Can someone point me at a supplier of thick lagging for external 42mm drainpipe? Something that will withstand a good drenching water, snow & ice on the outside? The run is horizontal'ish across a flat roof.
I've been around the usual sheds but they only have the foam stuff up to fit 32mm diameter pipe, not 42mm :-(
This is the sort of stuff I've seen being installed for datacentre aircon kit
Maybe an extra wrap of aluminium foil tape?
In article , Adrian C writes
BES code 19674, 1 5/8" Armaflex, 25mm wall, normally used in aircon and refrigeration, closed cell so fine in the wet, £10 per 2m + post:
Continuous sleeve like that will work better than wrapped stuff but don't expect miracles, there wont be much thermal mass in a plas pipe so if there's just a trickle then you'll lose heat quickly and it will still freeze in the extremes.
Could this be an application for heating tape? IIRC you can get tape to protect pipes in well insulated lofts which uses a small amount of current just to keep the pipe above freezing.
Cheers
Dave R
In article , fred writes
Just remembered I've seen PIR foam pipe lagging in a high spec install, a bit like this:
or
They do 48mm too and I wonder if that might be better for room over joints (I think the free airspace elsewhere would be less of an issue than possible deformations and resulting gaps at joints).
Again, it's closed cell so it can't get wet.
Marginally more than Armaflex at 5-6quid a metre but it will be near twice as effective (or you could use thinner at reduced cost).
Usually am arm and 3 legs expensive though! I have several water pipes fed through unheated buildings and would appreciate a modestly priced source.
Thanks all,
Me clicky eBay mouse decided to go with the rockwool solution and just waterproof it, I've got plenty of adhesive foil and butyl tape to wrap it, and also I'm going to straighten out out a small dip along the length where static water inside could very well freeze (which I admit, yes, it will do eventually...)
In article , Tim Lamb writes
Not self regulating but I wonder how many amps you'd need to pump down a length of 3A flat twin to get the desired effect on an insulated run. Running from a low voltage supply and perhaps with a pipe stat in the coldest area for control.
In message , fred writes
ISTR Andrew Gabriel mentioning he rolled his own/used something else for a cheaper solution
I replaced a friend's lead water main with MDPE. It wasn't possible to put it down to the recommended depth as both ends were less than 500mm deep (one end was only 50mm, but I could push that down to 500mm), and then it had to run through the unheated sub-floor.
The standard way to thaw a frozen supply pipe used to be to pass a very large current through it (although I don't think water companies will do this at all anymore). Given we were going to plastic, that stops being possible. So I taped a length of 1mm T&E to the MDPE for the whole length, all 3 cores crimped and lead-soldered together at the far and, and slightly protected with heatshrink. In the underfloor area, I insulated the pipework, but I didn't underground.
I think the run was about 15m. After it was installed, I bought a cheap 70-250W 12V electronic lighting transformer, and tried feeding the T&E. ISTR, the power consumption was something like 70W if I fed it into the live and neutral, and just over 100W if I paralleled up the earth conductor with one of them. That's 6W/m which probably isn't enough, particularly underground where the ground will conduct the heat away. One issue (which I was already aware of) is the skin effect of the high frequency output significantly raises the impedance of the wire over what it's DC or 50Hz resistance is. What I could do to increase the power output is to add some turns to the large ferrite cire in the transformer to crank up the output voltage, or buy a large old magnetic 50Hz transformer. I would probably want a higher W/m figure for the underground section than the insulated section, and this can be done by paralleling up the third wire only in the insulated section, to increase the proportion of the heat generated in the underground section. Alternatively, I could cut through the T&E at the boundary, and feed the two shorter sections separately,
I looked at heating tape (which looks exactly like T&E) and decided that at around £30/m, it was taking the piss. You can heat up standard T&E with the right choice of voltage/current flow across it, and we're not talking about actually making it hot - it only has to get the pipe to above freezing.
One other thing I did think about was burying a temperature sensor in the ground at some point along the pipe. If it was my house where I already have a 1-wire dallas temperature sensing network which I could simply add it to, I would have done this. It would be easy to add one to the subfloor insulated section anytime, but less so for the underground section, and I slightly regret not doing so.
In message , Andrew Gabriel writes
Interesting.
I suppose you could have done 2 runs of 2+E giving more choices.
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Indeed. TLC sell it for £10/m.
In message , charles writes
Still far too expensive for a 30m run to some stables. For £300 they can carry buckets!
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Well, I can hookup whatever power supply is needed to drive it, so I wasn't worried about choices. It's a contingency which I probably won't actually connect up unless/until it's needed. It probably won't ever be needed, but the cost and effort of installing the cable was so low compared with the lack of any contingency if it were ever to freeze.
For the benefit of anyone planning to do this:
15m of 1mm drops 44mV/A/m at 50Hz, so 15m = 0.66 ohms. 12v 0.66 ohms = 18A 12v 18A = 216w So unless the supply was 216w+ rated, and you wanted to dump 216w, cable R is too low for 12v, and the supply would be putting out what current it cou ld at much reduced voltage. So if you want more power dissipation you'd need to increase cable R. One w ay is to use 2 runs of bell wire, connecting them in series at the near end . Thinner pvc also means better heat transfer, reducing pvc temp.NT
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