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Fresh Water Accumulator Tank Benefits and Installation

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Ron Dittmer

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Fresh Water Accumulator Tank Benefits and Installation
« on: March 20, 2019, 08:58:48 am »
Does your on-board water pump irritate you with loud rapid cycles?
When taking a shower, is the water temperature a little inconsistent?
Would you like your on-board water system to be like at home, consistent and quiet?
There is a remedy called an accumulator tank.

What is an accumulator tank?
It is a water reservoir made of plastic, steel, stainless steel.  It has a rubber badder inside much like an inner tube in a bicycle tire with a standard air valve just like a tire has.  During installation, the bladder should be pressurized to roughly 20 psi.  During operation, the pressure in the bladder will fluctuate between that starting pressure of 20 psi to a high of around 40 psi after your RV's on-board pump has filled it.

What are the various types of accumulator tanks?
The most common accumulator tank for RVs are made of plastic.  They are small, about 0.2 gallons (24 oz.) in total volume.  Their popularity is primarily because they can be mounted in tight places.

A house grade accumulator tank is made of steel.  They are 2 gallons (256 oz.) in total volume.  These are easily found in home improvement centers and are affordable.

My personal favorite is this one made of stainless steel.  It is the same size as the steel house grade tank at 2 gallons total volume.  It's primary benefit is that it has feet for easy mounting, and it has a platform to mount the water pump on top to reduce the footprint.  These vary in price wildly from $139 to over $400 for the exact same tank, so do your internet shopping well.  Google search "Shurflo 3400-002".

Considering the bladder, how much water does the tank hold?
When the on-board water pump turns on at 20 psi, the actual water inside is roughly 1/3 of the total volume.  At 20 psi, the 2 gallon tank is holding about 0.7 gallons (90 oz) of water.  A 0.2 gallon plastic tank is holding about 8 oz.  For obvious reasons, a small plastic tank will have the pump cycling much more frequently than a large metal tank would.

Where should the tank be mounted?
Officially an accumulator tank can be installed anywhere on the cold side of the fresh water system.  But mounting the tank adjacent to the water pump, in-line with the piping, quiets pump operation because the tank absorbs the vibration of the pump, preventing the vibration from being amplified through your PEX plumbing.

Does size matter?
Absolutely!  The large 2 gallon tank will absorb much more vibration than a small 0.2 gallon plastic tank.  A bigger tank will also dramatically reduce the cycling of the pump.  My personal experience is that a 2 gallon tank is ideal.  The next size larger is 6 gallons which is way too much for an RV.

Tips On Installation
I recommend using a flexible braided stainless steel hose to connect the water pump to the accumulator tank, then flex or PEX plumb from the tank to the RV.  This type of hose is very reliable and significantly reduces the vibration to the tank.  If installing a small plastic accumulator tank, I recommend coiling a long flexible hose as shown to further reduce vibration.  Add some carpet padding between layers of the coil to further dampen vibration.  This hose is found in all home improvement centers.  Bring your tank and pump to help select the proper connections.

Orientation does not matter.  A tank can set upright, upside-down, on it's side, whatever works best for the installation.  This is because the pressurized badder inside will push water out regardless of orientation.

When winterizing your RV, understand that when there is no pressure in the pipes, there is no water in the tank.  So don't worry about wasting lots of pink antifreeze like you would with your hot water tank.

At the time back in 2007, not knowing about the stainless steel tank with feet and pump mount, I installed this standard house grade 2 gallon tank which continues to work flawlessly.  I bought it at Home Depot for around $40.  The picture does not show it, but I used a flexible braided stainless steel hose between the pump and tank.  The connection from the tank to the house is solid brass connecting to the RV PEX plumbing.  Our pump cycles on and off at a logical and comfortable intervals, and runs so quietly that you have to "listen" for the subtle hum.  During the night when going to the bathroom, "If" the pump turns on, it does not wake us up, and we sleep right above it.

The internal rubber bladder's air valve is on top, seen with the blue screw-off cap installed.

In our rig, this is inside the heated storage compartment, accessed from the outside.  I was concerned of damage from rough handling of stored items so I made a protective shroud of wood.  If using the stainless steel tank, I would have mounted the pump on top with no need for a shroud.  I would have also had more storage.

« Last Edit: March 23, 2019, 08:57:08 am by Ron Dittmer »
Ron (& Irene) Dittmer