Causes of fluctuations in the output flow rate of ATOS piston pumps

Brand

ATOS/Italian Atos

Application Areas

Food/Agricultural Products, Chemicals, Agriculture, Forestry, Animal Husbandry and Fishery, Petroleum, Comprehensive

ATOS Piston Pump Working Principle

The Italian ATOS piston pump is an important device in hydraulic systems. It relies on the reciprocating motion of the piston within the cylinder to change the volume of the sealed working chamber, thus achieving oil suction and pressure. Piston pumps have advantages such as high rated pressure, compact structure, high efficiency, and convenient flow adjustment, and are widely used in high-pressure, high-flow, and flow-adjustable applications, such as hydraulic presses, construction machinery, and ships.

The Italian ATOS piston pump is a type of reciprocating pump, belonging to the category of volumetric pumps. Its piston is driven by the eccentric rotation of the pump shaft, reciprocating in motion. Both its suction and discharge valves are one-way valves. When the piston is pulled outward, the pressure in the working chamber decreases, the outlet valve closes, and when the pressure is lower than the inlet pressure, the inlet valve opens, allowing liquid to enter. When the piston is pushed inward, the pressure in the working chamber increases, the inlet valve closes, and when the pressure is higher than the outlet pressure, the outlet valve opens, allowing liquid to exit. When the drive shaft rotates the cylinder block, the swashplate pulls the plunger out or pushes it back into the cylinder block, completing the oil suction and discharge process. The oil in the working cavity formed by the plunger and cylinder bore communicates with the pump's suction and discharge chambers via a distribution plate. The variable displacement mechanism changes the swashplate's angle, thus altering the pump's displacement.

The plunger and plunger sleeve are a precision pair, mated and ground together but not interchangeable. They require high precision, a smooth surface, and good wear resistance, with a radial clearance of 0.002–0.003 mm.

The plunger head has a groove cut into its cylindrical surface, communicating with the top through radial and axial holes. This changes the circulating oil supply. The plunger sleeve has inlet and outlet oil holes, both communicating with the low-pressure oil chamber inside the pump body. After the plunger sleeve is installed in the pump body, it is secured with a locating screw.

Different positions of the groove on the plunger head result in different methods of changing the oil supply.

The delivery valve and delivery valve seat are also a precision pair; they are not interchangeable after mating and grinding, with a clearance of 0.01mm.

The delivery valve is a one-way valve. Under spring pressure, the upper conical surface of the valve fits tightly with the valve seat. Its function is to isolate the high-pressure fuel line from the upper cavity of the plunger when fuel supply stops, preventing fuel from flowing back into the injection pump.

The lower part of the delivery valve has a cross-section, which serves both as a guide and allows diesel fuel to pass through. Below the conical surface of the delivery valve is a small cylindrical surface called a pressure-reducing ring. Its function is to rapidly reduce the fuel pressure in the high-pressure fuel line at the end of fuel supply, preventing dripping at the nozzle. When the ring falls into the valve seat, the upper volume rapidly increases, the pressure rapidly decreases, and injection stops quickly.

ATOS Plunger Pump Maintenance Type:

ATOS swashplate axial plunger pumps generally use a rotating cylinder block and end-face distribution design. A friction pair consisting of a bimetallic plate and a steel distributor plate is inlaid on the end face of the cylinder block, and most of them adopt a planar flow distribution method, so maintenance is relatively convenient. The distributor plate is one of the key components of the axial piston pump. When the pump is working, on the one hand, the high-pressure oil in the working chamber pushes the cylinder block towards the distributor plate, and on the other hand, the oil film pressure between the distributor plate and the cylinder block forms a hydraulic counter-thrust force on the cylinder block, causing the cylinder block to move away from the distributor plate. The hydraulic clamping force Fn of the cylinder block on the distributor plate is designed to be slightly greater than the hydraulic counter-thrust force Ff of the distributor plate on the cylinder block, that is, Fn/Ff=1.05~1.1, so that the pump works normally and maintains a high volumetric efficiency.

Troubleshooting for Italian ATOS piston pumps:

ATOS piston pump flow problems are as follows:

(1) Insufficient suction. The reason is that the resistance in the suction line is too high or the replenishment is insufficient. For example, the pump speed is too high, the liquid level in the tank is too low, the inlet pipe is leaking air, the oil filter is blocked, etc.

(2) Excessive leakage. The cause is excessive clearance in the pump, resulting in poor sealing. For example, the distributor plate may be scratched by metal fragments or iron filings, causing oil leakage at the end face; the sealing surface of the check valve in the variable mechanism may not fit properly; and there may be sand holes or scratches on the support surfaces of the pump body and the distributor plate. The damaged part of the pump can be identified by checking for foreign matter mixed in the hydraulic oil inside the pump body.

(3) If the swashplate angle is too small, the pump's displacement will be low. This requires adjusting the variable piston to increase the swashplate angle.

Discharge is not zero in the neutral position

When the swashplate angle of the variable axial piston pump is zero, it is called the neutral position, at which point the pump's output flow should be zero. However, sometimes the neutral position deviates from the midpoint of the adjustment mechanism, and there is still flow output at the midpoint. This is because the controller is misaligned, loose, or damaged, requiring readjustment, tightening, or replacement. Insufficient pump angle holding force and wear of the swashplate trunnion can also cause this phenomenon.

Output flow fluctuation

Output flow fluctuation is related to many factors. For variable displacement pumps, poor control of the variable displacement mechanism can be the cause. For example, foreign objects entering the variable displacement mechanism can scratch, wear, or damage the control piston, causing unstable movement of the control piston. Insufficient amplifier energy or damaged parts, or poor damping efficiency of the control piston containing a spring, can also cause unstable movement of the control piston. Unstable flow is often accompanied by pressure fluctuations. This type of fault generally requires disassembling the hydraulic pump, replacing damaged parts, increasing damping, improving spring stiffness, and increasing control pressure.

Abnormal Output Pressure

The pump's output pressure is determined by the load and is approximately proportional to the input torque. There are two types of abnormal output pressure faults.

(1) Output Pressure Too Low

When the pump is in self-priming mode, if there is air leakage in the inlet pipe or significant leakage in the hydraulic cylinder, check valve, or directional valve in the system, the pressure will not rise. This requires finding the leak, tightening, or replacing the seals to increase the pressure. If the relief valve is faulty or the adjusted pressure is too low, the system pressure will also not rise. The pressure should be readjusted or the relief valve should be repaired. If the hydraulic pump cylinder body and distributor plate deviate, causing significant leakage, the cylinder body may crack in severe cases. In such cases, the mating surfaces should be re-ground or the hydraulic pump should be replaced.

(2) Excessive Output Pressure

If the circuit load continues to increase, the pump pressure will also continue to increase, which is normal. If the load is constant and the pump pressure exceeds the required pressure value, hydraulic components other than the pump should be checked, such as directional valves, pressure valves, transmission devices, and return oil pipes. If the maximum pressure is too high, the relief valve should be adjusted.

Vibration and Noise

Vibration and noise occur simultaneously. They not only harm the machine operator but also pollute the environment.

(1) Mechanical Vibration and Noise

Noise will be generated if the pump shaft and motor shaft are not concentric or jammed, or if the bearings and couplings of the rotating shaft are damaged, the elastic pads are broken, or the mounting bolts are loose. For pumps that operate at high speeds or transmit large amounts of energy, regular inspections should be conducted, and the amplitude, frequency, and noise of each component should be recorded. If the pump's rotation frequency is the same as the natural frequency of the pressure valve, resonance will occur. The pump speed can be changed to eliminate resonance. (2) Noise Generated by Fluid Flow in Pipelines

Noise can be generated by various factors, including an excessively narrow inlet pipe, an inlet filter with insufficient flow capacity or blockage, air intake in the inlet pipe, excessively high oil level, insufficient oil suction due to low oil level, and liquid slugging in high-pressure pipelines. Therefore, proper design of the oil tank and correct selection of filters, oil pipes, and directional valves are essential.

Hydraulic Pump Overheating

There are two main reasons for excessive heating of hydraulic pumps: First, mechanical friction generates heat. Due to dry or semi-dry friction on moving surfaces, heat is generated through friction between moving parts. Second, fluid friction generates heat. High-pressure oil leaks into the low-pressure chamber through various gaps, resulting in a significant loss of hydraulic energy converted into heat. Therefore, proper selection of the clearance between moving parts, oil tank volume, and cooler can prevent excessive pump heating and high oil temperature. Additionally, a clogged return oil filter causing excessive return oil back pressure can also lead to high oil temperature and pump overheating. Oil Leakage

Oil leakage in plunger pumps is mainly caused by the following reasons:

(1) Damaged spindle oil seal or defects/scratches on the shaft;

(2) Excessive internal leakage, causing increased pressure at the oil seal, which damages or blows out the seal;

(3) The drain pipe is too thin or too long, causing oil leakage at the seal;

(4) Loose external oil pipes, damaged pipe joints, aged or cracked gaskets;

(5) Loose bolts in the variable adjustment mechanism, resulting in seal damage;

(6) Sand holes or poor welding in the cast iron pump casing. PVPC-LW-4046/1D 10

PVPC-LZQZ-3029/1D

PVPC-LZQZ-3029/1D/18

PVPC-LZQZ-4046/1D

PVPC-LZQZ-4046/1D/18

PVPC-LZQZ-5073/1D 11

PVPC-LZQZ-5073/1D/18

PVPC-R-3029/1D 11

PVPC-R-4046/1D 11

PVPC-SLE-3029/10 20

PVPC-SLE-4046/1D 20

PVPCX2E-C-3029/31036/1D 10 PVPCX2E-LW-3029/31036/1D 10

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