The requirement for this mod became apparent during a time when we were doing some serious dry camping, and wanted to try to conserve our batteries and freshwater to the greatest extent possible. Initially, while we were attempting to use as little water as possible to wash up, we found the water pump would be forced to operate frequently as it witnessed a small drop in cold water line pressure. The result was the pump would cycle almost continuously - giving short bursts of pressure increase to try to accommodate the small flow that was requested from the faucets. I tried to adjust the pressure switch to allow more of a pressure drop before the pump kicked in, but was not successful. And, I dared not mess with the adjustment on the pump bypass flow valve, as I was well aware that that I could quickly get into trouble from which there would be no safe return. I came away thinking that adjusting an RV water pump properly requires an education in the Dark Arts segment of RV plumbing.

My next thought was a vision I had of Grandpa Ron installing an accumulator in-line to his cold water plumbing. The first 1:20 of this video shows his install:

Grandpa Ron’s Freshwater Basics

What does an accumulator do? Well, the way I think of it – the accumulator “assists” the pump in keeping the water line pressurized. The RV water pump will turn on when the pressure drops, and turn off when the pressure gets high again. But, if you have an accumulator installed, when you first open a faucet, the accumulator will provide its own source of pressure to keep the pump from seeing a pressure drop and turning itself back on. Because of the accumulator, when you open that faucet and water flows out, the pressure in the line will not drop immediately. Eventually the accumulator runs out of “muscle” and the pressure drops to the point where the pump cycles back on. However, it’s this pressurized water flow before the pump cycles back on that you are paying for – the water flow out of the faucet without the aid of the pump is what saves electricity and wear and tear on the pump.

How does it work? There is a diaphragm in one half of the accumulator that you pressurize with an air compressor or tire pump. The inflation pressure should be a little bit less than the pressure output of the pump, so the pump can force water into one half of the accumulator and compress the diaphragm. When you open a faucet, the first thing that happens is the diaphragm in the accumulator pushes back against the water in the other half, and results in water flowing without the pump doing the work. When the diaphragm has fully expanded into the water portion of the accumulator, it has run out of “muscle” and pressure in the line will drop to the point where the pump is forced to cycle back on.

Initially when we were dry camping, and trying to conserve water by washing up with only a small flow of water, the pump would see a pressure drop and “blip” the pump to maintain delivery pressure. We’d get these continuous high frequency spurts of pump operation, and when compounded by a water heater “hammer” problem we had at the time, would result in a big racket under the bed. (Installing an accumulator solved the problem of the pump continuously cycling, but I had to get more creative to solve the unrelated water heater “hammer” issue.) So, now when we open a faucet to get a small water flow, the output from the faucet is strong for about six seconds before the water pump cycles on to pressurize the line. (How much water is that? Depends - we get enough flow to wash our hands, rinse dishes, or brush our teeth. If you immediately demand a large flow of water, such as a toilet flush, the advantages of an installed accumulator are not really noticed.) We don’t have an accumulator as large as the one Grandpa Ron installed, so we don’t get as much “free” water out of the faucet as he does, but the Shurflow accumulator we purchased from Amazon suits us just fine.

Shurflow 182-200 Accumulator Tank

I had read that the output of our water pump was about 45 psi, so I pre-charged the accumulator with about 40 psi of air to begin with. You can play with the accumulator pre-charge to try to optimize the amount of “free” water you get before the pump cycles on – just remember to always do the inflation with an unpressurized water line – pump off and a faucet open.

Where to put the accumulator? You will see from the instructions that you can install it anywhere on the pressurized cold water line, as long as you have a direct flow from the pump to the accumulator and not interrupted by a check valve, shutoff valve, or something similar. I had initially thought of installing it right beside the water pump to make 100% sure that the delivery pressure to anything downstream would be affected by the accumulator. But, it is such a pain to work in the area of the pump that I elected to install it where Grandpa Ron did – under the bathroom vanity sink. I knew the cold water line from the pump goes to the wet bay and then came back to the coach for delivery, so couldn’t imagine that the flow would be modified before it got to the vanity sink. And, if it worked well enough for Grandpa Ron, why not for us?

The in-the-box PEX in-line female dual coupler came to us without any gaskets, so was useless for this install. I had to rig up a length of flexible braided nylon tubing (1/2” inside diameter) and a couple of female PEX couplings, but the install was simple. The cold water input to the sink is connected to one side of the accumulator, and essentially the input to the cold water side of the faucet is attached to the other side of the accumulator. In essence, the accumulator was installed so it fits in-between the cold water line and the hookup to the cold faucet.

Here is what our installation looks like – you can see the length of flexible braided nylon tubing I rigged up to allow the accumulator output to hook up to the cold water input to the faucet. By the way, these PEX couplings just need to be hand tight – I wouldn’t recommend using too much torque, and you can damage the rubber gasket in the coupling.

The end result looks Ok – I tucked the accumulator in the wasted space of the vanity cupboard, up high. You could install a curtain to cover it up if you didn’t want to look at it when you opened the door, but then nobody would know what a great job you did of installing an in-line water accumulator…

I used a tie wrap to secure the tank to the coach plumbing, so it wouldn’t wobble around when on the road:

All in all – working as advertised and we’re very happy with its performance.


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