Accumulator tank or not?

[Leighb]

I thought I should start a new thread regarding my domestic water supply.

At present there is a - needs replacing - Flojet 4305 pump feeding a calorifier and galley and heads hot and cold taps. There is no inlet filter nor accumulator.

I am replacing the pump and obviously should fit a filter before the pump, however do I really need an accumulator? All the stuff I have read seems to suggest that it is necessary, but the system works fine as it is, or did before the pump went pear shaped.

It would make sense to fit one at the same time as the new pump and filter if it is useful/necessary. If forumites think it would be worth while, what size? Does it relate to the pump flow rate?

Thanks for any advice.

 

[Champagne Murphy]

When I did ours the advice seemed to be that an accumulator was only needed if say, someone would run a tap in the night. Then the pump wouldn’t fire up and make a noise. We haven’t got one.

 

[pvb]

An accumulator is certainly not essential; it may smooth out frequent cycling of the pump. I don't have one on my boat.

 

[vyv_cox]

An accumulator is certainly not essential; it may smooth out frequent cycling of the pump. I don't have one on my boat.

Originally my Sadler did not have one and I believe most others are the same. I installed one and think it is an improvement not to have the pump running every time the tap is opened.

 

[VicS]

I thought I should start a new thread regarding my domestic water supply.

At present there is a - needs replacing - Flojet 4305 pump feeding a calorifier and galley and heads hot and cold taps. There is no inlet filter nor accumulator.

I am replacing the pump and obviously should fit a filter before the pump, however do I really need an accumulator? All the stuff I have read seems to suggest that it is necessary, but the system works fine as it is, or did before the pump went pear shaped.

It would make sense to fit one at the same time as the new pump and filter if it is useful/necessary. If forumites think it would be worth while, what size? Does it relate to the pump flow rate?

Thanks for any advice.

An accumulator will smooth out the operation of the pump. Without one at low demand rates,the pump will tend cut in and out fairly rapidly in order to maintain the pressure between the cut in and cut out settings. With an accumulator the pressure cycling will be smoothed out so that the pump cuts in less frequently although it will run for longer when it does. The total running time will be the same , just in less frequent but longer bursts .

Some modern pumps have some sort of internal bypass that smooths out their operation without the need for an accumulator.
If the frequent cutting in and cutting out bothers you but you dont want to fit an accumulator fit one of the pumps which do not need an accumulator

Good info on accumulator ( and expansion ) tanks plus guidance on sizing here: https://www.jabscoshop.com/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf

 

[TQA]

I have owned boats with and without. IMHO they are unnecessary on a boat with one or two people.

 

[neilf39]

I don't have one as I have a jabsco pump which has a triple diaphragm and bypass and it says it doesn't need one. The pump comes on and stays on whilst I run the water which I am happy with. I have an expansion tank on the hot water though and that is needed if you don't want the pressure relief valve to deposit water.

 

[pvb]

I have an expansion tank on the hot water though and that is needed if you don't want the pressure relief valve to deposit water.

Not necessarily, I think it perhaps depends on the amount of pipework in the system. My boat has no expansion tank on the hot water, and it doesn't dump water from the PRV.

 

[thinwater]

The land plumbing code is pretty clear; hot water heater = expansion tank.

https://structuretech1.com/wp-content/uploads/2012/01/Expansion-tank-installed.jpg

Even without hot water, it is simply better engineering. Less cycling on the piping (fewer leaks), less cycling on the pump. Cheaper in the long run.

 

[Irish Rover]

The pump on my boat is really noisy and I switch off the power last thing before hitting the hay so I'm glad of the accumulator. I recently replaced the calorifer - the old system didn't have a separate accumulator so I was surprised my new Surecal calorifer needed one according to the instructions. Turns out the Surecal has a non-return valve on the inlet side whereas the old system didn't which allowed back pressure expansion.

 

[geem]

The life of a pump motor is influenced by the number of stop starts. Less stop starts will provide a longer life. An accumulator smooths out the pressure fluctuations so gives a more consistent pressure. We have had both but the accumulator is a nicer system and should extend the pump/motor life

 

[thinwater]

The pump on my boat is really noisy and I switch off the power last thing before hitting the hay so I'm glad of the accumulator. I recently replaced the calorifer - the old system didn't have a separate accumulator so I was surprised my new Surecal calorifer needed one according to the instructions. Turns out the Surecal has a non-return valve on the inlet side whereas the old system didn't which allowed back pressure expansion.

a. The pressure pump has a non-return valve, so the absence of one on the colorifier is irrelevant.
b. Plumbing codes require backflow prevention to prevent hot water from backflowing into cold water pipes. Legonella and other disease is the problem. UK and US. Google it.

 

[geem]

a. The pressure pump has a non-return valve, so the absence of one on the colorifier is irrelevant.
b. Plumbing codes require backflow prevention to prevent hot water from backflowing into cold water pipes. Legonella and other disease is the problem. UK and US. Google it.

On a boat I dont think backflow protection is critical since the system has the same source of water (the water tank). Its not fed,by an open header tank. The calorifier, unlike in a house, will fairly frequently be heated by the engine to circa 80/90degC which is a certain way to kill legionella. It is a recommendation in domestic systems that the hot water in relatively low temperatures hot water storage systems is heated to a higher temperature periodically to kill legionella.

In the south of England legionella is endemic in tap water. Its not a problem to drink but becomes a problem if aerated in shower heads and breathed in. If you are fit and healthy legionella is unlikely to be a problem to you and I dont see how backflow protection on a boat helps. If its already in your cold water tank then you are at risk from your shower head but probably not from your hot water feed to the shower head. If I have missed something here I am more than happy to be corrected

 

[RupertW]

We seem to have a lot of pipework with deck shower, calorifier, two sink galley and two heads so when the accumulator failed and I had to bypass it I wasn’t surprised to find that opening a tap doesn’t cause the pump to run until a fair bit of water has come out. We have a new accumulator but I’ve left it bypassed.

 

[thinwater]

On a boat I dont think backflow protection is critical since the system has the same source of water (the water tank). Its not fed,by an open header tank. The calorifier, unlike in a house, will fairly frequently be heated by the engine to circa 80/90degC which is a certain way to kill legionella. It is a recommendation in domestic systems that the hot water in relatively low temperatures hot water storage systems is heated to a higher temperature periodically to kill legionella.

In the south of England legionella is endemic in tap water. Its not a problem to drink but becomes a problem if aerated in shower heads and breathed in. If you are fit and healthy legionella is unlikely to be a problem to you and I dont see how backflow protection on a boat helps. If its already in your cold water tank then you are at risk from your shower head but probably not from your hot water feed to the shower head. If I have missed something here I am more than happy to be corrected

a. There are a lot of "maybes" in this.
b. If the calorifier is heated to 90C you REALLY need an expansion tank. And the engine cooling system has one, for good reason.
c. I did NOT suggest adding back flow protection. I explained that it already exists, in the form of the pressure pump check valves. This is central to the concept of pressurized water on a boat. This is why an expansion tank, in the presence of a calorifier, is good engineering.

I'm not trying to quantify the risk, just point out a few facts.

 

[Irish Rover]

a. The pressure pump has a non-return valve, so the absence of one on the colorifier is irrelevant.
b. Plumbing codes require backflow prevention to prevent hot water from backflowing into cold water pipes. Legonella and other disease is the problem. UK and US. Google it.

I'm not sure why you saw the need to take issue with my post. I would imagine Surejust http://www.surejust.co.uk/ have a sound reason for fitting a non return valve on their calorifers so it would hardly be irrelevant if I removed it. I'm a bit confused by the point you're making at B - If there's no NRV fitted on the calorifer then isn't the hot water feeding back into the cold water pipes between the pump and the calorifer - around 5 meters of piping in my case. Interesting you say there are lots of maybes but go on to refer to your own pronouncements as FACTS.

 

[geem]

a. There are a lot of "maybes" in this.
b. If the calorifier is heated to 90C you REALLY need an expansion tank. And the engine cooling system has one, for good reason.
c. I did NOT suggest adding back flow protection. I explained that it already exists, in the form of the pressure pump check valves. This is central to the concept of pressurized water on a boat. This is why an expansion tank, in the presence of a calorifier, is good engineering.

I'm not trying to quantify the risk, just point out a few facts.

The only MAYBEs are associated with the different ways installations can be plumbed together.
Our pipework is predominantly flexible plastic. We have no NRV installed on the calorifier but we have an large 5 litre accumulator on the pump. The distance between the calorifier and pump is circa 20ft so the pipework provides expansion as well as the accumulator. The system works perfectly. Our water only ever comes from the RO system on board so no risk of legionella here.
Unless you have a temperature control valve on the engine calorifier connection ( I dont mean on the secondary side to the taps) then your water in the calorifier will approach engine water temperature. On my boat that is 90degC at full operating temperature. Most calorifiers I see these days have thermostatic control of the water output from the calorifier for this reason. Water at 90 is dangerous. We have thermostatic control.

 

[thinwater]

I'm not sure why you saw the need to take issue with my post. I would imagine Surejust http://www.surejust.co.uk/ have a sound reason for fitting a non return valve on their calorifers so it would hardly be irrelevant if I removed it. I'm a bit confused by the point you're making at B - If there's no NRV fitted on the calorifer then isn't the hot water feeding back into the cold water pipes between the pump and the calorifer - around 5 meters of piping in my case. Interesting you say there are lots of maybes but go on to refer to your own pronouncements as FACTS.

Please don't be offended.

The non-return valve is now required by code in the US, and I believe in the UK. That is why it was added. But since there is another non-return valve just upstream (pump), it will have limited impact on operation. Irrelevant was probably the wrong word, or certainly an over simplification. The statement that expansion tanks are required in the terrestrial code is a fact in the US (plumbing code) and I believe also in the UK, but I did not dig that up.

Yes, the water can expand into 15M of presumably flexible pipe. That is your choice. It is my opinion, shared by most land engineers and code officials, that that is hard on equipment. I could ask, for example, why expansion tanks were invented an became common. This is the reason.

 

[thinwater]

...Unless you have a temperature control valve on the engine calorifier connection ( I dont mean on the secondary side to the taps) then your water in the calorifier will approach engine water temperature. On my boat that is 90degC at full operating temperature. Most calorifiers I see these days have thermostatic control of the water output from the calorifier for this reason. Water at 90 is dangerous. We have thermostatic control.

I was kind of hoping that was an error. 90C water is very, very dangerous.

 

[lw395]

Many boats get away with no accumulator/HW expansion vessel because the calorifier has air space in it, doing much the same job.