ATOS proportional relief valve DHRZA-P5-012/25/M in stock

Brand

ATOS/Italian Atos

ATOS Solenoid Valves, ATOS Amplifiers, ATOS Solenoid Directional Valves, ATOS Pressure Reducing Valves, ATOS Safety Valves, ATOS Control Valves

ATOS proportional relief valves are hydraulic control valves that allow the output hydraulic fluid parameters (pressure) to change proportionally to changes in input electrical signal parameters (current or voltage).

These valves work in conjunction with electronic amplifiers. The amplifiers provide the appropriate drive current to the proportional valve to calibrate the valve's adjustment amount, making it correspond to the input signal supplied to the amplifier.

ATOS proportional relief valve pressure stabilization function: The relief valve is connected in series in the return oil line. The relief valve generates back pressure, increasing the smoothness of moving parts.

ATOS proportional relief valve system unloading function: A small-flow solenoid valve is connected in series with the remote control port of the relief valve. When the solenoid is energized, the remote control port of the relief valve is connected to the oil tank, at which point the hydraulic pump is unloaded. The relief valve is then used as an unloading valve.

Safety protection function: The valve is closed during normal system operation. It only opens to relieve pressure when the load exceeds the specified limit (system pressure exceeds the set pressure), providing overload protection and preventing further pressure increase (typically, the set pressure of the relief valve is 10%~20% higher than the system's maximum working pressure).

Practical applications generally include: unloading valves, remote pressure regulating valves, high/low pressure multi-stage control valves, sequence valves, and generating back pressure (connected in series in the return oil line).

ATOS proportional relief valves generally have two structures: 1. Direct-acting relief valve. 2. Pilot-operated relief valve.

Main requirements for ATOS proportional relief valves: wide pressure adjustment range, small pressure adjustment deviation, small pressure fluctuation, sensitive operation, large overload capacity, and low noise.

Precautions for ATOS proportional relief valves:

Noise and vibration

Components in hydraulic systems that easily generate noise are generally considered to be pumps and valves, with relief valves and solenoid directional valves being the main contributors. Many factors contribute to noise generation. There are two types of noise from relief valves: flow velocity noise and mechanical noise. Flow velocity noise is mainly caused by oil vibration, cavitation, and hydraulic shock. Mechanical noise is mainly caused by the impact and friction of parts within the valve.

(1) Noise caused by uneven pressure

The pilot valve section of a pilot-operated relief valve is a vibration-prone part, as shown in Figure 3. During high-pressure relief, the axial opening of the pilot valve is very small, only 0.003~0.006 cm. The flow area is very small, and the flow velocity is very high, reaching 200 m/s, which easily causes uneven pressure distribution, resulting in an imbalance of radial force in the cone valve and vibration. In addition, the ellipticity generated during the machining of the cone valve and cone valve seat, dirt adhering to the pilot valve port, and deformation of the pressure regulating spring can also cause cone valve vibration. Therefore, the pilot valve is generally considered the source of noise. The presence of elastic elements (springs) and moving mass (cone valves) creates conditions for oscillation. The pilot valve's front chamber also acts as a resonant cavity. Therefore, vibration of the cone valve easily causes resonance throughout the valve, generating noise. This noise is usually accompanied by severe pressure fluctuations.

(2) Noise from cavitation

When air is drawn into the oil for various reasons, or when the oil pressure is lower than atmospheric pressure, some of the dissolved air in the oil will precipitate, forming bubbles. These bubbles are larger in low-pressure areas, but when they flow with the oil to high-pressure areas, they are compressed, causing their volume to suddenly decrease or the bubbles to disappear. Conversely, if the volume is initially smaller in high-pressure areas, it suddenly increases when flowing to low-pressure areas. This rapid change in bubble volume generates noise, and because this process occurs instantaneously, it causes localized hydraulic shocks, resulting in vibration. The pilot valve port and main valve port of a pilot-operated relief valve experience significant changes in oil flow rate and pressure, making them prone to cavitation, which in turn generates noise and vibration. (3) Noise from Hydraulic Shock

When a pilot-operated relief valve is unloaded, pressure shock noise occurs due to the rapid drop in pressure in the hydraulic circuit. The higher the pressure and capacity of the operating conditions, the greater this shock noise. This is because the unloading time of the relief valve is very short, resulting in hydraulic shock. During unloading, the rapid change in oil flow velocity causes a sudden pressure change, creating a pressure wave impact. The pressure wave is a small shock wave, producing very little noise itself. However, as it travels through the system with the oil, if it resonates with any mechanical part, it can amplify vibration and increase noise. Therefore, hydraulic shock noise is usually accompanied by system vibration.

(4) Mechanical Noise

The mechanical noise emitted by a pilot-operated relief valve generally comes from the impact of parts and friction caused by machining errors.

Sometimes, the noise emitted by a pilot-operated relief valve includes high-frequency mechanical vibration, generally referred to as self-excited vibration. This is the sound produced by the high-frequency vibration of the main valve and pilot valve. Its occurrence rate is related to factors such as the configuration of the return oil pipeline, flow rate, pressure, and oil temperature (viscosity). Generally, smaller pipe diameters, lower flow rates, higher pressures, and lower oil viscosity lead to a higher rate of self-excited vibration.

ATOS proportional relief valve preventative measures:

Measures to reduce or eliminate noise and vibration in pilot-operated relief valves:

Generally, vibration damping elements are added to the pilot valve section.

The damping sleeve is typically fixed in the front chamber of the pilot valve, i.e., the resonant chamber, and cannot move freely.

Various damping holes are provided on the damping sleeve to increase damping and eliminate vibration. Additionally, because the resonant chamber contains additional components, its volume decreases, and the stiffness of the oil increases under negative pressure. Based on the principle that stiffer components are less prone to resonance, the possibility of resonance is reduced.

The damping pad generally moves freely within the resonant chamber. The damping pad has a throttling groove on both sides, which dampens the oil flow, altering the original flow pattern. The addition of the damping pad introduces a vibration element, disrupting the original resonant frequency. The resonant cavity incorporates a vibration damping pad, which reduces its volume and increases the stiffness of the oil under pressure, thus reducing the likelihood of resonance.

The vibration damping plug has an air accumulator orifice and a throttling edge. The air accumulator orifice contains air, which is compressed under pressure. This compressed air has a vibration-absorbing effect, acting as a miniature vibration absorber. When the air in the orifice is compressed, oil fills in; when it expands, oil is expelled, thus adding an additional flow and altering the original flow pattern. Therefore, it can also reduce or eliminate noise and vibration.

Additionally, improper assembly or use of the relief valve itself can also cause vibration and noise. For example, improper concentric alignment of the three sections in a three-section concentric relief valve during assembly, excessive or insufficient flow rate during use, or abnormal wear of the cone valve can all cause problems. In such cases, careful inspection and adjustment, or replacement of parts, are necessary.

**Pressure Regulation Failure**

ATOS proportional relief valves sometimes experience pressure regulation failure during use. There are two types of pressure regulation failure in pilot-operated relief valves: one is that the pressure regulating handwheel cannot build up pressure, or the pressure does not reach the rated value; the other is that the pressure does not decrease when the handwheel is adjusted, or even continues to increase. Besides radial jamming of the valve core due to various reasons, the following are some other reasons for pressure regulation failure:

First, the damper of the main valve body (2) is blocked, preventing oil pressure from being transmitted to the upper chamber of the main valve and the front chamber of the pilot valve, thus the pilot valve loses its function of regulating the pressure of the main valve. Because there is no oil pressure in the upper chamber of the main valve and the spring force is very small, the main valve becomes a direct-acting relief valve with very small spring force. When the inlet pressure is very low, the main valve opens to overflow, and the system cannot build up pressure.

The reason why the pressure does not reach the rated value is that the pressure regulating spring is deformed or incorrectly selected, the pressure regulating spring compression stroke is insufficient, the internal leakage of the valve is too large, or the cone valve of the pilot valve is excessively worn, etc.

Second, the damper (3) is blocked, preventing oil pressure from being transmitted to the cone valve, thus the pilot valve loses its function of regulating the pressure of the main valve. When the damper (orifice) is blocked, the cone valve will not open to release excess oil under any pressure. No oil flows within the valve, and the pressure in the upper and lower chambers of the main valve remains equal. Because the annular pressure-bearing area at the upper end of the main valve core is larger than that at the lower end, the main valve remains closed and will not overflow. The main valve pressure increases with the load. When the actuator stops working, the system pressure will rise indefinitely. Besides these reasons, it is also necessary to check whether the external control port is blocked and whether the cone valve is properly installed.

Other ATOS proportional relief valve malfunctions:

During assembly or use, damage to the O-ring or combination seal, or loose mounting screws or pipe fittings, can cause undue external leakage in the ATOS proportional relief valve.

If the cone valve or main valve core is excessively worn, or if there is poor contact at the sealing surface, excessive internal leakage will occur, potentially affecting normal operation.

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