ISTR that you description of the plumbing at the tank top wasn't quite ideal.
But it's easy to test if your theory is correct, temporally bung a cork in the end of the vent pipe. If no more air appears after a few heat from cold cycles of the HW cylinder then youi are correct.
Don't worry about expansion when the water is heated that goes back up the cold feed anyway not up and over the vent pipe. The vent pipe is to vent any steam pressure should the HW cylinder be heated to boiling point...
The message from "Dave Liquorice" contains these words:
Not my system so I cannot test but I am in no doubt that my basic proposition is correct. That air is drawn into the system via the vent pipe because the outlet has a greater capacity than the inlet. What I am more doubtful about is my concentration on head in previous messages.
On further reflection it seems to me that I should have made more of the resistance to flow as well as the head (or rather lack of resistance). The higher the ratio of head to effective length of the pipe the faster the flow. There must be standard equivalents for fittings but unfortunately I couldn't find them so the figures I have used below to illustrate are entirely imaginary. (Units are metres).
Dividing point between inlet and out is the branch for the vent.
Inlet Outlet
Pipe run 2 4 Bends 2 1 Tank inlet/outlet 2 Other Fittings (tee) 1 Tap 2
Equivalent pipe length 7 7
Head 0.4 3
Ratio Head/effective length 0.4/7 3/7
In the example above for air not to be drawn into the system the equivalent pipe length would have to be less than 0.9 on the inlet. Upping the inlet pipe run from 22mm to 28mm would probably halve the figure for pipe run (2 down to 1) but wouldn't make much difference overall unless the figures I have invented for extras are wildly exaggerated or the bath tap is grossly understated. So does anyone have any real figures?
Well I've managed to source the 28mm->1" cylinder connectors (which I'm told have an increased bore size on the currernt 22mm->1" tank connectors I currently have installed, but since it hasn't arrived yet I'm keeping my fingers crossed)
I then need to hire a pipe bender and hope to use 28mm copper pipe with no elbows and sweeping bends to ensue the flow is as good as I can possibly make it.
I'm no plumber (obviously :-) ) but it does seem to me that if I double the flow in to the bottom of the cylinder (28mm bore being a about double the bore of 22mm) there will be more than enough capacity even if the pressure on the outgoing side (top of the cylinder) is fairly high due to the head of water to the bath tap.
Anyway, I guess we'll find out later this week when I've made the change, wish me luck!!
Thanks to every> The message
No, I wasn't. However I've also connecting up the second tank connector
22mm pipe to the bottom of the cylinder (so even if there was a blockage in the first feed from the cold storage I've 'fixed' that without draining down by connecting this second)Also, worth noting that after I connected this second feed from the cold header the problem did get slightly better (not as much air/water sucked from vent pipe). However, since both of these 22mm feeds from the header still feed in to a 22mm Tee before entering the 22mm->1" brass cylinder connector there is still a 22mm bottleneck. This is what I aim to fix by changing the 22mm->1" cylinder connector with a
28mm->1" connector and running a single copper 28mm pipe from the cold header.
I don't use gate valves, don't get on with them. I use the yellow handled full bore lever ones so as not to restrict the flow. I also find that they don't leak or stick like gate ones can.
Yep, done this and it helps. I also put on a 22mm pushfit end cap. Oddly it didn't seem to totally fix the problem, I think (I'm totally guessing here) because a vacumm was created somewhere. basically the flow wasn't as constant as I had hoped. I guess this again means the cold header isn't able to feed the hot cylinder fast enough.
For this scenario of using 28mm pipe from the tank to the cylinder, which in my case was to make sure that I could comfortably take two
22mm outputs from the cylinder (rather than a head issue), I used obtuse angles (135 degrees). For the run from the tank, I needed to do the following direction changes:- Drop the level from the tank connector by about 250mm to allow the pipe to pass under an access platform. This could be done with two obtuse bends and a middle piece of tube.
- Right angled bend to drop through the ceiling. Here a 300mm long middle piece was used.
- Right angled bend from corner of airing cupboard to bring pipe horizontally. 450mm middle piece here.
- Angled bend (135 degrees) to align pipe with cylinder connector.
This was easier than messing around with pipe benders and as long as there is a reasonable straight length between obtuse fittings is probably as good as bending.
If you can plan the pipe layout to allow gradual changes and none too close together, it will give the best outcome.
While you're at it, it's a really good idea to put in a 28mm lever ball valve on the pipe near to the cylinder.
thanks for the advice, I wasn't look forward to bending 28mm pipe. 15mm was bad enough, I never seemed to get the distance between bends right!
I guess 135 obtuse c> On 2006-09-24 18:23:51 +0100, snipped-for-privacy@yahoo.com said: >
Regulating flow, is actually one of the few things gate valves are good for!
Why not knock up a quick DIY surrey flange. That ought to make the symptoms go away if nothing else!
Well.... I just looked on the BES site and could only find them in end feed (7986) and solder ring (9236)
Do you not feel comfortable with soldering?
yeah I can solder. still prefer pushfit, but sometimes I'll admit you need to use copper.
I just h> On 2006-09-24 19:45:08 +0100, snipped-for-privacy@yahoo.com said: >
An update if anyone out there is still interested, or wonders which advice I decided to follow...
Today I upgraded the pipe from the cylinder to 28mm copper, using obtuse bends (4 in total as I need to change direction 90degrees twice). I even had to solder 'end feed' connections which I'd never done before. Only one minor mistake, I forgot to add the drain valve ;-) good job I noticed before I filled the cylinder with too much water, is was a pain to empty.
And guess what...it fixed the problem! No more air in hot water and a wonderful flow at the bath tap.
Thanks to all that replied with suggestions.
Graham
snipped-for-privacy@yahoo.com wrote:
Excellent news. Well done.....
Thank God you didn't take any notice of Roger and his Rogerness and his uk.d-i-y Lunatic Association (affiliated)
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