How far open should lockshield valves be?

[BlockABoots]

I was told by a plumber that the lockshield valve on my radiators should be 'just cracked open slightly', from my understanding you dont want the LS valve open too much as the water will flow through the radiator too quickly and not heat it up fully is this correct?

I took this plumbers advice and tightened up all the LS valves on my radiators and then just cracked them open slightly but in doing this i noticed only 2 radiators downstairs were getting hot the rest were luke warm at best.

So my question is how many turns should to open the LS valve and should the last radiator in the CH system have its LS valve open fully?

 

[Ric2013]

He's right in that the lockshields don't really do much to control the flow until the last half turn from fully closed. But yes, now your balancing will be out.

Croppie's Balancing Thread.

 

[BlockABoots]

Ok so anything over half a turn from fully closed doesnt do jack?, its just the first half turn?

 

[Ric2013]

Pretty much.

 

[BlockABoots]

Ok thanks, just need to work out which order there in from the boiler as a few of them seem to get more or less hot at the same time so its difficult to work out what order they go in

 

[doitmyself]

It will vary from installation to installation and from radiator to radiator.

Adjusting the LS valves is called "balancing"; the purpose is to make sure the flow through each radiator is correct. This is done by having the same temperature drop across each rad. As the water going into each rad is the same temperature, you just need check the water leaving each rad (colder side). This is normally the LS side, but it doesn't matter if it's not as you still adjust the LS valve.

1. Remove all TRV heads
2. Set all LS valves open one third a turn
3. Turn heating on and set the room stat higher than normal so the heating is not going on and off
   
4. Identify, by feel, the rad with the coldest return
5. Open the LS valve on that rad by 1/12 turn (half the flat on a hex nut)
6. Wait five minutes for change to take effect
   
7. Repeat from 4 until all return pipes feel the same temperature
8. Replace TRV heads and set as required
   
9. Set room stat a required.

 

[Dom Perkins]

Also depends if the system is clean, if you do a boiler change, no flush on what was an open system and update the valves too... chances are if you just crack them open, any crap left in the rads will get disturbed when you re-pressurise and may end up turning your 'cracked' valve into a semi blocked valve.
i like to make sure they are all opened up, turn on, heat up.. check all the rads are hot...often 1 or 2 not as hot..so then close them all down accept 1 rad and then balance back from there... better the rad temp down the return, the more i close it down to send the heat and pressure to where it's needed.

 

[Best]

I would say very generally speaking that the first radiator or two on a circuit need their lockshield valves just slightly open, but each rad beyond that should have lockshields increasingly more open until last radiator is full open. After all, why create any resistance in a rad that is at end of a circuit, or hardest to have flow to?
Obviously this varies with manifold systems and designer rads.

 

[doitmyself]

I would say very generally speaking that the first radiator or two on a circuit need their lockshield valves just slightly open, but each rad beyond that should have lockshields increasingly more open until last radiator is full open. After all, why create any resistance in a rad that is at end of a circuit, or hardest to have flow to?

That assumes the LS valve is still having some effect when it is fully open, which isn't true. Most LS valves are only effective over the first 1½ turns, the remaining 2 or more turns have no effect. This is why fine adjustments need to be made, e.g 1/12th turn, not ¼ or ½ turn.

You may still need resistance on the last rad if the temperature drop is too small. This could happen with a combi boiler where the pump has to run at top speed, even if it's not really necessary when CH is working.

 

[Best]

That assumes the LS valve is still having some effect when it is fully open, which isn't true. Most LS valves are only effective over the first 1½ turns, the remaining 2 or more turns have no effect. This is why fine adjustments need to be made, e.g 1/12th turn, not ¼ or ½ turn.

You may still need resistance on the last rad if the temperature drop is too small. This could happen with a combi boiler where the pump has to run at top speed, even if it's not really necessary when CH is working.

That's a good point about balancing the rads properly to achieve correct return temperatures. Although the folk doing it themselves will just want to get their rads all working evenly.
That's why I said, very generally speaking in my post, just to give a simple explanation.
Customers usually end up ruining the balancing by removing rads for decorating and then turned lockshield valve full open. Just literally left a job where the customer was complaining of noise from his copper cylinder on a system I had installed years ago. I found the 22mm gate valve for balancing had been turned full on by someone.