Unit Outcome 9 Speed control and design hydraulic circuit 2 W2020 PDF

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Unit Outcome 9 Speed control and design hydraulic circuit 2 Speed Control for Hydraulic Cylinder  Meter out  Meter in  By-Bass

Regenerative Cylinder Operation (Differential Cylinder)

Synchronize Cylinder Selections of Suction Pipe and Pressure line (Fluid Power data Book)

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 Speed Control for Hydraulic Cylinder

(http://www.hydraulicspneumatics.com/200/FPE/Circuits/Article/True/6477/Circuits)

 Series connected, Meter-Out

v

p2 A2

1) A flow control valve is Installed in the outlet line of a cylinder. A pressure relief valve must be parallel connected with pump.

Fload

p1 A1 FCV

Q pump  Qcyl  QPRV

2) During working process the pressure relief valve is always opened to allow surplus fluid QPRV to flow though it to tank. 3) Opening of FCV , Back pressure p2, p1  p0, QPRV↓, Qcyl↑ Qcyl  v A1 NOTE: Qcyl=vA1QExhaust=vA2

QPRV

Qcyl p0

Qpump PRV

4) Opening of FCV, Back pressure p2, p1  Qcyl  p0, QPRV, Qcyl, v  A1 5) Force balance in working direction Meter out always generates a backpressure p2

p1A1=p2A2+Fload (p2≠0, if p2 > p1, pressure is intensified) 6) Characteristics a) Suited for small power system and low speed. Speed stability is better than that controlled by meter in. b) Be able to resist impact. For example tool breaking, finish broaching operation (In this case the working direction is retracting direction.) c) Because surplus oil always flows though the relief valve, the energy in this discharged oil converted into heat. 2

 Series connected, Meter-In v

1) A flow control valve is installed in the inlet line of a cylinder. A relief valve must be parallel connected to pump.

p 1A 1 p2

FCV

Q pump  Qcyl  QPRV

p 1’

2) During working process the relief valve is always opened to allow surplus fluid QPRV to flow though it to tank. 3) Opening of FCV, Resistance , p1  p0, QPRV↓, Qcyl↑ Qcyl v  A1 4) Opening of flow valve, Resistance, p1  p0, Q cyl  QPRV, Qcyl, v  A1

Fload

p1

QFCV p2≈0, no backpressure

Relief valve

QPRV

Qcyl p0

Qpump

5) Force balance in working direction Meter in does not generate a backpressure p3

p1A1=Fload (p2=0) 6) Characteristics a) Suited for low power system and low speed. Best suited for a resistive load. b) Not be able to resist impact. Such as tool breaking, finish broaching operation c) Because surplus oil always flows though the relief valve, the energy in this discharged oil converted into heat.

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 By-Pass (Bleed-Off) Speed Control v

1) A flow control valve (needle valve) is connected between blind end port and tank.

p2≈0

p1 Apiston

Q pump  Qcyl  QFCV

FCV

QFCV

Fload

Qcyl

2) During the working process the relief valve is always closed, as a safety valve. Surplus fluid QFCV flows though the flow valve to tank. 3) Opening of FCV,

Relief valve

QFCV , Qcyl , vcyl 

Qcyl

p0

Qpump



Apiston

4) Opening of FCV, QFCV ,  Qcyl , vcyl 

Qcyl



Apiston

5) Retracting speed is not Influenced by the opening of the flow control valve (FCV). 6) Force balance in working direction p1 A1  Fload ( p2  0 ) 7) Speed is very sensitive to load Fload.  Q FCV  C v

Fload / A piston p1 p  Cv  Cv , Fload ↑  v cyl  SG SG SG

The speed stability is not as good as meter-out or meter in speed control. 8) Less heating comparing with meter-out and meter in circuits 9) Applications Suited for large power system and high speed applications. 4

Regenerative Cylinder Operation A2

1) Non-Regenerative cylinders extension : Q  v1 A1

A1

retraction : Q  v2 A2 Q (extending speed )  v1  A1 Q  v2  (retracting speed) A2  A1  A2  v1  v2 The extending speed is slower than retracting speed

blocked

Q1 Q2 Q

2) Regenerative Cylinders Connect the cylinder rod side to Piston side, allow the returning fluid

Q2

to flow to piston side

 v1 

Q1 Q  Q2 ,  A1 A1

v1 

Q  A2 v1  ( A1  A2 )v1  Q A1

 Q 2  A2v1

Q Q Extension : v1   A1  A2 Arod Extending sp eed is increased. 1 1 A1  D 2 , A 2   ( D 2  d 2 ) 4 4 1 Arod  A1  A2  d2  rod area 4

Q Q  A2 1 ( D 2 d 2 )   4  A2  A1  A2  A2 

Retraction : v2  if Arod

 A1  2A2  v1  v 2 

Q A2

Extending sp eed equals to retracting speed.

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3) The regenerative cylinder is also called the differential cylinder A2 p p Because the force difference (pA1-pA2) is used to balance load Fload,

A1

R

The force balance is pA1-pA2=Fload Fload=p(A1-A2)=pArod

Q1 Q2

Hence, at the same pump flow rate and the same pressure a differential cylinder (regenerative cylinder) has faster extending speed and smaller extending force than those of a non regenerative cylinder.

Q

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Application Two work speeds during cylinder extension by using a 4-way, 4position directional valve.

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 Cylinder Synchronizing Circuits 1)

Cylinder connected in Series

Operational principle: Cylinders lifting SOL A1 energized pressurized oil Cylinder A Cylinder A lifting Va=Q/AaExhaust oil of Cylinder A Cylinder E Cylinder E lifting Ve=Qexhaust/Ae, Qexhaust=VaAa, Ae=Aa Ve=Va (as Two cylinder bore sizes and rod sizes are the same, the two cylinders have the synchronizing speed) Cylinders lowering SOL B1 energized pressurized oil Cylinder ECylinder E lowering Ve=Q/AeExhaust oil of Cylinder E Cylinder ACylinder A lowering Va=Qexhaust/Aa, Qexhaust=VeAe, Aa=Ae Va=Ve (as Two cylinder bore sizes and rod sizes are the same, the two cylinder have the synchronizing speed) Error compensation B-LS

SOL C1

B-LS

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If cylinder A fully lowers down first and hit the limit switch B-LSSOL C1 energized  the exhaust oil from cylinder E4/2 DCV DTankCylinder E can continuously lowering down until both cylinders fully lower down. If cylinder E fully lowers down first and hit the limit switch B-LSSOL C1 energized  the pressurized oil 4/2 DCV DCylinder ACylinder A can continuously lowering down until both cylinders fully lowered down.

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Synchronize cylinder 2

Limit switch b control SOL4 and limit switch a controls SOL5 for error compensation. Assume the input flow rate for cylinder B is QB; The extension speed of cylinder B is VB=QBin/AnetB The exhaust flow rate from cylinder B is QBout=VBApB

The exhaust flow rate is the input flow rate of cylinder A. VA=QBout/AnetA For synchronizing cylinders VA=VB

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VA 

ApB Q Bout VB ApB   VB AnetA AnetA AnetA

 when AnetA  ApB ,  V A  VB

Synchronize cylinder 3 Cylinder 2 and cylinder 3 have the same dimensions. Cylinder 1 has the following dimensions Anet_1=Arod_1

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 Selections of Suction Pipe and Pressure line (Fluid Power data Book) If the fluid speed in pipe is high (that means for a fixed positive displacement pump the size of pipe is small, V=Q/A):

 Cost of plumbing material  Labour cost for installing   Energy loss  Cavitation possibility  If the fluid speed in pipe is low (that means for a fixed positive displacement pump the size of pipe is large, V=Q/A):

 Cost of plumbing material   Labour cost for installing   Energy loss   Cavitation possibility Thus, it has to find a balance between the system power loss and the cost of plumbing to select a proper pipe size (FPDB page 38 for flow rate, page 37 for pressure).

For inlet pipes (suction) the optimized fluid speed is 2ft/s ~ 4ft/s Pipe Schedule 40 For pressure pipes the optimized fluid speed is 15ft/s ~ 20ft/s Pipe schedule 80 (for medium pressure 500~2000 psi) Pipe schedule 160 (for high pressure, > 2000 psi)

Example A Hydraulic system has the following data Known: Working pressure Flow rate

= =

2000 psi 10 gpm 12

Find: 1) Suction (inlet) pipe size = ? 2) Pressure line pipe size = ? (use lower oil velocity of the table) Solution: Determine schedule (Page 38): 1) Schedule 40 pipe is generally used for inlet pipe. Lower oil velocity is 2ft/s, check the first column. To meet the flow rate 10 gpm, 1 2

inlet pipe size = 1 " NPT The pipe has a male NPT thread, while the elbow is female. American National Standard Pipe Thread standards, often called national pipe thread standards for short, are U.S. national technical standards for screw threads used on threaded pipes and pipe fittings.

2)

Schedule 80 pipe for medium pressure line Check page 37, look for working pressure in column 6. To meet 2000 psi, 1 2

Pressure line pipe size = " NPT 3) Verify the fluid speed. At page 38 in FPDB when pipe size is ½”, fluid speed is 15ft/s, the 13

pump flow rate is 10.95 GPM > required 10 gpm. Thus you can select ½” pipe for pressure pipe.

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