Introduction to Hydraulics Exam Review Sheets 2013/2014misshannahsclassroom.weebly.com/uploads/1/6/3/0/16300210/eoft_review... · Introduction to Hydraulics Exam Review Sheets –

Introduction to Hydraulics

Exam Review Sheets – 2013/2014

1. Answer each question below by writing True or False.

Statement True or False

Hydraulic motors are used to convert the hydraulic energy into mechanical energy by generating a Rotary movement in either one or two directions.

True

Pressure regulator valves are used to reduce the input pressure to a specified output pressure.

True

This pictures shows a 4/2 way valve

False

The flow velocity of a fluid is the distance the fluid travels in a given period of time.

True

The pump creates the flow rate in the hydraulic system.

True

2. Fill in the blanks.

a. ISO symbols show the component’s construction and size.

b. Hydraulic cylinders transfer fluid pressure into mechanical motion. The force of this motion depends on if the cylinder rod is extending or

retracting

c. Non-return valves are used to block the flow in one direction and allow free flow in the other direction.

d. The conductors are the pipes or hoses needed to transmit the oil between the hydraulic components.

3. If the Force applied by a car is 13,000 N at piston B, the diameter of piston A is 8 mm, and the diameter of piston B is 200mm. Find the force applied at

piston A.

4. A fluid flows at a velocity of 1.5 m/s at point 1. The diameter at point 1 is 40mm and the diameter at point 2 is 100 mm. Determine the flow velocity at

point 1.

5. a. Explain the relation between the hose size and the flow velocity of the

fluid through the pipe given the figure below.

A2 V2

A1 V1

Q1 Q2

b. If fluid flows at a velocity of 0.7m/s at section A1V1 and the area at

section A1V1 is 0.4m2 and the area at section A2V2 is 0.2m2. Determine

the flow velocity (m/s) and the flow rate in m3/s at A2V2.

6. The output piston of a hydraulic press has a cross sectional area of 0.20 m2.

(a) How much pressure on the input piston is required for the press to

generate a force of 1.5 x 106N?

Given: Area of output piston = 0.20m2

Force = 1.5 x 106N Required:

Pressure (Pa) =? Analysis:

Pressure = Force / Area

Solution: Pressure = Force / Area

Pressure = 1.5 x 106N / 0.20m2

Pressure = 7500000 N/m2 = 7500000 Pa

Paraphrase: The pressure applied on the output piston is 7500000 N/m2

(b) What force is applied to the input piston if that piston has a

diameter of 5.0cm?

7. Draw the I.S.O symbols.

Check Valve Shut off Valve

8. What is the difference between the normal check valve and the pilot check valve?

The pilot check valve has a pilot connection which can open the valve in the blocked direction, when a pilot signal is applied. But the normal check valve

allows the flow only in one direction; which means that the flow in the opposite direction will be completely blocked.

9. What is the equation for flow velocity? V = Q / A

10. Explain flow rate and flow velocity.

Flow rate: Determines the speed at which the output device (e.g., a cylinder) will operate. Flow velocity: The distance the fluid travels in a given period of time which is the extension speed of the cylinder.

11. The hydraulic circuit shown below has a piston area of 7 x 10-4 m2, a rod area of 3.5 x 10-4 m2 along with a pressure of 15000000 Pa. Calculate Fe and Fr in this hydraulic circuit.

12. A special machine is used to emboss graphic symbols on metal foil. The foil is fed through the embossing machine. The advanced motion of the stamp must be capable of being varied in accordance with the fed speed as shown in the picture below. The return motion must always be executed as a rapid traverse. A One way flow control valve is used to control the speed of the stamp, while a pressure relief valve is used to prevent the weight of the stamp from pulling the piston rod out of the cylinder. A 4/2 way valve is used to switch between advance and return motion. Draw the hydraulic circuit diagram by choosing the correct components seen in the box on your right.

Several stations on a rotary machining

station are driven by a hydraulic

power pack.

As individual stations are switched on and

off, they produce pressure

fluctuations throughout the hydraulic circuit.

This effect will be studied

on a drilling station. The fluctuations in

pressure and the tractive forces

created during drilling must not affect the

feed of the drilling station. A

flow control valve is to be used to ensure a

smooth adjustable feed rate,

while a pressure relief valve is to be used as a

counter-holding valve to compensate for the

tractive forces.

Answer the following questions.

1- Name each of the following. 0Z1: ___Hydraulic Power Pack___

1A: _______Double Acting Cylinder____

2- What is the function of 0Z2? It’s a pressure gauge and it’s used to read the pressure.

3- What is the main purpose of using 0V2?

To manually open and close the flow. (For Safety)

4- What is the main function of 1V1?

To open /close / change the flow paths.

5- Why are the valves 1V2 and 1V5 used here? They are check valves and they are used to allow the flow in 1 direction and block the flow in the

opposite direction.

Hydraulic circuit

The grinding table of a surface grinding machine

is driven by a hydraulic cylinder. Since the speed

is required to be the same in both directions, the

hydraulic control circuit must be designed to

provide compensation for the difference in

volume of the two cylinder chambers. A

differential circuit is suggested with a 3/2-way

valve and a flow control valve for speed

adjustment.

Answer the following questions.

1- State the name and the function of each of the following.

Number Name Function

0V1 Pressure

relief valve

Used to prevent the maximum permissible pressure from being

exceeded.

0V3 Two way flow

control valve

To provide a constant flow rate in the case of variable loads.

1V 4/2 way valve Open / Close / change the direction of the flow path

2- What is the main purpose of using 0V2?

As a safety precaution; if you manually close it the flow will stop.

Hydraulic circuit

A vehicle is to be lifted by a hydraulic jack. The load of the vehicle is 15000N.

a. What force F1 (in 1 decimal place) is required at the piston? Given: A1 = 40cm2 and A2 = 1200cm2

Convert both areas A1 and A2 into m2thus:

A1 = 40cm2 / 10000 = 0.004m2

A2 = 1200cm2 / 10000 = 0.12m2

From Pascal’s law: “The pressure in a confined fluid is transmitted equally to the whole surface of

its container”and Pressure: P1 = P2 then,

F1/ A1 = F2 / A2

F1 = (A1) (F2) / A2

F1 = (0.004m2) (15000N) / (0.12m2)

F1 = 500N

b. Analyze your answer in part (a). Is F1 smaller than F2? If yes, why is an amount of F1 sufficed to lift

and overcome the load resistance being applied at A2?

Yes F1 = 500N is smaller than F2 = 15000N. Small forces from the pressure piston can produce

larger forces by enlarging the working piston surface. This is the fundamental principle, which is

applied, in every hydraulic system from the jack to the lifting platform. The force F1 must be

sufficient for the fluid pressure to overcome the load resistance.

Circle the correct answer.

1. Which one of the following hydraulic system components is responsible for controlling the direction, pressure and flow of the hydraulic fluid.

A. Power input device

√ B. Control Device

C. Power Output Device

D. Liquid

E Conductors

2. Which of the following is not an example of a hydraulic system?

A. Heavy earth moving machines

B. Vehicle power steering

C. Hydraulic jack

√ D. Dental drill

E Vehicle power brake

3. The ________________ determines the speed at which the output device will operate.

√ A. Flow rate.

B. Flow Velocity.

C. Pressure.

D. Area.

E None of the above.

4. Which valve could be used to change the flow path?

A. Shut off valve

B. Check valve

√ C. 4/3 way valve

D. Pressure relief valve

E None of the above

5. Which valve is actuated manually and returned by a spring?

√ A. 4/2 way valve

B. 4/3 way valve

C. 4/4 way valve

D. Pressure relief valve

E. Shut off valve

6. In a hydraulic cylinder, the extension force (Fe) depends on ____________ .

I. Pressure

II. Piston Area

III. Rod Area

A. I only

√ B. I and II only

C. II and III only

D. I and III only

E. I, II and III

7. Which instrument is used to determine if a machine is operating properly?

√ A. Pressure Gauge

B. 4/3 way valve

C. Double acting cylinder

D. Pressure relief valve

E. Shut off valve

8. Circle the correct sentence :

A. The flow velocity is always constant.

B. The flow rate for different pumps is always the same.

√ C. The flow rate is constant and the diameter varies.

D. The flow rate is the distance the fluid travels in a system.

E None of the above.

9. Which non-return valves below are used to allow for fluid flow in one direction only; which means that the flow in the opposite direction will be completely blocked?

A. Pilot check valve.

B. Shut off valve.

√ C. Check valve.

D. Pilot check and check valves.

E Pilot check and shut off valves.

10. Flow velocity in a hydraulic system is usually expressed in:

A. Pascal (Pa).

B. Meters per second (m/s).

C. Newton (N).

D. Meter cube per second (m3/s).

E. Meter squared (m2).

11. Which valve below controls the direction of fluid flow?

A. Check valves.

B. Shutoff valves.

C. Pilot check valves.

D. 4/3 way valve.

E. Pressure relief valve.

12. The ISO symbol to the right represents the ____________________

√ A. Pilot check valve.

B. Check valve.

C. Shutoff valve.

D. 4/2 way valve.

E. 4/3 valve.

Question II

Answer the following questions.

1- Draw the ISO Symbol for the Single acting cylinder and explain how the forward and return strokes are achieved.

Forward stroke is achieved by hydraulic pressure.

Return stroke is achieved by the effect of the gravity

or the load.

2- Why is the extension force in a cylinder larger than the retraction force? (Use a drawing ) Fe = P x A while Fr = P x (A-a)

The equations above show that the extension force depends on the Piston area while the

retraction force depends on the difference of areas between the piston and the rod.

3- State one difference and one similarity between the single acting cylinder and the hydraulic motor.

Similarity: Both convert hydraulic energy into mechanical energy.

Difference: Hydraulic motor generates rotary movement in either 1 direction or 2 directions while

SAC generates linear movement in 1 direction

4- Calculate the forces (Fe) and (Fr) if you are given the following: a. The piston radius is 0.4 m.

b. The rod radius is 0.2 m.

c. The pressure is 15 bar.

i) Find Areas: Piston area: A = π x r2 = 3.14 x 0.42 = 0.5024 m2

Rod area: a = π x r2 = 3.14 x 0.22 = 0.1256 m2

ii) Change Pressure Units: P = 15 x 100,000 = 1,500,000 Pa

iii) Fe = P x A = 1500000 x 0.5024 = 753,600 N

iv) Fr = P x(A-a) = 1500000 x(0.5-0.1256) = 565,200 N

5. If the radius of Piston A is 5 mm and the force applied is 500 N, the force applied at piston B is

15,000 N find the radius of piston B.

i) Given: r1 = 5 mm

F1 = 500N

F2 = 15,000 N

R2 = ?

ii) Find Area 1: A1 = π x r2 = 3.14 x (5x10-3)2 = 7.85 x10-5 m2

iii) A2 = F2 x A1 = 15000 x 7.85 x10-5 = 2.355 x 10-3 m2

F1 500

iv) Find the Radius: r2 = √A/π = 0.027 m

6. A pipe size needs to be determined for a system in which the flow rate will be 150 m3/s .

Determine the pipe diameter if the flow velocity is not to exceed 12 m/sec.

i) Find the Area:

Q = V x A -> A = Q / V = 150 / 12 = 12.5 m2

ii) Find the Diameter:

A = π x D2 -> D =√ 4xA / π = √ 4 x 12.5 / 3.14 = 3.99 = 4 m

4

7. Draw the ISO symbol for the 4/2 way valve and state how the fluid flows in the actuated and in the normal position .

Normal position: Flow from P to A and B to T

Actuated position: Flow from P to B and A to T

8. Draw the ISO symbol for the three way pressure regulator valve and explain A) its function and B) when the hydraulic fluid is drained off at (T).

A) Function: used to maintain a constant

output pressure despite fluctuating

input pressure

B) when the pressure at connection (A) exceeds

the operating pressure.

Question III

Draw the ISO symbol for each of the following.

Detailed Hydraulic Power

Pack

4/3 way valve Double Acting Cylinder

Question IV

Match between the component / symbol in column A and its name in column B. Write your answer in the

provided table.

Column A Column B

1

A Hydraulic Motor

2

B Pressure Relief Valve

3

C Hydraulic pump

4

D Reservoir

5

E Electric Motor

6

F Two Way Pressure Regulator Valve

G Hydraulic power pack

H Shut off Valve

Question 1 2 3 4 5 6

Answer C A B H D F

Question V

Draw the ISO symbol for each of the following.

Two way flow control valve Pressure relief valve One way flow control valve

a. The hydraulic circuit shown above has a piston area of 6 x 10-4 m2, a rod area of 2.5 x 10-4 m2 along with a pressure of 30 bar. Calculate Fe and Fr in this hydraulic circuit. [6M]

In this case, the student shall know (based on their answer to a above) that the pressure is 0.

Fe = P x A

Fe = (0) x (6x10-4)

Fe = 0N

Convert 30 bar to Pa > 30 x 105 = 3000000 Pa

Fr = P (A-a)

Fr = (3000000) x (6x10-4 - 2.5 x 10-4)

Fr = (3000000) x (3.5 x 10-4)

Fr = 1050N

Question VI

Shown below to the right is a D0 = 1.0-cm-diameter pipe widens to D1 = 2.0 cm, and then narrows to D3 =

0.5 cm. Liquid flows through the first segment at a speed of 4 m/s, the second segment at 1 m/s, and the

third segment at 16 m/s. Calculate the flow rate if it is not to exceed 5.12x10^-5m/s.

√ A. Ѵ1 = 1.96x10^-5m/ s

B. Ѵ1 = 4.56x10^-5m/ s

C. Ѵ1 = 2.26x10^-4m/ s

D. Ѵ1 = 1.96x10^5m/ s

E. Ѵ1 = 0.96x10^-5m/ s

Given:

D0 = 1.0cm, S0 = 4m/s

D1 = 2.0cm, S1 = 1m/s

D2 = 0.5cm, S2 = 16m/s

Required:

Volumetric Flow Rate Ѵ =?

Analysis:

Velocity = Volumetric Flow Rate / Area

Or A

Qv

where

A

Qv

v : Extension velocity of a cylinder ( sm / )

Q : Flow rate ( sm /3

)

A : Area (2

m )

Solution:

All the students need to do is to look and work with one section of the pipe. Thus, for section one

Diameter = D1 = 2.0 cm = 0.02 m thus, Radius = r1 = .01 m

Area of pipe = (pi)*(r12) = (pi) * (.01 m)2 = (3.14) (1.0 x 10^-4) = 3.14 x 10^-4m2

Volumetric Flow Rate = 1 m/s * 3.14 x 10^-4= 3.14x10^-4m/ s

Paraphrase:

The volumetric flow rate for Ѵ1 is 3.14x10^-4m/ s

Question VI

Draw the ISO symbol for the pilot check valve and explain the function of each port.

It has (3 ports A , B and X )

(A): port for input pressure

(B): port for output pressure

(X): port for pilot pressure