Can anyone please help with a water hammer problem?

[DIY Keith]

My cold water feed (from a private supply) has a pump because the head isn't great. This has worked well for years but recently started to make a hammering noise. I can see that this is due to the pump starting and stopping when the water level in the tank is almost enough to close the valve . I have fitted a new float valve and a water hammer arrestor. I have tried making the pipe more secure but nothing has worked so far. As far as I can see there is no adjustment on the pump to reduce the pressure.
Any ideas please?

 

[ShaunCorbs]

What size expansion vessel have you fitted ?

 

[rpm]

There are different rated valves so is the new one the same as the old one, Brass with long arm?

 

[DIY Keith]

There are different rated valves so is the new one the same as the old one, Brass with long arm?

Yes just the same but I thought a new one would have less "play" in it and a new washer might help.

 

[rpm]

Yes just the same but I thought a new one would have less "play" in it and a new washer might help.

You talking about play being side to side in the arm linkage or somewhere else? Sorry not following re new washer either at the moment.

 

[DIY Keith]

You talking about play being side to side in the arm linkage or somewhere else? Sorry not following re new washer either at the moment.

Yes there was some side to side play in the old one and to be honest the new one's about the same. My thought about the washer was that the old one might have hardened with age and that a new one might close with a bit more of a cushioned movement. I get the impression that the arm is bouncing just very slightly but it's not visibly moving.