Lecture 4. Lab this week: Cartridge valves Flow divider Properties of Hydraulic Fluids. Lab 8 Sequencing circuit Lab 9 Flow divider

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1 91 Lecture 4 Lab this week: Lab 8 Sequencing circuit Lab 9 Flow divider Cartridge valves Flow divider Properties of Hydraulic Fluids Viscosity friction and leakage Bulk modulus Inertance

2 Cartridge Valves 92 Integrate circuits with many components using a manifold Manifold = aluminum block with internal passages Standard configurations

3 93 Cartridge valves Screw-in types (smaller flow rates, single unit) [as in lab] Single valve performs the intended function screws into cavities in manifold cavities are generally common Slip-in type (larger flow rates) essentially a check valve versatile functions accomplished by different covers that provide for additional circuits. Area ratio play a role in the operation of both types of cartridge valves.

4 94 Screw-in Cartridge Valve Single piece implements the function Plugs into standard manifold porting manifold itself being custom built

5 Slip-in example: check valve 95 Possible leakage Preferred!

6 Slip-in Cartridge Valves Area Ratios 96 Closing force: P A P A A P + F s p Opening force: P A A A + P B A B Open! Open or closed?

7 Slip-in Cartridge Pilot Operated Check 97 x B A Slip-in part is just a poppet check valve

8 Slip-in Pilot Operated Relief Valve 98

9 Slip-in: Pilot Operated Directional Control Valve 99

10 Individually Controlled DCV configuration 100 Potential for better energy savings.

Flow Divider Valve How to design a flow divider with 2:1 ratio?

11 101 Identify flow measurement sensors What happens when Q left > Q right? What happens when Q right > Q left? Equilibrium position? Flow Divider Valve How to design a flow divider with 2:1 ratio? Some valves are flow combiner/divider? Can this one combine flow?

12 102 Modeling and Analysis of Flow Divider Qa = Qb+Qc Qb = C1(x)*SQRT(Pa-Pb) Qc = C2(x)*SQRT(Pa-Pc) P1 = Pa-(Qb/c1(x))^2 P2 = Pa-(Qc/c2(x))^2 Adjust x based on P 1 and P 2

13 A (fake) Car Talk Puzzle 103 You discovered that on your garage floor that your car is leaking oil. You took it in to the mechanic Joe. Joe was busy, so you had to leave the car at the shop s parking lot for the night. Next morning, Joe took your car into the shop and examined the car for leaks, and found nothing. You took your back home, but lo and behold, the car leaked again on your garage floor. Neither you nor Joe is delusional. What is going on?

14 104 Hydraulic Fluid in Fluid Power Systems Primary role is POWER TRANSMISSION Secondary roles Lubrication Enables moving parts prevents wear, metal/metal contact Load carrying ability parts spot welded together if lubrication film breaks down or too thin Sealing leaks Dimensional clearance may induce leak Certain property of fluid may prevent leak (viscosity) Heat transfer / cooling transfer of heat from work area to reservoir / heat exchanger some fluid properties may vary with temperature

15 105 From: M. Radhakrishnan, Hydraulic Fluids ASME Press

16 Some fluid properties 106 Dynamic Viscosity µ = τ v / N/(m^2s) = sec * kg m/sec ^2/m = kg / (m sec) = 1000 poise y Kinematic Viscosity Easy to measure. If density = 1000kg/m 3, Shear (N / m^2) Tangential speed gradient (1/sec) 1 poise = 10-3 kg /m/s 1 cp = centipoise = 0.01g/m/s υ = µ ρ y Shear force v (y) No shear when there is no velocity gradient normal to flow m 2 /sec = stoke 1 stoke (St) = cm 2 /sec 1 centi-stoke (cst) =0.01 St µ = 3.78 cp υ = 3.78 cst Density (kg/m^3)

17 107 SAE 40 Viscosity decreases with temperature 15 cs at 100degC (212F) 150 cs at 40degC (104F) SAE 10W 4 cs at 100 deg C(212F) 20 cs at 40 degc (104F) Usually data is given at two temperatures use linear interpolation to find intermediate values 5 to 10 times variation with 60degC variation! Water has much lower viscosity than hydraulic oil Which one for winter or for summer? Water: ~1cS for wide range of temperature!

18 108 High viscosity Viscosity is a compromise reduce leak (better sealing) lower chance of oil break down parts spot welded to each other requires larger pressure to sustain flow (sluggish) pump may cavitate (air getting into system) oil / air separation difficult Low viscosity lower drag better efficiency possibility of thin film break down worse leakage (water hydraulics)

19 109 Dynamic viscosity = 4500 cp Diameter of pipe D = 0.05m Length of pipe L = 1 m Velocity at y = 0.5cm is 5m/s Velocity at y = 0cm is 0m/s Example v y Find a) shear drag on and b) pressure drop across the pipe Assume linear velocity profile shear = 4500cP / (1000 N/m^2/sec) * (5m/s / 0.005m) = 4.5 (N/m^2)*sec * 1000/sec = 4500 N/m^2 Drag force = 4500 * pi * D * L = 706 N Pressure drop = Drag force / Area = 4500*4*L/D = 360 kpa

20 Darcy laws: ΔP = Resistance in Pipes and Hoses f (Re) L ρv D 2 2 = f (Re) L D 8ρQ 2 π D 2 4 speed Re = vd v 110 Laminar f=64/re Δ 128µ L πd P = 4 Q Re < 2000 Kinematic viscosity Inertia versus viscous Turbulent Smooth pipe ΔP = / Re 1/ 4 L 8 ρq 2 D π D > Re > 4000

21 Friction Factor Moody Diagram 111

22 Example: 3MW Wind Turbine, 35MPa 112

23 Loss in Connectors 113 K-factor K factors ρv ΔP = K 2 Tee s deg elbow deg elbow 0.75 Ball check valve 4.0 Return bend 2.2 Example: Elbow Q = 15gpm, Pressure drop = 0.6psi Q = 37.5gpm, Pressure drop = 4psi 2 v = (outlet) velocity [m/sec] g = gravity const [m/sec^2] Note: K is unit-less and independent of units ΔP Equivalent formula: ρg 2 v H L = K 2g = H L 2 v = K 2g H L = head loss [m]

24 114 Leakage Leakage flow Q = 3 a w 12µ L ΔP P2 Example: a spool in a sleeve w = pi * D (circumference) L = length of land a Q L a = clearance P1 w Note high viscosity decreases leaks

25 115 Example L clearance = 0.1mm Cylindrical Spool P 90 deg elbow diameter = 0.5cm Sleeve Q = 30 LPM?1: Assuming small leakage, determine pressure P.?2: How long does L have to be for leakage to be less than 0.01% of the flow?

26 116 Efficiency vs Viscosity vs Temperature For hydraulic components (e.g. pumps, motors, actuators) with moving parts, there is always a trade-off between Volumetric efficiency [leakage] Mechanical Efficiency [friction] Total efficiencies for pumps and motors given by: Optimal viscosity Optimal viscosity exists for a given component (and system) However, viscosity changes dramatically by temperature!

High V-I Fluids 117 Viscosity Index (VI): measures temperature dependence of viscosity Modified using chemical additives High VI = low temperature

27 High V-I Fluids 117 Viscosity Index (VI): measures temperature dependence of viscosity Modified using chemical additives High VI = low temperature dependence Low VI = large temperature dependence VI index is a measure of this slope! ( Defined relative to 2 standard fluids : VI=0, and VI=100 )

28 A (fake) Car Talk Puzzle 118 You discovered that on your garage floor that your car is leaking oil. You took it in to the mechanic Joe. Joe was busy, so you had to leave the car at the shop s parking lot for the night. Next morning, Joe took your car into the shop and examined the car for leaks, and found nothing. You took your back home, but lo and behold, the car leaked again on your garage floor. Neither you nor Joe is delusional. What is going on?

Lecture 5. Labs this week: Please review ME3281 Systems materials! Viscosity and pressure drop analysis Fluid Bulk modulus Fluid Inertance

Lecture 5. Labs this week: Please review ME3281 Systems materials! Viscosity and pressure drop analysis Fluid Bulk modulus Fluid Inertance Labs this week: Lab 10: Sequencing circuit Lecture 5 Lab 11/12: Asynchronous/Synchronous and Parallel/Tandem Operations Please review ME3281 Systems materials! 132 Viscosity and pressure drop analysis