|
One for the plumbers.
I am considering fitting an additional expansion vessel to our heating
system. Advice specifies boiler return pipe location. Why? -- Tim Lamb |
One for the plumbers.
On 27/10/2020 18:38:30, Tim Lamb wrote:
I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? Probably where the boiler pressure gauge/sensor is fitted, and so would change least under normal operation if buffered by the expansion vessel? It might affect the firing of the boiler if it wildly fluctuated when valves/pumps were turned on or off? BICBW |
One for the plumbers.
On Tue, 27 Oct 2020 18:38:30 +0000, Tim Lamb
wrote: I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? Because you wouldn't want to pump pushing water *towards* the tank? Cheers, T i m |
One for the plumbers.
On 27/10/2020 19:38, T i m wrote:
On Tue, 27 Oct 2020 18:38:30 +0000, Tim Lamb wrote: I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? Because you wouldn't want to pump pushing water *towards* the tank? Cheers, T i m I'd say rather that any pump noise at vane passing frequencies will be effectively damped after going all the way around the system. But TBH I don't think it would matter much. One bit of advice, though. Include a service valve between the system and the tank, and also a drain cock on the tank side. Then it is very easy to check the tank pressure in the future. Just remember to open the valve afterwards. (I have a lever type ball valve on mine so that its setting is always immediately obvious). |
One for the plumbers.
On 27/10/2020 21:09, Jethro_uk wrote:
On Tue, 27 Oct 2020 18:38:30 +0000, Tim Lamb wrote: I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? It's that bit cooler so less wear on the diaphragm. But it is a dead leg, so not much conduction unless it is very short. |
One for the plumbers.
On Tue, 27 Oct 2020 20:20:51 +0000, newshound
wrote: On 27/10/2020 19:38, T i m wrote: On Tue, 27 Oct 2020 18:38:30 +0000, Tim Lamb wrote: I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? Because you wouldn't want to pump pushing water *towards* the tank? Cheers, T i m I'd say rather that any pump noise at vane passing frequencies will be effectively damped after going all the way around the system. Ah, I was thinking 'expansion tank' not 'vessel'. Not got any CGH here, let alone a sealed system. ;-) But TBH I don't think it would matter much. No, I agree, especially in the vessel case. There might be some 'best practice' reasons to do it one way or some technical reason to do it so though. One bit of advice, though. Include a service valve between the system and the tank, and also a drain cock on the tank side. +1 Then it is very easy to check the tank pressure in the future. An advantage of a vented system, you can peer in the top of the expansion tank? Just remember to open the valve afterwards. Depending on why Tim thinks he needs a second expansion vessel, it may not make any noticeable difference? (I have a lever type ball valve on mine so that its setting is always immediately obvious). When I was doing all the plumbing here 40 years ago they typically recommended gate valves (low pressure) and conventional stopcocks (mains pressure), I'm not sure ball valves were used much outside washing machine attachments? Cheers, T i m |
One for the plumbers.
On Tue, 27 Oct 2020 21:20:59 +0000, newshound wrote:
I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? It's that bit cooler so less wear on the diaphragm. But it is a dead leg, so not much conduction unless it is very short. Well it's dead in that it goes nowhere but there is still the flow/return due to the expansion of the water from cold to hot and back. I think that expansion is about 1 l per 100 l 10 to 70 C, guesstimate that's a metre or two of 15 mm pipe. -- Cheers Dave. |
One for the plumbers.
In message l.net,
Dave Liquorice writes On Tue, 27 Oct 2020 21:20:59 +0000, newshound wrote: I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? It's that bit cooler so less wear on the diaphragm. But it is a dead leg, so not much conduction unless it is very short. Well it's dead in that it goes nowhere but there is still the flow/return due to the expansion of the water from cold to hot and back. I think that expansion is about 1 l per 100 l 10 to 70 C, guesstimate that's a metre or two of 15 mm pipe. Umm. My boiler modulates but, due to the characteristics of underfloor heating, is mostly returning water at reasonably high temperature. I'll do some checks. There is an 8L vessel in the boiler anyway. A question for another day is how to adapt the *weather compensation provision* to run the system at a lower temperature when there is no call for re-heating the DHW. The actual issue is that the diverter valve momentarily blocks the pump flow leading to water hammer which opens the boiler relief valve thus losing system water:-) An alternative solution is to fit a bypass valve: to maintain flow during the transition. Soldering access is a pig! -- Tim Lamb |
One for the plumbers.
On Wed, 28 Oct 2020 09:28:59 +0000, Tim Lamb wrote:
The actual issue is that the diverter valve momentarily blocks the pump flow leading to water hammer which opens the boiler relief valve thus losing system water:-) Have some relays that switch the pump off when the divert valve is being motored? An alternative solution is to fit a bypass valve: to maintain flow during the transition. Soldering access is a pig! That might not stop the hammer unless reasonably open... Will adding another expansion vessel do anything? After all you have one already and they have quite high interia due to their size. It would have to connected close to the divertor valve an on a short pipe as well. Surely one of the small "water hammer arrestors" would be better? Screwfix have several, can't persuade Toolstations site to cough anything up. -- Cheers Dave. |
One for the plumbers.
In message l.net,
Dave Liquorice writes On Wed, 28 Oct 2020 09:28:59 +0000, Tim Lamb wrote: The actual issue is that the diverter valve momentarily blocks the pump flow leading to water hammer which opens the boiler relief valve thus losing system water:-) Have some relays that switch the pump off when the divert valve is being motored? System boiler, internal pump. An alternative solution is to fit a bypass valve: to maintain flow during the transition. Soldering access is a pig! That might not stop the hammer unless reasonably open... The idea was to divert the flow through the hot tank coil with an automatic bypass valve (Honeywell DU144) Will adding another expansion vessel do anything? After all you have one already and they have quite high interia due to their size. It would have to connected close to the divertor valve an on a short pipe as well. Tucked away in the boiler, I don't know which leg it is on. Also 8L is a bit meagre for very cold weather when more heating circuits are running. Surely one of the small "water hammer arrestors" would be better? Screwfix have several, can't persuade Toolstations site to cough anything up. Pass. What I hear as water hammer may be the boiler safety valve opening and re-closing. Plumbed in to the condensate pipe so hard to tell. -- Tim Lamb |
One for the plumbers.
On 28 Oct 2020 at 12:50:41 GMT, "Tim Lamb"
wrote: In message l.net, Dave Liquorice writes On Wed, 28 Oct 2020 09:28:59 +0000, Tim Lamb wrote: The actual issue is that the diverter valve momentarily blocks the pump flow leading to water hammer which opens the boiler relief valve thus losing system water:-) Have some relays that switch the pump off when the divert valve is being motored? System boiler, internal pump. An alternative solution is to fit a bypass valve: to maintain flow during the transition. Soldering access is a pig! That might not stop the hammer unless reasonably open... The idea was to divert the flow through the hot tank coil with an automatic bypass valve (Honeywell DU144) Will adding another expansion vessel do anything? After all you have one already and they have quite high interia due to their size. It would have to connected close to the divertor valve an on a short pipe as well. Tucked away in the boiler, I don't know which leg it is on. Also 8L is a bit meagre for very cold weather when more heating circuits are running. Surely one of the small "water hammer arrestors" would be better? Screwfix have several, can't persuade Toolstations site to cough anything up. Pass. What I hear as water hammer may be the boiler safety valve opening and re-closing. Plumbed in to the condensate pipe so hard to tell. How about a motorised valve opening a bypass pipe a few seconds before the diverter valve operates? I think short delay mains relays are probably a commodity. Though I haven't looked. -- Roger Hayter |
One for the plumbers.
In message , Roger Hayter
writes On 28 Oct 2020 at 12:50:41 GMT, "Tim Lamb" wrote: In message l.net, Dave Liquorice writes On Wed, 28 Oct 2020 09:28:59 +0000, Tim Lamb wrote: The actual issue is that the diverter valve momentarily blocks the pump flow leading to water hammer which opens the boiler relief valve thus losing system water:-) Have some relays that switch the pump off when the divert valve is being motored? System boiler, internal pump. An alternative solution is to fit a bypass valve: to maintain flow during the transition. Soldering access is a pig! That might not stop the hammer unless reasonably open... The idea was to divert the flow through the hot tank coil with an automatic bypass valve (Honeywell DU144) Will adding another expansion vessel do anything? After all you have one already and they have quite high interia due to their size. It would have to connected close to the divertor valve an on a short pipe as well. Tucked away in the boiler, I don't know which leg it is on. Also 8L is a bit meagre for very cold weather when more heating circuits are running. Surely one of the small "water hammer arrestors" would be better? Screwfix have several, can't persuade Toolstations site to cough anything up. Pass. What I hear as water hammer may be the boiler safety valve opening and re-closing. Plumbed in to the condensate pipe so hard to tell. How about a motorised valve opening a bypass pipe a few seconds before the diverter valve operates? I think short delay mains relays are probably a commodity. Though I haven't looked. Heading back towards Y plan complexity which I wanted to avoid. One day, a visiting plumber is going to try making sense of this system! Currently it is W plan with some relays to fudge the underfloor heat control requirements. I think an automatic bypass would be simpler to understand. -- Tim Lamb |
One for the plumbers.
On Tue, 27 Oct 2020 18:38:30 +0000, Tim Lamb wrote:
I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? As an aside when our new Worcester Bosch combi boiler was fitted I read the installation manual. If there were more than a certain number of radiators it required an additional expansion vessel to be fitted (beyond the one which came inside the boiler). I presume because the extra volume of water caused more expansion when heated. The plumber had never heard of this before. [Was also indecently amused that anyone would bother to read the manual.] Anyway, no idea about the recommended location. It was a while back. I assume that the pressure difference between pump out and return might affect the expansion vessel? Pop the release valve if there is one? Cheers Dave R -- AMD FX-6300 in GA-990X-Gaming SLI-CF running Windows 7 Pro x64 -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
One for the plumbers.
On 27/10/2020 22:00, T i m wrote:
On Tue, 27 Oct 2020 20:20:51 +0000, newshound wrote: On 27/10/2020 19:38, T i m wrote: On Tue, 27 Oct 2020 18:38:30 +0000, Tim Lamb wrote: I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? Because you wouldn't want to pump pushing water *towards* the tank? Cheers, T i m I'd say rather that any pump noise at vane passing frequencies will be effectively damped after going all the way around the system. Ah, I was thinking 'expansion tank' not 'vessel'. Not got any CGH here, let alone a sealed system. ;-) But TBH I don't think it would matter much. No, I agree, especially in the vessel case. There might be some 'best practice' reasons to do it one way or some technical reason to do it so though. One bit of advice, though. Include a service valve between the system and the tank, and also a drain cock on the tank side. +1 Then it is very easy to check the tank pressure in the future. An advantage of a vented system, you can peer in the top of the expansion tank? Just remember to open the valve afterwards. Depending on why Tim thinks he needs a second expansion vessel, it may not make any noticeable difference? (I have a lever type ball valve on mine so that its setting is always immediately obvious). When I was doing all the plumbing here 40 years ago they typically recommended gate valves (low pressure) and conventional stopcocks (mains pressure), I'm not sure ball valves were used much outside washing machine attachments? Cheers, T i m I reckon the modern small ball valves are pretty good, and not silly money. You can get full bore ones that are only slightly larger than the standard service valves. I also favour the ones with a proper lever on them. I have an extra couple for "easy access" on the gas and water mains. You can even train wives and children how to use them. |
One for the plumbers.
On 28/10/2020 00:10, Dave Liquorice wrote:
On Tue, 27 Oct 2020 21:20:59 +0000, newshound wrote: I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? It's that bit cooler so less wear on the diaphragm. But it is a dead leg, so not much conduction unless it is very short. Well it's dead in that it goes nowhere but there is still the flow/return due to the expansion of the water from cold to hot and back. I think that expansion is about 1 l per 100 l 10 to 70 C, guesstimate that's a metre or two of 15 mm pipe. And how long does that take, and how quickly does a foot of warm copper pipe cool down, especially if it is not lagged. (Actually thinking about it, mine is on a braid covered flexible hose). |
One for the plumbers.
On 28/10/2020 19:07, David wrote:
On Tue, 27 Oct 2020 18:38:30 +0000, Tim Lamb wrote: I am considering fitting an additional expansion vessel to our heating system. Advice specifies boiler return pipe location. Why? As an aside when our new Worcester Bosch combi boiler was fitted I read the installation manual. If there were more than a certain number of radiators it required an additional expansion vessel to be fitted (beyond the one which came inside the boiler). I presume because the extra volume of water caused more expansion when heated. The plumber had never heard of this before. [Was also indecently amused that anyone would bother to read the manual.] Anyway, no idea about the recommended location. It was a while back. I assume that the pressure difference between pump out and return might affect the expansion vessel? Pop the release valve if there is one? Cheers Dave R No relief valve, relies on the one in the boiler. Difficult to over-pressurise anyway until the diaphragm fails. Probably the schraeder valve that is the weak link. |
One for the plumbers.
On Wed, 28 Oct 2020 20:10:01 +0000, newshound
wrote: snip When I was doing all the plumbing here 40 years ago they typically recommended gate valves (low pressure) and conventional stopcocks (mains pressure), I'm not sure ball valves were used much outside washing machine attachments? I reckon the modern small ball valves are pretty good, and not silly money. You can get full bore ones that are only slightly larger than the standard service valves. Yeah ... and I think they are worth spending the extra money on, for all the advantages they offer. I also favour the ones with a proper lever on them. Agreed. I've seen too many people twist the plastic caps off the appliance ones because they have seized. Using a small adjustable first is all they normally need to get them moving first though. I have an extra couple for "easy access" on the gas and water mains. We used to have a communal water main that ran across the back of the cottages and off that to each house in some galvanised steel pipe. When isolating my supply via my underground tap I suddenly found I had a pond in the garden. Luckily I knew a guy who worked for the water board who came round and repaired the broken bit (it has rusted away). [1] When we built the extension it meant it would go over the communal main so we paid to have it bypassed (in plastic) around our extension (to the boundary) and a new main run in directly (plastic, inside some plastic ducting). Some years later we got a knock on the door saying that there was a burst in the communal bit and I'd have to pay my share. I explained why I didn't and how the leak in their main couldn't be in my garden. ;-) You can even train wives and children how to use them. Daughter is quite practical and I'm not sure the Mrs could get to it with her knees (or not comfortably). It's a conventional stopcock and I try to work it closed and back once in a while, just to make sure I can ... but a quality ball valve would be nice. Cheers, T i m [1] I had a temporary standpipe in the kitchen when I first bought this place but was still living with my parents. I came round after work to do some more work and found the bib tap on the kitchen floor and a rod of ice sticking out of the stand pipe! *Luckily* it was still all frozen so I was able to isolate it outside and put the tap back on with not a drop of water spilled. ;-) |
One for the plumbers.
On 28 Oct 2020 at 16:09:40 GMT, "Tim Lamb"
wrote: In message , Roger Hayter writes On 28 Oct 2020 at 12:50:41 GMT, "Tim Lamb" wrote: In message l.net, Dave Liquorice writes On Wed, 28 Oct 2020 09:28:59 +0000, Tim Lamb wrote: The actual issue is that the diverter valve momentarily blocks the pump flow leading to water hammer which opens the boiler relief valve thus losing system water:-) Have some relays that switch the pump off when the divert valve is being motored? System boiler, internal pump. An alternative solution is to fit a bypass valve: to maintain flow during the transition. Soldering access is a pig! That might not stop the hammer unless reasonably open... The idea was to divert the flow through the hot tank coil with an automatic bypass valve (Honeywell DU144) Will adding another expansion vessel do anything? After all you have one already and they have quite high interia due to their size. It would have to connected close to the divertor valve an on a short pipe as well. Tucked away in the boiler, I don't know which leg it is on. Also 8L is a bit meagre for very cold weather when more heating circuits are running. Surely one of the small "water hammer arrestors" would be better? Screwfix have several, can't persuade Toolstations site to cough anything up. Pass. What I hear as water hammer may be the boiler safety valve opening and re-closing. Plumbed in to the condensate pipe so hard to tell. How about a motorised valve opening a bypass pipe a few seconds before the diverter valve operates? I think short delay mains relays are probably a commodity. Though I haven't looked. Heading back towards Y plan complexity which I wanted to avoid. One day, a visiting plumber is going to try making sense of this system! Currently it is W plan with some relays to fudge the underfloor heat control requirements. I think an automatic bypass would be simpler to understand. I agree, but I thought there was some risk it wouldn't open fast enough to prevent the overpressure/water hammer effect. -- Roger Hayter |
One for the plumbers.
On 29/10/2020 00:29:33, Roger Hayter wrote:
On 28 Oct 2020 at 16:09:40 GMT, "Tim Lamb" wrote: In message , Roger Hayter writes On 28 Oct 2020 at 12:50:41 GMT, "Tim Lamb" wrote: In message l.net, Dave Liquorice writes On Wed, 28 Oct 2020 09:28:59 +0000, Tim Lamb wrote: The actual issue is that the diverter valve momentarily blocks the pump flow leading to water hammer which opens the boiler relief valve thus losing system water:-) Have some relays that switch the pump off when the divert valve is being motored? System boiler, internal pump. An alternative solution is to fit a bypass valve: to maintain flow during the transition. Soldering access is a pig! That might not stop the hammer unless reasonably open... The idea was to divert the flow through the hot tank coil with an automatic bypass valve (Honeywell DU144) Will adding another expansion vessel do anything? After all you have one already and they have quite high interia due to their size. It would have to connected close to the divertor valve an on a short pipe as well. Tucked away in the boiler, I don't know which leg it is on. Also 8L is a bit meagre for very cold weather when more heating circuits are running. Surely one of the small "water hammer arrestors" would be better? Screwfix have several, can't persuade Toolstations site to cough anything up. Pass. What I hear as water hammer may be the boiler safety valve opening and re-closing. Plumbed in to the condensate pipe so hard to tell. How about a motorised valve opening a bypass pipe a few seconds before the diverter valve operates? I think short delay mains relays are probably a commodity. Though I haven't looked. Heading back towards Y plan complexity which I wanted to avoid. One day, a visiting plumber is going to try making sense of this system! Currently it is W plan with some relays to fudge the underfloor heat control requirements. I think an automatic bypass would be simpler to understand. I agree, but I thought there was some risk it wouldn't open fast enough to prevent the overpressure/water hammer effect. I can't think of anything acting faster than a pressure senstive bypass valve? |
One for the plumbers.
On Wednesday, 28 October 2020 19:07:06 UTC, David WE Roberts (Google) wrote:
If there were more than a certain number of radiators it required an additional expansion vessel to be fitted (beyond the one which came inside the boiler). The plumber had never heard of this before. [Was also indecently amused that anyone would bother to read the manual.] Heaven forbid he would actually calculate the volume of water in the system Owain |
One for the plumbers.
On 29 Oct 2020 at 01:10:33 GMT, "Fredxx" wrote:
On 29/10/2020 00:29:33, Roger Hayter wrote: On 28 Oct 2020 at 16:09:40 GMT, "Tim Lamb" wrote: In message , Roger Hayter writes On 28 Oct 2020 at 12:50:41 GMT, "Tim Lamb" wrote: In message l.net, Dave Liquorice writes On Wed, 28 Oct 2020 09:28:59 +0000, Tim Lamb wrote: The actual issue is that the diverter valve momentarily blocks the pump flow leading to water hammer which opens the boiler relief valve thus losing system water:-) Have some relays that switch the pump off when the divert valve is being motored? System boiler, internal pump. An alternative solution is to fit a bypass valve: to maintain flow during the transition. Soldering access is a pig! That might not stop the hammer unless reasonably open... The idea was to divert the flow through the hot tank coil with an automatic bypass valve (Honeywell DU144) Will adding another expansion vessel do anything? After all you have one already and they have quite high interia due to their size. It would have to connected close to the divertor valve an on a short pipe as well. Tucked away in the boiler, I don't know which leg it is on. Also 8L is a bit meagre for very cold weather when more heating circuits are running. Surely one of the small "water hammer arrestors" would be better? Screwfix have several, can't persuade Toolstations site to cough anything up. Pass. What I hear as water hammer may be the boiler safety valve opening and re-closing. Plumbed in to the condensate pipe so hard to tell. How about a motorised valve opening a bypass pipe a few seconds before the diverter valve operates? I think short delay mains relays are probably a commodity. Though I haven't looked. Heading back towards Y plan complexity which I wanted to avoid. One day, a visiting plumber is going to try making sense of this system! Currently it is W plan with some relays to fudge the underfloor heat control requirements. I think an automatic bypass would be simpler to understand. I agree, but I thought there was some risk it wouldn't open fast enough to prevent the overpressure/water hammer effect. I can't think of anything acting faster than a pressure senstive bypass valve? If it works, that's fine. What acts "faster" is delaying the diverter closing. See my suggestion above. -- Roger Hayter |
One for the plumbers.
On Thu, 29 Oct 2020 01:10:33 +0000, Fredxx wrote:
I think an automatic bypass would be simpler to understand. I agree, but I thought there was some risk it wouldn't open fast enough to prevent the overpressure/water hammer effect. I can't think of anything acting faster than a pressure senstive bypass valve? Small pocket of air trapped in a stub of pipe? Aka a water hammer arrestor? Pressure sensistive bypass will spring shut after the transient, possibly making the hammer worse. Water hammer does not behave how one might expect. The sudden pressure build up caused by the interia of the moving water needs to be dissipated/absorbed by something. -- Cheers Dave. |
One for the plumbers.
|
One for the plumbers.
In message , Roger Hayter
writes On 29 Oct 2020 at 01:10:33 GMT, "Fredxx" wrote: On 29/10/2020 00:29:33, Roger Hayter wrote: On 28 Oct 2020 at 16:09:40 GMT, "Tim Lamb" wrote: In message , Roger Hayter writes On 28 Oct 2020 at 12:50:41 GMT, "Tim Lamb" wrote: In message l.net, Dave Liquorice writes On Wed, 28 Oct 2020 09:28:59 +0000, Tim Lamb wrote: The actual issue is that the diverter valve momentarily blocks the pump flow leading to water hammer which opens the boiler relief valve thus losing system water:-) Have some relays that switch the pump off when the divert valve is being motored? System boiler, internal pump. An alternative solution is to fit a bypass valve: to maintain flow during the transition. Soldering access is a pig! That might not stop the hammer unless reasonably open... The idea was to divert the flow through the hot tank coil with an automatic bypass valve (Honeywell DU144) Will adding another expansion vessel do anything? After all you have one already and they have quite high interia due to their size. It would have to connected close to the divertor valve an on a short pipe as well. Tucked away in the boiler, I don't know which leg it is on. Also 8L is a bit meagre for very cold weather when more heating circuits are running. Surely one of the small "water hammer arrestors" would be better? Screwfix have several, can't persuade Toolstations site to cough anything up. Pass. What I hear as water hammer may be the boiler safety valve opening and re-closing. Plumbed in to the condensate pipe so hard to tell. How about a motorised valve opening a bypass pipe a few seconds before the diverter valve operates? I think short delay mains relays are probably a commodity. Though I haven't looked. Heading back towards Y plan complexity which I wanted to avoid. One day, a visiting plumber is going to try making sense of this system! Currently it is W plan with some relays to fudge the underfloor heat control requirements. I think an automatic bypass would be simpler to understand. I agree, but I thought there was some risk it wouldn't open fast enough to prevent the overpressure/water hammer effect. I can't think of anything acting faster than a pressure senstive bypass valve? If it works, that's fine. What acts "faster" is delaying the diverter closing. See my suggestion above. Ok but where does the boiler output go? Stop the pump and it would lock out on over temperature surely. -- Tim Lamb |
One for the plumbers.
In message l.net,
Dave Liquorice writes On Thu, 29 Oct 2020 01:10:33 +0000, Fredxx wrote: I think an automatic bypass would be simpler to understand. I agree, but I thought there was some risk it wouldn't open fast enough to prevent the overpressure/water hammer effect. I can't think of anything acting faster than a pressure senstive bypass valve? Small pocket of air trapped in a stub of pipe? Aka a water hammer arrestor? Pressure sensistive bypass will spring shut after the transient, possibly making the hammer worse. Water hammer does not behave how one might expect. The sudden pressure build up caused by the interia of the moving water needs to be dissipated/absorbed by something. Hopefully a pressure sensitive by-pass would restrict the pressure rise. I may have miss-described the boiler relief valve opening. -- Tim Lamb |
One for the plumbers.
On 29 Oct 2020 at 18:52:34 GMT, "Tim Lamb"
wrote: In message , Roger Hayter writes On 29 Oct 2020 at 01:10:33 GMT, "Fredxx" wrote: On 29/10/2020 00:29:33, Roger Hayter wrote: On 28 Oct 2020 at 16:09:40 GMT, "Tim Lamb" wrote: In message , Roger Hayter writes On 28 Oct 2020 at 12:50:41 GMT, "Tim Lamb" wrote: In message l.net, Dave Liquorice writes On Wed, 28 Oct 2020 09:28:59 +0000, Tim Lamb wrote: The actual issue is that the diverter valve momentarily blocks the pump flow leading to water hammer which opens the boiler relief valve thus losing system water:-) Have some relays that switch the pump off when the divert valve is being motored? System boiler, internal pump. An alternative solution is to fit a bypass valve: to maintain flow during the transition. Soldering access is a pig! That might not stop the hammer unless reasonably open... The idea was to divert the flow through the hot tank coil with an automatic bypass valve (Honeywell DU144) Will adding another expansion vessel do anything? After all you have one already and they have quite high interia due to their size. It would have to connected close to the divertor valve an on a short pipe as well. Tucked away in the boiler, I don't know which leg it is on. Also 8L is a bit meagre for very cold weather when more heating circuits are running. Surely one of the small "water hammer arrestors" would be better? Screwfix have several, can't persuade Toolstations site to cough anything up. Pass. What I hear as water hammer may be the boiler safety valve opening and re-closing. Plumbed in to the condensate pipe so hard to tell. How about a motorised valve opening a bypass pipe a few seconds before the diverter valve operates? I think short delay mains relays are probably a commodity. Though I haven't looked. Heading back towards Y plan complexity which I wanted to avoid. One day, a visiting plumber is going to try making sense of this system! Currently it is W plan with some relays to fudge the underfloor heat control requirements. I think an automatic bypass would be simpler to understand. I agree, but I thought there was some risk it wouldn't open fast enough to prevent the overpressure/water hammer effect. I can't think of anything acting faster than a pressure senstive bypass valve? If it works, that's fine. What acts "faster" is delaying the diverter closing. See my suggestion above. Ok but where does the boiler output go? Stop the pump and it would lock out on over temperature surely. My suggestion was having a valve open a bypass pipe, and after a second or so operate the diverter. No need to stop the pump. -- Roger Hayter |
One for the plumbers.
In message , Roger Hayter
writes On 29 Oct 2020 at 18:52:34 GMT, "Tim Lamb" wrote: . My suggestion was having a valve open a bypass pipe, and after a second or so operate the diverter. No need to stop the pump. OK. That should work. I may try the valve first as the plumbers fitted one! Sadly in the wrong place! -- Tim Lamb |
One for the plumbers.
On 28/10/2020 19:07, David wrote:
The plumber had never heard of this before. [Was also indecently amused that anyone would bother to read the manual.] name and Shame him ! |
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