Accumulator

[mainshiptom]

Accumulator - ok on advice which I got here I bought a big one and it arrived with a NRV (non return valve). Should I fit that on my accumulator or what that stops the action that I really want to occur?

Tom

 

[mm1]

sorry you have lost me,need more info please,regards m m 1.

 

[mainshiptom]

My water pump keeps breaking down, I was told that i use it too much??

So the advise given here was to put a new pump maybe with a better heavy duty switch and have a large accumulator fitted.

When got the accumulator it arrived with a nrv which I think is put in place to protect the pump ?

Tom

 

[David2452]

as you suspect, the NRV goes between pump and accumulator.

 

[mm1]

Hi,yes sorry i am with you now,i think you will find that does the trick,regards m m 1.

 

[paulrh]

I think you will find that David is right the non return will take the pressure away from the pump once the system is charged.
and not srquired.

paul

 

[paulrh]

just to add something else it also means the the pump don't start under load.

 

[mainshiptom]

If i got this right the nrv will go right after the pump and before the T junction which will split between the taps and the accumulator.


Tom

 

[David2452]

[ QUOTE ]
If i got this right the nrv will go right after the pump and before the T junction which will split between the taps and the accumulator.


Tom

[/ QUOTE ]

Yes, it will then in effect isolate the taps from the pump until the pressure drops and the pump kicks in. Put it in the right way round mind /forums/images/graemlins/wink.gif

 

[mainshiptom]

/forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

 

[pennycar9]

If I may put my two pennuth worth in here, It is my perception that an accumulator tank works like a cushion in the pressurized water system.In simple terms there is the water tank, a pump, a pressure switch, and the distribution pipework and taps. The system should be pressurized by the pump, when a tap is opened,the pressure switch senses the drop in pressure and switches the pump on, thus distributing the cold water around the boat. Now, when you switch the tap off, the pump stops,but not before building up a pressure in the system which has nowhere to go, in doing so puts strain on the pump and the rest of the system.Installing an accumulator tank downstream of the pump will act as a cushion for the water pressure and so alleviating stresses on the system. This is called water hammer, when the system out let is suddenly closed. I can see no reason whatso ever to install a non return valve in relation to the accumulator.

I would suggest that the non return valve serves no purpose in a simple cold water system equipped with an accumulator tank. I think you would need to put the non return valve in between the cold feed tee and the calorifier, this will then prevent back flow of hot water into the cold system.

 

[John100156]

A non-return valve is fitted to prevent water creeping back through a pump to the CW tank (if one is not an integral part of the pump assembly) to prevent pressure loss and hence pump cycling that would otherwise occur.

Although it's true the accumulator will absorb some of the energy caused by a shock wave, caused when valves/taps are closed quickly (water hammer), its main function is to allow sufficient space in the system for water to expand into when it is heated.

 

[pheran]

[ QUOTE ]


Although it's true the accumulator will absorb some of the energy caused by a shock wave, caused when valves/taps are closed quickly (water hammer), its main function is to allow sufficient space in the system for water to expand into when it is heated.

[/ QUOTE ]I thought the main function of the accumulator was to ensure an even pressure within the system, particularly at the delivery end, and so avoid the pulsing that would otherwise occur due to the action of the pump.

 

[John100156]

Mmmmmm Open a tap to see how long it takes for your pump to activate/pulse!

The volume of water in the accumulator is not that great, the pressure in the system drops fast and will be lower than the pressure in the accumulator. Some benefit, but not that much.

However, if the system had no expansion vessel, the pressure when the CW is heated would build-up and could activate the PRV, hence the need for expansion space and the expansion vessel or accumulator.

 

[pheran]

Not sure what you're saying here. There are many boats around with NO accumulator which seem to survive (I've had a few in the past) so can't see pressure relief as the major function. We now have a 20 litre accumulator and when I turn on a tap on our boat, water is available immediately as a steady stream. Absolutely essential if there are other pressure-sensitive devices in the system eg a multi-point gas water heater as in one of our previous boats. I once saw a boat with such a heater and no accumulator and the flames were 'wooshing' up and down in time with the pulsing of the pump. Condemned by the engineer as dangerous!!

This extract from the Jabsco catalogue seems to sum the matter up

'Store of pressurised water maintains full flow when system demand temporarily exceeds pump capacity, which means smoother flow, quieter water system, better control of hot water temperature, longer pump life.'

No mention of expansion capacity or pressure relief.

 

[John100156]

Yes - but this refers to an instantaneous water heater, with no storage capacity! I assumed (perhaps incorrectly?) that this was referring to a CW pump serving also a HW system with HW storage tank - hence an expansion vessel is essential and mandatory to pressurised systems in the UK.

If I have misconstrued and the HW system comprises an instantaneous HW heater, your statement would be correct. Perhaps the OP can enlighten us!

 

[mainshiptom]

I got the accumulator to save my pumps.

 

[John100156]

OK I now understand your perspective, so:

If its a CW system with instantaneous HW heater and you want to reduce pump cycling and pressure variations then a large accumulator (same function as an expansion vessel will do the trick, as follows:

If however you have a HW storage cyclinder (as fitted to my FL T34) then you should install an expansion vessel or accumulator, primarily as a safety feature to permit room for water to expand into. A secondary benefit is easing pressure fluctuations. As follows:

As installed to domestic mains fed HW systems in the UK. A seperate EV is fitted or as with the a Megaflow system, an expansion space is manufactured into the top of the cylinder which needs to be checked and replenished when serviced.

Hope the OP now has all the info he requires!