BCIT: Millwright Level 3 (Hydraulics: Fluids)

What is pressure?

Pressure is the amount of force applied over a given area.

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?

When pressure is applied to a confined fluid at rest, it is distributed equally throughout all parts of the system.

If a pump delivers flow through an open-ended pipe that has no restriction to the flow, is the pressure at any point in the pipe high, low or zero?

If a pump delivers flow through an open-ended pipe with no restriction, the pressure in the pipe is zero.

Why is pressure transmitted almost instantly through hydraulic fluid?

Pressure is transmitted almost instantly because hydraulic fluid is nearly incompressible.

What is meant by gauge pressure?

Gauge pressure is the pressure indicated by a gauge that does not include atmospheric pressure.

Why does a cylinder have a lower load capacity when it retracts than when it extends?

A cylinder has a lower load capacity when it retracts because the piston rod reduces the effective area, resulting in less force.

How can you increase the force exerted by a cylinder of any given size?

The force exerted by a cylinder can be increased by increasing the operating pressure.

Would you use a larger or a smaller cylinder if you needed to increase the load capacity at a given pressure?

A larger cylinder would be used to increase the load capacity at a given pressure.

At a given pressure setting, what is the load capacity of a 2-to-1 cylinder when it extends compared to when it retracts?

At a given pressure, a 2-to-1 cylinder has twice the load capacity when extending compared to when retracting.

Does a pump produce pressure, flow, or both pressure and flow?

A pump produces flow.

Will there be high flow, low flow, or no flow if the pressure is 10,000 psi on the upstream side of an orifice and 10,000 psi on the downstream side?

If the pressure on both sides of an orifice is the same, there will be no flow.

For a given flow rate, which moves faster: a large diameter cylinder or a small diameter cylinder?

For a given flow rate, a smaller diameter cylinder moves faster than a larger diameter cylinder.

How fast does a two-to-one cylinder extend compared to how fast it retracts?

A two-to-one cylinder extends at half the speed that it retracts.

What is the purpose of a regenerative circuit?

The purpose of a regenerative circuit is to increase cylinder speed while maintaining force in both directions.

How does a reduction in pipe size affect pressure?

A reduction in pipe size increases pressure.

How does a decrease in pipe size affect velocity?

A decrease in pipe size increases fluid velocity.

How does an increase in velocity affect fluid friction?

An increase in velocity increases fluid friction.

What is laminar flow?

Laminar flow is smooth, parallel fluid flow in which the fluid layers move without mixing.

What type of flow is more efficient for transmitting power: laminar or turbulent flow?

Laminar flow is more efficient for transmitting power.

What is the recommended velocity range in pressure lines?

The recommended velocity range in pressure lines is between 7 and 20 feet per second.

If you hear a rattling or buzzing sound in a hydraulic cylinder, would you suspect cavitation or aeration?

A rattling or buzzing sound in a hydraulic cylinder usually indicates aeration.

If you suspect cavitation around the pump area, should you look for leaky seals or fittings?

If cavitation is suspected around the pump area, leaky seals or fittings are usually not the cause.

When the velocity of fluid increases, does pressure increase or decrease?

When the velocity of fluid increases, the pressure decreases.

f 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?

If the load does not move, no work is done regardless of the amount of force applied.

If the flow is increased and the operating pressure is kept constant, will the amount of power transmitted increase?

If the flow increases while the operating pressure remains constant, the power transmitted will increase.

If the operating pressure is increased and the flow rate is kept constant, will the power transmitted increase?

If the operating pressure increases while the flow rate remains constant, the power transmitted will increase.

Is a hydraulic system a source of power?

A hydraulic system is not a source of power.

Does a pump produce pressure or flow?

A pump produces flow.

What is Pascal's Principle?

Pascal’s Principle states that pressure applied to a confined fluid is transmitted equally in all directions.

What produces pressure?

Pressure is produced by resistance to flow.

What two (2) things cause resistance to flow?

Resistance to flow is caused by friction and load.

What is the absolute pressure if the gauge pressure is 100 psi?

If the gauge pressure is 100 psi, the absolute pressure is 114.7 psi.

If the feet of head in a system using hydraulic oil is 100 feet, what is the gauge pressure?

If the hydraulic oil head is 100 feet, the gauge pressure is approximately 40 psi.

How does pressure affect the output of a cylinder?

Pressure determines the force output of a hydraulic cylinder.

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?

A 2-inch cylinder with a 1-inch rod can pull approximately 1.2 tons when retracting at 1000 psi.

What size cylinder would you need to move a 5-ton load if you had the operating pressure set at 2000 psi?

A cylinder with a diameter of approximately 2.5 inches would be required to move a 5-ton load at 2000 psi.

At what pressure would you set the maximum pressure relief valve in order to move a 4-ton load using a 4-inch cylinder?

The maximum pressure relief valve should be set at approximately 637 psi to move a 4-ton load using a 4-inch cylinder.

What is the retraction force on a 4-inch, two-to-one cylinder if the operating pressure is 1000 psi?

The retraction force on a 4-inch two-to-one cylinder at 1000 psi is approximately 6283 pounds.

What two (2) things produce flow?

Flow is produced by a pump or by fluid moving downward due to gravity.

How does flow affect the output of a cylinder?

Flow determines the speed of a hydraulic cylinder.

What size cylinder would you need to use with a 10 gpm pump if the cylinder is required to extend at 1 foot per second?

A cylinder with a diameter of approximately 2 inches would be required.

What is the speed of retraction of a two-to-one cylinder if it extends at 400 feet per minute?

If a two-to-one cylinder extends at 400 feet per minute, it retracts at 800 feet per minute.

Draw a regenerative circuit.

A regenerative circuit is represented by the diagram provided in the notes (refer to your notes).

What happens to the velocity of the fluid if you substitute a 2-inch standard weight return line with a 2-inch heavy wall pipe?

The velocity of the fluid increases.

What is the recommended inlet velocity for a hydraulic system?

The recommended inlet velocity for a hydraulic system is between 2 and 4 feet per second.

List three (3) negative effects of high fluid velocities in a hydraulic system.

High fluid velocities can cause component wear, increased pressure losses, and wasted power.

Name six (6) causes of turbulent flow.

Six causes of turbulent flow include fittings, short-radius bends, changes in pipe diameter, changes in flow direction, friction, and high fluid velocities.

What is cavitation?

Cavitation is the collapse of vapor bubbles within a fluid.

List three (3) causes of cavitation.

Three causes of cavitation include a clogged inlet filter, a pump located above the fluid level, and turbulence in the fluid.

What is the basic cause of aeration?

The basic cause of aeration is air entering the hydraulic system.

What is Bernoulli's Principle?

Bernoulli’s Principle states that as the velocity of a fluid increases, its pressure decreases.

Name three (3) applications of Bernoulli's Principle.

Three applications of Bernoulli’s Principle include airplane wings, the pressure drop in a carburetor that draws fuel into the air stream, and a venturi air-line lubricator.

What is work?

Work is the product of force and distance.

What is power?

Power is the rate at which work is done.

When the gpm of a pump is known, how can you calculate the horsepower required to drive a hydraulic system to move a given load?

The required horsepower can be calculated using the formula:

horsepower = (gpm × psi) ÷ 1714.

What is meant by power efficiency in a system?

Power efficiency is the ratio of output power to input power, expressed as a percentage.

What is meant by volumetric efficiency?

Volumetric efficiency is the ratio of actual fluid output to theoretical fluid output.

What causes a decrease in volumetric efficiency?

Volumetric efficiency decreases due to wear or internal leakage in the system.