When operating from the water tank rather than a shore connection, water conservation and stretching the gray tank capacity are often goals. Adding a pressure accumulator tank to an RV’s water system creates power and water savings by reducing the run time of the pump and improves overall usage by smoothing out the water pressure when the pump cycles.
RV water pumps work best at full output and tend to stutter when a faucet is open at a trickle. Fixtures with flow rates that don’t match the pump’s nominal flow rate can also cause it. This stutter results in pulsating water pressure and often causes any DC lighting to flicker in sync with the pump’s cycling. The reason for the latter is the voltage fluctuation that happens when the pump cycles through high draw/low draw/high draw/low draw/etc — it effectively behaves as if there was a dimmer installed on the light circuit with someone constantly adjusting it.
The water pump (a Shurflo 4008-101-A65) can handle this behavior and is designed to tolerate quick cycling, but it’s better for longevity if it doesn’t have to. Adding an accumulator tank in line with the pump takes some of that burden and makes the system more pleasant to use, offering a few ounces of water before the lines even hit a pressure to kick the pump on.
For this installation I used the Shurflo Pressure Accumulator Tank and one hose out of the Shurflo Pump Silencing kit. Any hose of the same size and threading will work, but they’re pretty hard to find at that size and these are well made.
Installation is easy but benefits from a little planning. Beyond the obvious space needs for the tank itself, it’s helpful to position it in a way that allows use of the existing line off of the pump. The air valve should also be positioned accessibly to allow for easy setting of the tank pressure.
The tank is ideally placed as the first element after the pump, prior to the water splitting off to feed the hot and cold lines. The instructions included with the tank outline other possible configurations that may be easier in some systems, but I will not cover them here.
Step 1: Purge the Lines
To avoid having to clean up a bunch of water after disconnecting the pump, I started by purging enough water out of the lines so that the remainder could be absorbed easily by paper towels.
There are two ways I know of for doing this, the latter of which I used:
- Attach an air compressor at pump pressure (40-55 psi) to the shore water connection as if winterizing and blow out the lines.
- Open a faucet and run the pump until the line looks mostly empty. It should be visible through the translucent tubing.
Step 2: Mount the Tank
The mounting location will vary by model. In my case, on the Timber Ridge 25RDS, the best available spot was on the rear side of a set of drawers, just above the pump.
Because the width of the cabinet backing was wider than the attachment points of the tank, I first attached a leftover block of HDPE to mount to. The tank was then mounted to that.
Step 3: Connect the Plumbing
The tank is bidirectional — it doesn’t matter which hose is connected to which side. I unscrewed the existing flexible hose from the pump, connected it to the close side, and then used one of the hoses from the pump silencing kit to connect the other side back to the pump.
Step 4: Pressurize the Tank
The tank must be pressurized under static conditions (i.e., open a faucet first). Unscrew the valve stem cap and use a standard tire adapter to fill it up, either via a hand pump or an air compressor (it fills quick!). The pressure should be set equal to the turn on pressure of the pump, which is 40 psi in my case. Once set, put the valve stem cap back on to avoid pressure loss over time.
Step 5: Re-pressurize the System
Refill the system with water, running the pump if needed to bring it up to working pressure. It’s now ready to use and to check the changes for any sign of leaks.