I am under more pressure than the pipes!

[Tinkerin_wit_tools]

Last year, I replaced our kitchen faucet because of a leak. Had to turn off the water to the house since it's older and noticed it didn't have shutoffs. Recently had time to add some 1/4 turn shutoffs on the pipes and the guy at the hardware store talked me into thin compression fittings to install from our iron pipe to shutoff and after springing a leak, replaced the pvc with copper. I noticed the water pressure drop, but I figure going from a 3/8 iron pipe to a much thinner compression line to shutoffs, then to braided hoses to hookups to faucet(same diameter as compression line), it would make sense. Always heard that going from a larger diameter to smaller, then back again would drop water pressure some. Decided to get some iron threaded pipes to connect from existing to shutoffs, but now, I get even lower water pressure. The old hardware installed on existing coming from basement were weird sizes, so I took them off and found a 3/8" internal thread that I connected from this existing to the shutoffs. Can someone who knows what plumbing mistake I am making please weigh in on this issue?

[Nestor]

The rust that's formed over the years on the inside of your iron pipes is coming loose and clogging up your plumbing. That's why your pressure is low.

Take the aerator off the end of the spout in your kitchen or bathroom sink faucets and I expect you'll find a bunch of rust in them, and it's clogging up the aerators.

Is the pressure better at your bathtub spout or laundry room faucet?

"the guy at the hardware store talked me into thin compression fittings"

I have some ocean front property in Nebraska you might be interested in.

Please don't put in any more compression fittings. They're more of a problem than they're worth. Either learn to solder or go with PEX fittings.