Hydraulic Systems

Question 1

What is an open center hydraulic system?

Answer 1

A system that allows the pump oil flow to return to the reservoir when the directional control valve is in the neutral position

Question 2

What might an open center hydraulic system composed of?

Answer 2

• A fixed displacement pump
• A open center directional control valve
• A differential/conventional double acting cylinder
• A relief valve
• A return line filter with bypass valve.

Question 3

What is another name for a open center hydraulic system?

Answer 3

A constant flow system.

Question 4

How does a constant horsepower open center hydraulic system work?

Answer 4

A pressure compensated variable displacement pump is used to reduce flow as pressure increases, this allows the engine to stay in a constant horsepower range for efficiency.

Question 5

What might a constant horsepower open center hydraulic system composed of?

Answer 5

• Variable displacement pump
• Open center directional control valve
• a differential/conventional double acting cylinder
• A relief valve
• An anti cavitation device
• A return line filter with bypass valve.

Question 6

What might a closed center hydraulic system composed of?

Answer 6

• Variable displacement ressure compensated pump
• Close center directional control valve
• A gas charged accumulator
• An unloader with reverse flow check valve

Question 7

What hydraulic system is common on excavators

Answer 7

A variable displacement load compensated (sensing) open center system.

Question 8

Does a variable displacement load compensated system have flow in the neutral position?

Answer 8

No, the makeup for leakage in the system is not considered flow.

Question 9

What is the most efficient hydraulic system with regards to horsepower use and heat loss?

Answer 9

A variable displacement load sensing system.

Question 10

What hydraulic system is common on loaders?

Answer 10

A fixed displacement open center system.

Question 11

What hydraulic system is common on a skid steer?

Answer 11

A hydrostatic system.

Question 12

What hydraulic system uses a closed loop design?

Answer 12

A hydrostatic system.

Question 13

What is the shuttle valve system used for in a Hydrostatic system? What is it used for?

Answer 13

To replenish and replace the oil in the hydrostatic’s closed loop system to make up for leakage and aid with fluid cooling.

Question 14

What system is common on a dozer application?

Answer 14

A variable displacement load sensing closed center system.

Question 15

What effect does a power shift system have on an excavators Variable displacement, load sensing, open center hydraulic system?

Answer 15

As power shift pressure (hydraulic load) decreases, pump output increases. As power shift pressure (hydraulic load) increases, pump output decreases.

Question 16

How is a power shift solenoid (PRV) used in a hydraulic system.

Answer 16

Pump output pressures are read by the ECM, the ECM then opens or closes the PRV to regulate pilot oil pressures in the pump to either stroke or destroke the pumps to manage the load on the engine.

Question 17

Is a negative flow control (NFC) system used in an open center or closed center system?

Answer 17

Closed loop system, the NFC system senses that the operator controls are in the neutral position, the closed loop system allows pressure to build in the NFC circuit and the NFC circuit then destrokes the hydraulic pumps for unit efficiency.