Sucking air into system. Move flow restrictor? Help please?

[Unklian]

Hi Again.

Problem with (sucking?) air in my system.
I have a system which WAS gravity hot water, it is now fully pumped.
I realise (thanks to this site) that it is piped very badly.
Because of the layout of our nicely decorated house, it is impossible to re-plumb correctly.
There is a gate valve restrictor in the downstairs boiler room for restricting the flow round the DHW circuit. It also I believe acts as a restrictor to the system filling. (Unintentionally).
I am thinking that when the DHW is satisfied and the pump starts for heating, because it cannot suck water in other than through the restriction, it is creating negative pressure in the radiator return pipework and pulling in minute quantities of air. (I have to bleed the system about once a week).
If I moved the gate valve to the alternative position adjacent to the cylinder upstairs, would there be less "suction" "negative pressure" placed on the system?
ie, the "fill" pipe is unrestricted, the only restriction is in the DHW pumped part of the circuit.

EDIT:....Or, looking at the diagram.....would an alternative position be at the top of the coil where it feeds into the cylinder?

Thanks for having a look.
Any other suggestions / tips.
I really don't want to have landing carpets / floors up!

EDIT2:......Would a better idea be to install a dedicated feed / expansion pair of pipes?
I'll have to bite the bullet and lift floors......like this......

Cheers.
Ian.

 

[Unklian]

Just added additional pipework suggestion.
Anybody Please?

 

[doitall]

If the gate valve is fully open where it is, and the pipe isn't blocked it should suck in air.

 

[twgas]

your alteration idea is not bad, but I would put vent and feed before the HW flow, or possibly seal the system if that is an option for your boiler.

 

[Unklian]

If the gate valve is fully open where it is, and the pipe isn't blocked it should suck in air.

The gate valve is opened only 1/2 a turn.
Flow from boiler round heating loop takes about 20 seconds.
With it opened any further, I have pumping over problems.
If I DO add the 2 dedicated pipes, I will move the gate valve into the "flow" side.

Ian.

 

[Unklian]

your alteration idea is not bad, but I would put vent and feed before the HW flow, or possibly seal the system if that is an option for your boiler.

Yes, I can do that.
I've seen it on this site somewhere but can't remember......
What is the "preffered" order?

vent......feed......DHW......Rads?
feed......vent......DHW......Rads?

Thank you both for your advice.

Ian.

 

[doitall]

You don't need to alter the pipework.

The gate valve should be fully open, if it then pumps over you need to raise the header tank and vent or turn the pump speed down.

 

[doitall]

Separate issue, was the pump moved when the system was altered.

If so where was it before, and what is the make/model of the boiler.

 

[Unklian]

You don't need to alter the pipework.

The gate valve should be fully open, if it then pumps over you need to raise the header tank and vent or turn the pump speed down.

The restriction was put in so that the (22mm) DHW didn't take all the flow from the pump. All the heating is in 15mm. So as soon as there was demand for hot water with the heating running, the water chose to flow round the DHW loop and the radiator flow was reduced to almost nothing.

 

[Unklian]

Separate issue, was the pump moved when the system was altered.

If so where was it before, and what is the make/model of the boiler.

The pump has always been there.

The boiler is an old Glowworm Energy saver 40.

It was wired......

DHW on timer only.
Timer on......boiler on....water finds it's way round by convection......
DHW gets very very hot until timer switched boiler off.

If thermostat in living room called for heat, the pump started and pumped
water round the radiators.

There were NO actuators in the system at all, no DHW temperature adjustment !


It now has 2 SM5023 5 wire valves, a cylinder stat and a clever Horstmann timer so we can have "normal" temperature hot water
instead of "lukewarm" to "steam" temperature.

Come summer, there is JUST enough space to plumb......

Boiler......feed......vent......pump......DHW valve......Heating valve.
Boiler......vent......feed......pump......DHW valve......Heating valve.
(Or any better suggestion).

Thanks again.

Ian.

 

[doitall]

Thats a better design but you still need to move the balancing valve into the return.

A by-pass around one or the other MV's would stop 90% of your problems.

 

[Unklian]

Thats a better design but you still need to move the balancing valve into the return.

A by-pass around one or the other MV's would stop 90% of your problems.

I've modified the sketch to put it in the flow as you suggest.

The Balancing Valve......could you possibly put me an "X" whereabouts?

Thaks All for the advice up to now!

Ian.

 

[doitall]

Balancing valve is fine in the return where you now show it.

You still need an auto by-pass valve across one or the other motorized valves.

Just a simple link from the inlet port to the outlet with an auto by-pass valve in the middle, is all thats needed.

 

[twgas]

You don't need to alter the pipework.

surely in the first pic, the cf and ov are wrongly position and there will be problems with pumping over or sucking in air.If you think not can you explain.

 

[doitall]

You don't need to alter the pipework.

surely in the first pic, the cf and ov are wrongly position and there will be problems with pumping over or sucking in air.If you think not can you explain.

The first pic was a standard way of doing it with gravity primaries, and the pump return should go into a spreader bar, if the pump is connected to the wrong tapping it will give problems.

The last drawing is the best way, but it needs an auto by-pass valve across one of the MV's.