Fresh water "Pressure Capacity Tank" - Keep or Toss ?

obxjeff · Jun 18, 2023

Keep,

without an accumulator when you run the faucet the pump runs to keep the set pressure, once it reaches pressure the pump shuts off, then the pressure drops at the faucet so the pump turns back on, maybe several times a second, your pump wont last. the bladder in the accumulator holds some water at pressure to subsidize the system when the pump shuts off and absorb some of the water when the pump is on.

In residential wells, the accumulator is plumbed between the pump and the home, you are correct, if off on a side branch of the system the water may get very stale.

FastOlson · Jun 18, 2023

If the PVC tank does not leak, look at it as a way to have a little added water storage. In general it's always better to have some more water on board.

Ralph Johnstone · Jun 18, 2023

Deep six it.

The PVC tank does not have a bladder and so the water is in contact with the air. Water will dissolve air so the air in the PVC pressure tank will soon disappear and offer no help to the water system.

Scott T-Bird · Jun 19, 2023

I thought the purpose of a variable speed pump was to eliminate the need for an accumulator tank. Instead of a pressurized bladder in the accumulator, the variable speed evens out the flow based on demand. I also read that despite the advantage of a VSP, they may not be as reliable (that's just net opinion, I think). So, the fact that the pump runs immediately when you open the faucet isn't surprising. I suspect that there is no downside in having the small accumulator tank.

But I don't really understand why the half-gallon PVC tank (without any bladder?) would serve any purpose (I assume you mean 3-inch diameter by 15" long). I don't know why it would be tee'd off the main system. But I also suspect it does no harm.

I have a 4 gpm shureflo with a small Whale accumulator. It doesn't cycle when I'm running water and the flow is even ... doing what it is supposed to do .... it is noisy.

capntmitch · Jun 19, 2023

I tossed

ricksoth said:
I need guidance on my fresh water system.

The PO had a 3" x 15" PVC 'tank' plumbed into the system which I'm guessing was a DIY attempt at an accumulator tank. The old pump was noisy, so I replaced it with a Seaflow 42 variable flow pump and added a small 0.75 liter Seaflow accumulator, and it worked fine but the pump cycles (albeit quietly) after opening a faucet for just a few seconds. I then re-plumbed in the "PVC" tank, and now a full glass or more of water can be drawn from a faucet without the pump cycling.

My question is should I keep this PVC "capacity tank" in the system or remove it? It's nice not having the pump cycle for a glass of water, but maybe that is a stupid reason to keep it.

If I keep it, does it matter where in the boat it's located? It's currently secured next to the hull at a point where it's basically at the same level as the water tank. It seems like the water in this tank will become stagnate since it's not in the main pathway (tubing) where water is coming from the tank to the faucets.

Keep it or Toss It ??
I tossed mine and put on a Shur Flo pump that doesn’t need a pressure tank or cycle.

captcoho · Jun 19, 2023

Did you adjust the pressure of the bladder in the accumulator?
That will affect how much water will flow when the faucet is opened before the pump runs

LloydB · Jun 19, 2023

Do you have a diagram of how this supply system is supposed to work with the variable pump?

Radio Flyer · Jun 19, 2023

ricksoth said:
I need guidance on my fresh water system.

The PO had a 3" x 15" PVC 'tank' plumbed into the system which I'm guessing was a DIY attempt at an accumulator tank. The old pump was noisy, so I replaced it with a Seaflow 42 variable flow pump and added a small 0.75 liter Seaflow accumulator, and it worked fine but the pump cycles (albeit quietly) after opening a faucet for just a few seconds. I then re-plumbed in the "PVC" tank, and now a full glass or more of water can be drawn from a faucet without the pump cycling.

My question is should I keep this PVC "capacity tank" in the system or remove it? It's nice not having the pump cycle for a glass of water, but maybe that is a stupid reason to keep it.

If I keep it, does it matter where in the boat it's located? It's currently secured next to the hull at a point where it's basically at the same level as the water tank. It seems like the water in this tank will become stagnate since it's not in the main pathway (tubing) where water is coming from the tank to the faucets.

Keep it or Toss It ??

Keep it. Know that like any well pump tank without a bladder, it will fill eventually. Bladders in well pump pressure tanks are new technology since 1970 or so. Before then it was just a galvanized tank with no bladder. The solution was to drain it whenever you begin to "short-cycle" the water pump. Just make sure to mount your tank vertically (long axis pointing up). That way it won't easily burp out air and fill with water.

Ward H · Jun 21, 2023

My understanding is newer pressure pumps are designed to work as stand alones, not needing an accumulator. I think that's what @Scott T-Bird has.

JBP-PA · Jun 22, 2023

ricksoth said:
It's nice not having the pump cycle for a glass of water, but maybe that is a stupid reason to keep it.

That's the best reason to keep it. If it makes you happy, keep it until it doesn't anymore. It's your boat.

If, down the line, you need to repressurize it too often and it no longer makes you happy or if you suspect it causes a bad taste, then toss it.

jviss · Jun 22, 2023

Ralph Johnstone said:
Deep six it.

The PVC tank does not have a bladder and so the water is in contact with the air. Water will dissolve air so the air in the PVC pressure tank will soon disappear and offer no help to the water system.

Wow, I can't even figure out what that means! Why would there be air in that tank? What does it mean that "water will dissolve air?"

jviss · Jun 22, 2023

ricksoth said:
.75 liter accumulator

That's not much of an accumulator. I have a Groco 2 gallon accumulator, which is like 7.6 liters. I can use the head sink a few times at night without the pump kicking on. (I have been trying to figure out how to wire a pushbutton I can depress when I turn in to fully pressurize the system so I don't hear the pump 'til morning.). I would imagine with a .75 liter one I'd hear the pump every time the sink is used.

Scott T-Bird · Jun 22, 2023

jviss said:
Wow, I can't even figure out what that means! Why would there be air in that tank? What does it mean that "water will dissolve air?"

Think about it this way ... The offline tube is going to be installed into the system filled with trapped air. In essence, it is a home-made accumulator tank except that it is made without a bladder. It depends upon the compressibility of air to provide the buffer that an accumulator tank provides with an air-filled bladder. The purpose of the bladder is to separate air from water, because air does dissolve in water (that's one way how water becomes oxygenated for fish to "respire" - water plants also respire oxygen at night when photosynthesis isn't working). The air won't dissolve immediately, but it will eventually be absorbed and when that happens, the homemade tank is filled with water, which doesn't compress and by then it serves no function.

The difference between the home-made tank and a manufactured accumulator tank is that the pressure can't be regulated in the homemade tank and the air in the homemade tank will eventually disappear and the tank will be filled with incompressible water until the tank is removed and drained again and again during the life of it's service. When it is completely filled with water (after the air has been dissolved), it serves no purpose.

I had a 3/4 quart (24 ounce) Shurflo accumulator tank and now a half-gallon (2-liter) Whale tank with the same fixed speed pump (Shurflo Aqua-King 4 gpm). and I notice very little difference between the 2. Both tanks had about the same pre-set bladder pressure (22 psi vs 30 psi) but both could be adjusted with a bicycle pump. They both buffer the flow for even discharge pressure when the pump is running. The pump generally turns on within a few seconds after opening the faucet. My pumps always run continuously as long as I have the faucet open. A much larger accumulator tank may allow the pump to cycle on and off, I suppose, and it also delays the call for water when you first open the faucet. The delay with your 2-gallon tank sounds about right. I couldn't really tell much difference between the 3/4 liter and 2 liter tanks that I have used.

But the purpose of the variable speed pump is to eliminate the need for an accumulator tank. Of course, you don't really need an accumulator tank with a fixed-speed pump, but they say it helps, so most of us install it.

jviss · Jun 22, 2023

Scott T-Bird said:
Think about it this way ... The offline tube is going to be installed into the system filled with trapped air. In essence, it is a home-made accumulator tank except that it is made without a bladder. It depends upon the compressibility of air to provide the buffer that an accumulator tank provides with an air-filled bladder. The purpose of the bladder is to separate air from water, because air does dissolve in water (that's one way how water becomes oxygenated for fish to "respire" - water plants also respire oxygen at night when photosynthesis isn't working). The air won't dissolve immediately, but it will eventually be absorbed and when that happens, the homemade tank is filled with water, which doesn't compress and by then it serves no function.

The difference between the home-made tank and a manufactured accumulator tank is that the pressure can't be regulated in the homemade tank and the air in the homemade tank will eventually disappear and the tank will be filled with incompressible water until the tank is removed and drained again and again during the life of it's service. When it is completely filled with water (after the air has been dissolved), it serves no purpose.

I had a 3/4 quart (24 ounce) Shurflo accumulator tank and now a half-gallon (2-liter) Whale tank with the same fixed speed pump (Shurflo Aqua-King 4 gpm). and I notice very little difference between the 2. Both tanks had about the same pre-set bladder pressure (22 psi vs 30 psi) but both could be adjusted with a bicycle pump. They both buffer the flow for even discharge pressure when the pump is running. The pump generally turns on within a few seconds after opening the faucet. My pumps always run continuously as long as I have the faucet open. A much larger accumulator tank may allow the pump to cycle on and off, I suppose, and it also delays the call for water when you first open the faucet. The delay with your 2-gallon tank sounds about right. I couldn't really tell much difference between the 3/4 liter and 2 liter tanks that I have used.

But the purpose of the variable speed pump is to eliminate the need for an accumulator tank. Of course, you don't really need an accumulator tank with a fixed-speed pump, but they say it helps, so most of us install it.

Hi Scott,

My intuition is that your analysis of a tank without a bladder is wrong. When it's filling wouldn't the entering water displace the air, pushing it out? Also, I don't think the bladder in a proper expansion tank is to stop air from dissolving into water, it's to keep the air in the tank, the air behind the bladder acting as a spring. You're not going to get a lot of air dissolving into water at 35 psi!

Scott T-Bird · Jun 22, 2023

jviss said:
Hi Scott,

My intuition is that your analysis of a tank without a bladder is wrong. When it's filling wouldn't the entering water displace the air, pushing it out? Also, I don't think the bladder in a proper expansion tank is to stop air from dissolving into water, it's to keep the air in the tank, the air behind the bladder acting as a spring. You're not going to get a lot of air dissolving into water at 35 psi!

Turn a bottle upside down and plunge it in a bucket of water. What happens? How is trapped air going to escape? The "tank" that @ricksoth describes is going to have trapped air in it until it eventually dissolves. Why won't pressurized air dissolve? Of course it will ... the amount of air that can be dissolved in water decreases with temperature and increases with pressure. In fact, it is directly proportional with pressure. You can look it up. More pressure, more soluble. It takes time, but eventually it will dissolve.