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RV Accumulators

Accum-Top30.jpg, 80kB
Here is an accumulator. A simple wine bottle, mounted upside down. This one is mounted under the sink cabinet.

I like these way better than the store bought bladder types. In time the bladders always leak.

Reasons for an Accumulator:

BBALLBLU.GIF, 139B A pulse pressure buffer.
On demand water pumps produce high pressure pulses. The continual vibration and stress will cause connections to leak. Perhaps only a drop or two, but still causes hidden mold and rot.

BBALLBLU.GIF, 139B Water reserve
You can use the bathroom without the pump coming on.

BBALLBLU.GIF, 139B Pump longevity
The accumulator makes life easer for the pump.
Also the pump can be adjusted to consistently shut off a repeatable pressure.

BBALLBLU.GIF, 139B Quietness
You can brush your teeth in quietness. A simple thing like this means a lot to me.
Accum-OutsidePannel-Refreg.jpg, 25kB
My Main Accumulator is a 4 ft piece of 2.5 inch PVC pipe. I easily installed it vertically, behind the refrigerator, in the refrigerator vent area. The perfect place: vertical, out of the way, unused space, and high up. You want it as high as possible. The top of this one goes to the roof. The top of the refrigerator hold gets warm, but no where close to melting PVC or ABS.

You can see the bottom of it in the picture at the upper right corner. Such a PVC pipe is about 3.8 Liters or 235 cubic inches. Most commercial bladders are about 620mL or 37.8 Cubic inches. So I have a better accumulator than any "store bought". Stores lots of water too. All night long, the pump never comes on, even after you can flush the toilet many times.
Accum-BottomS.jpg, 31kB Looking vertically up...
I use all 1/2 inch reinforced vinal hoses with barbed fittings and gear clamps. The connector ends of the original hoses were not rated above 50 lbs pressure, and I have had several unexpected leaks; some slight and some catastatic. So much as even one drop of water is intolerable, and can cause thousands of dollars in damage! The "hard" PEX lines have been ok and have not leaked. And it is just as well, because the ends are expensive and difficult to work with.
I have had no trouble with the vinal, and it is easy to work with.
For my accumulator I like white PVC better than black ABS because the cementing is bullet proof. There can not be even the slightest of an air leak. And still with a non-bladder and no air leaks, the reservor will have to be occasionally recharged.

Limnic-Eruption.jpg, 6.6kB

Absorbed gasses...
Pressure in the accumulator, or pressure deep at the bottom of Lake Limic, causes water to hold more gasses. My pressure is between 20lbs and 30lbs, and eventually the air in the top of the accumulator will be absorbed in the water and "go away". In this picture, pressure at the bottom of Lake Limic is reduced by an "Overturn", and a huge eruption of CO2 gas is liberated out of the water. Clearly, even with no air leaks in the accumulator, you will naturally loose air. And hopefully, nothing this violent happens inside my RV.
... And an event this violent would surely be difficult to hide from my wife.

The accumulator eventually becomes "water logged". The trapped air is absorbed and the accumulator does not function well. The needle on the pressure gauge "vibrates", pressure builds faster, and the target pressure overshoots and undershoots. For me it is about every three months, and I try to not let it get this far.
Recharging is easy...
Disable the pump, and just open any valve that is lower than the bottom of the accumulator. After the water is emptied, air will begin to slowly gurgle up into the accumulator. The bathtub faucet works for me, but you may have to use the drains under the trailer. Besides higher pressure ratings, another advantage of throwing away of the stock hoses is that now you can see what is going on and you can see the air bubbles rising into the accumulator. I like to "see" stuff...

BANASTAR.gif, 1.5kB Now faith is confidence in what we hope for and assurance about what we do not see.
This is what the ancients were commended for.
By faith we understand that the universe was formed at God's command, so that what is seen was not made out of what was visible.

Hebrews 11
I am an Engineer of over 40 years.
Show me!
Give me evidence. "Give me a sign."

WineBottle.jpg, 35kB
A Wine Bottle Accumulator: "Seeing things"...
Which leads me to my second accumulator. This accumulator is more of a "viewing" accumulator.

My main accumulator, which is mounted in the refrigerator hold, has no sight-glass. It is just PVC pipe, and I can not see inside. And sure, I could have installed a section of clear vinal hose along side the PVC, but I did not think about it then. If I had thought about it, I could see how much air was inside. Now the cement is dried. It is finished, and can't go back.

I did not particularly like the contents of the bottle, and I gave it away without much of a problem. The bottle is a 1.5 liter, or about 91 cubic inches. A 1.5 liter wine bottle is over twice the volume of a commercial accumulator.
WineBottleNeck.jpg, 17kB
The neck needs to be long and unincumbered with things like a finger hold as found on an apple cider jug.
The mouth is close to 1 inch across. But I choose 3/4 inch (inside, ID) Vinal hose. Take the hose end above a burner on the stove. Gentle heat untill soft. Once you work the hose end over the neck, and after the vinal cools, you can put a clamp on it for esthetics. Actually, esthetics does not work. As tight as the vinal seemed, it will leak without a clamp!

I like the setting of just under 30 lbs: It is perfectly two atmospheres, or 29.392 PSI, and 33 ft of head. And it is well below the 50 lbs rated pressure of most RV hose connectors.

Bursting pressure for a wine bottle is about 400 psi, if the glass has no thin spots, nor surface defects, nor side pressure from my mounting hardware.
I went over to Michaels, a bead and pretty thing store, without too many women seeing me, and bought some floating beads. I placed the beads in the bottle before all the hook ups. I thought the beads would float on the water line inside the bottle. Make sure the beads are too big to pass through the connections. You do not want them to leave the bottle when you purge the system. I noticed the beads sink further down when under pressure; I hope they do not break. The pieces would be free to migrate into a valve or something. Perhaps I should not have done this. And the beads don't really help in seeing the water line anyway. It is yet another one of my lame ideas. I had no business in that store anyway.

After only one day the balls began to break. They were not made of glass. I could see parts had fallen down inside the clear vinal hoses. The pieces were in my system, just as I had feared. Everything had to be disassembled. A needless, time consuming process. At every step of the way I kept reiterating under my breath: "stupid idea". After all lines were back in place, I reapplied pressure, and observed another piece that I had not seen before. It must have been deeper in the lines. I do not know where it came from. Bad news...
The piece was slowly moving toward the bottle. I went ahead and pumped to 30 lbs. The nearest exit was the cold water tap on the kitchen sink. I opened the tap as far as it would go. With full force the water came out, and I could see the piece was traveling in the lines and soon shot out the tap into the sink. It went pass the valve and was lying in the bottom of the sink. Lucky! I won't do that again!

Accum-Barb34to12.jpg, 26kB
Connect the bottle's 3/4 hose (on the left) to the standard 1/2 vinal hose (on the right) with a barb to barb adaptor. I use 1/2 inch hose all over the place, and I must get to it as soon and directly as possible. Also stay away from metal connectors as they are heavy and expensive; this is a light weight RV. Careless accumulation of weight is not needed.

Accum-Cabinet.jpg, 72kB
Here is the accumulator installed in a cabinet of choice. I chose under the kitchen sink. There is red nut driver laying in the bottom section. Nut drivers are the only way to adjust gear clamps in a manner that allows good control. And vinal is soft and slowly flows, so check it again in a month or two. What is absolutely, for sure, tight today may not be tight in a month or two.

Accum-Top30.jpg, 80kB
Here the water level is at 30 lbs. And it is exactly at the top of the brace and at the bottom of the threads of the brace screw. I also have marks at 20 lbs and 10 lbs. But the marks are only valid at initial charge.

Note that the wine bottle is about 2/3 water, and about 1/3 air.

Eq-PV-Real.gif, 8.3kB
The amount of air in the wine bottle is starting out at Atmospheric pressure. This reads "zero" on the gauge. But the pressure is really 14.7 lbs per square inch.

Eq-PV-30lbs.gif, 8.2kB
For example:
For my setting...
The volume in the wine bottle will always be one third of the "zero" gauge pressure.
This is when the pressure switch is set at 30 lbs.

There exsists the posibility, but I have not seen it in over two years, that the air volume in the wine bottle will become smaller and smaller as air is obsorbed into the water.
And the accumulator's buffering action will be less and less.
Although, I have seen this happen in Dad's non bladder water tank at the well. The tank had to be drained or recharged with air.

Accums-OneGallon.jpg, 25kB The accumulators, the glass bottle and the ABS pipe, hold one gallon of water. To get this measurement, have the pump deliver its normal 30 lbs, and after it stops turn it off. The water level will be approximately 2/3 full in the glass accumulator and approximately 2/3 full in the pipe accumulator. Use a tap at a sink to fill a container, and see how munch water is stored under pressure.

My big PVC pipe accumulator holds 2/3 of 3.8 Liters.
And my glass "see-in" accumulator holds 2/3 of 1.5 Liters.
Both together is 3.5 liters.
I guess there is a couple of pints in the water lines.

Perhaps, from time to time, God gives life in a little extra abundance?

Eq-PV-23lbs.gif, 7.9kB In reality, the pump cycles between 30 lbs and 23 lbs. How much water is this?
Eq-PV-Diff.gif, 3.8kB So you get a gallon available and completely drained, and only .3 liter under pressure.
Huge difference. The two pressure choices seems disapointing.

Of course, you could always reduce the cut-in pressure on the pressure switch. Yes, you would have more water. But you would have little pressure on the low end. And that pressure would have a wider swing and less pressure consistency. But, what the heck, that is exactly what I did...

Accum-CutIn1Atm-Meter.jpg, 23kB Accum-CutOut2Atms.jpg, 28kB
I lowered the cut-In pressure to one atmosphere, 1.0 Atm, 15lbs/sqin, and the cut-out to aprox 2 atmospheres.

Eq-PV-15lbs.gif, 7.8kB Eq-PV-Diff1.gif, 3.9kB
There is something esthetically pleasing about 2 atmospheres and 1 atmospheres. So this is where I set my water system. Much more water can be had with a lower Cut-In pressure. And my science training says there is something pretty about it.
Accum-175Down.jpg, 59kB
All accumulators will read the same:
32 lbs is exactly at the top of the brace on this glass accumulator.
And 15 lbs is at the mark. Or, about 1.6 inches down from the 32 lbs mark.
The whole body portion of the bottle is about 10 inches long. So 1.6/10 is 0.16, great agreement with the calculation from above at 1.67.
Accum-DiffJug.jpg, 14kB
Turned on the sink facit, and drained down from 32 lbs to 15 lbs. I collected the water in this 1.75 liter jug. And again, I have been given a little more than expected. I would say this is at least a liter. I was only expecting 0.89 liters.

God pores out goodness with a little extra measure. At least for water.