I don’t think a filter strainer is part of the equation on a reducing
valve. A pair of pump pliers….large adjustable pliers some call slip
joint or channal locks….is all you need. There are very good products
on the market…lime away is one…..

I would have a  check valve the filter strainers or aereators on the faucets for lime
deposits first…that is what I suspect anyway. If it really has gotten
to the valve you will need two good pipe wrenches and perhaps learn how
to solder as you don’t inform us how the valve is attached in the
system.

If its old plumping it could mean the pipes themselves are coated badly and thus need replumbed.
All pressure reducing valves are serviceable. Turn the water off to your
valve and undo the nut which is holding in the strainer. It all comes
out without having to take it off the pipe. Then soak it in a weak
solution of vinegar or the like to remove the build up. Then wash it
thoroughly to remove any other deposits.

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