Drain cylinder aswell?

[markyyyyyy]

Hi,

i'm replacing gate valve on cold feed to bottom of cylinder.

Im also replacing cold pipework in kitchen so turning off mains in kitchen and then turning on both hot and cold taps to drain the hot pipework and also cold pipework in house.

My question is this (i've read elsewhere but not sure if its the case??):

Once i've drained the cold water storage tank in loft via turning the hot taps on, this will then leave a tank full of water in the cylinder, however this will remain as there is no water to push it through and out of the top of the cylinder to taps.

I read elsewhere that once i loosen the compression fitting on the gate valve, to replace it, this will provide an escape route for the water that will be in the cylinder - is this true?

If so, i'll also drain the cylinder aswell - partially or fully?

p.s. the gate valve on cold feed is approx 6inch higher than the top of the cylinder
thanks

 

[ianmcd]

you will have to drain the Cylinder as well to lower than the level of the gate valve, if the gate valve is higher than the top of the cylinder then you wont have to drain it

 

[markyyyyyy]

you will have to drain the Cylinder as well to lower than the level of the gate valve, if the gate valve is higher than the top of the cylinder then you wont have to drain it

Great thanks. Here is a picture of my boiler and the gate valve on cold feed on the left... So basically I don't have to drain cylinder?

Also, just for my knowledge, what's the reason you have to drain if to lower than the level of the valve? Is it a pressure issue?

Cheers.

 

[ianmcd]

No you wont need to drain the cylinder in your case,not pressure , once you empty the cistern in the loft the HW Cylinder remains full of water as there is no downward force of water to push the water out of the HW Cylinder top connection, but as the gate valve is above the outlet simply opening a hot tap below the cylinder will mean that the pipework will be empty, why are you draining the Cold water cistern in the loft ?

 

[markyyyyyy]

No you wont need to drain the cylinder in your case,not pressure , once you empty the cistern in the loft the HW Cylinder remains full of water as there is no downward force of water to push the water out of the HW Cylinder top connection, but as the gate valve is above the outlet simply opening a hot tap below the cylinder will mean that the pipework will be empty, why are you draining the Cold water cistern in the loft ?

I'm installing a kitchen and at the same time I am redoing the hot and cold pipework in kitchen, fitting some isolation valves in toilet room sink and need to drain cold water storage tank as gate valve is seized. So in order to replace hot pipework, I need to close gate valve (or in my case, drain CWSC and install new gate valve)

 

[markyyyyyy]

simply opening a hot tap below the cylinder will mean that the pipework will be emp

Purely for my understanding (eager to learn!), Let's assume my gate valve was 12 inch lower than it is (ie 6 inch lower than top of cylinder), why would I need to drain below the gate valve level because my understanding is that the pipe from top of CWSC to bottom of cylinder would be dry?

 

[ianmcd]

because the water will always find its level so if the water level in the cylinder was higher than the gate valve then when you undid the gate valve nut, the water would come backwards from the cylinder until the levels were equal, there should be another gate valve at the cold water cistern and if that is ok just close that and open the hot taps , no need to drain the Cistern

 

[terryplumb]

Water finds its own level. Think about what would happen if the gate valve was 12 inch's up from the floor . The water in the cylinder would come out of the cold feed pipe when you remove the gate valve ,and the entire volume of water higher than that point would drain out .

 

[markyyyyyy]

Ah brilliant thanks to you both for your replies. That makes total sense! I'll look in the loft to see if there is a gate valve up there. Cheers.