Accumulator - Where do I install it?

[TedS]

Just for reference, the water pressure may rise 50 to 100 psi per degree F as water heats in a water solid system.

[Cate&Rob]

Howard,

I would not worry about the pressure rise from the hot water tank since the plumbing is more than capable to handle that. The accumulator is used to stop pump pulsations and to reduce cycling. Set the air pressure to 2 psi below cut in pressure and its all good.
Also one blip of a hot water faucet will normalize the pressure. Some folks will talk about their relief valve purging on the first heating cycle where this is normal due to initial expansion from heating.

Jim

Guest howson

Hi Jim,

Your theory is correct for an accumulator tank large enough to supply water to the system when the pump is off. The accumulator that Howard has chosen is too small to do this . . . it is intended only to absorb the water expansion from heating and thus should come into play only when the system pressure rises above pump cut-out pressure.

Agreed that one blip of a faucet (or a brief opening of the pressure relief valve) will relieve this pressure increase due to heating. Ironically, the less soft hose that you have in the water system, the greater the pressure rise. Expansion of the soft hose acts like an accumulator tank.

Rob

[Cate&Rob]

Any idea what I did wrong (if anything)?

In retrospect I can see one mistake. It should have worked as installed, but when the white selector valve on the Nautilus is turned to use the pump (water from fresh tank) it would have isolated the accumulator. <sigh>

Isolating the accumulator will reduce it's effectiveness . . . LOL!
Tee in the accumulator downstream of the pump to make it functional for either city or tank supply.

Rob

[howson]

I moved the accumulator under the sink. Not a "pretty" install but it's functional and accessible without encroaching on the DW's storage space under the sink.




The accumulator performed well in the first test in this location, but upon repeating the test (to verify) the pressure exceeded the accumulator's setting. Not as dramatic (the dial wasn't pegged all the way clockwise) but still higher than I'd hoped.



And of course there's a leak I'm going to have to fix, dang it.

[Cate&Rob]

howson

Hi Howard,

I am surprised that accumulator can’t absorb the volume increase associated with water heating. Does the air pressure in the bladder (measured at the schrader valve) match the pressure on the water gauge? It should if things are working correctly.

With my 2 gal accumulator tank, system pressure goes up less than 5 psi with heating.

Rob

[howson]

howson

Hi Howard,

I am surprised that accumulator can’t absorb the volume increase associated with water heating. Does the air pressure in the bladder (measured at the schrader valve) match the pressure on the water gauge? It should if things are working correctly.

With my 2 gal accumulator tank, system pressure goes up less than 5 psi with heating.

Rob

The accumulator is set for 58 psi -- at least that's what my small tire gauge shows. I double-checked it before running the second series of tests. On the next test I'm going to adjust it down (but above standard water pressure) to see if there's a difference in the performance.

Side note / related question: when I hook up to city water and before turning on the water heater (WH) I ensure all the air is out of the lines by running all the faucets, both cold and hot. I do not open the T&P valve on the WH. If there was air in the lines I assume there'd be less measured pressure on the water gauge, right, since air is compressible? Should I "burp" the water heater tank's T&P to ensure the air gap at the top is correct when first hooking up? Question assumes all air is out of the water lines and the water tank is "full".

[Guest]

Guest howson

Hi Jim,

Your theory is correct for an accumulator tank large enough to supply water to the system when the pump is off. The accumulator that Howard has chosen is too small to do this . . . it is intended only to absorb the water expansion from heating and thus should come into play only when the system pressure rises above pump cut-out pressure.

Agreed that one blip of a faucet (or a brief opening of the pressure relief valve) will relieve this pressure increase due to heating. Ironically, the less soft hose that you have in the water system, the greater the pressure rise. Expansion of the soft hose acts like an accumulator tank.

Rob

Thanks Rob. I guess the small volume unit with the higher air pressure and a larger volume unit at the low air pressure setting would be perfect. I will order a unit for the low pressure purpose of eliminating pump pulsations and cycle time and will blip the faucet during the initial heating cycle where expansion would be the greatest. It may also be good to replace the soft hose every other year?

You guys have me thinking about the soft hose even though I have only one on the pump outlet. Can't plumb this in with pex due to vibration. I have taken your advice on shutting the pump off when we leave the campsite where the water alarms are another good idea.

Jim

[Cate&Rob]

The accumulator is set for 58 psi -- at least that's what my small tire gauge shows.

I think you missed my question. When the pressure climbs on the water pressure gauge is this matched by a similar air pressure reading using your tire gauge on the schrader valve? The reason for my question is wondering whether the accumulator is actually absorbing an increase in water volume which would compress the air behind the bladder in the accumulator.

Rob

[howson]

I think you missed my question. When the pressure climbs on the water pressure gauge is this matched by a similar air pressure reading using your tire gauge on the schrader valve? The reason for my question is wondering whether the accumulator is actually absorbing an increase in water volume which would compress the air behind the bladder in the accumulator.

Rob

Hmmm...I don't know. I'll check next time I fire up the water heater.

[Country Campers]

I think that the 58 psi in the tank is too much pressure.

Brian

[Guest]

I think that the 58 psi in the tank is too much pressure.

Brian

What is the cut in pressure of the pump? Accumulator should be placed at the outlet of the pump and set 2 psi below cut in pressure.

Jim

[Cate&Rob]

Country Campers Guest howson

Brian & Jim . . . you guys are thinking of this tank in its traditional use to "accumulate" water between the cut-off and cut-on pressures. Howard is using this tank as an "expansion" tank to gather the increase in water volume caused by heating. Thus, it should not come into play until the system pressure rises above the pump cut-off pressure, to provide the maximum possible volume for thermal water expansion. Setting the tank bladder pressure just above the pump cut-out pressure would be correct.

I am wondering if something is blocking water access to this tank. Even with its relatively small volume, there should be more than enough room for thermal water expansion without reaching the pressures that Howard is seeing. (Thus, my suggestion to check tank air pressure at the higher water pressure, to see if it matches)

Rob

[howson]

What is the cut in pressure of the pump? Accumulator should be placed at the outlet of the pump and set 2 psi below cut in pressure.

Jim

Jim--I'm not using the pump to supply water to the camper's faucets during these tests. The camper is connected to city water at a constant 50 psi (at the pressure regulator). The camper gauge on the Nautilus panel shows a constant 45 psi. (Why it's different? Probably gauge variances.)

When the water heater is turned on the camper pressure gauge spikes off-scale high. I want to mitigate that pressure rise. A better term than accumulator is I want an expansion tank. Expansion Tank - Water Heater Expansion Tank

When I tried using the accumulator as an expansion tank, I expected pressure in the lines to increase to the set value of the accumulator (58 psi). At that point the accumulator should absorb any pressure increase until the internal bladder reaches the maximum contraction. The accumulator can only absorb a small amount of water based on my test results.

The answer is a larger expansion tank, configured as shown in the video.

What's really interesting (an confusing to this ignorant plumber-wanna-be is that an accumulator and an expansion tank are the same thing, with just a different name. From https://www.sheridanmarine.com/produ...xpansion-tanks

Accumulator Expansion Tanks Information

The Accumulator Expansion Tanks can be used as either an accumulator or an expansion tank in your boats water system. The enamelled steel tank features an internal rubber membrane with a stainless steel connecting flange.

The rubber membrane expands and contracts depending on the air pressure inside the accumulator tank. This regulates the amount of water which can be stored in the tank depending on your boat water pumps cut-in pressure.

It is a good idea to fit an accumulator tank to your boats water system if you are using a pressure water pump. The tank can be fitted in any orientation just after the pump. These accumulator tanks are designed for small to medium sized water systems on small to medium sized boats. If in doubt it is better to fit a larger accumulator tank.

What is an Accumulator Tank

Accumulator tanks act as a buffer, smoothing the flow of water from the water pump to the tap. The tank keeps a reservoir of water which helps ease the strain on the pump. With an accumulator tank the pump doesn't need to start immediately and doesn't rapidly cycle on and off meaning you get a much smoother flow of water and reduce wear on the pump at the same time. An accumulator tank can be used with both cold or hot water systems.

Smoother water flow from your tap (the water no longer pulsates)
Reduce wear on your pump
Reduce battery usage as the pump doesn't turn on as frequently
Quieter water system operation

What is an Expansion Tank

Expansion tanks act as extra storage for your hot water. As the water in your calorifier heats up it expands. This 'extra' hot water has nowhere else to go but back along the cold water supply. The expansion tank, when fitted after a non-return valve and before the calorifier, stores this extra hot water and stops it interfering with the cold water supply. An expansion tank is only need with a hot water system.

Howard

P.S. It may seem counter-intuitive, but increasing the set pressure in the small accumulator may allow for more water expansion. I'm going to bump it up to 65 psi and try it again.

[howson]

Cate&Rob -- you beat me to it! (I was researching as you were typing!) I'll check that pressure as suggested and report back later.

Howard

[Cate&Rob]

howson . . . we were obviously typing at the same time .

Rob