Accumalator on water systems

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prescott56

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HI All,
Am thinking seriously of removing teh little 1 litre a accumalator, ( the pressure tank thing) in teh water system. reason being, the shower has a good flow of water then it slows down until the pump kicks in, then starts to slow down again when the pump stops. and keeps cycling like this.
I am told these accumalators save wear and tear on pumps, is this true.
How much wear and tear or is it just another marketing ploy to help us spend money?
(sorry getting old and cynical)

Regards
 
Are you sure your accumulator is not knackered? I thought they were supposed to prevent this by keeping a steady pressure in the water system and prevent this "pumping".???

Alan.
 
dunno if its knackered, it is most certainly "holding pressure" so the bag must e ok, wether the pressure valve is , i dunno.
how does one check?

regards
 
I have one that has a cushion of air which is slowly absorbed by the water over man months. When this happens the pump cycles very quickly and the brushes rapidly wear causing the pump to pack up. A major strip down is then required to sort this out.

I think the accumulator is essential and under o ircumstances should you remouve it.
 
Hi,
Your problem is not the accumalator, but the pump is set at the wrong pressure. Try increasing the cut in pressure at the pump, or decreasing the pressure in the accumalator, but only very slightly at a time.
 
The accumalator has two functions.

First is to allow for expansion when the water is heated.
Second is to even out the flow from the pump.

Seems like you may have a problem with the pressure switch.
These are normally set to about 2.5 bar.

Steve
 
My water flow behaved exactly like yours on my previous boat. I tried adjusting pressure in accumulator but to no effect.

But even when the flow was at max it was still pathetic. So I bought a new pump with both higher flow rate & higher operating pressure. From memory I think 1st pump was 25psi & 7lpm. New one was about 50psi & either 13 or 17lpm.

I had checked previously that the accumulator was good for the extra pressure & it was (written on side)

So I fitted the new pump and after a bit of tinkering with the accumulator pressure there was a significant improvement, both to the flow rate obviously but also to the eveness of the flow.

Having the higher pressure pump did make me a bit nervous though. I had visions of something parting and the water tank emptying into the boat. So I gave the system fittings a good check and as an extra precaution I try to remember to switch the pump fuse off whenever I'm not on the boat.
 
I agree with the others here who say that the problem lies with the pressure switch. Too big a difference between the switch on and switch off pressures makes for a poor showering experience. I also think that a bigger pressure accumulator is a good idea, as a small one coupled with a close pressure difference encourages short cycling. My own accumulator tank is 6 litres, and works pretty well.
 
I thought that is how/why an accumulator works. It's when the water absorbs the air, or it leaks out, and there's no "pressure reservoir" that you get on-off cycling.

I am given to understand...
 
Re: Accumulator on water systems

The accumulator is simply a reservoir to allow for fluctuations in line pressure.

Let us assume your pump is set for 15psi cut in pressure and 25psi cut out. The pump will run until the pressure in the system reaches 25psi then cut out, once the pressure drops to 15psi the pump cuts in and tries to build the pressure back up.

To allow this to work one needs an accumulator in the line. Without one in the line the pump would "cycle" on and off very rapidly.

With one in line, as the pump runs water is forced into the accumulator against a gas blanket or rubber diaphram (or both) allowing the pump to run longer before the pressure reaches cut off pressure (25psi). Once this pressure is reached the pump stops. When you open a tap (or shower) the pressure starts to fall as the diaphram returns to normal shape (think balloon) or the gas forges water out of the accumulator. This allows you to draw off a larger volume of water before the pressure reaches cut in pressure(15psi). The range of the pressure swing is determined by the pressure switch in the pump and is not adjustable on the "run of the mill" pumps so with this type of pump you will have to live with pressure fluctuations. Having said that fitting a large accumulator will reduce pump cycling as it can store a larger volume of water while maintaining the pressure between 15psi and 25psi.

With a smaller pressure difference (20psi/25psi) the pump will cycle faster for any given flow rate.

So we have to draw a balance between pressure differential and accumulator size.

The smaller the pressure differential the faster the pump cycles and the larger the accumulator the slower the pump cycles.

Do also note that the pressure of the gas in the gas filled accumulators is critical for efficient operation. The installation manual for the pump should give the optimum accumulator pressure setting to allow max volume within the pressure range.

The alternative is to go for impeller type shower pumps and bypass the boats main water system pump.
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In my earlier post I've alluded to the fact that the accumulator pressure is critical to good operation. Someone else mentioned it as well. I should be more specific.

For instance if the air pressure in the accumulator is higher than the pump pressure output the accumulator will not work AT ALL. The bladder will simply refuse to be deformed by the water pressure and store no energy.

I used a car tyre pressure gauge to see what pressure there was in the accumulator. Without a pressure gauge it would be very hit or miss.

Another thing is to be sure to adjust the charge in the accumulator with NO pressure on the water side. I.E turn the pump fuse off the open the tap & let the water pressure out.

As a starting point I believe the charge pressure should be 1/3 to 1/2 of the pump operating pressure. Put some pressure in, close the tap & turn the fuse back on. See how it goes. Experiment with the air pressure to see what works best but always let the water pressure out again before adjusting the air pressure.
 
"Experiment with the air pressure to see what works best but always let the water pressure out again before adjusting the air pressure. "

This is a method that I have used successfully, without using a pressure gauge. My accumulator is pressurised with a bicycle pump. Turn on one of the water taps and leave it running. Mentally note the time between pump cut-in and cut-out. Give a couple of pumps on the bike pump and find whether this increases or decreases the cut-in/out time. Either keep pumping or let out some air to maximise this time. Job done.
 
>these accumalators save wear and tear on pumps, is this true.

Yes it's true, fit the biggest accumulator you can fit in the space available. It's the cycling on and off that wears pumps and the bigger the tank the less the cycling. Domestic tanks tend to be bigger than marine tanks.
 
hokay, seems unanimous that i should leave teh accumalator in teh system. mi'thinks a bigger accumalator would help.....
also a bigger pump....i assume i will then use more water....can't win in thi sgame :-)

Many thanks for all your replies.

Regards
 
[ QUOTE ]

Sounds like air trapped in the top of the accumulator tank.


[/ QUOTE ]That's whats supposed to be there, although in a bladder, otherwise it wouldn't work would it ?
 
Have you tried routine maintenance on the accumulator tank? The air reservoir can be slowly absorbed. Instructions for the PAR/Jabseco are:

a. Turn off power to pump
b. open tap furthest from accumulator
c. Remove plug in top of accumulator
d. open drain cock or loosen pipe on pump delivery side to drain system,
e. Replace plug in accumulator
f. reverse procedure at d, leaving tap open while turning on pump until flow settles.
 
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