Float Valve Noise Problem

[Roger2]

In my loft I have a (plastic) cold water tank fitted with a 1/2 inch equillibrium float valve.
Tank and valve were installed by me about 12 years ago. An equillibrium valve was fitted as previously we had had problems with water hammer with the the existing float valve as it was shutting off. At the time (12 years ago) mains pressure averaged about 5 bar. It now averages 3.
The tank supplies cold water to bathroom and HW cylinder. Since being installed it has worked faultlessly.
Over the last month as the valve approched shut or as water is started to be drawn off from the tank a there is a period when a vibration/hum starts in the mains supply. Frequency of the hum/vibration is constant and similar to mains hum. The noise particulaly when the tank is approching shut off can last several minutes and can get very loud. It can be stopped by turning on a mains fed appliance (washing machine / dishwasher) or cold tap in the kitchen. Turn them off an noise will come back.
I assumed the float valve was faulty and changed it for a new one. Both old and new valves were the same. Pegler 901 stamped on them.
Fitted new valve still got the problem.

Any ideas what I shoud try next.

 

[Moz]

get a valve on the mains an turn it off partially , or get the empty youghot cup on string over the valve in the tank with holes in it , lol

 

[noodlz]

Are you absolutely sure its not a toilet float valve causing it?

 

[ChrisR]

Noodlz question seconded - it's usually a rubber washer vibrating and new ones don't usually do it.

 

[Roger2]

I am absolutly sure the noise is related to the closure of my cold water tank float valve. My only option now I think is to replace the "new" valve.

Roger

 

[TicklyT]

I had similar a while ago. I replaced the valve, but it was still noisy. In the end I rebuilt the old valve using the new valve as a donor to replace worn parts. After swapping bits around a couple of times I got a combination that worked correctly and quietly.

It's probably down to manufacturing tolerances, mains pressure and pipe run lengths. I reckon the chances are another 'identical' valve would behave differently (but maybe no better)