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Mod #83: DIY Water Accumulator

Posted By ModMyRV On June 10, 2009 @ 8:19 am In plumbing | 27 Comments

This mod comes to us courtesy of RV.net senior member professor95, otherwise known as Randy Agee, and is copyright with all rights reserved.

It is 3:00 o’clock in the morning. You and your significant other are out camping in your RV when you have the need to get out of bed and shed some water from your bladder. You manage to make it to the potty room with out awakening anyone and in a few moments you feel tremendous relief as the pressure on your bladder subsides. Just like your Mother taught you, flushing the potty is a desired practice after usage. You press your foot on the flush pedal and watch as the valve in the bottom of the bowl opens and a swirl of clean water comes in. Then, it happens!

The water pump on the RV turns on. It just so happens that the pump is under the bed where your significant other is sound asleep. There is a loud banging from the pump as it builds pressure. The plastic water lines vibrate against each other and the flimsy inside walls of the RV. Your significant other is no longer peacefully sleeping. In fact, she (or he) is wide awake and extremely unhappy. If any of this sounds familiar, you most likely do not have an accumulator as part of your RV’s self contained water system.

Mod Difficulty:

When hooked to city water there is little need for an accumulator. But, when you are drawing water from your RV’s storage tank and using the onboard 12 volt pump an accumulator can make camping a lot more pleasurable – perhaps even save a relationship.

Accumulators connect to the water line after the pump. They act as a water storage unit that can significantly reduce the frequency of pump cycling and smooth out water flow. Accumulators accomplish this by having a sealed cylinder that fills with water until the air pressure above the water level is equal to the maximum water pressure from the pump. When you do something, like flush the potty in the middle of the night, there is usually more than enough water and pressure stored in the accumulator so that the flush can be accomplished without the pump cutting on.

After market accumulators made specifically for RV’s are readily available. Their cost ranges from around $40 to well over a $100 depending on the size and construction features selected. The best accumulators have a rubber bladder inside that expands against an air charge. A simpler accumulator that does not have a rubber bladder but simply compresses air with water is almost as effective and can cost a lot less. In fact, you can easily make this type of accumulator yourself from easily found materials.

You may be wondering why anyone would want to make an accumulator when they can be purchased ready made so cheaply. The answer is each RV is different and finding the space for an accumulator can be a challenge. By making your own, you can custom select the size that fits your available space.

Photo #1 shows all of the needed parts to build your own accumulator. This particular accumulator is made from 3” schedule 40 PVC pipe that is 12” long. I could have just as easily selected a piece of 2” pipe or even 4”. The length is determined by available space to mount the accumulator vertically. Typically, large accumulators work better, but even small accumulators can make a big difference in water flow.

“A” is a 3” PVC pipe cap.
“B” a 12” long section of 3” schedule 40 PVC pipe.
“C” is a slip reducer that changes 2” to 1”.
“D” is a 1” slip reducer that has a ½” pipe thread in the center.
“E” is the cleaner and cement to join PVC pipe.
“F” is a brass ½” threaded pipe to ½” PEX adapter.
“G” is a ½” brass PEX Tee connector.
“H” is a short piece of ½” PEX pipe
“I” shows several ½” PEX compression ferrules
“J” is a tool for compressing the PEX ferrules
and “K” is a tubeless tire metal valve that has a threaded shaft, nut and seal.

All of these parts were purchased at Lowe’s, with the exception of the tire valve which came from a local Advance Auto supply store.

Photos #2 and #3 are close ups of a few pieces showing part numbers and sizes in detail.

In photos #4 and #5 you can see how a hole the same size as the tubeless tire valve shaft was drilled into the center of “A” for attachment of the valve “K”.

Photos #6 and #7 are of a dry fit for all the parts. Note than in photo #7 a section of ½” PEX has been attached between the adapter and the T.

Most all modern RVs are plumbed with a plastic pipe called PEX. It is extremely strong, easy to install and durable. The only “problem” with PEX is that you cannot make up connections with just a gear type hose clamp. Special tools and ferrules are needed to properly make a leak proof connection if not opting for the more expensive and cumbersome push-in connectors.

The small tool with the yellow handles (“J”) shown in photo #8 and #8a is one of the less expensive crimping tools available. A closer view giving more detail is shown in photo #8b. It works well with all squeeze PEX ferrules ranging in size from ¼” to 1”. The ferrules are a little more expensive, but the ranges of sizes that can be connected with this simple tool make it worthwhile to own. The red handled tool at the bottom is for the solid copper ferrules and is considerably more expensive. It also only compresses one size of ferrule necessitating owning several sizes if pipe diameters are mixed.

Photo #9 shows the difference in the squeeze ferrule and the solid copper ferrule. You must have the right tool for each type. If you do not want to invest in these tools, you can rent them (Home Depot) or perhaps even borrow them from a friend.

You may also find that none of these tools will be needed. Some RV water pumps are attached with conventional ½” white water hose that can be tapped with barbed fittings and gear clamps.

The accumulator must be mounted vertical so the air valve is at the highest point. You do NOT have to mount the accumulator next to the pump. It will work quite well even when mounted some distance away, perhaps in a kitchen cabinet where you have more room for a larger accumulator.

Draining all of the water from the system naturally rests the pressure inside the accumulator.

The accumulator shown in the last photo is in my 5th wheel’s basement area close to the water pump. Despite what advertising literature may tell you, all pumps – even the variable speed models – perform much better with an accumulator.

ModMyRV recommends these parts for this mod:
All-Purpose Pipe Cleaner
PVC Glue - 12 pt.
PEX Pocket Crimper - Combination 3/4, 1/2, 3/8
Milton 470 Metal Valve


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