Intro to hydraulics part A/B

Question 1

Why is pressure transmitted almost instantly through hydraulic fluid?

Answer 1

Because hydraulic fluid is almost incompressible.

Compresses about 1/2% at 1000 psi.

Question 2

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

Answer 2

By increasing the operating pressure.

Question 3

Does a pump produce pressure, flow or both?

Answer 3

It only produces flow

Question 4

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

Answer 4

A larger cylinder because area would increase

Question 5

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

Answer 5

It extends at half the speed of retraction.

Question 6

Defined the characteristics of velocity and pressure in a large diameter pipe and a small diameter pipe.

Answer 6

In a larger diameter pipe the pressure is high while the velocity is low. (Good)

In a smaller diameter pipe the pressure is low while the velocity is high. (Bad)

Velocity + pressure are inversely related.

Question 7

How does flow affect the output of a cylinder?

Answer 7

It affects the speed.

Question 8

How does pressure affect the output of a cylinder?

Answer 8

It affects the force the cylinder exerts.

Question 9

How does cavitation occur?

Answer 9

It’s when gases dissolved in hydraulic fluid enter a low pressure area and boil out. When the gas comes in contact with a high pressure area the gasses implode causing cavitation.

Question 10

How is pressure created?

Answer 10

By a restriction to flow.

Question 11

What 2 properties are directly related to force?

Answer 11

Area and pressure

Question 12

What 2 properties are directly related to speed?

Answer 12

Flow rate and area

Question 13

What are 2 ways flow can be produced?

Answer 13

By a pump or a pressure drop across an orifice.

Question 14

Describe volumetric efficiency.

Answer 14

Volumetric efficiency measures how much fluid you get out of a pump compared to how much you put in.

Question 15

How big is the reservoir on an open loop circuit typically?

Answer 15

3 x the pump output

Question 16

What is the annulus area referring too?

Answer 16

The position area minus the rod area

Question 17

What is aeration?

Answer 17

Aeration occurs when air becomes mixed with the fluid that has leaked into the system through inadequate sealing or air becoming entrapped during maintenance on the system.

Question 18

How do you distinguish a hydraulic line that connects to another line compared to a line that crosses over and does not connect?

Answer 18

A like that connects to another line will be simply attached or will have a black dot at the point of connection. A line that crosses over will have a little bump over the line.

Question 19

What are you setting, when you set the pressure on a pressure relief valve?

Answer 19

You are setting the maximum force the cylinder exerts

Question 20

What is a directional control valve?

Answer 20

A valve that allows you to direct the flow to either end of the cylinder.

The valve can be operated manually, electrically, hydraulically or pneumatically.

Question 21

What are the 4 ports on a directional control valve?

Answer 21

A and B are working ports

P and T are the pressure port and return to tank port

Question 22

What does a flow control valve do?

Answer 22

It controls the speed at which the cylinder operates.

Question 23

What does a diagonal arrow on a hydraulic symbol represent?

Answer 23

That the component is variable (adjustable) in its output.

Question 24

What is the job of a pressure reducing valve?

Answer 24

It’s job is to reduce the pressure below the system pressure and thus the force the cylinder can exert.

Question 25

Is a pressure reducing valve normally open or normally closed?

Answer 25

Normally open until something happens to push the valve closed.

Question 26

What is the system pressure when you actuate a cylinder to move a load?

Answer 26

It will be just what is required to move the load and when the cylinder bottoms out the system pressure will increase to the maximum pressure which will open the maximum pressure relief valve.

Question 27

What is the small dotted line coming from the spring on a pressure reducing valve for?

Answer 27

It is a drain line that goes back to tank that prevents pressure build up on top of the valve element (the build-up would prevent the valve from operating)

Question 28

What is a hydraulic sequence valve used for?

Answer 28

A sequence valve stops the flow to the second cylinder, but then releases the flow to the second cylinder as soon as the first cylinder reaches the end of its stroke.

(Clamping a work piece with the first cylinder and then a punch coming down with the first cylinder to punch a hole in said piece.)

Question 29

A cylinder that pushes up on a load is called a?

Answer 29

Opposing load

Question 30

A cylinder that pulls up on a load is called a?

Answer 30

Tractive load

Question 31

Is a hydraulic sequence load normally open or normally closed?

Answer 31

Normally closed

Question 32

Does a meter-in flow control attach to the cap end or rod end?

Answer 32

Cap end on an opposing load

Question 33

Does a meter-out flow control attach to the cap end or rod end?

Answer 33

Rod end on a tractive load

Pulling up

Question 34

What happens to the flow produced by the pump that is not used by the cylinder?

Answer 34

It is wasted through the maximum pressure relief valve.

Question 35

What is bleed-off flow control?

Answer 35

The flow control can be connected so it bleeds off a set amount of the flow before the flow is delivered to the cylinder. Bleeding off flow through the flow control from the supply line to the directional control allows you to control the speed of the cylinder when it extends and retracts.