can i fit non return valve to hot water vent pipe

[goateater]

hi
last yeat i re-routed my hot water pipes, as i wanted more space on lpft floor ( dromer bungalow)
since then the water in the hot taps downstairs comes out splattery, as if air trapped in system
i done the tricks to remove the air,( mains cold water put into hot tap)
works out for few days
once the splattery water is out, full hot water pressure is there
after lots of checkes for air leaks in new water pipe i put in place
i found an anwser on net, that the cold water supply to hot water cylinder may be choked and to put on 28mm pipe instead on 22mm
the acticle says the cold water flow in is not filling the cylinder up as quick as its draining, so the water in the hot water vent pipe is being drawn off and then that drawns in air
it makes sence to me
so can i fit a oneway valve to the hot water vent pipe that would allow only a limited amount of water to be drawn off before a vaccum is formed in the vent pipe
do you think that would work
the cold water tank is less than a 1mt above the hot water cylinder

 

[leakydave]

No, no, no, I repeat NO. No valves, taps etc should be fitted on a vent pipe

 

[HERTS P&D]

IN A WORD..........................NO!

Andy

 

[neiltheplumber]

No you can't fit anything as above. How old is the current system? 22mm feed is the norm, but you may have scale build up in your cylinder and the inlet may be partially blocked. Do you live in a hard water area?

 

[goateater]

no don't live in hard water area
the system is around 30 years old
the pipes i removed when i re-routed the hot water pipework had almost NO build up inside them
i was thinking about replacing some of the cold water feed (22mm replace with 28m) to the cylinder
but because of the run, i could only replace about 2mts of pipework, (where it comes along the ceiling then down the wall stop cock then down into the cylinder)
but not sure that would work

 

[Jackrae]

Lack of head is your problem. You could try a surrey flange in the HW tank.

 

[Onetap]

No valves.

It's due to lack of head &/or the pipes being undersized between the tank outlet and the open vent connection. When there is a draw-off, the frictional pressure losses are too high and the pressure is below atmospheric at the open vent tee; air gets sucked in.

Check all the valves are open, increase the size of the pipes or reduce the friction (pulled bends instead of elbows, soldered copper, not push-fit, etc..).
Or don't open the bath taps fully, or fit flow regulators to the taps that cause it (probably the bath).

Check there is a continuous rise along the open vent pipe so that air bubbles (released from the cold water on heating) can escape.

 

[goateater]

thanks for all the replies
i've been think about how to increase the inlet side of hot water cylinder
was thinking of getting some 28mm plastic hose, but thought the plastic inserts would reduce the flow too much
and 28mm copper pipe neds too many bends to get though to where it needs to be

 

[gaswizzard]

Seen this a few times where the insulation is trimmed away around the immersion heater boss and dropped into cylinder , the insulation will float to the top and block the hot water draw off , remove hot draw off from top of cylinder and check it isn't chocked up with foam , if the cylinder is 30 years old it could well be the foam lagged type.

 

[goateater]

thanks for that,
i'll look at that first,
as i said it worked ok until i re-routed the pipes in the loft,
the pipe work length & dia to this bathroom hardly changed
another run i changed from 15mm to 22mm, but we hardly use the taps on that run,

 

[onlyfitidealboilers]

Does the hot pipe work go up and over the loft as well?

 

[goateater]

no hot pipe comes out of hot water cylinder then down under floor boards into first floor loft space (its a dormer bunglow)
then down into the downstairs bathroom