blowing out a well

I have a well that was originally 600 foot deep. I lowered my pump from 520 to 540 deep. I intended to lower it to 560 but hit bottom at 521. My well is not replenishing as fast as it did only one week ago. I have determined that the water table is probably not the problem, rather the silt in the bottom of the well. I have decided it would be best to blow out the silt but have never attempted this myself in the past. I would assume I would need to pull the pump to do so. I have been warned that some wells have been ruined by blowing them out (with compressed air) I am not clear why this would hurt the well. My questions are as follows:
1) What harm could blowing out the silt with compressed air do?
2) What are the steps to performing this operation?
3) What pressure and volume and pipe size do I need to use (I assume I would remove the pump and use the same pipe with an extra joint?)?

Any comments from someone with experience would be appreciated.

silt

1) What harm could blowing out the silt with compressed air do?

Probably none, unless the outward pressure were to cause the porous water layer to compress and seal up. But the bigger question is HOW you would do it. Unless the static water level in the well is up to the top of the pipe, so you can cause the water and silt to overflow it, all you will be doing is roiling up the silt and it will resettle to the bottom.

3) What pressure and volume and pipe size do I need to use (I assume I would remove the pump and use the same pipe with an extra joint?)?

If the well is full of water, then you would need about 270 psi, just to get the air to the bottom of the well then you would need additional pressure to disturb the silt.

corrections

Thank you for your reply. I suppose it would help if I proof-read my comments. The new pump depth is 540 foot not 520. The water seems to be about 80 foot over the pump according to the wet pipe we pulled up. So we have 460 foot of empty pipe. When I have seen this done in the past (16 years ago) the silt and water were blown about 20 foot in the air and this was done for about 24 hours to clear it out. So according to this I am trying to find out what kind of pressure and volume of air I need so I can rent an air compressor. Again, thanks for your response.

Do ya think it might be something you should let a well expert handle for you... I mean trucking in water could get expensive if you do something to your water source... Even more expensive if you do something to your neighbors water source!