how do I stop pipe hammer?

Energy waves bouncing around in the pipework.

You can see something similar if you sit in the bath and slosh the water about - it hits the end wall - rises up high and rushes back towards you.

Electronic signal wires can suffer a similar effect with electronic reflections of energy back along a cable.

Wikipedia has an excellent article about water hammer. Before you try any solution just close the main water stop tap half a turn or so to reduce the incoming pressure.

http://en.wikipedia.org/wiki/Water_hammer



Good luck...

Peccavi
June 2013