The harm of hydraulic impact and the measures to reduce hydraulic impact

The harm of hydraulic impact

1.The huge the instantaneous pressure causes the hydraulic components, especially the hydraulic seals, to be destroyed.
2.The system produces strong vibration and noise, and the oil temperature rise.
3.The pressure control components (such as pressure relays, hydraulic sequence valves, etc.) to produce a false action, resulting in equipment failure and accidents.

Measures to reduce hydraulic impact

1.Extension of valve closing and moving parts reverse braking time
When the valve is closed and the reverse braking time of the moving part is more than 0.3s, the hydraulic impact is greatly reduced. Hydraulic directional valves with adjustable commutation time can be used to control hydraulic impact. Such as the use of damping solenoid operated relief valve can be adjusted by damping and slow down the speed of the main valve spool through controlling the pilot valve pressure and flow, hydraulic valve is similar.
2.Limiting the flow rate of the liquid in the pipe and the speed of the moving parts
Machine tool hydraulic system, often limit the liquid flow rate in the pipeline to 5.0m/s, the speed of moving parts is generally less than 10m/min.
3.Increase the pipe diameter or the use of rubber hose
It can reduce the propagation velocity of the pressure shock wave in the pipeline, at the same time, increase the inner diameter of the pipeline can also reduce the flow rate of the liquid.
4.Arranged accumulator near the hydraulic impact source
The pressure shock wave reciprocating time is shorter than the valve closing time, and reduce the hydraulic impact.

What is hydraulic

It is a term of hydraulic machinery industry, electromechanical industry .Hydraulic power can be used as a hydraulic transmission. Hydraulic pressure can also be used as a control method, called hydraulic control.

Hydraulic transmission use liquid as the working medium, use liquid pressure energy to transfer power.

Hydraulic control is the control signal transmission mode using pressure liquid. Hydraulic control usually includes hydraulic open loop control and hydraulic closed loop control. Hydraulic closed-loop control is also called hydraulic servo control, usually including the electric hydraulic servo system and mechanical hydraulic servo system etc..

A complete hydraulic system consists of five parts, namely an energy device, an executive device, a control adjustment device (hydraulic valve), an auxiliary device and liquid medium. The hydraulic pressure is widely used in industry and civil industry because of its large transmission power, easy to transfer and configuration. The executive component of hydraulic system (hydraulic cylinder and hydraulic motor) is to convert the pressure energy into mechanical energy. The energy source of hydraulic system (hydraulic pump) is to convert the mechanical energy of the prime mover to the pressure energy of the liquid.

BSTIND is professional in designing and manufacturing,sales of electric hydraulic control valve. Factory With more than 20000 square meters workshops.And there are about 300 workers and 50 among which are senior or intermediate technical engineers. BSTIND had passed ISO9001:2008 and CE certificates.Annual production is selling about 0.6 millions hydraulic valves.

what-is-cavitation/

In the hydraulic system, the air in the oil will be separated and a large number of bubbles will be formed if the pressure is lower than the air pressure at the working temperature of the oil; when the pressure is further reduced to the saturated vapor pressure at the working temperature of the oil, the oil will rapidly vaporize and produce a large number of bubbles. These bubbles are mixed in the oil, resulting in cavitation, so that the oil filled in pipes or hydraulic components turn into a discontinuous state, this phenomenon is generally known as the cavitation phenomenon.

Cavitation occurs at the inlet and outlet of the hydraulic pump. When the oil flows through the narrow channel of the manual hydraulic valve port, the liquid flow rate increases, the pressure drops sharply, and the cavitation phenomenon appears. Hydraulic pump installation height is too high, oil suction pipe diameter is too small, oil absorption resistance is too large, or hydraulic pump speed is too high, inadequate oil absorption, etc., are likely to cause cavitation.

Cavitation occurs in hydraulic system, the bubble with the oil flow to the high pressure area, under high pressure air bubbles will quickly break down, the liquid around to fill this hole at high speed, the liquid in the high-speed collision and form local hydraulic impact, the local temperature and pressure increased sharply, caused a strong vibration and noise.

Pipe wall and element surface near bubble condensation, due to the long-term impact of hydraulic shock and high temperature, as well as the strong corrosion of the gas in the oil, so that the metal element and particles of the wall surface are spalling, the corrosion on the surface of the cavitation phenomenon called gas etching.

In order to prevent cavitation and gas etching, the following measures can be taken:
1.Reduce the flow of small holes and gaps in the pressure drop, the general hope that the pressure ratio before and after the gap is p1/p2<3.5.
2.To correctly determine the diameter of hydraulic pump suction pipe in the pipe, limit the flow of liquid, reduce the suction height of hydraulic pump, reduce the pressure loss in the pipe joint oil pipeline, a good seal, the auxiliary pump for high-pressure cartridge hand pump.
3.The entire pipeline system should be as straight as possible, avoid sharp bends and local narrow.
4.Improve gas etching resistance of components.

The causes of hydraulic impact

1.Hydraulic shock caused by sudden closing of valve
When the hydraulic valve is opened, the liquid flow in the pipe. When the valve is suddenly closed, start the rapid conversion of the kinetic energy of liquid into pressure energy from the valve, resulting in a high pressure shock wave from the valve to the chamber; since then, the cavity began to convert the pressure of liquid into kinetic energy, liquid reverse flow; then, the liquid kinetic energy is transformed into pressure energy and a high pressure shock wave is formed, so the energy conversion is repeated, and the pressure oscillation is formed in the pipeline. Because of the influence of the internal friction and the elastic deformation of the pipe, the oscillation process will gradually decline and become stable.

2.Hydraulic impact caused by sudden braking or reversing of moving parts
The hydraulics directional control valve closes the oil return passage of the hydraulic cylinder and the moving part is braked, the kinetic energy of the moving part in the moment can be transformed into the pressure energy to closed the oil, and the pressure is increased rapidly, forming the hydraulic impact.

3.Hydraulic shock caused by malfunction or insensitivity of some hydraulic components
When the hydraulic system relief valve in the system to do the use of safety valve, if the system overload while the safety valve can not be opened in time or simply can not open, it will lead to a sharp increase of the pressure of the pipeline system, lead to hydraulic impact.

The principle of the hydraulic system

It consists of two cylinders （click here to learn more about BSTIND hydraulic cylinder check valve） of different sizes, filled with water or oil in the liquid cylinder. Filled with water called “water press”; oil filled with the “oil press”. Each cylinders with a sliding piston, if add a certain value pressure on the small piston , according to Pascal’s law, the small piston pass the pressure through the liquid to the large piston, lift the large piston up. Set the cross-sectional area of the small piston is S1, the downward pressure on the small piston is F1. Thus, the small piston pressure on the liquid is P=F1/SI, the size of the liquid can be transferred to all directions. The pressure on the piston is also equal to P. If the cross-sectional area of the large piston is S2, the pressure P on the piston is generated by the upward pressure F2=PxS2, cross-sectional area is multiples small piston cross-sectional area. From the type known to add in a small piston of a smaller force, the piston will be in great force for which the hydraulic machine used to suppress plywood oil extract heavy objects such as forging steel.

The principle of hydraulic pressure in a certain mechanical and electronic systems, relying on the hydrostatic pressure of the liquid medium, the completion of the backlog of energy, transmission, amplification, to achieve the lightweight, scientific, maximize of the mechanical function.

By using hydraulic principle, the hydraulic transmission system can be constructed.

BSTIND is professional in designing and manufacturing,sales of Hydraulic System Valve. Factory With more than 20000 square meters workshops.And there are about 300 workers and 50 among which are senior or intermediate technical engineers. BSTIND had passed ISO9001:2008 and CE certificates.Annual production is selling about 0.6 millions hydraulic valves.

The components of hydraulic system

A complete hydraulic system consists of five parts, which are power components, executive components, control components, auxiliary components and working media.

The function of a power element is to convert the mechanical energy of the machine to the pressure energy of the liquid. A power element is a hydraulic pump in a hydraulic system that supplies power to the entire hydraulic system. The structure of the hydraulic pump generally divide into gear pump, vane pump, piston pump, screw pump.

The function of the executive element is to convert the pressure energy of the liquid into the mechanical energy, and to drive the load for a linear reciprocating or rotary motion. Executive element has a hydraulic cylinder and a hydraulic motor.

Control components (which is a variety of hydraulic valves) in the hydraulic system to control and regulate the pressure, flow and direction of the liquid. According to the different control functions, hydraulic valves can be divided into hydraulic pressure control valves, hydraulic flow control valves and hydraulic directional control valves. Pressure control valve is divided into relief valve, pressure relief valve, sequence valve, etc.; flow control valves including throttle valve, regulating valve, diversion valve; directional control valve includes one-way valve, shuttle valve, reversing valve, etc.. According to different control methods, hydraulic valves can be divided into switch control valve, fixed value control valve and proportional control valve.

Auxiliary components including accumulators, filters, cooler, heater, tubing, pipe fittings, oil tank, pressure gauge, flow meter, sealing device, effect of their connection, oil filter and oil pressure measurement.

Working medium refers to various types of hydraulic transmission of hydraulic oil or emulsion, there are a variety of mineral oil, emulsion and synthetic hydraulic oil. The hydraulic system is to realize the movement and power transmission.

Reasons for the leakage of the hydraulic solenoid operated directional valves

Adjustable hydraulic pressure relief valves more or less have the problem of internal leakage, this is related to the structure and working principle of the solenoid operated directional valves, a certain range of internal leakage is normal, can not be completely avoided. The working principle of the pressure operated relief valve is that electromagnetic power push rod to make the relative movement of the spool after the electric drive, so as to open or close the corresponding oil hole. In order to ensure the smooth movement of the valve core in the valve body, need to maintain a certain gap between the two, otherwise the adjustable hydraulic pressure relief valve and the valve body will keep in close contact and  not be able to move under the influence of friction.

The gap size of the adjustable hydraulic pressure relief valve body and the valve core is known as the matching precision. It need to be strictly controlled in order to ensure the stability of the 50 psi pressure relief valve. The internal leakage of the hydraulic system directly affects the working efficiency of the hydraulic system, and can easily lead to malfunction of the system.

But need to point out that the matching precision of the pressure operated relief valve is not simply the pursuit of precision, but should select the most appropriate solution based on the requirements of the work conditions and cost.As we all know, the hydraulic system in the hydraulic oil is very easy to mix with small impurities and it is difficult to completely eliminate. It is usually used to filter the impurities in the fuel tank with a single filter. This method is relatively simple, but the accuracy of the low cost filter is limited, can not effectively filter small impurities. If the matching precision of the hydraulic solenoid valve above the filter precision, valve core is easy to be blocked by the impurities not filtered , resulting in the solenoid valve failure. For high precision solenoid operated directional valve, it is generally recommended to adopt high precision filtration equipment, such as cotton core, which will increase the cost of the whole system. Therefore, the requirements for the electromagnetic solenoid operated directional valves leakage should be based on the actual work situation.

Some low price 50 psi pressure relief valves can increase the internal leakage after a certain period of time, may be due to the valve body using of low hardness material, the gradual wear and tear in the work lead to poor accuracy.

If pressure operated relief valves connection surface oil leakage, generally should check the installation of adjustable hydraulic pressure relief valve and the bottom plate is flat or not, the torque and the material of connecting bolts should be consistent. The problem that is often overlooked is that the hardness of the O type ring is mounted. The lower hardness of the sealing ring should not be used for the sealing of the high-pressure system, can be replaced if necessary.