Hydraulic Valves Part 1

Question 1

How do hydraulic valves assert their control over the system?

Answer 1

• controlling pressure - regulating flow through the branches of a system - determining the path of oil flow

Question 2

When selecting a pressure gauge to read hydraulic pressures what is a good rule of thumb?

Answer 2

Select a gauge with a range twice that of the max system spec for more accurate results.

Question 3

Do you need to run a main system relief in a system that also runs an unloader valve?

Answer 3

Yes, when the unloader valve closes and pump pressure is allowed to build and run actuators the main relief still maintains maximum system pressure, the unloader is only used to relieve the strain on a pump in a closed centre hydraulic system when the directional valve is in the closed position.

Question 4

How is a counterbalance valve different from a brake valve?

Answer 4

Pilot pressure is sensed at the outlet of a counterbalance valve whereas pilot pressure is sensed on both inlet and outlet of a braking valve.

Question 5

What’s is spring constant?

Answer 5

The stiffness of a spring in PSI, the greater the spring constant the greater the pressure overide

Question 6

Are pressure reducing valves normally open or closed?

Answer 6

Open

Question 7

Accumulators are installed for what 4 reasons?

Answer 7

-energy storage -shock absorption -gradual pressure buildup -constant pressure maintenance

Question 8

How does a counterbalance valve allow the reversed flow of oil?

Answer 8

A check valve

Question 9

What are the 7 common types of pressure control valves?

Answer 9

-pressure relief valve -unloaded valve -pressure reducing valve -sequence valve -counter balance valve -brake valve -line lock valve

Question 10

3 types of accumulators are:

Answer 10

-weighted -spring loaded -gas charged

Question 11

How is the second actuator in a sequence valve connected in the circuit?

Answer 11

Always in series with and downstream of the valve.

Question 12

What flow control valve is this?

Answer 12

Unloader valve

Question 13

Are pressure relief valves normally direct acting or pilot operated?

Answer 13

Direct acting (one spring)

Question 14

Where is a counterbalance valve usually located physically?

Answer 14

Attached to the base end of a cylinder

Question 15

What does the term pressure override refer to?

Answer 15

The difference between cracking pressure and full flow pressure

Question 16

How is a counterbalance valve often used in a circuit

Answer 16

A safety device on a linear actuator

Question 17

What flow control valve is this?

Answer 17

Lock valve

Question 18

What flow control valve is this?

Answer 18

Counterbalance valve

Question 19

How does a hi-low pump operate?

Answer 19

2 pumps run in parallel when high flow is required, as system pressure rises an unloaded valve set to a specific pressure will dump 1 pump to tank and allow the prime mover to deliver max horsepower to the other pump to deliver more torque.

Question 20

How do unloader valves differ from relief valves?

Answer 20

• they are always used in conjunction with a check valve
• pilot pressure used to open the valve comes from the high pressure side of the check valve

Question 21

When is a brake valve used?

Answer 21

On the return line of a hydraulic motor to prevent the load from over speeding the motor, and provide controlled deceleration.

Question 22

What is another term for a pilot controlled pressure control valve?

Answer 22

A compound pressure control valve

Question 23

How does a pressure reducing valve function?

Answer 23

Oil is allowed to flow freely through the valve to an actuator until the pilot line sees enough pressure to close the valve and Maintain pressure to that actuator while diverting the flow of oil out of the valve to send full system pressure to another actuator

Question 24

What similarities does a unloader valve share with a relief valve?

Answer 24

• always normally closed
• inlet port is in parallel with the circuit it unloads
• outlet always connected to the reservoir

Question 25

A technician replaced the brake valve on a picker truck but did not reconnect the pilot line that is in parallel with the inlet. The driver complains that the load won’t lower. Why?

Answer 25

Inlet pilot pressure needs to be seen to aid the outlet pressure and act upon the spool to open and allow the flow of oil.

Question 26

How does a sequence valve allow the reverse of flow?

Answer 26

A check valve

Question 27

What is a lock valve sometimes referred to?

Answer 27

Pilot operated check valve

Question 28

In a modern hydraulic system where are circuit relief valves often located?

Answer 28

The directional control valve

Question 29

Why is it important for an unloader valve to have an accumulator upstream of the valve?

Answer 29

once pump flow is directed away from the outlet port the accumulator maintains pressure on the check valve inside the valve, thus keeping the pump unloaded

Question 30

How does a lock valve operate?

Answer 30

Flow to the inlet of the valve through a check valve and also acting on a shuttle valve that opens the check valve attached to the return circuit, and vice versa. Without flow directed through either inlet our outlet, flow on the other side of the valve is locked.

Question 31

How do sequencing valves function?

Answer 31

Pilot pressure is sensed upstream of the valve. the inlet port, which is connected to the pilot, has to operate first in the sequence. When pilot pressure builds, the spool shifts to allow oil to flow to the outlet and operate the second sequence

Question 32

What flow control valve is this?

Answer 32

Brake valve

Question 33

To test circuit relief settings how should system relief be set?

Answer 33

Higher than system pressure settings, with care taken to only actuate the circuit in question, and always following the service manual.

Question 34

What flow control valve is this?

Answer 34

Pressure reducing valve

Question 35

Two basic forms of pressure control valves are:

Answer 35

Direct acting and pilot operated

Question 36

How is the flow of oil reversed in a brake valve?

Answer 36

Check valve

Question 37

3 types of gas charged accumulators are:

Answer 37

-bladder -piston -diaphragm

Question 38

Why is a braking valve important on hoisting equipment?

Answer 38

To eliminate the chance of the motor stopping abruptly when the flow of oil stops, which could cause severe shock load

Question 39

What is the biggest disadvantage of using direct acting pressure control valves?

Answer 39

Direct acting valves have a higher pressure overide. A higher pressure overide leads to unwanted heat and wasted power generated in the circuit

Question 40

How does a counter balance valve function?

Answer 40

Oil is allowed to flow through the valve to fill the base end of a cylinder. The oil is held in the base end of the cylinder until enough force is excerpted on the rod end to build enough pressure on the intensifier piston inside the valve and force the spool to overcome spring pressure, open, and allow the cylinder to lower. When the rod end pressure drops the spool closes, and the cylinder stops lowering.

Question 41

How does a brake valve function?

Answer 41

pilot pressure is sensed on both the inlet and outlet of the valve, when lowering, pilot pressure is sent to the inlet and outlet and opens the valve and allows oil to flow to turn the motor, when the directional control valve is in the closed position pressure drops in the inlet and the outlet pressure alone cannot keep the valve open and the spool is closed slowly braking the motor.

Question 42

Are sequencing valves normally open or closed?

Answer 42

Closed

Question 43

Can system pressure be tested with a hand actuated hydraulic pump?

Answer 43

No: only circuit pressures can be tested with a hand actuated pump.

Question 44

On a pressure relief valve where is pilot pressure drawn from in the system

Answer 44

Always upstream of the valve.

Question 45

The constant movement of a valve under spring and oil pressure is known as?

Answer 45

Modulation

Question 46

Hydraulic pumps in tandem are sometimes referred to as

Answer 46

Hi-low pump

Question 47

How is a brake valve often used

Answer 47

As a safety device on a rotary actuator