ 0.9 • p1
with a permissible pressureratio ofp2/p0 ≤ 8 : 1(welded construction up to 2 Lnominal volume)p2/p0 ≤ 4 : 1(welded construction up to 2 Lnominal volume)p2/p0 ≤ 10 : 1(threaded construction)
4.2.3 Temperature effectIn order that the recommendedgas pre-charge pressures arebeing maintained even atrelatively high workingtemperatures, p0 ,t0 for chargingand testing cold accumulatorsmust be selected as follows:
In order to take the temperatureeffect into account when sizing ahydraulic damper p0 at tmin mustbe selected as follows:
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4.3. PULSATION DAMPER AND SUCTION FLOW STABILISER
pressure sidesuction side
V0 V0
Formulae:
4.3.1 SizingOn the suction and pressure sideof piston pumps almost identicalconditions regarding nonuniformity of the flow rate occur.Therefore the same formulae fordetermining the effective gasvolume are used for calculatingthe damper size. That in the endtwo totally different damper typesare used is due to the differentacceleration and pressure ratioson the two sides.Not only is the gas volume V0 adecisive factor but also theconnection size of the pump hasto be taken into account whenselecting the pulsation damper.In order to avoid additional crosssection changes which representreflection points for vibrations,and also to keep pressure dropsto a reasonable level, theconnection cross section of thedamper has to be the same asthe pipe line.The gas volume V0 of the damperis determined with the aid of theformula for adiabatic changes ofstate.By giving the residual pulsation orthe gas volume, the damper sizecan be calculated with the aid ofthe HYDAC ASP software(Accumulator SimulationProgram). The results can thenbe printed out or the data files canbe stored in ASP format.The ASP program is availablefree of charge via our websitewww.hydac.com or by e-mail [email protected].
flow rate 244 l/minoperating temperature 20 °Coperating pressure- pressure side 200 bar- suction side 4 bar
Required:a)Suction flow stabiliser for a
residual pulsation of ± 2.5%b)Pulsation damper for a residual
pulsation of ± 0.5%
Solution:a)Determining the required suction
flow stabiliser
b)Determining the requiredpulsation damper
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v = v max
v < v max
PRESSURE SURGEP = maximal
v = 0
v = 0
v = 0
4.4. SHOCK ABSORBERPressure surge produced when a valve is closed without a hydraulic accumulator
4.4.1 CalculationSimplified pressure surgecalculation for the closing of avalve.Estimate of Joukowsky's max.occurring pressure surgeΔp(N/m²) = ρ • a • Δvρ (kg/m³) = fluid densityΔv = v - v1Δv = change of the
fluid speedv (m/s) = speed of the fluid
before the changein its condition
v1 (m/s) = speed of the fluidafter the changein its condition
a (m/s) = velocity of thepressure waveprogagation
a (m/s) =
K (N/m²) = compressionmodulus of the fluid
E (N/m²) = modulus of elasticityof the pipe line
D (mm) = internal diameter ofpipe line
e (mm) = wall thickness ofpipe line
Determining the requireddamper sizeThe accumulator must absorb thekinetic energy of the fluid byconverting it into potential energywithin the pre-determinedpressure range. The change ofstate of the gas is adiabatic inthis case.
m (kg) = weight of fluid inthe pipe line
v (m/s) = speed of fluidp1 (bar) = zero feed height of pumpp2 (bar) = permissible working
pressurep0 (bar) = pre-charge pressure
A special calculation programmeto analyse the pressure curve isavailable for sizing during pumpfailure or start-up and formanifolds.
2 • La
The pressure wave runs to theother end of the pipe line and willreach the valve again after time t(reflection time), whereby:t (s) =L (m) = length of the pipe lineT (s) = effective operating
time (closing) ofthe valve
If T < t:pmax = p1 + ΔpIf T > t:pmax = p1 + ρ • a • Δv • t
T
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with m = V • ρ = π • D2 • L • ρ 4
4.4.2 Calculation exampleQuick closing of a shut-off valvein a re-fuelling line.Parameters:Length of pipe line L:2000 mNW of pipe line D:250 mmWall thickness of pipe line e:6.3 mmMaterial of pipe line:steelFlow rate Q:432 m³/hr = 0.12 m³/sDensity of medium ρ:980 kg/m³Zero feed height of pump p1:6 barMin. operating pressure pmin:4 barEffective closing time of valve T:1.5 sec(approx. 20 % of the totalclosing time)Operating temperature:20 °CCompression modulus of thefluid K:1.62 • 109 N/m²Elasticity modulus (steel) E:2.04 • 1011 N/m²
Required:Size of required shock absorber,when the max. pressure (p2) mustnot exceed 10 bar.
Solution:Determination of reflection time:
a = 1120 m / s
t = = 2 • 2000 = 3.575 s * 1120
* since T < t the max. pressuresurge occurs and the formulaas shown under 4.4.1must be used
Determining the required gasvolume:p0 ≤ 0.9 • pmin
p0 ≤ 0.9 • 5 = 4.5 bar
V0 = 1641 l
Selected:4 off shock absorbersSB35AH-450.
2 • La
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4.5.3 Damping curve
frequency f [Hz]
dam
ping
leve
l [dB
]
4.5.4 Pressure drop
flow rate Q [L/min]
pres
sure
dro
p [b
ar]
SD330-1.3 ...
SD330-S10 ...SD330-4.2 ...
flow rate Q [L/min]
pres
sure
dro
p [b
ar]
HFC
HFD
HFC
HFD
mineral oil (HLP)
mineral oil (HLP)
SD330-1.3
SD330-S10
SD330-4.2
SD330-S15
SD330-L10
4.5. SILENCER4.5.1 Sizing
The sizing calculation of theHYDAC silencer is designed toresult in a small unit with the bestpossible damping. The startingpoint for the selection table is todetermine the level oftransmission damping D from20 dB upwards.
D = 20 • log Δpo
Δpm
Δpo = height of pressurefluctuations without silencer
Δpm = height of pressurefluctuations with silencer
For the selection of the damperthe following has to be taken intoaccount:
1) the size of the silencer body2) the fundamental frequency f
of the pump.f = i • n / 60 in Hzi = number of displacement
elementsn = rpm in min-1
4.5.2 Calculation exampleParameters:Axial piston pump with 9 pistonsrpm 1500 min-1
connection G 1corresponds to Di = 19 mmflow rate 300 l/minoperating fluid: mineral oilmax operating pressure 210 barSolution:
1) Fundamental frequency ff = i • n / 60 in Hz
= 9 • 1500/60= 225 Hz
2) From the "Damping curve" graph,the following silencer type can beselected:SD330-S10/012U-330AE/AEtransmission damping D ≈ 31 dBPressure drop ≈ 2 bar
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flow rate Q [L/min]
pres
sure
dro
p [b
ar]
SD330-L10 ...
SD330-S15 ...
flow rate Q [L/min]
pres
sure
dro
p [b
ar]
HFC
HFD
HFC
HFD
mineral oil (HLP)
mineral oil (HLP)
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5. TECHNICAL SPECIFICATIONS5.1. MODEL CODE
PULSATION DAMPER, SUCTION FLOW STABILISER, SHOCK ABSORBER(also order example)
for SBO 250 P - 0.075 E1 and for SBO 210 P - 0.16 E1:AK = ISO 228 (BSP), standard connection
1) Not available for all models2) Not all combinations are possible3) When ordering spare bladders, please state smallest bladder connection port size at gas charging end4) Please give full details when ordering
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5.2.7 Permissible operatingtemperature263 to 353 K (-10 °C to +80 °C)for material code 112.Others on request.
5.2.8 Permissible pressure ratioRatio of maximum operatingpressure p2 to gas pre-chargepressure p0 (see 4.2.2).
5.2.9 General safety notesOn no account must any welding,soldering or mechanical work becarried out on the accumulatorshell.After the hydraulic line has beenconnected it must be completelyvented. Work on systems withhydraulic dampers (repairs,connecting pressure gauges etc.)must only be carried out once thepressure and fluid have beenreleased.Please see operatinginstructions.
5.2. GENERAL5.2.1 Operating pressure
See tables (may differ fromnominal pressure for foreign testcertificates).
5.2.2 Nominal volumesSee tables
5.2.3 Effective gas volumeSee tables, based on nominaldimensions. This differs slightlyfrom the nominal volume andmust be used when calculatingthe usable volume.On the diaphragm accumulator,the effective gas volumecorresponds to the nominalvolume.
5.2.4 Usable volumeVolume of fluid which is availablebetween the operating pressuresp2 and p1.
5.2.5 FluidsMineral oils, hydraulic oils, non-flam fluids, water, emulsions,fuels. Other fluids on request.
5.2.6 Gas chargeUse only nitrogen for charging;NEVER use oxygen (danger ofexplosion). When supplied, theaccumulator is only pre-chargedfor storage purposes. Higher pre-charge pressures are possible byarrangement.
1) M 56 x 4, high pressure connection DN 16; others on request2) Standard connection code = AI; others on request* Pressure Equipment Directive PED 97/23/EC
( ) brackets indicate different dimensions for stainless steel version2) standard connection code = AI; others on request* Pressure Equipment Directive PED 97/23/EC
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SBO...P-...A6/347...(PTFE)
5.3.3 Pulsation damper for aggressive media
2)Pulsation damper in stainless steel(AISI 316) with PTFE coated diaphragmand PTFE or FFKM seals. Version insynthetic material possible on request.Also available without connection block.
6. NOTEThe information in this brochurerelates to the operating conditionsand applications described.For applications or operatingconditions not described, pleasecontact the relevant technicaldepartment.Subject to technical modifications.