New evohome installation - valve "whistle"
Reply With Quote
This is part of the reason why a whistle can occur - mechanical wax pellet TRV's don't tend to hold a very stable position for long and tend to move in small jumps instead tiny incremental movements so they "jump past" a valve opening point that might result in the valve whistling. The HR92 once it finds an equilibrium can make very small, fine adjustments and holds the position steady for each 4 minute period before (maybe) making another small adjustment. So if it happens to hit a point where the valve is whistling slightly it will sit at that point for at least a few minutes.Originally Posted by TonyHayers
I don't think the issue is related to cavitation, that would cause a noise at the pump, not at the radiators.- We've reduced the "bypass" volume of un-TRVed radiators from 2 (hallway and towel rad in bathroom) to 1 (bathroom towel rad only), increased speed through open valves.
- Due to above, is maybe the pump cavitating when it's trying to push hot water round the system to only one rad and creating fine bubbles which contribute to whistling noise? Pump speed too high?
Don't confuse differential pressure across the radiators with the absolute precharge pressure in a sealed pressurised system. The pressure gauge on a sealed system is measuring the static water pressure relative to atmospheric pressure, this is present whether or not the pump is running. (And when the pump is not running this pressure is the same on both flow and return circuits)- I've checked boiler pressure gauge while it's got only one zone in demand and rad valves are whistling but it doesn't increase, stays pretty stable between 1-2 bar which is normal operating pressure.
The differential pressure is the difference in pressure between flow and return sides of the radiators when the pump is running - this increases as radiators close and it is this differential pressure that an automatic bypass valve responds to. It's also the differential pressure that matters in regards to noisy valves.
Bi-directional valves are designed to work in either direction without "hammering", where they get into a loud oscillation/vibration, but it doesn't necessarily mean that they work optimally in both direction though in terms of quieter noises like a quiet whistle. I don't think that will be your problem though.- Some of my TRVs appear to be on flow side and some on return, it doesn't seem to make a difference to which rads whistle. All valves are "bi-directional" too.
If you've already bought the ABV I'd just go ahead and fit it - the whistling noise is most likely being provoked by excessive differential pressure when most of the radiators are closed, coupled with a valve body design that is "noisy" with high flow velocity through it. By limiting the differential pressure when most of the radiators are closed to a more reasonable level, the whistling will probably stop.- I checked/lubricated all of the TRV pins before fitting the HR92 heads, and confirmed they open and close the full range with the black wheel. So I know none of them are physically stuck.
- I have bought an ABV which I plan to fit later this week (although I would imagine that the towel rad would offer enough more "bypass" on it's own than a valve)
- Can reduce/remove the whilstling by removing the head and moving the black wheel a little in one direction or another.
You may have to experiment a bit with the pressure setting on the ABV - lower will reduce noise more but may result in insufficient flow through radiators (reduced heat output) and excessive return flow temperature into the boiler which depending on the boiler may cause a error condition and is not the most efficient for a condensing boiler since you won't get your expected temperature drop through the radiators as seen at the boiler. So I would start at about 0.5 bars and work your way down from there to see what effect it has and don't set it any lower than necessary.
You could also try reducing your pump speed by one step but you may find the warm up time and heat output with all radiators open is insufficient at the lower speed.
For what it's worth, despite having an ABV on my system our two bedroom radiators occasionally whistle quietly at night when the HR92's are at very particular positions. I only notice it now and then. None of the other radiators do the same. I put it down to the cheap valve bodies that are installed (which probably suffer from turbulent flow through the valve when only slightly open) however I'm not too worried about it because I will be replacing all the valve bodies soon.
Good luck.
