sizing accumulators

129 Parker Hannifin CorporationHydraulic Accumulator DivisionRockford, Illinois USA

Accumulator Sizing For: Shock Suppression Thermal Expansion Pulsation Dampening Auxiliary Power Source

Sizing and Selection Piston Accumulators Bladder Accumulators KleenVent


Hydraulic AccumulatorsPiston and Bladder Type

Catalog HY10-1630/US

Sizing and Selection SoftwareParker offers leading edge application assistance, in theform of the TM Accumulator Sizing and SelectionSoftware (see page 16).For manual sizing calculations, see below and on thefollowing pages.For further engineering assistance, contactParkers Accumulator Technical Support Groupat (815) 636-4100.

Where:

P2 = Maximum operating pressure in PSIAP3 = Minimum operating pressure in PSIAP1 = Pre-charge pressure required in PSIAVW = Volume of fluid collected or discharged by accumulator, In3V1 = Required Accumulator volume, In3f = Nitrogen gas constant-charging of Accumulators (see charts on pages 134-135)n = Nitrogen gas constant-discharging of Accumulators (see charts on pages 134-135)

Note: Gas Precharge usually 100 psi below minimum pressure for Piston Accumulators*.Gas precharge is 90% of minimum pressure for Bladder Accumulators.

*90% where minimum system pressure is less than 1000 psi.

Calculations for accumulator sizing take into consideration the charge and discharge rate of the accumulator.

Auxiliary Power Source

Sizing and Selection

Accumulator Sizing for: Shock Suppression Thermal Expansion Pulsation Dampening Auxiliary Power Source

V =1

VwPP

3

1

1 f/

0.95 1 PP

3

2

1 n/




Hydraulic line shock suppression

Thermal Expansion

Where: = Coefficient of Linear Expansion of Pipe Material per F = Coefficient of Cubical Expansion of Fluid per Fn = Discharge Coefficient (see charts on pages 134-135)P1 = PrechargeP2 = Minimum System Pressure @ T1 (PSIA)P3 = Maximum System Pressure @ T2 (PSIA)V1 = Accumulator SizeVa = Fluid Volume Subject to Thermal ExpansionT1 = Initial Temperature (Lower Temp Kelvin)T2 = Final Temperature (Higher Temp Kelvin)

Where:W = weight of fluid (lbs)V = fluid velocity (ft/sec)n = Discharge coefficient (see charts on pages 134-135)P2 = system pressureP

m= Shock pressure

V1 = accumulator size requiredP1 = pre-charge pressureG = force of gravityQ = flow rate in GPM

( )( )V1 =

V T T PP

PP

a

n

n

2 12

1

2

3

1

1

3

1


V =1

PP

2

1

1 n/

2 (g) (P )2 PPm

2

(n-1) n/

(12W) (V ) (n-1)2+ (Q 1.155)

*

1

Coefficient of LinearExpansion of PipeMaterial per FSteel: 6.33 x 10-6Cast Iron: 6.55 x 10-6Aluminum: 10 x 10-6

Coefficient of CubicalExpansion of Fluid per FWater: 1.15 x 10-4Oil: 4.60 x 10-4




Piston pump pulsation dampening

Where:K = Pump output coefficientn = Coefficient of discharge (see charts on pages 134-135)P1 = Nitrogen gas pre-chargeP2 = System operating pressureP3 = Maximum allowable shock pressureA = Piston areaL = Piston strokeV1 = Accumulator size required

Existing accumulator output used in an auxiliary power source application.Calculations for accumulator sizing takes into consideration the charge and discharge rate of the accumulator.


Pump output coefficient is calculateddepending on single acting or doubleacting pump:

Simplex single .60Simplex double .25Duplex single .25Duplex double .15Triplex single .13Triplex double .06Quadruplex single .10Quadruplex double .06Quintiplex single .06Quintiplex double .02

V =1

ALKPP

2

1

1 PP

2

3

1 n/

1 n/

Where:P2 = Maximum operating pressure in PSIAP3 = Minimum operating pressure in PSIAP1 = Pre-charge pressure required in PSIAVW = Volume of fluid collected or discharged by accumulator, In3V1 = Required Accumulator volume, In3f = Nitrogen gas constant-charging of Accumulators (see charts on pages 134-135)n = Nitrogen gas constant-discharging of Accumulators (see charts on pages 134-135)

Note: Gas Precharge usually 100 psi below minimum pressure for Piston Accumulators.Gas precharge is 90% of minimum pressure for Bladder Accumulators.

V =wPP

3

1

1 f/

1 PP

3

2

1 n/0.95 V1




Temperature VariationTemperature variation can seriously affect the precharge pressure of an accumulator. As the temperature in-creases, the precharge pressure increases; conversely, decreasing temperature will decrease the prechargepressure. In order to assure the accuracy of your accumulator precharge pressure, you need to factor in thetemperature variation. The temperature variation factor is determined by the temperature encountered duringprecharge versus the operating temperature expected in the system.

Temperature During Precharge

Lets assume the temperature during precharge is 70F, the expected operating temperature is 130F, and yourdesired precharge is 1000 psi. Find the charging temperature of 70F in the top horizontal row. Next, find theoperating temperature of 130F in the left hand, vertical column. Extend lines from each value until they intersectto find the temperature variation factor; in this case, 0.90. Multiply the desired precharge of 1000 psi by thetemperature variation factor of 0.90 to obtain the actual precharge pressure required 900 psi.

30. 40. 50. 60. 70. 80. 90. 100. 110. 120. 130. 140. 150. 160. 170. 180. 190. 200. 210. 220.30. 1.00 1.02 1.04 1.06 1.08 1.10 1.12 1.14 1.16 1.18 1.20 1.22 1.24 1.27 1.29 1.31 1.33 1.35 1.37 1.3940. .98 1.00 1.02 1.04 1.06 1.08 1.10 1.12 1.14 1.16 1.18 1.20 1.22 1.24 1.26 1.28 1.30 1.32 1.34 1.3650. .94 .98 1.00 1.02 1.04 1.06 1.08 1.10 1.12 1.14 1.16 1.18 1.20 1.22 1.24 1.25 1.27 1.29 1.31 1.3360. .92 .94 .98 1.00 1.02 1.04 1.06 1.08 1.10 1.12 1.13 1.15 1.17 1.19 1.21 1.23 1.25 1.27 1.29 1.3170. .92 .94 .96 .98 1.00 1.02 1.04 1.06 1.08 1.09 1.11 1.13 1.15 1.17 1.19 1.21 1.23 1.25 1.26 1.2880. .91 .93 .94 .96 .98 1.00 1.02 1.04 1.06 1.07 1.09 1.11 1.13 1.15 1.17 1.19 1.20 1.22 1.24 1.2590. .89 .91 .93 .95 .96 .98 1.00 1.02 1.04 1.05 1.07 1.09 1.11 1.13 1.15 1.16 1.18 1.20 1.22 1.24100. .88 .89 .91 .93 .95 .96 .98 1.00 1.02 1.04 1.05 1.07 1.09 1.11 1.13 1.14 1.16 1.18 1.20 1.21110. .86 .88 .89 .91 .93 .95 .96 .98 1.00 1.02 1.04 1.05 1.07 1.09 1.11 1.12 1.14 1.16 1.18 1.19120. .84 .86 .88 .90 .91 .93 .95 .97 .98 1.00 1.02 1.03 1.05 1.07 1.09 1.10 1.12 1.14 1.16 1.17130. .83 .85 .86 .88 .90 .92 .93 .95 .97 .98 1.00 1.02 1.03 1.05 1.07 1.08 1.10 1.12 1.14 1.15140. .82 .83 .85 .87 .88 .90 .92 .93 .95 .97 .98 1.00 1.02 1.03 1.05 1.07 1.08 1.10 1.12 1.13150. .80 .82 .84 .85 .87 .89 .90 .92 .93 .95 .97 .98 1.00 1.02 1.03 1.05 1.07 1.08 1.10 1.11160. .79 .81 .82 .84 .85 .87 .89 .90 .92 .94 .95 .97 .98 1.00 1.02 1.03 1.05 1.06 1.08 1.10170. .78 .79 .81 .83 .84 .86 .87 .89 .90 .92 .94 .95 .97 .98 1.00 1.02 1.03 1.05 1.06 1.08180. .77 .78 .80 .81 .83 .84 .86 .88 .89 .91 .92 .94 .95 .97 .98 1.00 1.02 1.03 1.05 1.06190. .75 .77 .78 .80 .82 .83 .85 .86 .88 .89 .91 .92 .94 .95 .97 .98 1.00 1.02 1.03 1.05200. .74 .76 .77 .79 .80 .82 .83 .85 .86 .88 .89 .91 .92 .94 .95 .97 .98 1.00 1.02 1.03210. .73 .75 .76 .78 .79 .81 .82 .84 .85 .87 .88 .90 .91 .93 .94 .96 .97 .99 1.00 1.01220. .72 .74 .75 .76 .78 .79 .81 .82 .84 .85 .87 .88 .90 .91 .93 .94 .96 .97 .99 1.00





Selection Chart for Charge Coefficient f& Discharge Coefficient n Chart No. 1

0 - 8 Seconds 9 - 30 Seconds

Pressure (PSI) Pressure (PSI)

61 - 120 Seconds31 - 60 Seconds


n &

fn &

f





Selection Chart for Charge Coefficient f& Discharge Coefficient n Chart No. 1

Instructions for selection ofCharge Coefficient f & Discharge Coefficient n

1. Determine Average System Pressure.

2. Determine the time required in seconds to chargethe accumulator with fluid.

3. Determine the time in seconds to discharge the oilfrom the accumulator.

4. Select the graph which corresponds to the time(seconds) required to charge (discharge) theaccumulator with fluid.

5. Select the curve on the graph which correspondsto the gas operating temperature. (If gas tempera-ture under operating conditions is not known,assume 100F.)

6. To use the graph, locate the average systempressure along the bottom portion of the graph.Move vertically along this column until you inter-sect the line corresponding to the gas temperature.Then move horizontally along this line, read thecharge coefficient f on the left side of the graph.f = Charge Coefficient.

7. Repeat for the discharge coefficient n startingwith Step #4.n = Discharge Coefficient.

121-500 Seconds 501-900 Seconds


n &

fSizing and Selection




*Safety Note:In any accumulator circuit, a means should be availableof automatically unloading the accumulator when themachine is shut down. Such a valve could be located atthis point in the circuit.

Control of Usable VolumeThe usable volume of an accumulator should bedischarged at a controlled rate. If an accumulator isrequired to maintain system pressure, this controlledrate is automatically achieved by the leakage fluid it hasto replace. However, an accumulator which is used todevelop a pressurized flow can discharge its usablevolume too rapidly as a downstream directional valve isshifted. For this reason, accumulators in this applicationare often equipped with a flow control and bypasscheck at their inlet-outlet port.

Pump Unloading inAccumulator CircuitsTo keep a pump/electric motor fully unloaded until it isrequired to re-charge an accumulator, an electricpressure switch can be used.In the circuit illustrated, a pressure switch sensesaccumulator pressure sending and cutting-out electricalsignals at various pressure levels. The electrical signalsare transmitted to a normally-open, solenoid operated2-way valve which vents and de-vents a pilot operatedrelief valve. When the accumulator is being charged,the pressure switch sends an electrical signal to the 2-way valve solenoid. With the accumulator charged, thepressure switch cuts out the signal, venting the reliefvalve and unloading pump/electric motor. The setting ofthe pressure switch determines the pressure rangewithin which a pump/electric motor works.Using a pressure switch to vent a relief valve results ina pump/electric motor being fully unloaded whensystem conditions dictate.In the circuit illustrated, an unloading valve is used todump a flow back to tank once an accumulator ischarged to the unloading valve setting.Once the valve closes, pump/electric motor must there-fore generate power to recharge the accumulator to theunloading valve setting.

*

*

M

Pilot OperatedRelief Valve(SimplifiedSymbol)

PressureSwitch

M

Unloading Valve

*

Applications




Differential Unloading Relief ValveInstead of using a pressure switch and solenoid valveto vent a relief valve while an accumulator is charged,one hydraulic component can be used a differentialunloading relief valve.A differential unloading relief valve is specificallydesigned for use with accumulators. As its nameimplies, the valve unloads a pump/electric motor over adifferential pressure range.A differential unloading relief valve consists of a pilotoperated relief valve, check valve, and differential pistonin one valve body. The valve body includes pump, tank,and accumulator passages.

Maintaining PressureAccumulators are used to maintain pressure. This canbe required in one leg of a circuit while pump/electricmotor is delivering flow to another portion of thesystem.In the circuit illustrated, two clamp cylinders are re-quired to hold a part in place. As the directional valvesare shifted, both cylinders extend the clamp at thepumps compensator setting. During this time, theaccumulator is charged to the setting also.System demands require that cylinder B maintainpressure while cylinder A retracts. As directional valve Ais shifted, pressure at the pump, as well as in line A,drops quite low. Pressure at cylinder B is maintainedbecause the accumulator has stored sufficient fluidunder pressure to make up for any leakage in line B.Accumulators not only maintain pressure by compen-sating for pressure loss due to leakage, but they alsocompensate for pressure increase due to thermal fluidexpansion or external mechanical forces acting on acylinder.In the illustrated circuit, assume that the cylinder isoperating near a furnace where ambient temperaturesare quite high. This causes the fluid to expand. With anaccumulator in the circuit, the excess volume is takenup, keeping the pressure relatively constant. Without anaccumulator, pressure in the line would rise uncontrolla-bly and may cause a component housing, fitting, orconductor to crack.The same situation can also occur if an externalmechanical force acts to retract the cylinder. Assumenow that the cylinder is clamping a curing press. Ascuring occurs, heat within the press causes it to expandresulting in a force acting to retract the piston rod. Theaccumulator once again absorbs the additional volume,maintaining the pressure at a relatively constant level.

*Safety Note:In any accumulator circuit, a means should be availablefor automatically unloading the accumulator when themachine is shut down. Such a valve could be located atthis point in the circuit.

*

Extra VolumeAbsorbed

Heat ExpandsFluid

F

FF

Force ToRetract

CuringPress

*

*

Valve A

Valve B

Cylinder A

Cylinder B

M

Passage toTank

Pilot ValveDart

DifferentialPiston

Passage toAccumulator

CheckValve

PassageFromPump

Orifice Main ValveSpool

DifferentialUnloading

ReliefValve

F

Applications




Developing FlowSince charged accumulators are a source of hydraulicpotential energy, stored energy of an accumulator canbe used to develop system flow when system demandis greater than pump delivery. For instance, if amachine is designed to cycle infrequently, a smalldisplacement pump can be used to fill an accumulatorover a period of time. When the moment arrives for themachine to operate, a directional valve is shifteddownstream, and the accumulator delivers the requiredpressurized flow to an actuator.Using an accumulator in combination with a smallpump in this manner conserves peak horsepower. Forinstead of using a large pump/electric motor togenerate a large horsepower all at once, the work canbe evenly spread over a time period with a small pump/electric motor.

Absorbing ShockHydro-pneumatic accumulators are sometimes used toabsorb system shock even though in this applicationthey are difficult to properly design into a system.Shock in a hydraulic system may be developed fromthe inertia of a load attached to a cylinder or motor. Or,it may be caused by fluid inertia when system flow issuddenly blocked or changed direction as a directionalvalve is shifted quickly. An accumulator in the circuit willabsorb some of the shock and not allow it to be trans-mitted fully throughout the system.Shock may also occur in a hydraulic system due toexternal mechanical forces. In the circuit illustrated, theload attached to the cylinder has a tendency to bouncecausing the rod to be pushed in and shock generated.An accumulator positioned in the cylinder line can helpreduce the shock effects.

*Safety Note:In any accumulator circuit, a means should be availablefor automatically unloading the accumulator when themachine is shut down. Such a valve could be located atthis point in the circuit.

M

Restriction ControlsAccumulator Discharge

*

*

Developing System Flow

M*

Load Bounces

100GPM

Applications




Please fill out and fax to 815-636-4113.For assistance, call 815-636-4100.

CUSTOMER:ADDRESS:

CONTACT:PHONE:

FAX:EMAIL:

Quantity/Release: ___________________________

Quantity (Annual): ___________________________Type (Piston or Bladder): _____________________Bore Size (piston only): ______________________Capacity: __________________________________

Working Pressure/Design Factor. _______________

Seal Type/Compound:________________________

Hydraulic Port:______________________________

Gas Port:__________________________________

Operating Temperature Range:_________________

System Fluid: ______________________________

Gas Valve:_________________________________

Precharge:_________________________________

Water Service? ____________________________

Plating/Coating: ____________________________

Material Type: ______________________________

Paint: ____________________________________

Switches: _________________________________

Certification: _______________________________

Special Test?_______________________________

Special Label? _____________________________

Customer Drawing Included? _________________

Customer Part # ___________________________

Envelope Restrictions: _______________________

Contact Information

Application Description/Comments

Customer Requirements

FORM-0117, Rev. 1

Application Data Sheet



Catalog HY10-1630/USNotes

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sizing accumulators

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