Sizing an Air Receiving Tank

Increasing the size of the receiving air tank does help a litter bit in the filter bag cleaning problem but your jet valve and the air pipe need to be change to slightly bigger diameter from 1" to 1 ½" otherwise the air pipe will restrict the air flow to the filters bag.

On other angle of solving this problem is to ensure that the suction dust is really dry and not wet otherwise, it will clog the filter bag and with wet or damp dust, it will stick to the filters bag. These dusts are very difficult to be removed out by the jet pulse system.

How is the life time of your filters bags?. Filters bags need to be replace after few years on operation.

Perhaps you can increase the frequently of the purging time and see the result before any modification is done on it.

the air lines and valve are previously mount was 1/2". then i change it to 1" valves. these valves also fix to the same receiving tank.

filters are old at about 6 yeras!!.. i will change them.

should i need to change the receiving tank size also?

<...should i need to change the receiving tank size also...>

Change the filters first, and see how it goes.

Since you have change the air lines and valve from previously 1/2" to 1" valves, like what Mr.PW Slack said, change these filters first and test it out before decide on the receiving tank size.

It would be the filters problem that, it had accumulate to many small particle that stuck inside the filters and the jet air not able to purge it out. During you change these bag filters, please check the opening and closing of the filters bag compartment diagram valve. There is two valve that should be close during the jet pulse cycle.

If these valve is not properly close then you will loss the jet air flow in to your filters bag and the filters bag will not able to be cleaned.

These systems work by a sharp pulse of air dislodging the dust from the bag followed by sufficient air to blow the loosened dust clear. To do this the valves must open and close smartly and a good volume of air must be sent to clean the bag.

No good loosening the dust if you have insufficient air to blow it clear.

Good advice from others is to clean the filters on your air system, then test.

Next step would be to increase the size of jets feeding cleaning air into the bags, then test.

If that doesn't work, come back and some one will be sure to devise a solution for you.

Good luck

thank you!

first i will replace the filters and check the system

Hi

It may be cost effective to remove the bags and have these manually cleaned with compressed air and brush throughly. If there is thick crust / cake of dust deposit, then it will be indicative of moisture. It is apparent that the system had worked satisfactorily for over 6 years with the old air receiver and its associated pulse jet cleaning mechanism. Since the time lag between two jet pulses will be more than 3 seconds, it does not necessitate resizing of air receiver now. Please make a note of pressure drop across the filter bags before & after cleaning and kindly post your observations for further analysis and possible help & solution.

Joshi

I agree with Simon_Wan with respect to changing the filters. In my experience with reverse flow systems, filter performance drops off significantly over time as small particulate becomes embedded into the fibers. You will never pulse the filter back to 100% clean, so as time goes by the pulsing becomes less and less effective. 6 Years seems like a long time for a these filters to be in service.

If this fails then check the blow pipes supplying the reverse jet to the filters. If the pipes are too far away, too close, or blocked then you wont distribute the air to the filter no matter how much air you use. This is often overlooked and changing from a 1/2" pipe to a 1" may of altered the performance. There is no hard and fast rule for the design (and many patents) so I would advise you experiment a little.

If you are still having problems then I would suggest you look at the pulse pressure. Cleaning works on impulse, so increasing the pressure would increase the energy of the impulse. I know of reverse flow applications where pulse pressure is up to 7 Bar, however you do need to have the right filter for this application otherwise you run the risk of damaging the fibres in the filter and reducing the efficiency. As a side bar - what type of filters are you using, Cartridge type or Bags or other?

Increasing the volume of the reciever will not increase the peak impulse, however it will ensure the pulse is "square" and does not tail off. You have not stated how many valves you are pulsing at once, is it possible (or do you currently) pulse each valve individually? Reducing the number you pulse at any given time would achive similar results to increasing the size of the reciever and would increase the time taken to cycle all 4 valves.

Is Pulsing initiated by a timer or pressure loss? If you're using a timer then increasing the frequency of pulsing may help also. You may also want to investigate how long each valve is open for, opening the valve for longer may help you to move the disloged dust further away from the filter and reduce the chance of it being sucked right back on.

All of the above changes and checks assume your current setup is working as designed and is simply not sufficient. I would advise before you make any more changes you check each component works as intended, such as valves, reciever pressures, compressed air pumps and filters.

Good luck and let me know how it goes. I'm a long time listener, first time caller so don't let my registration date to CR4 put you off.

Frank

thank you for ur kind advise. this contain 12 filter bags. each valve clean 3 filter bags. also only one valve is operate at a time.

this system not properly work all these 6 years because the pressure was given below 4 bars, also too much moisture in the pressurized air. first i done was increase the pressure up to 5bars and placed a FRL (only for drain water). somebody changed the air pipes 1" to 1/2" and installed 1/2" steam solenoid valves... so i changed them to 1" pipe size and install 1" diaphragm valve. i ordered new filter bags but it not received yet.

after several days i got the complain about this pressure drop.. that is why i mentioned to change the air receiver. i could get the pressure difference because i have not the instruments and the system also doesn't have a magnehelic gauge.

i appreciate your help on this matter!

There are many reasons your filters may not be cleaning properly, only one of which is the receiver size. Questions to be answered:

1) How long have you had problems? (You state 6 years, since system was put in. Has problem gotten worse over this time?)

2) What is your dust and what is the application (mixer, dryer, pneumatic transfer)?

4) What is your filter length?

5) What size is the pipe over each filter row and pulse hole size in that pipe? Each diaphragm valve produces a given air flow (based on line pressure, Cv of valve, size/length of pipe over the filters, hole size in pipe over the filters, etc.).

6) What are the pulse cleaning settings ("on-time" and "off-time") between each row cleaning? Can these be adjusted?

7) What are your filter sizes and the spacing between the filters? Often the problem is not with the cleaning system itself but with what is called "can velocity", the upward air flow between the filters that will not allow dust to fall down into the hopper or silo below the dust collector.

8) Your line pressure is very low (4.5 bar / 65 psig) for any filters over about 1.3 m (4 ft) in length. To correct larger valve size is usually needed with longer pulse "on-time".

Your solution may not be with a larger receiver (as noted you can recover pressure in 3 seconds, which indicates slightly undersized receiver - pressure should recover in 1 to 1.5 seconds), but this may also be caused by the filter being too far from the compressor or the piping to the filter being too small for the distance. In addition, since you don't have a magnehelic gauge to know the pressure drop at the filter, you must be assuming a high differential due to lack of pick up of dust at the source. This could also be caused by too much static loss in the ductwork from the source to the filter, or by inadequate fan flow. You need to look much further to determine the problem. (FYI, I've worked in the dust collection industry for over 37 years.)

Hi Ruchiraslk

I think valve open time is too long. You need to send air in short bursts to properly clean bags. Your observation of pressure drop in the header confirms my line of thought.

What is the pressure drop across filters? This will show how efficient bag cleaning is.

Please respond to other posts where more information on dimensions of bags etc were sought.

We will try to help you through CR4. I myself have a lot of experience designing of pulse jet type bag houses. Incorrect cleaning can be due to many factors such as insufficient air, too much air, high velocity inside the chamber, type of dust and also many more! Perhaps getting help from a local expert will be a cheaper and faster way of resolving your problem than trying out many different options!

Sisira,

Lower air pressure in tank after pulse could be caused by longer than needed pulse "on time" as you note. However, two other causes are more likely. First is that the tank is undersized for 1" valves. This tank is more appropriate for 3/4" diaphragm valves with smaller air consumption (typically about 0.8 scfm/pulse) than for 1" diaphragm valves (consumption about 1.5 scfm/pulse). Secondly, the slow recovery time in this small tank (almost 3 seconds) implies that the piping to the tank is too small (possibly 3/4" pipe or 1" pipe) and/or that the tank is too far away from the compressor for the piping used. When the pulse valve fires, it takes air from the tank as well as using some of the incoming air from the resupply. If the resupply is too small, more air is taken from the tank and the pressure will drop more.

I agree with you,those are also possibilities.

Let us wait for Ruchiraslk to revert to us with more data.

Dear Friend.

Let me know the operating pressure of the unit, because as per manufacturer recommenadations it may be OK, Check once again in your working perameters like humidity etc.

Regards

Sivakumar

dear all,

thank you very much for your support,

i change the filters and installed 3/4" air supply line to the receiver. at first all pneumatic components and receiver has only one air line, so i arranged it for two lines. one for receiver and other for pneumatic actuators. now pressure is not get below 4bars.

also pulse time is shortened. now reverse pulse system is working properly.

again, thank you very much for your support!!!