High mineral content in your water? Don't use steel connectors!

Hi all;
I have a gravity water system.  2200'+ of 1.5" poly line with 300' of drop. Average of  125+ psi at the house.
I have made my electricity with this pressure for 23 years.
Every year I have a slow down of flow at the hydro. A build up of debri in the line.
Shut off the tank and disconnect the main line at the union, drain the line down to the house. Connect a large industrial air compressor to the freeze-less hydrant in the yard and blow backwards 2200' up the line... Works every time, one shot, done deal till next year... EXCEPT this year.
Compressors are not cheap to rent. 80$ for 4 hrs or 120$ for 24 hrs !  First time this year I rented it for 4 hrs ... worked great  , fixed ... for 4 days... then not.
As I was working out of state at the time, I could only do things on the weekends...
A second rental the following week, this time for 24 hrs... I blew it and refilled it three times !!! It only worked for 2 days !!!
Oh good grief!  Next I rent a mini trakhoe for $400. I dig up the line down here in the yard as I have a sneaky suspicion of what has happened...
Sure enough the 1.5" galvanized fittings I used down near the house have grown beautiful mineral deposits. Effectively shrinking the size of my line down to .75" or less !!!
Creating a flow restriction and a great spot for any new debri at all to get hung up. Thank you high mineral content!
The good news is minerals do not grow on plastic...
Most all my line uses plastic fittings except down in the yard.

I now have all new 2" PVC line here in the yard!  Big job and of course, our first temps in the lower teens and below freezing all day arrived in the middle of my project !
It did take 23 years for this to be a problem but... I would have rather found a different project to work on just before winter sets in!

I get the opposite with my well water. Flow technically gets better as my water eats away at the steel until it fails.

That's a very important tip to remember Thomas. I've seen this before many times (but not quite as bad as yours) when I have to replace one of our many electric hot water tanks where the plumber had used a galvanized Tee. Its such a simple thing that can be avoided and also good to reminder if diagnosing a water flow problem on another project.

Hi All;
OK; Finally got all the new 2" line in place.  I discovered that on the main line. 23 years ago I used an 1.25 valve instead of 1.5".  This made bunches of fitting's the wrong size! I also discovered there is a BIG difference between high pressure and low pressure pvc fittings... mine must all be high pressure! They blow apart quite spectacularly!
Dang ANOTHER trip to the fitting store! I made several such trips before this job was up and running.
I installed a stand pipe upstream of the shutoff. This pipe has its own shut off and a "Chicago" style air fitting. In years to come, when it comes time to blow debri out of the line. I will not need to use / damage a freeze less hydrant. I now have a perfect spot  to run air pressure up the line and block it from going back towards the house.
I used plastic fittings everywhere!

The path to the greenhouse/studio goes rite over the water line. It has always turned into a mud path in the spring.
My plans included a sidewalk. A two part pour.  The first came over to the edge of the water line. The second will lay directly over the line. The second slab has metal wire inside.  My hope... is that some new owner, far far in the future. Would be able to remove just that slab to access the water line.  
Of Course My Belief... is that I did such an outstanding job, the water line will never need see the light of day again!
Had two spots that were dripping at first.  One was the hydro outlet. Easy fix, as it was beyond the shutoff valve. The other was downstream of the main shutoff . That one would have required cutting the new line to install a high pressure union.
I chose to ignore both drips while I began backfill.
I've seen this happen before... by the time most of the backfill was done, Both leaks had stopped dripping !
 
Work continues, If I'm really lucky I can finish this before the nasty cold returns!