Hot water flow rate problemo!

[Winston]

Been asked to have a look at customers poor hot water flow rate. The scenario is 50 gallon cold water tank fed by 15mm from mains. Tank is then in 22mm to hot water cylinder. But to my suprise the hot distribution pipe from the top of the cylinder is a tee with the vent directly above. In other words there is no offset other than for the hot water.

Now am I being stupid but if there is not the min offset of 450mm when the customer turns a hot tap on alot of the flow is going directly up to the vent and then falling back restricting the flow of hot water to the distribution pipe. Your views would be gratefully recieved.

I forgot to mention as well due to the positioning of the cylinder there is not enough room for me to provide a min 450mm off set but I could do 400mm though.

 

[david williams]

in some instancies it is not possible to fully offset,but if pipes are clear this should not effect flow

 

[Plumbstar Tom]

Just how poor is the Hot flow rate?

What head does the CWST have?

 

[Winston]

Flow rate is very poor considering all pipework is in 22mm especially in the kitchen. The tank and cylinder are way up in the loft. CWST head to HWC is approx 1.6 metres. I just felt this was a silly place for the vent to be It could also be scaled up as hard water area cylinder dated 2001

 

[jonathanb]

Has the customer had work done recently and had the tank drained down - could be a partial air lock or debris in cold feed from tank.

 

[Bernie2]

From the top of the cylinder the combined vent and draw off usually runs horizontal and at 450mm splits, the vent goes up the hot supply down. You can have other configurations of course.

The idea is to try and stop one pipe circulation in the vent.

In practice I have found, if the vent goes straight up and the tee for the draw off is where you say. It pulls down loads of air and the water coming out the hot taps splutters and coughs all the time. Which basically is what you would expect it to do.

You could fit an Essex flange in the top of the cylinder and take the hot from there, leaving the vent as a free flowing vent. You usually get a better supply that way. But it obviously doesn't prevent one pipe circulation up the vent.

I would do as you suggest. Its seems about the best answer you can get considering the site conditions.

 

[david williams]

if tank is 1.6 mts above cylinder it should not pull air into hot pipewrk even if vent does rise streight off of cylinder ,if it did it would indicate problem with cold feed .the effect described can be down to to high a water temp,how old is cylinder/is it hard water area if so bottom of cylinder could be full of scale stopping cylinder fill .here in kent i have removed a 36/18 indirect that had so much scale in it it took two of us to lift it

 

[Plumbstar Tom]

Hi

If it is going straight up with no horizontal run then you will be drawing in hot water and air

As water heats in the cylinder air bubbles are created, these rise to the top and out the vent, so if the draw off is taken directly from this then you will pull air in.

If it ran horizontal and Teed after 450mm. You can take your feed from below this T so most of the air will rise up through the vent pipe and avoid being drawn by the feed to appliances.

Products like pumps and power showers will fail if fitted straight on this vent pipe due to air getting to the pump.

An essex flange will avoid taking a lot of air in to the appliances and is and accepted method to plumb from

 

[Bernie2]

Hmm!

Not to discount lime scale as a possible cause and an undersized cold cylinder supply.

On some old systems it was common to use either a 3/4" bsp Female x 22mm x 22mm tee or a 3/4" male bsp x 22mm x 22m tee, to go straight up with the vent and across for the hot supply.

If you took one off, what you generally found was that it restricted the flow out of the cylinder by the way it was made. This had the effect of a clear 22mm draw off past the tee pulling water off the cylinder faster than the cylinder could make it up, and so it drew the water and air down the vent instead.

Hi!

Anybody tried one of those Albion Bath Booster gizmos yet? Any good?

 

[Winston]

Hi gents thanks for all the input regarding this, job done I have done as I had thought moved the vent 400mm away I have also removed the 22mm gate valves and fitted with full bore. I also noted the cold water level level was half way so have put new ball valve in. The customer eventually has good hot running water.

I have mentioned though the hot water cylinder is very scaled up, and I have suggested descaling with Fernox DSX3. All has been good but I think in future when replcing gatevalves to remove olive and nut I had great difficulty in getting one of them water tight. I looked at the nut the iso comes with which is the same but does not appear to want to fully. Anyway sealed it with a bit of ptfe and lsx on top of the olive.

Took me alot longer than I had thought

 

[stevetheplumber]

Hi gents thanks for all the input regarding this, job done I have done as I had thought moved the vent 400mm away I have also removed the 22mm gate valves and fitted with full bore. I also noted the cold water level level was half way so have put new ball valve in. The customer eventually has good hot running water.

I have mentioned though the hot water cylinder is very scaled up, and I have suggested descaling with Fernox DSX3. All has been good but I think in future when replcing gatevalves to remove olive and nut I had great difficulty in getting one of them water tight. I looked at the nut the iso comes with which is the same but does not appear to want to fully. Anyway sealed it with a bit of ptfe and lsx on top of the olive.

Took me alot longer than I had thought

some full bore valves seem to have a finer pitched thread than the normal gatevalves nut geos on but doesnt realy tighten properly some motorised valves ars similar always best to chamge the nuts if possible

 

[Winston]

Thanks Steve will remember that next time was difficult as hot and cold feeds very close together with the rising main as well.

 

[Phil]

I'm glad you got his hot water restored Winston.

Sometimes the old gate valve will have a deeper or shallower fitting depth which can cause leaking problems if the new valve has a shallower depth, also brass nuts on a chrome body don't really go together.

I must get some 22mm olive splitters.

 

[Winston]

Yer me to phil though I dont think I would have got them in I really had to yank the pipe out to fit my spanner One hand on the spanner the other pushing the pipe to make sure fully engaged hard work in a dark hot loft . But job done and learnt lots from it, I do wonder with this as a occupation that one never stops learning .

 

[Plouasne]

Yer me to phil though I dont think I would have got them in I really had to yank the pipe out to fit my spanner One hand on the spanner the other pushing the pipe to make sure fully engaged hard work in a dark hot loft . But job done and learnt lots from it, I do wonder with this as a occupation that one never stops learning .

With regard to the noble skill of plumbing, the only time you stop learning, is after you have drawn your last breath, and you are what is so nicely known as defunct, or in other words "DED" as my youngest said to his brother, when they had a row, I will kill you dead, "ded" understand

 

[david williams]

plumbing is not a trade its a terminal illness.you just cant stop it .

 

[Winston]

Something I wanted to ask regarding this when I removed the vent I foound the pipe was so long it was actually at the bottom of the cold water tank. The copper was also very red in colour is this due to the hot water going through the vent or is it a form of corrosion. Sorry to ask such a dum question I am just curious.

And as I said earlier the tank is scaled up and suggested using fernox DS3 has anyone tried this and is it worth it?

 

[Bernie2]

No wonder they had problems.

 

[stevetheplumber]

Something I wanted to ask regarding this when I removed the vent I foound the pipe was so long it was actually at the bottom of the cold water tank. The copper was also very red in colour is this due to the hot water going through the vent or is it a form of corrosion. Sorry to ask such a dum question I am just curious.

And as I said earlier the tank is scaled up and suggested using fernox DS3 has anyone tried this and is it worth it?

if the vent was submerged its probably been circulating through the tank dont know what the red is but have seen this a lot on the ends of vent perhaps it heat and moist causes it

 

[Plucky]

If the vent was submerged that could hve been half the reason the water flow was poor. The air at the top of the vent would have been trapped because the open end of the pipe is under water.

 

[tcplumbing]

Hi all...
my first posting on here... glad to be onboard.
In response to the 'submerged vent' issue....

An open vent needs to be as described...'Open' It has two main functions.

1. To maintain atmospheric conditions in the hot-water pipework.
2. A key safety component in the hot-water system.

The principal overiding factor with the issue of poor hot water flow as you described was simply because of a submerged vent. It simply creates a vaccuum in the pipework and seriously reduces the flow of water at the draw-off points.
Bit of a weird scenario that, cos' it should have been like that from day one of the installation?
In respect of the 450mm min off-set distance from the draw off point on the cylinder to the open vent..... It's not something than can be left as... (400 will have to do...) It's actually a legal requirement under British Standards BS6700!
It doesn't have to be 450mm in a straight line.., you can bend your 22mm pipe in a slow radius curve to obtain the 450mm if space is tight.
But as I said... Its not a suggestion... Its the Standards and done for tried and tested safety reasons.

Hope this helps mate.

Tom.

 

[Hugh]

in some instancies it is not possible to fully offset,but if pipes are clear this should not effect flow

He's all ready said it

 

[tcplumbing]

Yeah thanks for the highlight Hugh..... Mine was an educational post highlighting the legal implications also... but erm.. yeah.., thanks anyway?