Pneumatic solenoid valve is always faulty, how to deal with it correctly?

Update:05 Nov 2020

Speaking of solenoid valves, they are very common in industrial applications, especially in the petroleum and chemical industries. Many process pipelines must be equipped with on-off valves. Because the work site is very dangerous, safety requirements are more stringent than other industries. Large chemical industries Enterprises have specialized instrument workers, and small electricians are basically responsible for daily management and maintenance.

What I'm talking about here is the pneumatic solenoid valves commonly used in this industry. Some are mounted on the cylinder, and some are mounted on a bracket beside the cylinder. Pneumatic solenoid valves can be widely used in these high-risk industries. They have the advantages of fireproof, explosion-proof, good safety, and no pollution, which are not available in other transmission components. The basic composition is divided into electromagnetic parts and valve body electromagnetic parts; fixed iron core, moving iron core, coil. Valve body; slide valve core, slide valve sleeve, spring base.

Basic overview of two-position three-way solenoid valve, two-position four-way solenoid valve, and two-position five-way solenoid valve. The working process of the two-position three-way solenoid valve; the coil is energized, the coil excitation electromagnet is attracted, and the sealing block of the charged spring on the moving iron core closes the exhaust port by the spring pressure, and the compressed air enters the valve cylinder from the intake port to act Control effect. When power is lost, the electromagnetic force disappears, and the moving iron core moves down from the fixed iron core under the force of the spring, opening the exhaust port, closing the air intake port, and the valve cylinder changes its state due to loss of air. The working principle of the two-position four-way solenoid valve and the two-position five-way solenoid valve is the same as that described above, except that the number of exhaust ports is different. The two digits mentioned here mean; for the solenoid valve itself, it is energized and de-energized, and for the controlled valve, it is on and off. The meaning of several passes; refers to the number of air holes of the solenoid valve, which is clear at a glance when you get the actual product.

The power supply of solenoid valve has 220V power supply and 24V power supply. 24V power supply is mostly used in high-risk industries. In general, each has its own advantages. The use of 220V power supply is not conducive to on-site explosion protection, but is conducive to long-distance transmission. The reason is that the power supply voltage is high, and the voltage drop caused by the transmission cable will not affect the normal operation of the solenoid valve. The use of 24V power supply is conducive to explosion-proof on site, but the transmission distance is relatively long, and the impact of the voltage drop of the transmission cable on the operation of the solenoid valve must be considered. Therefore, it is necessary to calculate the maximum allowable length of the transmission cable according to the minimum operating voltage of the solenoid valve.

For example, a 24V power supply is used, the minimum operating voltage of the solenoid valve is 20V, the maximum allowable voltage drop of the line is 4V, and the rated power is 12W. The PVC insulated sheathed control cable is adopted with a wire diameter of 2.5mm2 and a two-wire system. Calculate the solenoid valve operating current I=0.5A. The calculation of the maximum length L of the allowable control cable can be obtained by looking up the table. It is found that the maximum DC resistance of the control cable is 7.1Ω/Km, and because the resistance R=8Ω, the voltage drop generated by the line, the maximum allowable control The cable length is 1.079Km. And because it is a two-wire control cable, the length of each control cable is 539m. Through theoretical calculations, it is known that when the solenoid valve is not lower than the normal operating voltage of 20V, the maximum transmission distance can reach 539m using a 2.5mm2 wire.

Common faults in solenoid valve application process

The solenoid valve terminal is loose and falls off, the coil is burned out, and the solenoid valve is stuck. The wiring of the solenoid valve is loose and falling off. This is tightened again. For the coil burned out, check whether the light-emitting diode of the coil head is on or off or if a metal object is inserted into the coil hole to see if it is pulled in. The solenoid valve coil is damaged and replaced. For the problem of solenoid valve jamming, remove the slide valve core, slide valve sleeve, and spring base, clean it, and apply grease after cleaning. The reason is that the exhaust port is not equipped with a silencer, impurities in the air enter the valve, or the compressed air is not clean enough and contains impurities, water, oil and other dirt.

When solving, the solenoid valve exhaust port is not equipped with a silencer for installation, and the air filter pressure reducing valve should be installed in the front section of the solenoid valve intake. The advantages of the air filter pressure reducing valve can filter out impurities, absorb the compressed air containing water, oil, etc., so as to purify the compressed air and avoid unnecessary damage to the solenoid valve body and cylinder.

The air filter pressure reducing valve can also adjust the pressure in addition to the above. The compressed air used in a general factory is 10 kg, which is 1 MPa. If the air filter pressure reducing valve is not installed to adjust the pressure, the damage to the cylinder is large, and it is not conducive to the control of the switching speed. Normally, the valve's working air source pressure is about 0.4MPa to meet the valve's switching requirements. Therefore, the compressed air from the air compressor station must be depressurized and adjusted to the air pressure suitable for the valve action to better protect the valve. And control of switching speed.