accumulator/day tank

[Ron in BC]

I hate pumps cycling on and off frequently and I like to be able to get a little water in the middle of the night without disturbing anyone.

I could have installed a ready made accumulator but I made one that allows for use as an accumulator while the pump is running and acts as a day tank and gives a nice amount of water without having to turn the pump on.

The tank is 3" X 17" and I mounted it vertically in the closet. I was going to mount it out of sight horizontally above the little coat hanger rod but I got lazy. It works amazingly well It gives a usable amount of water without having to turn on the pump. I removed the pump to test the whole assembly out of the trailer. I knew I'd be living in the trailer by myself if I installed it untested and it spewed water all over When I reinstalled the pump I mounted it on grommets, and the two items, the accumulator and the soft mounting, seem to have quieted the pump quite a bit.

All in all, a good result for very little money.

[cpaharley2008]

How do you fill the tank and does it only feed the toilet? Accumulators have a bladder installed to eliminate trapped air. Your section may not fill if it has trapped air.

[GMike A]

You peaked my curiosity as I have a well but always called them pressure bladders. I found one for small boats for 33 bucks which seems like a good investment. Made by Jabsco Mini-Accumulator with internal bladder. Think I found something else to add.
Thanks for bringing that up.

[Brian B-P]

Originally Posted by cpaharley2008

Accumulators have a bladder installed to eliminate trapped air. Your section may not fill if it has trapped air.

The bladder separates the water from the air, but air is needed for the tank to work as an accumulator. The compressed air is what pushes the water out; yes too much air for a specific combination of tank volume and operating pressure will mean less capacity than ideal.

I have a well at my house. To reduce pump cycling, well water systems use an accumulator, just like this RV system but larger. I believe that accumulators - known as pressure tanks - are available with or without bladders.

[Donna D.]

These things work well for folks that get up in the middle of the night and don't want to disturb their partner when the toilet flushes and the pump runs!

[Ron in BC]

The feed line for the tank is teed off near the output from the pump. First time I used a SharkBite fitting. Worked really well and I like the way you can still swivel it afterwards.

The tank charges/fills when the pump is operated. The contents are under pressure from the pump as well as higher than any of the fixtures. When the tap is opened the compressed air forces out the water quickly. As the pressure drops the rate slows but the flow continues because of the gravity feed.

Internal bladders do prevent air from being absorbed by the water and the tank losing its' cushioning effect but based on my previous experience with one in my boat that doesn't happen very quickly. If it did I would just remove the plug on the top of the tank and let some more air back in.

[Thomas G.]

I made a similar accumulator with no internal bladder. It works great.

[cpaharley2008]

I can't understand how any water will get inside the tank since there is no room for air to escape. Just like priming your pump, until you bleed the air out no water is getting into your lines. So pumping water into a sealed tank can't happen unless you have a way of letting the air out.

[Brian B-P]

Originally Posted by cpaharley2008

I can't understand how any water will get inside the tank since there is no room for air to escape. Just like priming your pump, until you bleed the air out no water is getting into your lines. So pumping water into a sealed tank can't happen unless you have a way of letting the air out.

The air can't escape, but it is compressible, which is the point of these devices. The water is pumped into the sealed tank, and it gets in because the air is compressed - squeezed into a smaller space - and so acts as a spring to push the water back out when it is needed, without starting the pump until enough water is used for the air pressure to drop to the pump's switch-on point.

There are two differences between this and filling a water system:

1. water pumps don't work well pumping air, so you need to get the air out of the pump itself
2. air in the plumbing is in the way of getting the water to where it is wanted, while here the air is in a "dead end", and the whole path from tank to faucet is filled with only water

Originally Posted by GMike A

I found one for small boats for 33 bucks which seems like a good investment. Made by Jabsco Mini-Accumulator with internal bladder.

Good find. Here's the manufacturer's website: Xylem Flow Control - Pressure System Accessories

These Jabsco accumulators are pre-charged, meaning that they are shipped with the air in them already under pressure. The extra air means more usable capacity - that is, more water delivered before the pressure falls too low to be useful. I suspect that the protrusion on top is an air fill valve - like a vehicle tire valve - to allow for adjustment of air charge. You can just see the air valve on top of the vertical pressure tanks in my earlier link.

Originally Posted by Ron in BC

The contents are under pressure from the pump as well as higher than any of the fixtures. When the tap is opened the compressed air forces out the water quickly. As the pressure drops the rate slows but the flow continues because of the gravity feed.

The use of gravity in this case is clever. Pre-charging with some air, or restoring some air content as it eventually gets absorbed, might improve performance even further.

Originally Posted by Ron in BC

Internal bladders do prevent air from being absorbed by the water and the tank losing its' cushioning effect but based on my previous experience with one in my boat that doesn't happen very quickly. If it did I would just remove the plug on the top of the tank and let some more air back in.

An air valve could allow the addition of air without depressurizing the system, but perhaps in the small volume of any RV system this is not important

[Brian B-P]

Update: I just confirmed in the Jabsco 30573-0003 Mini Accumulator Tank manual that it is a tire valve on the end, to adjust pre-charge. Because this tank has a bladder, the system pressure can just be completely relieved to adjust the air.

This installation and operation manual gives a nice illustration (with cutaway drawings) of the principle of operation.