In this case, the static pressure is built up in the cylinder of around 2 bar, maybe more at night as pressure rises through little mains network use. The pressure vessel will be pressurized absorbing pressure and some water. The pressure is *locked* in the cylinder as there is a non-return valve on the cold inlet. This is normal operation. If there is a drop in mains pressure, less that what is locked in the cylinder, or if the cylinder is cooling after the mains water supply was closed off, a vacuum inside the cylinder can result. The mains pipe's _dynamic_ pressure will drop substantially when a tap is open - as is normal on most mains supplies. Measure the mains pressure from a garden tap and turn on the cold tap at the kitchen sink and observe the readings, from when no draw off to full draw-off. So, lets say the static pressure rises to over 2 bar during the night, being locked in the cylinder by the non-return valve. In the morning this maybe under 2 bar, like 1.8 bar as Elliot recorded, as people in the district start to use the mains network. ♦ In the cylinder we have over 2 bar pressure locked in via a non-return valve on the incoming mains pipe; ♦ 1.8 bar in the main pipe, over 2 bar in the cylinder; ♦ Open up a tap fully, the pressure and water flow in the cylinder is only going one way, out through the hot draw off pipe to the tap, aided by the pressure vessel; ♦ *No water* will enter the cylinder as the non-return valve is locked up as the cylinder pressure is _higher_ than in the mains pipe, preventing water entering the cylinder; ♦ The pressure vessel maintains the pressure in the cylinder until the cylinder pressure drops below 1.8 bar; ♦ The non-return valve on the incoming mains stays locked, with no water coming in, until the pressure in the cylinder is less than 1.8 bar; ♦ _Negative_ pressure is created in the cylinder, causing it to partially implode until the cylinder pressure is less or equal to the mains pressure; ♦ The pressure in the cylinder and mains pipe equalizes, preventing full cylinder implosion This all a matter of _pressure_ rather than water flow.
Yes, but what happens if the mains water is turned off and somebody turns on the hot tap? There would be whole new estates with crushed cylinders if, for example 'United Utilities', decided to work on a water main.
@@adamdavies163 As the contents of the cylinder will not empty the cylinder, the negative effect will be small and temporary. The cylinder construction should resist the implosion.
Just starting in the industry, don't expect pulling vacuums in unvented cylinders is covered! Now I know something else to look out for when helping customers with faults!
That seems ridiculous. I thought that the regulated mains water pressure was what 'pushes' the water out of the top of the cylinder. So if the flow rate coming in is slow then the flow rate going out should be equally slow. What you are saying is that the syphon effect from running the lower taps is enough to crush the cylinder? That is obviously dangerous, also means that if the mains water is ever interrupted, regardless of pipe sizes, and somebody turns the hot tap on, then you have a crushed cylinder? There must be more wrong with that installation than just a low input pressure. If I turned down the input to my old Megaflow then the hot taps would also slow by the same amount.
Spot mate... This guy is Talking Bollocks... CRUSHING THE CYLINDER . Completely non sense. The main thing about installing a unvented Cylinder is the pressure... Which it should be a minimum 1.8bar. Definitely it could have been something else gone wrong with this Cylinder.
@@AKosta-zf3vn nonsense. If you bung a hot water system and then open a hot water tap the cylinder will IMPLODE. This is due to a negative vacuum inside the cylinder. If you have less going in to a cylinder than going out you will always create a vacuum.
@@keithwebster6164 That's why I asked the original question. What prevents this happening on an unvented? Otherwise they would implode every time the mains water supply was interrupted and the hot tap turned on.
Very useful Mine started being noisy only when after 6 moths but only when running a bath It’s 22 in 22out but of course only the baths are on 22 to cause the noise when there in full wack Interestingly the pressure and flows good, especially when first installed but the water company have been messing around with the supply over the last 6 months and have been having drastic swings in pressure since Thing is if we do have problems down the line I doubt the water company going to put there hands up ( or in there pockets) ! For changing the quality of the supply! Certainly going to look at an aav retrofit, generally try not to overcomplicate installs as they have there own problems too, Also no mention of this in any of the install manuals! So really useful video thanks
In the early days when IMI made the copper tribune cylinders they had anti siphon valves as standard to stop this from happening .especially being made of softer copper and they were prone for splitting but it was more from lack of maintenance and flat expansion tanks
I’ve heard of it happening to open vented cylinders when the cold feed and vent freeze in the loft and the cylinder is on the top floor and the customer runs a tap and bang the cylinder implodes, but never heard of it with an unvented every days a school day!
You are totally correct my friend this should never happen on an unvented cylinder What the video fails to explain is that gledhill have made a cylinder so cheap that an anti vacuum valve is required. To stop this from happening No quality cylinder would require. So in the video he mentioned not enough water flow creating the problem. So if the mains water is turned off accident or becomes frozen The potential of it imploding is real. However in hard water areas the valve will fail within 3 years so this is a quick fix not a solution.
Similar thing happened to me a long time back, unknown to me previous home owner had fitted a NR valve into the HW expansion vent pipe, presumably to stop air down draw on the shower HW feed. Years later I wanted to change a washer on the bathroon hand basin, no local isolation so closed the cold feed from header tank to the HW cylinder and drained down, took much longer than expected. On refilling the HW circuit, water pouring through bedroom ceiling. Check in loft found HW cylinder crushed by atmospheric persssure and leaking form many parts. needles to say the NR valve was found and removed after a new cylinder installed.. Expensive tap washer....
Jesus Alan that’s bad that mate that plumber who did that should be struck off the list common sense really I never put a cyl on 15 even megaflos some people are clueless when it comes to unvented like the lever valve on the hot only put an isolater on the cold mi say that loads of new builds I go to there putting gate valves on the hot outlet 🤦♂️ shocking
My unvented cylinder is on 15mm and works fine. The installation manual also suggests 15mm is fine. I'd like to know your reasoning for saying that you never put unvented cylinders on 15mm.
@@koolio67890 It is the *flow and pressure that matters,* not pipe bore. You could have 8 bar on a 15mm pipe with excellent flow. It will be reduced in pressure at the unvented cylinder to 3 or 4 bar by a PRV. Then 22mm pipe around the house from the cylinder to avoid flow and pressure drop. Many unvented cylinders are constructed robustly to prevent implosion when there are short and small negative pressures - hence why there are few, if any these days, of copper unvented cylinders. If you have a high mains pressure with a high flow there will rarely be problems. That is not the case with many installations. Opening taps slowly helps to avoid problems.
I worked at gledhill till a few months ago honestly they would be closed down if you all knew what went on at there oldbury Depot selling faulty returned items that still was leaking. The copper and stainless steal is so thin to cut cost They would have a 17 year old trainer who hasn’t a clue sending out cylinders The manager is a con artist who doesn’t care about anything but how many his got out the door. Even the Blackpool branch is joke. Check for back stays if you know u know another cost cutting method which ended up causing dangerous leaks
I don't fit Gledhill following a bad experience and it would appear other engineers share my policy. I didn't fit this particular system a Gledhill Boilermate (thermal store) I just removed and re-fitted the F&E after a wardrobe re-fit. Drain off was via a ground floor radiator and after re-filling all worked well. The customer reported a leak from the cylinder after a few months which was coming from the main copper cylinder. Gledhill had then discontinued the model so it was replaced with a Megaflo. After taking it away and cutting open for investigation I was appalled at the thin construction and sub standard soldering. The customer viewed it contacted Gledhill who didn't want to know so he paid me in full for the new Megaflo. Gledhill also manufactured similar cylinders using a Fortic system and when I was asked to do work on these I politely declined.
This sort of comment always makes me laugh lol copper boilermates are over 20 years old only started leaking after you worked on it so must be gledhills fault lol hasn't done bad if it lasted that long properly would have lasted longer if wasn't touched
@@AllenHart999 yes very good videos ,plumbing and heating all week and then look forward to video from you on a Sunday !! I did a hose clean and flush out on a viessmann 100 series boiler the other day and I thought of you as I started the job and said “me names Allen Hart “! I use a VAX aqua hoover with a hosepipe I’ve attached and suck out the whole hydro block and heat exchanger& hoses . the vax machine it works a treat You’ll be surprised how much it pulls out . you need to try it
You need a G3 qualification to install and register unvented cylinders , I assume the installer of this doesn't have this then ?? I did mine 10 years ago , not renewed it as not installing anymore but I remember it was a minimum of 1.5 bar and 20 litres a minute . If you have 3 bar incoming pressure and more than 20 litres a minute then supplying the cylinder in 15mm isn't an issue . Ideally upgrade to a 22mm but sometimes it's impossible.
I watch an American plumber. When they install there cylinders they install a 'vacuum breaker' on the cold inlet to the tank (basically a dirgo valve) and its if a fire truck connects to the mains in the road as without a vacuum breaker it can implode the cylinder... this is a useful video tho!
Expensive .... I bought a similar cylinder for my re-plumb... 2 heat exchanger coils (solar/heating) & it cost me €750... 🙄😒 Another thing with stainless steel is it work-hardens as it is flexed like that & a split is inevitable... 😎👍☘🍺
Isn't it a bit odd however that there are other reports of Gledhill cylinders in particular doing this? In addition this is the cheapest and lightest cylinder on the market...
Copper unvented cylinders regularly imploded if no anti-vacuum valve was fitted, or it failed. Unvented cylinders have to be robust enough to resist implosion as well as the high mains pressures. BES sell an anti-vacuum valve at £10. fitting two is the best way, in case one fails. *If no anti-vacuum valve is fitted by the makers, it is always best to fit one on the draw-off pipe just at the cylinder port.*
seen so many of these fitted by non qualified so called plumbers. No ACS but because they can connect a pipe they don't see the issue. Cylinders never registered
I have this exact problem with my Gledhill tank. Plumbers who fitted it have come and gone 6 times trying to fix the problem and no luck. Banging all day with or without the water running. GLedhill refuse the visit...
Did you put your WhatsApp details in mate I run my own gas company in Scotland have a few different cylinder pictures and bio mass jobs i have done I can you send you pics if your interested 👍
@@AllenHart999 cheers mate I am doing mi gas runs from the meter box to the property’s just now can send in a video on a job on an external wall insulation contract we are doing on electric rigid threader and chain vice il get it sent to you in the next few days👍
@@AllenHart999 Gibberish... Crap.. Talking nonsense... Not just Rubbish.!! It must have been something else wrong with that Cylinder. ( Installation probably).. But as long as you have the Pressure at 1.8bar min. You can have Unvented cylinder..no probs whatsoever.
From what I remember from college (instrumentation course) as the flow increases the pressure decreases. It may be 1.8 bar when there is no flow but this is likely going to reduce considerably under flow, taking into account there is
