Pressure: Water pumps and accumulators

[HopCar]

Originally Posted by atoll

errr no that is possibly the worst example of a domestic water system in use ,totally reliant on electrical power etc

domestic systems world wide generally rely on gravity fed systems with header tanks fed by persurised municiple water that keeps the tank topped up,or direct in to the water system,no tanks or pumps needed
.
i have never seen a pressurised water tank on a yacht,the only case of that i saw was when someone tried to fill his tank with the vent closed with integral tanks and the tank exploded.

Of course you have seen a pressure tank on a boat, we usually call it an accumulator tank. The home system pictured is exactly like a boat system except the water storage tank is replaced by a well.

My house had a system just like that until the county brought a water main down my street and I hooked into the main.

The municipal water system is just a big version of the home well system. In your example the pressurized accumulator tank is replaced by a water tower.

[a64pilot]

I believe overseas it’s common to have the storage tank on the roof, this tank is often filled by pumping the water up to it as the supply water pressures is not sufficient enough to do it, the water supply systems are often very old and were never meant to supply water under pressure like modern systems are.
Of course the height of the tank determines the pressure of the houses water system.

[atoll]

Originally Posted by HopCar

Of course you have seen a pressure tank on a boat, we usually call it an accumulator tank. The home system pictured is exactly like a boat system except the water storage tank is replaced by a well.

My house had a system just like that until the county brought a water main down my street and I hooked into the main.

The municipal water system is just a big version of the home well system. In your example the pressurized accumulator tank is replaced by a water tower.

now i understand why you guys are so screwed when there is a storm and the power goes off

most houses here have a 50-100 liter tank in the attic that supplies the water pressure,municipal water keeps that topped up with a ball cock valve,simple but effective,no power needed.

[HopCar]

Originally Posted by atoll

now i understand why you guys are so screwed when there is a storm and the power goes off

most houses here have a 50-100 liter tank in the attic that supplies the water pressure,municipal water keeps that topped up with a ball cock valve,simple but effective,no power needed.

I was without running water for several days after Hurricane Andrew until I managed to buy a generator to get my well pump running. Don't forget that municipal water systems also rely on electricity. I'm sure they all have back up generators. You can still lose municipal water from broken water mains or the line between the main and your house.

After Andrew I actually supplied some water to my house by filling 55 gallon drums at my store and back feeding it into the house with a little Jabsco pump.
Worked pretty well but it was a lot of work. At least the toilets flushed and I could take short cold showers.

Now that I have several generators, I may rig my sprinkler pump to supply water to the house if the municipal water goes out.

[deluxe68]

Originally Posted by atoll

now i understand why you guys are so screwed when there is a storm and the power goes off

most houses here have a 50-100 liter tank in the attic that supplies the water pressure,municipal water keeps that topped up with a ball cock valve,simple but effective,no power needed.

And those tanks never ever leak?

[mikedefieslife]

I've never heard of a leak, but I think modern homes have cold water direct from the mains outside.

[sveinung]

Originally Posted by canyonbat

Since we are on the subject, our accumulator has an air pressure fitting at the top. Any idea what pressure to fill the bladder?

I assumed this was simply a dump valve, and not for filling?
The chamber will fill with water until the air reaches the cut off pressure, so at 2 bars/30 psi differential pressure it would be about 1/3 full of air and 2/3 water.
If you pressurized it with water you'd blow air into the lines if it still had pressure when emptying before pump got back into action.
I guess you could perfectly pressurize it to the pumps cut in pressure so the tank would have 0% water in it when the pump came in, but I think the annoyance of air in the lines would make up for that.

[oceantools]

Hello all.

I've just joined the Forum to try to find a solution that has been plaguing my boat - a 2009 Oceanis 40 - for years. The plumbing is per it came out the yard, namely a Jabsco pump, accumulator, Quick 20l heater.

When we open a tap we get decent pressure & flow. However, when the water pump kicks in once the accumulator pressure falls, the water temperature falls until the accumulator is 'full' and the temperature rises again. This makes showering all but impossible as one is either frozen or scalded.

I removed the thermostat/mixer on the output of the Quick heater hoping that might have been the cause of the problem but that didn't help. Replaced the accumulator with a new one - still the same.

To me, it suggests the diameter of the output of the Quick heater must be a smaller diameter (therefore with a smaller cross-sectional area) than that of the cold water pipes and therefore is acting as a flow restrictor but that's only a guess.

Any suggestions greatly appreciated.

[desdestiny]

This problem is caused by different pressure drop in the hot water circuit, and the cold water circuit.
The accumulator also adds to the problem. Accumulators are designed to slow down the rapid cycling of the pressure pump.
There is a solution to this problem.
I will attempt to send am message to you direct
Des

[GordMay]

Greetings and belated welcome aboard the CF, oceantools.

Des: Why not post your solution, for everyone to see, and benefit?

[deluxe68]

I just finished replacing my plumbing with Whale tubing and quick connect fittings. I replaced the old freshwater pump with a Whale pump with integrated 2L pressure tank. Per one of the mfr web sites I connected an additional 2 gallon expansion tank off the hot water side. I also added a one-way valve on the cold water input to the water heater. I added a new sprayed for the shower with an on/off control. First thing I noticed was that when taking a shower, after I stop the water flow for a moment, I get a blast of cold water when starting again. I need to check the pressure on the small air tank to see if it matches the bigger tank, and may try adding a one way valve on the hot water output to the shower. It is also possible I forgot to place the one-way valve into the water heater.

[desdestiny]

Re "why not post your solution.."
When I have responded in detail to explain the technical problems in the past, I have been accused of breaking forum rules by a Modrator and using the forum to market a product.
Then I have been locked out of the forum unable to post a reply.

I do not wish to break forum rules, and do not know how to avoid this problem.
Des

[waterman46]

Originally Posted by BruceS

In answer to pressure to have in the accumulator ....
In my motorhome I carry a pushbike pump that has an adapter that will screw onto a car or truck valve & by turning on a cold water tap a weeny bit until the pump goes on/off/on/off I gradually pump up the pressure until I get the longest cycle time. If you go too much it shortens again .... just let a tiny bit out again.
Yes, there are now pumps that don't require them but they go all the time the tap is open. They use a LOT more power though.

This is exactly right, and he has given the correct way to adjust your accumulator pressure. However, a long cycle time might actually add to your problem of hot water delay.

A combination of flow restriction in line between accumulator and hot water tank, and too much air in hot water tank, could lead to delay in getting hot water pressure in tank up to same level as cold water pressure as the pump cycles on. These effects could also depend very much on the tubing distances between each component. I think our shower is fine in this respect because the hot water tank is less than 4 feet from the shower valve in the aft cabin. And the hot water tank is supplied by a tee off the cold line from accumulator, also close to shower so they get the same pressure point at that tee.

[oceantools]

Hello all

Thanks for your input and comments. I eventually got to the bottom of the problem. The boat was based in Mallorca for the last ten years, in Alcudia, where the water is very chalky and contains a lot of minerals. I'd clean the filters on the taps and showers on a regular basis and also change the heater element in the heater.

It never really occurred to me that the hot water output of the tank could also become heavily calced - but it was the only thing I hadn't checked. There's no easy way to check it so I bit the bullet and fitted a new tank. And bingo! We now have a perfectly balanced system with no temperature fluctuations other than a very minor one when the pump kicks in.

Happy days!