Components and functions of a safety oil suction valve for excavator

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Components and functions of a safety oil suction valve for excavator

1. Overview

The safety oil suction valve is installed on each branch oil circuit of the hydraulic device (cylinder, motor). It has the following two functions (taking a cylinder as an example):

(1) When the working device receives an abnormal impact from the outside, abnormally high pressure will be generated in the cylinder, and the safety suction valve will be opened to release the abnormally high pressure back to the fuel tank. In this case, the valve acts as a safety valve to protect the associated hydraulic cylinders and hydraulic tubing.

(2) When negative pressure is generated in the oil cylinder, the valve acts as an oil suction valve, replenishing the oil from the fuel tank pipeline to the negative pressure zone to avoid the formation of vacuum and cavitation.

4. Working principle    

Security effect:

(1) Oil pressure in the high-pressure oil zone rises to 390kg / cm²

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(2) High-pressure oil pushes the poppet valve (5) to open upward get over the force of the spring (6)

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(3) The oil in the throttle groove of the piston (3) starts to flow in small amounts

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(4) The pressure difference between the upper and lower piston (3) due to the throttling effect of the throttle groove

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(5) The main valve (2) is opened upward gets over the force of the spring (4) due to the pressure difference.

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(6) A large amount of high-pressure oil was leaked back to the fuel tank, and the pressure of the main oil circuit decreased.

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(7) Protected the oil cylinder and oil pipe

Oil absorption effect:

(1) When the E area is negative pressure, the oil pressure is lower than the tank pressure

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(2) The oil pressure of the fuel tank acts on the circular force receiving surface of ΦA-ΦD and pushes the suction valve (1) to open upward.

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(3) The fuel tank oil is replenished into this negative pressure area to avoid the formation of air bubbles and gas turbidity.

5.Troubleshooting

Malfunction 1

Symptom: The boom cylinder bulges after being exposed to high pressure.

Inspection result: The main valve (2) of the booming bottom safety oil suction valve is stuck and cannot be moved.

Failure analysis: When the abnormally high pressure reaches 390kg / cm² or more, the main valve (2) cannot be opened, resulting in continuous abnormal high pressure, and the cylinder barrel is deformed by huge internal forces.

Troubleshooting: After the decomposition, the main valve (2) was found to be seriously damaged (there were two deep scratches). It ca n’t be repaired, so replace the safety oil suction valve. After disassembling the boom cylinder, it is found that the bulge is bad and cannot be repaired. Therefore, the boom cylinder shell is replaced.

Malfunction 2

Symptom: The boom is clearly lowered.

Inspection result: The cone surface of the cone valve (5) has obvious scratches.

Failure analysis: Due to the obvious scratches on the pushing surface of the cone valve (5), the pressure oil at the bottom of the boom cylinder leaked back to the tank through the cone surface (5). 

Troubleshooting: Replace the boom safety valve and the machine returns to normal.

Section:

At this point, we can master the basic working principle of PC200-7, and at the same time, we can master the general fault diagnosis method. Below we give examples to explain more fault diagnosis. Please follow this method to diagnose.

1) If the main relief valve fails and the set pressure is low, the whole machine will be weak.

2) If the unloading valve is opened in advance, the whole machine will be weak.

3) If the pilot pressure output from the pressure reducing valve is low, it will cause the machine to work slowly.

4) If the PPC valve fails, it will generally cause a certain working speed to be slow.

5) If the safety suction valve and the setting pressure of the safety valve are low, the corresponding action will be weak.