Experiment 2-3Experiment 2-3Fluid FrictionFluid Friction

Fluid FrictionFluid FrictionObjectives:Objectives:

1. Demonstrate that all hydraulic components have an internal 1. Demonstrate that all hydraulic components have an internal frictional resistance to fluid flow which causes a pressure drop as frictional resistance to fluid flow which causes a pressure drop as fluid flows through the component. fluid flows through the component.

2. Explain how flow rate and orifice size affect the 2. Explain how flow rate and orifice size affect the fluid pressure drop across a hydraulic component.fluid pressure drop across a hydraulic component.

3.Determine the pressure at any point in a fluid power 3.Determine the pressure at any point in a fluid power system based on the pressure distribution.system based on the pressure distribution.

4. Determine the pressure drop between several points 4. Determine the pressure drop between several points in a fluid power system given the pressure gauge in a fluid power system given the pressure gauge readings at specific points.readings at specific points.

5. Apply Pascal’s Law to a fluid power system in order 5. Apply Pascal’s Law to a fluid power system in order to determine the pressure at a given point.to determine the pressure at a given point.

Source of Fluid FrictionSource of Fluid Friction

Frictional resistance to fluid flow comes from many sources. Frictional resistance to fluid flow comes from many sources. First, the fluid itself will resist movement. Next, coming into First, the fluid itself will resist movement. Next, coming into contact with any surface, be it in pipe, tubing, or hose, will contact with any surface, be it in pipe, tubing, or hose, will cause resistance. Resistance is unavoidable but can be cause resistance. Resistance is unavoidable but can be reduced to an acceptable degree with good design practices. reduced to an acceptable degree with good design practices. Reducing bends and turns in fluid conductors will have a Reducing bends and turns in fluid conductors will have a positive effect on friction as well as considering the internal positive effect on friction as well as considering the internal surfaces of components. A very important fact to remember surfaces of components. A very important fact to remember that resistance will cause energy loss in a fluid power system. that resistance will cause energy loss in a fluid power system. It is therefore necessary to discuss frictional loses in order to It is therefore necessary to discuss frictional loses in order to appreciate system designs that minimize pressure drop. A appreciate system designs that minimize pressure drop. A pressure drop is simply the difference in pressure between pressure drop is simply the difference in pressure between any two points in a fluid power system.any two points in a fluid power system.

Factors Affecting Pressure DropFactors Affecting Pressure Drop

As stated in the lab manual, all components through which As stated in the lab manual, all components through which fluid flows will cause a pressure drop to some degree. The fluid flows will cause a pressure drop to some degree. The degree of pressure drop or “delta P” will be determined by degree of pressure drop or “delta P” will be determined by pressure, flow, and the inside characteristics of the component pressure, flow, and the inside characteristics of the component to include its size, roughness, and shape. Fluid moves more to include its size, roughness, and shape. Fluid moves more smoothly over smooth, contoured surfaces rather tan blunt, smoothly over smooth, contoured surfaces rather tan blunt, rough surfaces. Sharp bends and turns should always be rough surfaces. Sharp bends and turns should always be avoided. The last statement may be hard to understand as avoided. The last statement may be hard to understand as you notice certain equipment in which it may appear that you notice certain equipment in which it may appear that somebody disregarded this rule.somebody disregarded this rule.

Hydraulic System Pressure DistributionHydraulic System Pressure Distribution

Operating pressure refers to the pressure at the outlet of the pump during Operating pressure refers to the pressure at the outlet of the pump during machine operation. Pressure at other points may vary greatly depending on the machine operation. Pressure at other points may vary greatly depending on the movement of the fluid. While fluid is in movement, the pressure at any point will movement of the fluid. While fluid is in movement, the pressure at any point will be equal to the sum of all pressure drops from that point back to the pump outlet. be equal to the sum of all pressure drops from that point back to the pump outlet. This rule follows the rule of series circuits in electricity.This rule follows the rule of series circuits in electricity.

Pascal’s Law Applied to Pressure DistributionPascal’s Law Applied to Pressure Distribution

Pascal’s Law states the property of a fluid to transmit pressure equally and at right Pascal’s Law states the property of a fluid to transmit pressure equally and at right angles to all containing surfaces. With this in mind, consider what happens when a angles to all containing surfaces. With this in mind, consider what happens when a cylinder extends as far as it can go and then stalls out. While fluid is moving, cylinder extends as far as it can go and then stalls out. While fluid is moving, meaning that the cylinder is moving, pressure will vary from point to point. meaning that the cylinder is moving, pressure will vary from point to point. However, after the cylinder stalls by reaching the end of its stroke, or encountering However, after the cylinder stalls by reaching the end of its stroke, or encountering a load it cannot move, the pressure at all points between the pump outlet and the a load it cannot move, the pressure at all points between the pump outlet and the cylinder will be equal to the relief valve setting.cylinder will be equal to the relief valve setting.

Charts and GraphsCharts and Graphs

A graph such as the one illustrated above, is used to show an existing relationship A graph such as the one illustrated above, is used to show an existing relationship between two variables where a predictable outcome may be established. In the between two variables where a predictable outcome may be established. In the chart above, a valve is slowly closed resulting in an increase of pressure as chart above, a valve is slowly closed resulting in an increase of pressure as resistance to flow is increased.resistance to flow is increased.

ReviewReview

1. Explain the meaning of “delta-P.”1. Explain the meaning of “delta-P.”

2. Give the delta P of A and C.2. Give the delta P of A and C.

3. Name the characteristics of a component that affect the pressure 3. Name the characteristics of a component that affect the pressure drop of fluid flowing through the component.drop of fluid flowing through the component.

4. What is the pressure of the fluid at any point in a fluid power 4. What is the pressure of the fluid at any point in a fluid power system determined by? Assume the fluid is in movement.system determined by? Assume the fluid is in movement.

ReviewReview

5. In the circuit below, what is the value of gauge S, or in other 5. In the circuit below, what is the value of gauge S, or in other words, what is the relief valve set at?words, what is the relief valve set at?

ReviewReview6. In the circuit of question 5, what is the pressure at the cap end of 6. In the circuit of question 5, what is the pressure at the cap end of the cylinder? Assume the fluid is moving.the cylinder? Assume the fluid is moving.7. In the circuit for question 5, what is the pressure at the cap end of 7. In the circuit for question 5, what is the pressure at the cap end of the cylinder if the cylinder stalls out?the cylinder if the cylinder stalls out?

8. Why do you suppose that one component might have cause more 8. Why do you suppose that one component might have cause more delta P than another?delta P than another?

9. In the illustration above, what happens to delta P if the pressure is 9. In the illustration above, what happens to delta P if the pressure is increased but all else remains the same?increased but all else remains the same?

10. In the illustration for number 9, what happens to delta P if the 10. In the illustration for number 9, what happens to delta P if the needle valve is opened and pressure from the left remains the same?needle valve is opened and pressure from the left remains the same?