Hydraulic valves part 2 - part b

Question 1

What do directional control valves usually consist of?

Answer 1

A housing and a moveable valve

Question 2

What care should be taken with disassembling directional control valves?

Answer 2

Valves and housings are commonly mated and should not be interchanged

Question 3

What is the simplest type of directional control valve?

Answer 3

Poppit (check) valve

Question 4

What is a common type of rotary spool valve in a steering system?

Answer 4

Orbital spool valve

Question 5

Why are rotary spool valves limited in application?

Answer 5

Rotary spool valves have higher internal leakage which limits the pressures they can operate under. They are sometimes used to control pilot oil flow that operates a larger directional control valve.

Question 6

What is the most common spool valve used in off road heavy equipment?

Answer 6

Sliding spool.

Question 7

What are the metering notches often seen machined in a sliding spool valve or in the housing of a directional control valve?

Answer 7

Feathering notches used for precise control of oil flow through a control valve.

Question 8

What are the grooves often seen machined in a sliding spool valve?

Answer 8

Annular grooves used to trap oil for better lubrication and seeling, and to allow pressurized oil to act on the full circumference of the valve land which centres the spool in its bore to prevent binding and excessive wear.

Question 9

What is another name for a diverter valve?

Answer 9

A 2 position 3 way valve.

Question 10

How does an open center control valve work?

Answer 10

In the neutral position the valve allows free flow to tank

Question 11

What type of control valve is used to actuate a double acting cylinder or reversible motor?

Answer 11

A 4 way directional control valve.

Question 12

What are 4 types of directional control valve center positions often found on heavy equipment?

Answer 12

Open center, closed port. - Closed center, closed port. - Open center, open port. - Closed center, open port.

Question 13

What type of pump is used in a directional control valve with an open center, open port float position

Answer 13

Fixed displacement pump (float motor)

Question 14

What type of pump is used in a directional control valve with a closed center, open port float position

Answer 14

Variable displacement pump (float motor)

Question 15

What are the most common types of directional control valve actuators?

Answer 15

• Mechanical actuation (lever, foot pedal, push button.
• pilot operated (hydraulic or air)
• electrical (solenoid)

Question 16

What is a common fault with mechanical valve actuation?

Answer 16

Linkage wear causing improper valve actuation

Question 17

What is a pilot circuit?

Answer 17

A smaller hydraulic system used to actuate a larger hydraulic system.

Question 18

What type of pump is often used to supply flow to a pilot system?

Answer 18

Fixed displacement pump.

Question 19

What center position is commonly used in a pilot directional control valve that has a delay in operation

Answer 19

Open center, Open port.

Question 20

What type of pilot control is used in a faster acting pilot system?

Answer 20

Pressure regulated controls - allows for a smoother operation and faster valve actuating times.

Question 21

What center position is used in a pilot directional control valve that uses pressure regulated controls?

Answer 21

Closed center, open port

Question 22

Are discreet solenoids variable or fixed?

Answer 22

Fixed, on or off.

Question 23

What is the issue with using discreet solenoids acting on a larger hydraulic system.

Answer 23

Less control over the hydraulic functions. Lots of amperage required for solenoid actuation

Question 24

What is the most common type of electrical hydraulic actuation?

Answer 24

Electrical pilot over hydraulic control.

Question 25

What are detents used for in a directional control valve.

Answer 25

The spool is held in an actuated position for ease of operation for the operator.

Question 26

What is a load check valve used for?

Answer 26

The load check vale prevents reverse flow of oil from the work port of the pump passage when the valve spool is stroked, the cylinder cannot move until the pressure in the oil flow from the pump is high enough to open the check valve.

Question 27

What is an anti cavitation check valve used for?

Answer 27

The check valves block the flow of oil from the work port to the tank, but allows flow from the tank to the work port when the pressure in the actuator falls below the pressure in the return line.

Question 28

Where are anti cavitation valves often found in a directional control valve?

Answer 28

They are often incorporated into the circuit relief valve.

Question 29

What is the disadvantage to a unibody directional control valve?

Answer 29

• costs more

- often not repairable.

Question 30

What is the advantage to a unibody directional control valve

Answer 30

• compact design

- less leakage

Question 31

What is the disadvantage to a stacked style directional control valve?

Answer 31

• bulky in design

- many more places for oil to leak

Question 32

What is the advantage to a stacked style directional control valve?

Answer 32

• versatile in design
• easily repaired or replaced
• cheaper than unibody.