problem with water hammer......

I have a problem with water hammer. The cistern has an old Portsmouth valve; this makes a loud noise when the cistern fills. I have a DIY book, and this advises replacing the valve with an equilibrium valve. Would it be possible to replace the full assembly with a modern plastic diaphragm valve?

you can replace the old valve with a plastic valve. The valve in the pipeline that fills the cistern (or water storage tank) should be a Ball Check Valve. The purpose of a ball check valve is to stop the reverse flow of water; so the water doesn't flow backward to the source. Do not use a swing check valve as that will cause "water hammer" (loud noises and hammering on the pipes.) The equilibrium valve that you mentioned is also called a Balance valve. You would not want to balance/or restrict the water going into your tank (cistern.) Always have the valve to your tank fully open. There are situations in which balance valves are used to stop water hammering, but not in your situation. Let me know Nadine, how you made out. And if you have anymore problem than you can go through.

When connecting a plastic valve to metal/steel Pipe the plastic valve should have male threads screwing into female steel pipe threads. You may have to put a steel coupling or union on to the pipe end to make this transition. Plastic female fittings have been known to split (break) when connected to male fittings on steel pipe.