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Millwright Mechanics- 3rd Year Exams - Introduction to Hydraulics, Exams of Mechanics

Madison Area Technical College Mechanics

Millwright Mechanics Millwright Mechanics- 3rd Year Exams - Introduction to Hydraulics

Typology: Exams

2024/2025

Available from 06/18/2025

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Millwright Mechanics- 3rd Year Exams - Introduction to

Hydraulics

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1. 1. What is the main hazard to always be aware of when you are working on

hydraulic systems?: 1. high pressure

2. 2. What hazard can exist after a hydraulic system has been locked out?: 1.

The system can still be charged with high-pressure fluid.

3. 3. What is the safety reason for taking time to completely understand a

hydraulic system before you begin work on it?: 1. so you can isolate and

depressurize the part of the system on which you will be working

4. 4. Does a hydraulic system develop power?

a) yes

b) no: 1. b) no

5. 5. List the five main parts of a hydraulic system.: 1. reservoir, conductors,

pump, control valves, actuators

6. 6. What is the first main valve after the pump in a hydraulic system?: 1. the

maximum pressure relief valve

7. 7. What are the three functions of a maximum pressure relief valve?: 1. to

protect the system from overload; to divert excess fluid not required by the actuator

back to the tank; and to set the maximum operating pressure in the system

8. 1. Is a pressure-reducing valve normally open or closed?: 1. normally open

9. 1. What is the purpose of a sequence valve?: 1. to allow an actuator to operate

only after another actuator has completed its cycle

10. 1. What valve would you use to prevent the uncontrolled fall of a load due

to gravity?: 1. a counterbalance valve

11. 1. Why is it important to attach an external drain to a sequence valve or to

a pressure-reducing valve?: 1. to prevent the valve from locking up under load

12. What is the purpose of a flow control?: 1. to control the speed of the actuator

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Hydraulics

1. What is the main hazard to always be aware of when you are working on hydraulic systems?: 1. high pressure
2. What hazard can exist after a hydraulic system has been locked out?: 1. The system can still be charged with high-pressure fluid.
3. What is the safety reason for taking time to completely understand a hydraulic system before you begin work on it?: 1. so you can isolate and depressurize the part of the system on which you will be working
4. Does a hydraulic system develop power? a) yes b) no: 1. b) no
5. List the five main parts of a hydraulic system.: 1. reservoir, conductors, pump, control valves, actuators
6. What is the first main valve after the pump in a hydraulic system?: 1. the maximum pressure relief valve
7. What are the three functions of a maximum pressure relief valve?: 1. to protect the system from overload; to divert excess fluid not required by the actuator back to the tank; and to set the maximum operating pressure in the system
1. Is a pressure-reducing valve normally open or closed?: 1. normally open
1. What is the purpose of a sequence valve?: 1. to allow an actuator to operate only after another actuator has completed its cycle
1. What valve would you use to prevent the uncontrolled fall of a load due to gravity?: 1. a counterbalance valve
1. Why is it important to attach an external drain to a sequence valve or to a pressure-reducing valve?: 1. to prevent the valve from locking up under load
What is the purpose of a flow control?: 1. to control the speed of the actuator

Hydraulics

1. Name three types of flow controls.: 1. meter in, meter out and bleed-off
1. Which type of flow control is the most energy efficient?: 1. the bleed-off control
1. What is the purpose of cross port relief valves on a hydraulic motor?: 1. to protect the motor against shock loads, especially when suddenly shifting from forward to reverse
1. What is pressure?: 1. Pressure is force on a unit of area.
1. When pressure is applied to a fluid that is at rest and confined in a system, is this pressure distributed equally throughout all parts of the system or is it concentrated in some parts of the system?: 1. It is distributed equally to all parts of the system.
1. If a pump delivers flow through an open-ended pipe that has no restric- tion to the flow, is the pressure at any point in the pipe high, low or zero?: 1. zero at all points.

Hydraulics

1. How does a reduction in pipe size affect pressure?: 1. decreases the pressure
1. How does a decrease in pipe size affect velocity?: 1. It increases the velocity.
1. How does an increase in velocity affect fluid friction?: 1. It increases the friction.
1. What is laminar flow?: 1. Flow paths are parallel.
1. What type of flow is more efficient for transmitting power: laminar or turbulent flow?: 1. laminar flow
1. What is the recommended velocity range in pressure lines?: 7 to 20 feet/second
1. If you hear a rattling or buzzing sound in a hydraulic cylinder, would you suspect cavitation or aeration?: 1. aeration

Hydraulics

1. If you suspect cavitation around the pump area, should you look for leaky seals or fittings? a) yes b) no: 1. b) no
1. When the velocity of fluid increases, does pressure increase or de- crease?: Decrease
1. If the force applied to a load is increased from 20 tons to 30 tons and the load does not move, will the amount of work done on the load be greater when the 30-ton force is applied? a) yes b) no: b) no (in fact, no work will have been done in any case if the load does not move).
1. If the flow is increased and the operating pressure is kept constant, will the amount of power transmitted increase? a) yes b) no: 1. a) yes
1. If the operating pressure is increased and the flow rate is kept constant, will the power transmitted increase? a) yes b) no: 1. a) yes
1. Is a hydraulic system a source of power? a) yes b) no: 1. b) no
1. What term is used for the output component of a hydraulic system?: 1. an actuator

Hydraulics

to show a :

into awkward locations

components that are very compact with respect to the amount of power they can transmit
power can be transmitted very efficiently through fluids with very little loss from friction.

1. Name three disadvantages of hydraulics.: Any three of the following are correct.

they are expensive
they are heavy
there is a high-pressure fluid hazard if a conductor fails
fluid leaks are messy and difficult to control
regular hydraulic fluid presents a fire hazard.

1. Draw a schematic diagram using standard hydraulic graphics circuit that can extend and retract a cylinder and control its speed.
1. Name three types of conductors used in hydraulics.: 1. tubes, hoses and pipes
1. Does a pump produce pressure or flow?: Flow
1. What safety function does a maximum safety relief valve perform?: 1. It provides overload protection for all the components in the system.
1. What valve controls the maximum force at which an actuator can oper- ate?: 1. the maximum pressure relief valve
1. What valve controls the speed of the actuator?: 1. the flow control valve

Hydraulics

ve on one aximum erates with

1. What is a typical maximum pressure that you can expect in a hydraulic system?: 1. 20 000 kPa or 2900 psi
1. What valve reduces the output force of a cylinder below the force it would have at the maximum pressure relief valve setting?: 1. pressure-reducing valve
1. Draw a two-cylinder circuit using a pressure-reducing val cylinder.: This a two-cylinder circuit where one cylinder operates at m system pressure and with speed control, while the other cylinder op reduced force.
1. What would happen if you did not connect the drain line to a pressure-re- ducing valve?: 1. It would become stuck open.
1. In what direction should the V-shaped seat (shown in the graphic of a check valve Figure 19) point when it is used in a reverse flow bypass for a pressure-reducing valve?: 1. in the same direction as the flow arrow in the valve

Hydraulics at right angles to every point on the inside surface of the container.

1. What produces pressure?: 1. a resistance to flow
What two things cause resistance to flow?: 1. restriction in the flow path and a load on the actuator
1. What is the absolute pressure if the gauge pressure is 100 psi?: 114. psi
1. If the feet of head in a system using hydraulic oil is 100 feet, what is the gauge pressure?: 40 psi
1. How does pressure affect the output of a cylinder?: 1. It affects the force.
1. What load, in tons, can a 2-inch cylinder with a 1-inch rod pull when it is retracting if the operating pressure is set at 1000 psi?: 2355.8 pounds = 1.3 tons. However, to account for frictional losses you must reduce the load by approximately 10 % = 1 ton.

Hydraulics

1. What size cylinder would you need to move a 5-ton load if you had the operating pressure set at 2000 psi?: 2.532 inches. Since this is not a standard size, go to the next available size above 2.3 inches = 2.75 inches to ensure that the cylinder is big enough to move the load.
1. At what pressure would you set the maximum pressure relief valve in order to move a 4-ton load using a 4-inch cylinder?: 636.6 psi. Set the pressure approximately 10% higher to allow for friction losses. The setting would be approximately 700 psi
1. What is the retraction force on a 4-inch, two-to-one cylinder if the operating pressure is 1000 psi?: 6283 lb
1. What two things produce flow?: a pump and a pressure drop across an orifice
1. How does flow affect the output of a cylinder?: 1. affects speed
1. What size cylinder would you need to use with a 10 gpm pump if the cylinder is required to extend at 1 foot/second?: 2.02 inches. The nearest standard size is a 2-inch cylinder. To ensure that sufficient speed is available, select a cylinder smaller than the one that you calculate. Remember that a small cylinder fills faster and therefore extends faster than a large cylinder.
1. What is the speed of retraction of a two-to-one cylinder if it extends at 400 feet/minute?: 800 feet/minute
Draw a regenerative circuit.:
1. What happens to the velocity of the fluid if you substitute 2-inch standard weight return line with a 2-inch heavy wall pipe?: Velocity increases
1. What is the recommended inlet velocity for a hydraulic system?: 2 to 4

Hydraulics

produce a very low pressure at the inlet, this will in turn cause the entrained gas to boil out of the fluid;

the pump is mounted too high above the reservoir; with this set-up, there will be insufficient pressure on the fluid in the reservoir to push the fluid up into the pump;
the fluid is too thick (viscosity is too high); the fluid will require more than just atmospheric pressure to make it flow up into the pump, typically this thickening of the fluid occurs in an unheated reservoir that is exposed to winter temperatures;
a clogged breather which causes reduced pressure on top of the fluid when its level drops; too many bends or fittings in the plumbing will cause too much friction resistance to the inlet flow;
too high a velocity caused by the inlet pipes being too small will in turn cause a loss in pressure to move the fluid into the pump and also causes turbulence which interferes with flow; turbulence will agitate the fluid and release some of the entrained gas. This turbu- lence can be due to too many fittings and sharp bends in the inlet piping.

What is the basic cause of aeration?: 1. Aeration occurs when air gets into the fluid from an outside source.
1. What is Bernoulli's Principle?: 1. As velocity increases, pressure decreas- es.
1. Name three applications of Bernoulli's Principle.: 1. Air flow of the wing of an aircraft to provide lift; pressure drop in the throat of a carburetor to allow the fuel to enter the air stream; the venturi in an air line lubricator to drop the air pressure so that the lubricant can enter the air stream.
1. What is work?: 1. Work is force applied over a distance or force x distance.
1. What is power?: 1. Power is the rate of doing work = force x distance/time.

Hydraulics

1. When the gpm of a pump is known, how can you calculate the horsepow- er required to drive a hydraulic system to move a given load?: 1. Horsepower = gpm x psi/1714.
What is meant by power efficiency in a system?: 1. percent of the output power/input power
1. What is meant by volumetric efficiency?: 1. percent output volume/input volume
1. What causes a decrease in volumetric efficiency?: 1. internal leakage, usually due to wear
Bernoulli's Principle states that when fluid velocity increases and the flow rate is constant, the pressure will: a. remain constant b. fluctuate

Hydraulics

**1. Meter in

meter out
bleed-off
Bleed in with integrated check valve:** 3. bleed-off
A 50 hp electric motor is driving a hydraulic pump you calculate the pump is delivering 23,100 ft/lbs per sec what is the hp and the power efficiency of the the pumping system? 1hp=33000 ft pounds per minute power efficiency= output hp/input hp x 100 a. 70% and 32hp b. 65% and 30hp c. 84% and 42hp d. 90% and 48hp: c. 84% and 42hp

Millwright Mechanics- 3rd Year Exams - Introduction to Hydraulics, Exams of Mechanics

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