Issues regarding the air supply for pneumatic control valves
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The positioners of our company’s pneumatic control valves keep having problems, and the root cause is always the oil and water issues in the air supply. We have used many different brands, from Aka, Yamatake, Siemens, Wuzhong, to Shanghai ValveTech, ranging from mechanical to intelligent types. The one that can best withstand our tests is the Yamawa locator. But it also has a relatively high failure rate, especially in winter. Many air circuits and positioners have frozen over—there’s too much oil and water. . . It has caused a lot of trouble for our maintenance work. Our air compressors have oil and water separators, but it still doesn’t work. . . 1. I would like to ask how your company handles this issue. Which air compressors there are the best at dealing with oil and water? What equipment is needed to remove the oil and water from them? 2. Because it’s impossible for our company to replace the compressor. But add some adsorption equipment to the pipeline for further treatment. Do you have any good equipment recommendations? 3. Are there any good pressure relief valves with filtering functions? Could you provide me with the exact model numbers? Thank you all. . .
It seems to be due to improper maintenance of the air compressor! Generally, only filters are used for water removal; if higher standards are required, a cold dryer can be added for this purpose. To lubricate pneumatic components, oil misters are usually installed in the pneumatic pipelines to mix lubricating oil into the gas; could there be an issue with the choice of lubricating oil?
Place a filter pressure regulator in front of the valve’s air supply; there are many options available to search for online. There are also problems with the air compressor; it contains too much water, which should be drained regularly.
After the compressed air is produced, there should be a separate dryer, and this dryer is controlled by a PLC to carry out drying and dehumidification functions, with regular switching between modes of operation. It seems that the drying equipment in your factory needs better maintenance ； Furthermore, low-point drains should be installed at the locations of the instrument air pipelines; especially in winter, they need to be drained regularly to reduce the amount of condensate in the pipelines.
Pneumatic control valves don’t get damaged very often due to trace amounts of oil and water in the instrument air. Under what operating conditions do you use them? If trace amounts of oil and water still have an impact, it is advisable to consider installing a sophisticated oil and water removal system; for example, containers filled with substances with adsorption capabilities such as activated carbon or molecular sieves can be used to remove these trace amounts of oil and water. It is best to consult a design firm for specific design solutions!
It’s likely that the air compressor isn’t maintained properly; it’s not clear what size the compressor is or whether there is someone dedicated to taking care of it. Oil and water should be drained regularly to address the issue at its source. It is necessary to add a filter in front of the instrument, but it is only auxiliary. Our company’s instruments are only located within the neighborhood, while the main pipelines are under the responsibility of the power workshop.
Most of the positioners in our company were damaged due to oil and water issues. Initially, electric control valves were used, but after 2003, new projects and renovations all switched to pneumatic control valves. The air compressors are not under our control; the air that comes in at first comes from a compressor used in the production process, so sometimes acid gas can flow back from that area as well. These really bother us. Multiple proposals were made to have a separate unit, but the managers disagreed; therefore, I thought of adding something to the pipeline to provide protection. Don’t you company also experience failures due to oil in the gas supply? So what brand of locator are you using?
We have also encountered the situation mentioned by the original poster. Another solution is to install an intermediate storage tank for instrument air at the compressor outlet; it is possible to carry out purification, filtering, and drying before the air enters this tank, as the requirements for instrument air are higher than those for compressed air.
The simplest solution: install a air tank at the outlet of the air compressor, equipped with a drain valve, to regularly remove oil and water. It can also stabilize pressure, and it will be somewhat effective.
After coming out of the air compressor station, compressed air passes through a separate dryer; when instrument air is supplied to each workshop, there is an air filtration tank in place. Drainage of oil and water takes place regularly at the low points, and in winter, extra measures are taken to insulate and protect the instrument pipelines from freezing.
Add an intermediate tank; it’s cost-effective and the effect is quite noticeable
Our factory’s solution: compressor – refrigerated dryer – desiccator, which results in a dew point of around -60 degrees for the gas supply.
I agree with the view from floor 11; adding an intermediate channel would be useful, and devices for regular drainage, oil removal, filtration, and drying can also be installed. It would be best to find out the real cause; it’s likely that there is a problem with the compressor or the drying unit.
If there are no proper drying and filtering devices, they must be installed (to ensure that the instrument air is free of dust and oil, with a dew point of -40). If such devices are already in place, it’s possible that the desiccant has lost its effectiveness; in that case, it needs to be replaced. Condensate should be drained regularly from the low points. A high-quality pressure reducing valve from SMC should be installed before the positioner. The most important thing is to identify the cause before taking action to resolve it
We have added a micro-thermal adsorption unit to our compressed air outlet.
Generally, a drying device needs to be installed in front of an air compressor. By the way, what model of air compressor is the original poster using?
Was filtering and drying not carried out or not done properly? Check the operation of the dryer
Gas for instruments should be strictly separated from gas for process operations, and they must not be used together. Instrument air should be very clean. In the past, our company did not separate the two types of air used, and due to improper operation by the operators (pressure imbalances), air from the instrument air supply entered the system, thereby damaging the valve positioners. The instruments used in our company are operated with high-purity nitrogen, which is purchased externally and does not require oil or water removal.
1. Air compressors use screw or centrifugal types; reciprocating types are not suitable. It would be best if screw compressors could operate without oil, but they are more expensive, so it’s not necessary. 2. Separate purified air from unpurified air. 3. Use heat-free or slightly heated regeneration to remove oil and water from the purified air. The cold dryer is not effective enough. Install a dew point meter on the main purification air duct to measure the moisture content and assess the effectiveness of the treatment. Note: The required dew point is the pressure dew point. 4. Each unit is equipped with a purified air buffer tank, and the bottom drain valve is left slightly open to drain water and oil under normal conditions. It works very well. 5. Regularly check whether there is water accumulated in the air filter pressure regulator of each table. The key is the first three points
To identify the root cause, poor quality of compressed air containing water is the issue; generally, air stabilization tanks are available in such systems, and regular drainage of air and water should have a positive effect.
Screw press -- oil-water separator -- precision filters (2 units) -- refrigerated dryer -- precision filters; it has been in use for four or five years without any problems.