I dunno, fwiw;
I'm in st pete. Shallow wells on 1hp jet pump.
US Geological/hydrolical? survey maps for my surrounding area show water depth here starting at 10 feet below surface topped with a mineral hard pan. Water extends down another 20 feet where at 30 feet deep there is the bottom hard pan.

The river of water flows at around 1 foot per day through a real fine sand with a few specs of clay and some decomposed vegetation or organic matter in it.
~ I suspect your well water is pulled out of a similar or probably basicly the same type layer or river of sand. Yours is just located a bit deeper than mine. That's why you have the deep well, thats soo shallow.

Hard to remove all that sand here so I have a screen filter just after the pump outlet which will filter out a very small handfull of sand at each start up. It will get a load of sand if I've been out there with a post hole digger or pounding on nails & tossing around lumber. Think any more serious ground vibrations cause the extra sand. Probaly clears some of the larger sand from the well points slits. Larger grains build up over time at the well points filtering the smaller grains of sand.

Valves really aren't very expensive and the labor to replace all of them shouldnt really be a major time consuming chore above just comming out to replace only one or two.

I'd replace all of them if you're not a diy'er and make sure they remove all your heads and flush all your zones which I would think would be standard practice when relacing a valve.

You might also ask about adding a screen filter.. Cost for me for a filter was under $50 and I put a manual flush valve on the bottom. An electric valve can also be used for flushing if your timer has provisions to automatically flush for a couple seconds at every start or shurt down cycle.

With a filter you will not totally eliminated sand from the pipes, but will have greatly reduced it.

i just wanted to know from the expert, why there is brown sand coming out from our 50 meter deep well? what is the realm regarding this inccidence? please give us information so that we may understand