trying to make a vacuum

[boaz]

Good Morning Engineers,
I have a Worcester Greenstar open vented boiler, feeding rads and hot water system via a 3 port motorised valve. I live in a bungalow, and all pump/valve/control systems are in the roof - boiler down stairs. I need to replace the 3 port motorised valve, but do not want to drain down the system.
Question :- The header tank has a gate valve feeding the system, the open vent running into the top of said tank. If I closed the gate valve, and blanked off the vent pipe entry with a push on stop end, would this cause a vacuum in the pipework so that I could remove the 3 port valve without having to drain down?.
Any advice would be welcome,
Kind regards,
boaz.

 

[Riley]

You can probably get away with bunging it as long as you can turn off one of the pump valves. The bunging process will work with two open ends but as soon as there is a third it won't hold not to be tried if you're not confident the bung can give at any point. Why not just drain off a little water until it is just below the level of the valves

 

[finchy01]

Do you need to change the body of the valve? Often it's just the head that's needed which doesn't require any draining as nearly all are removable.

 

[boaz]

Thanks riley, I did mean to include that in my post - must be the Scottish water working !!!. I am confident, just lazy !,
Kind Regards,
boaz

 

[boaz]

Finchy01, Thanks for your reply, sadly, the valve does require a change, as I fitted a new actuator when I had to replace the pump. At my age I should know there is never a short cut to a proper job. As I said to Riley - I am inherently lazy at times, but thank you anyway,
Kind Regards,
boaz

 

[Riley]

Well the short answer is you can get a vacuum but work bloody quick

 

[boaz]

Thank you for that - I will,
Kind Regards,
boaz

 

[heliotrope]

As all the controls, pump etc are in the roof you should not need to bung
or drain down.

Turn off the gate valve at the F&E tank , hold an old towel or rag under the valve
crack open one of the nuts and drain off what little water comes out.

Would probably be only about a cup full.

You should now be able to take your time on the valve change.

 

[GasmanxxxR1]

I use the bung method all the time, close as many valves as you can, as this helps a lot, pump valves, cylinder balancing valves if you have one.

Then with it bunged release the 'system pressure' about a bucket full of water from a suitable drain off point.

Crack a nut on the 3 port, i use a rubble sack as a flexible bucket to catch any water in. Have the new one ready to go.

And there you are, new 3 port

 

[boaz]

heleotrope - Thanks for your reply, but without "bung" fully in place on both pipe ends ( central heating and hot water) would not all of the standing water in the feed lines to the hot tank and all the rads need to drain out as the 3 port valve is at the same level as all the feed pipes ie laying on the floor joists?. I could understand if the valve was say 6 inches higher that all of the other pipework, but as I said it at the same level. In no way am I doubting what you have said, just require clarification,
Kind Regards,
boaz

 

[boaz]

Gasman - Thanks for your reply "system pressure" - do you mean the weight of water in the pipes, or, water pressure as it is not a pressurised system it is open vented.
Kind Regards,
boaz