Please forgive my ignorance, but I've forgotten my O level physics - what is pH please?
David. _____ From: Owen Jenkins [mailto:[email protected]] Sent: 28 May 2012 00:28 To: mogtalk2 Subject: Re: [mogtalk2] Heater Control Valve 2005 Aero 8 Rainwater is always acid, as it has carbon dioxide dissolved in it. It can also have oxides of sulphur and nitrogen from the burning of fossil fuels, internal combustion engines, volcanoes, the action of lightning etc. The rainwater I collect for my garden has a pH of 6.5, typically. Lower when Icelandic volcanoes erupt. It is quite instructive to read the "pH at source" on bottles of mineral water. Deeside water, bottled about ten miles from here, has a "pH at source" of 6.1. If you measure what's in the bottle, it varies. This latter is true of all bottled water. Some bottled water can have a "pH at source" as high as 8.0. Pure water, if you do a pukka job of demineralising it, should have a pH of 7.0 at STP. Leave it exposed to the air and it will drop, typically, to around 6.7 or so as it dissolves acid gases from the atmosphere. Water from your dehumidifier will also be slightly acid. If you boil it, you get the gases out and the pH should be much closer to 7.0, when cool. Now store it in full, stoppered bottles and, if you're lucky, it will stay neutral. In theory. If you don't get algae growing in it. One of the other problems you may get, where you have hoses clamped onto corrodible metal, is crevice corrosion. It could well be the main issue here. If you are relying upon maintaining a passive film for corrosion inhibition, you'll be out of luck. Most passive films require oxygen. That gets eaten up in the initial corrosion, now there's no oxygen to regenerate the passive film, so you get an auto-catalytic corrosion reaction, with the area between hose and valve containing an increasingly acid fluid, with the metal under the hose acting as the anode in a corrosion cell and dissolving, while the metal exposed to the free fluid acts as the cathode. Have a look and you'll see that the valve nozzle appears to have corroded from the outside (in contact with hose) inwards. Following recommended fluid mixtures and regular maintenance should minimise the risk of problems like this occurring. Which reminds me... I used to be good at changing hoses fairly frequently. Can't say I've been as attentive in this area in recent years as once I was. Meanwhile, if he really can't source a replacement and this one still works, but for the failure of the stub pipe nozzle, I'd be inclined to see if I could fit a new stub pipe to replace the badly corroded one. Then flush the system properly and fill with the Morgan-recommended, low-electrical conductivity, inhibited cooling mixture. Regards, Owen. ----- Original Message ----- From: Martyn <mailto:[email protected]> J Culling To: mogtalk2 <mailto:[email protected]> Sent: Sunday, May 27, 2012 5:12 PM Subject: Re: [mogtalk2] Heater Control Valve 2005 Aero 8 Good point Owen. Many people think, "it won't freeze, so I don't need antifreeze" and forget the stuff is choc full of corrosion inhibitors. Pure water I think, is naturally slightly acid, but most tap water has lord knows what dissolved in it and can be either acid or alkali. The trike runs antifreeze for the inhibitors - along with distilled water! (By product of de-humidifier). rgds Martyn On May 27 2012, Owen Jenkins wrote: What's he been running in the cooling system? It should never have corroded like that if he'd had sufficient corrosion inhibitor it here. Being in S.A., I suspect he runs a very high water content and hasn't thought much about what else ought to be in there. With mixed metal systems, you can't do that. It may be closing the stable door after the horse has bolted, but if he ever finds a replacement, he needs to make sure he's following some sensible guidance on anti-corrosion measures, otherwise it will happen again. Regards, Owen. View posts on The Mail Archive http://www.mail-archive.com/[email protected]/ <https://www.listbox.com/member/?&; 186> Modify Your Subscription <http://www.listbox.com> _____ No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2176 / Virus Database: 2425/5025 - Release Date: 05/27/12 ------------------------------------------- View posts on The Mail Archive http://www.mail-archive.com/[email protected]/ [http://www.mail-archive.com/[email protected]/] Modify Your Subscription: https://www.listbox.com/member/?member_id=22459785&id_secret=22459785-4a39ddf8 Powered by Listbox: http://www.listbox.com
