Gate valve query and noisy system on old Myson Apollo

[MICHAELHUG]

No it is not!!


Hello if it's not just just an isolation valve can you tell me what it is exactly and should that be balanced between the other valve or is fully open or even half way sufficient thanks

 

[Hugh Jaleak]

Lockshield Valve on cylinder return is a balancing valve to restrict the flow of water through the cylinder coil. Should 3 port valve open to provide flow to both HW Cylinder and CH simultaneously, the flow of water will take the path of least resistance, (which is likely to be through the cylinder), thus starving the CH circuit of flow, until such a time as the Cylinder is up to set temp, the 3 Port valve closes to the HW circuit, and gives full flow to the CH.

CH would then probably take a lot longer to heat the house up, and meanwhile if hot water is drawn off, the cylinder may then call for heat again, taking flow for the Radiators. By fitting a valve in the cylinder return, the flow through the cylinder can be restricted, forcing flow through the CH side, ensuring the Rads heat up in good time. I'd suggest having it about half way open and see how the system fares.

The other is a bypass, to allow a flow through the system should the 3 Port Valve close to the HW side, and the TRV's on the Rads shut down as rooms reach desired temperature.

 

[DP]

I don't see a bypass on typical Y plan drgs but i was thinking this is because they don't allow for trv valves on the circuits?

At least one radiator would not or should not be fitted with TRV ( both valves be lockshields) That often is the case with hall radiator where a thermostat is often fitted so a three port valve does not need a bypass if one was being pedantic because one port will always be open regardless what position the valve is in

 

[ianmcd]

The 1st valve is simply a tank isolation valve. Leave it well open.

As @Hugh Jaleak says it is a flow restriction valve, when HW and CH are both requested to run, the flow will take the easiest route of least resistance so on some systems you have to restrict the return from the coil, to get enough flow to force the water through the rads, it should nener have been touched if set up correctly, the other valve is a manual by-pass and again should never have been touched if you dont know what you are doing

 

[BlueLoo]

As @Hugh Jaleak says it is a flow restriction valve, when HW and CH are both requested to run, the flow will take the easiest route of least resistance so on some systems you have to restrict the return from the coil, to get enough flow to force the water through the rads, it should nener have been touched if set up correctly, the other valve is a manual by-pass and again should never have been touched if you dont know what you are doing

Yea......hmmm.

Tanks should have a valve on the ports anyway for shut off, maintenance, etc.
I suspect this is that but which can also be used to throttle the flow as its on the return.

But why would you throttle?

In A mode(heating) the line is closed to the tank.
In B mode (Tank) the line is closed to the rads.
In AB mode (standby or dual call), both ports are open so you probably get priority heating to the hw tank (because its the lowest resistance) which is what you want isn't it?
And how do you balance between the two if you have the TRVs opening and closing and a second bypass already open?

I get the logic but it isn't really working for me. A bit like having the bypass if you have a rad lockshielded open.

 

[ianmcd]

In AB mode (standby or dual call), both ports are open so you probably get priority heating to the hw tank (because its the lowest resistance) which is what you want isn't it?

But in reality, if the DHW coil is unrestricted 22mm or 28mm pipe , and the CH circuit is 22mm x 8mm manifolds, the flow of water will always take the easiest path, both systems share the return, so if the flow is unrestricted on some HW circuits the boiler reaches temp and cuts out before all the rads start getting hot, this is an ancient system, and probably has more add ons than one of your posts

I have never seen an indirect coil with isolation valves on the coil

 

[BlueLoo]

But in reality, if the DHW coil is unrestricted 22mm or 28mm pipe , and the CH circuit is 22mm x 8mm manifolds, the flow of water will always take the easiest path, both systems share the return, so if the flow is unrestricted on some HW circuits the boiler reaches temp and cuts out before all the rads start getting hot, this is an ancient system, and probably has more add ons than one of your posts

Mid position valve listens to both stats on both circuits at the same time.
Once one is satisfied, the valve moves accordingly.

Without throttling the returns, You prioritized the HW (Good idea),
once that's hot, if your Rad/heating is still calling for heat, it gets all of it because the HW has stopped calling.

I mean, yea, you could want to have the HW and CH reach temp at the same time but i would think that illogical,

I have never seen an indirect coil with isolation valves on the coil

Pg 53, CIBSE, DHDG, 2003

 

[ianmcd]

I am not going to argue with you, boiler thermostats and external controll thermostats work completely independently, you are wrong end of discussion

 

[BlueLoo]

Who mentioned anything about boiler thermostats?

I can PM you a copy of the DHDG if you want.
Just ask.