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Hi guys 

need a bit of guidance on my my mates plumbing issues . As I understand it the system has 2 vessels plumbed into the pipe work . One being an accumulator and one being an expansion .what pressures do these need to be set at for the pump to work properly? 
ta in advance 

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The accumulator is to smooth out the water pump cycles when the demand (tap opening) is less than the pump delivery rate. So it should fill up when the pump runs, and nearly empty when the pump isn’t running, the pump should cut in just before it’s empty. Which means the accumulator air pressure (with pump switched off and taps open) should be a bit below pump cut-in pressure. Typically this means around 15psi.

 

The expansion vessel doesn’t have a direct impact on the pump. It’s purpose is to prevent excessive pressure build up in the calorifier (hot water tank) because the calorifier is often fed through a non-return valve, meaning the volume of water is “trapped” so that when it is heated up, it expands and pressure becomes high. So the expansion vessel should be empty when the pump has just run, but fill up if the water is subsequently heated. In other words, its pressure (with pump off and taps open) should be around the pump cut-out pressure, perhaps around 30psi.

 

Once you have set the accumulator to roughly the right pressure, and because the air pressure can never be less than the water pressure and is normally equal to it, you can measure the air pressure in the accumulator just after the pump has cut out, and this will tell you what to set the expansion vessel pressure to.

17 minutes ago, Tracy D'arth said:

Accumulator set at or slightly below the pump cut in pressure, expansion set at at or slightly above pump cut off pressure.

… because the aim is to avoid the accumulator becoming totally empty before the pump cuts in.

Edited by nicknorman
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3 minutes ago, nicknorman said:

The accumulator is to smooth out the water pump cycles when the demand (tap opening) is less than the pump delivery rate. So it should fill up when the pump runs, and nearly empty when the pump isn’t running, the pump should cut in just before it’s empty. Which means the accumulator air pressure (with pump switched off and taps open) should be a bit below pump cut-in pressure. Typically this means around 15psi.

 

The expansion vessel doesn’t have a direct impact on the pump. It’s purpose is to prevent excessive pressure build up in the calorifier (hot water tank) because the calorifier is often fed through a non-return valve, meaning the volume of water is “trapped” so that when it is heated up, it expands and pressure becomes high. So the expansion vessel should be empty when the pump has just run, but fill up if the water is subsequently heated. In other words, its pressure (with pump off and taps open) should be a bit above the pump cut-out pressure, perhaps around 30psi.

 

Pnce you have set the accumulator to,roughly the right pressure, and because the air pressure can never be less than the water pressure, you can measure the air pressure in the accumulator just after the pump has cut out, and this will tell you what to set the expansion vessel pressure to.

… because the aim is to avoid the accumulator becoming totally empty before the pump cuts in.

Fair enough. With my method of lowering the pressure until the pump just kicks in it probably finishes up very slightly lower. At or around will be good enough.

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1 minute ago, Tracy D'arth said:

Fair enough. With my method of lowering the pressure until the pump just kicks in it probably finishes up very slightly lower. At or around will be good enough.

Yes in reality I don’t think it is critical, but in theory if the acc pressure is higher than the pump cut-in, as the accumulator empties the pressure momentarily falls to zero just before the pump has time to start up, causing a momentary interruption in the flow. But in reality it doesn’t seem noticeable, probably due to the momentum of the moving water.

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5 minutes ago, nicknorman said:

Yes in reality I don’t think it is critical, but in theory if the acc pressure is higher than the pump cut-in, as the accumulator empties the pressure momentarily falls to zero just before the pump has time to start up, causing a momentary interruption in the flow. But in reality it doesn’t seem noticeable, probably due to the momentum of the moving water.

It would only become noticeable if the hysteresis on the pump pressure switch was very wide.

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They need repressurising every so often. Perhaps once a year. Air does diffuse through the rubber bladders inside over time, just like car and bike tyres. A bike, or car pump and pressure gauge are useful things to have available. When installing them it is a good plan to make the air valves easily accessible. The two pressure vessels on my boat need doing, but the accumulator needs triple jointed arms to reach. I really should move it.

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11 hours ago, ditchcrawler said:

I thought about getting one of these image.png.b7b61838f21391e376ad00ab851f23de.png

No comment to make on the battery pump you selected, but a shout out for being a user of KeePass. I see it open on your taskbar. Used it for years, it's perfect for password management.

Edited by Puffling
  • Greenie 1
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5 minutes ago, Puffling said:

No comment to make on the battery pump you selected, but a shout out for being a user of KeePass. I see it open on your taskbar. Used it for years, it's perfect for password management.

 

Until someone finds a vulnerability in KeePass, and then you're worse off than if you never used it as they'll have access to EVERYTHING you use it for. 

 

 

At least remove your email account from it, if you use KeePass for it in the first place. 

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19 minutes ago, MtB said:

 

Until someone finds a vulnerability in KeePass, and then you're worse off than if you never used it as they'll have access to EVERYTHING you use it for. 

 

 

At least remove your email account from it, if you use KeePass for it in the first place. 

I've always wondered how you know that a password manager hasn't deliberately put a hidden back door in there so they can harvest your passwords.

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17 minutes ago, MtB said:

 

Until someone finds a vulnerability in KeePass, and then you're worse off than if you never used it as they'll have access to EVERYTHING you use it for

There are vulnerabilities and vulnerabilities; not every software exploit results in a miscreant gaining complete access.

 

KeePass is open source (FOSS), which gives it a head start over closed-source password managers, since the code is open for inspection.

 

Personally, I prefer having control of my own password database locally, instead of entrusting it to a cloud-based option, such as Last Pass, where encryption might be first class, but you have no way of testing the claim. Don't forget the tendency for fee based services to hush up hack attempts, often for months, so as not to lose customers.

 

Additionally, the inherent security depends on how you use KeePass. If you use drag-drop wherever possible the system clipboard is bypassed, leaving a much smaller surface of vulnerability. One of the recent exploits did not directly target KeePass itself but the system clipboard, which is only involved if you double-click a vault entry.

12 minutes ago, David Mack said:

I've always wondered how you know that a password manager hasn't deliberately put a hidden back door in there so they can harvest your passwords.

In the present political climate, that's a valid concern. Another advantage of using FOSS. (see above)

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I used KeePass (IIRC) but changed from it when multi machine working became the norm. At that time, if not now, it only supported use with a local database so saving a password on one device did not make it available on another.

 

I migrated to LastPass and although I still use that for some things I had difficulties when the company was taken over.

 

I now, with a great deal of reluctance at first, I use Google Password as this means I can easily move between desktop, laptop, tablet and mobile at least when accessing sites via Chrome. It can, as with other managers, be used to store info that can be looked up directly as well as when logging in. 

 

Whilst I still harbour residual concerns about PW managers, the fact that it has allowed me to adopt the much more secure pws offered by them impossible to remember!) more than offsets that concern. I am gradually replacing the older pws which were memorable for at least the time it takes to copy them into a log in box. I did, however, recently come across one site that does not allow cut and paste whilst permitting a pw manager.

Edited by Mike Todd
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26 minutes ago, Mike Todd said:

I used KeePass (IIRC) but changed from it when multi machine working became the norm. At that time, if not now, it only supported use with a local database so saving a password on one device did not make it available on another.

It's more involved but you can upload your KBDX database to a site which supports WebDAV (I use NextCloud) and instruct KeePass to load a database from the cloud. This way multiple devices can share the same identical database In case there is no internet connection, it will work from a locally cached copy. The most recently updated database will always prevail.

Doing it this way, I can sync between my main computer running KeePass and two mobile phones using KeePass2Android.

 

It adds layers of complexity and failure, though.

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On 31/05/2022 at 22:50, nicknorman said:

 Which means the accumulator air pressure (with pump switched off and taps open) should be a bit below pump cut-in pressure. 

 

Correct. I thought this was pinned somewhere as it comes up so often but I can't see it now. So can one of the mods pin this somewhere please so people don't keep getting it the other way around? 

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2 hours ago, blackrose said:

 

Correct. I thought this was pinned somewhere as it comes up so often but I can't see it now. So can one of the mods pin this somewhere please so people don't keep getting it the other way around? 

911_731.rH.indd (totalapex.com)  

 

The accumulator contributes to longer pump life, less noise, less amperage draw, and reduced water pulsation. The most efficient use of the accumulator occurs with the pre-charge set at the SAME pressure as the pump’s pressure switch “turn on” setting. Typically, a 45 psi [3 bar] pump will turn on around 30 psi [2.07 bar]. Therefore, the pre-charge should also be 30 psi [2.07 bar]. The pre-charge MUST be set in a “static” condition (pump off and at least one water fixture opened). Depending on pre-charge pressure to the accumulator, in relation to the pump turn on/off pressures, stored liquid is about 2 to 4 oz. [60-120 ml]. If accumulator tank pre-charge exceeds pump turn on pressure, the liquid volume is reducedThe accumulator contributes to longer pump life, less noise, less amperage draw, and reduced water pulsation. The most efficient use of the accumulator occurs with the pre-charge set at the SAME pressure as the pump’s pressure switch “turn on” setting. Typically, a 45 psi [3 bar] pump will turn on around 30 psi [2.07 bar]. Therefore, the pre-charge should also be 30 psi [2.07 bar]. The pre-charge MUST be set in a “static” condition (pump off and at least one water fixture opened). Depending on pre-charge pressure to the accumulator, in relation to the pump turn on/off pressures, stored liquid is about 2 to 4 oz. [60-120 ml]. If accumulator tank pre-charge exceeds pump turn on pressure, the liquid volume is reduced

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1 hour ago, ditchcrawler said:

911_731.rH.indd (totalapex.com)  

 

The accumulator contributes to longer pump life, less noise, less amperage draw, and reduced water pulsation. The most efficient use of the accumulator occurs with the pre-charge set at the SAME pressure as the pump’s pressure switch “turn on” setting. Typically, a 45 psi [3 bar] pump will turn on around 30 psi [2.07 bar]. Therefore, the pre-charge should also be 30 psi [2.07 bar]. The pre-charge MUST be set in a “static” condition (pump off and at least one water fixture opened). Depending on pre-charge pressure to the accumulator, in relation to the pump turn on/off pressures, stored liquid is about 2 to 4 oz. [60-120 ml]. If accumulator tank pre-charge exceeds pump turn on pressure, the liquid volume is reducedThe accumulator contributes to longer pump life, less noise, less amperage draw, and reduced water pulsation. The most efficient use of the accumulator occurs with the pre-charge set at the SAME pressure as the pump’s pressure switch “turn on” setting. Typically, a 45 psi [3 bar] pump will turn on around 30 psi [2.07 bar]. Therefore, the pre-charge should also be 30 psi [2.07 bar]. The pre-charge MUST be set in a “static” condition (pump off and at least one water fixture opened). Depending on pre-charge pressure to the accumulator, in relation to the pump turn on/off pressures, stored liquid is about 2 to 4 oz. [60-120 ml]. If accumulator tank pre-charge exceeds pump turn on pressure, the liquid volume is reduced

I think that due to the limitations of most boat calorifiers, fresh water pumps are usually much less than 45psi cut out, more like 30psi. So if the above advice is followed it’s likely that the accumulator will remain empty and contribute nothing to the party. In my limited experience cut in pressure is not much over 1/2 cut out pressure and around 17psi, but of course this will vary with pump / pressure switch model. It can of course easily be measured by pressurising to perhaps 10 psi, then turning the pump on with a tap partially open so that the pump cycles. Because the accumulator air pressure must equal the water pressure, as the pump cycles the cut out and cut in pressures will be revealed by observing the accumulator air pressure.

 

Having turned off the pump an opened a tap, the accumulator air pressure can then be set appropriately. Since total precision isn’t likely, IMO it is better to set the pressure a couple of psi low, which means the accumulator never quite empties and smooth flow prevails. If the accumulator pressure is slightly high it means that the accumulator fully empties, water pressure momentarily drops to zero, and there is, in theory at least, a momentary interruption of flow whilst the pump starts up.

Edited by nicknorman
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16 hours ago, nicknorman said:

I think that due to the limitations of most boat calorifiers, fresh water pumps are usually much less than 45psi cut out, more like 30psi. So if the above advice is followed it’s likely that the accumulator will remain empty and contribute nothing to the party.  

It says in capital letters SAME     "pre-charge set at the SAME pressure as the pump’s pressure switch “turn on” setting"  before giving typical figures. Mine runs at even even lower pressure.

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1 hour ago, ditchcrawler said:

It says in capital letters SAME     "pre-charge set at the SAME pressure as the pump’s pressure switch “turn on” setting"  before giving typical figures. Mine runs at even even lower pressure.

Yes I know, you are correct, but bearing in mind human nature, someone will see 30psi, not bother to read it properly, and just set it to 30psi. There is a difference between being technically correct and precise, and communicating with humans. Especially boaters!

Edited by nicknorman
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Just now, nicknorman said:

Yes I know, but bearing in mind human nature, someone will see 30psi, not bother to read it properly, and just set it to 30psi. There is a difference between being technically correct and precise, and communicating with humans!

Well if they are reading this they should get it now. 😈

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