If the pipes are continually knocking or banging it may be that the pressure fluctuation is causing vibration - If those pipes are not supported (clipped in to a rigid position) they will effective...
Generally, steel pipe, not less than Sch. 40, A-53 or A-120 ERW or DOM. Steam Condensate pipe is sometimes specified at Sch. 80.Steam pipes normally black steel sometimes copper tubingDepending on...
When a valve is closed quickly the flow of water is interupted causing a water hammer. A water hammer arrestor or air chamber can be used to absorb the hammer.