Adding an accumulator tank

[RSD559]

I'm going to put in a 2 gallon residential accumulator tank. Went looking for the parts to hook it up. Couldn't find what I was looking for so I asked the Lowes guy. He told me that RVs usually have odd sized water lines and that I probably needed to get the T-fitting from an RV dealer. He said that the lines are most likely smaller than the residential stuff. Have any of you done this? Did you have problems with regular push-to-fit parts off the shelf?
The water heater is under the bottom full-sized bunk. 3/4 of the space under there is sealed off, and mostly empty. I plan on putting the tank under there and tie into the cold water line going to the water heater. Thanks.

[Bobbo]

drsteve wrote:
What he said. Plus, if you empty the accumulator before the pump starts, water delivery fluctuates.

No more than turning on a faucet in a rig with no accumulator tank. However, that said, the difference between 2 over and 2 under is small enough as to make very little difference.

[mbopp]

DrewE wrote:

Lynnmor wrote:

BFL13 wrote:
There ought to be a way to use the hot water tank as the accumulator, but it would need some creative arrangements.

But it already does if the air pocket is maintained at the top.

The air pocket (at least on my RV water heater) is pretty small, and doesn't provide for a whole lot of accumulation. If, however, you use the entire tank for an accumulator--which of course precludes having hot water--it can indeed be quite effective and of a sizable capacity. I found that out, and in the process made myself rather befuddled before I figured it out, by wrongly resetting my bypass valves a year or so ago.

After a week of dry camping the air pocket goes away & the TP valve starts to weep. The accumulator tank fixed that.

[drsteve]

2112 wrote:
More water will flow in/out of the accumulator at a lower bladder pressure. The idea is to compress the bladder air as the accumulator fills. Compressing the bladder air will increase its pressure. The higher the bladder pressure when empty the less effective the accumulator is. You essentially turn a 2gal accumulator into a 1gal accumulator with higher bladder pressure.

What he said. Plus, if you empty the accumulator before the pump starts, water delivery fluctuates.

[2112]

More water will flow in/out of the accumulator at a lower bladder pressure. The idea is to compress the bladder air as the accumulator fills. Compressing the bladder air will increase its pressure. The higher the bladder pressure when empty the less effective the accumulator is. You essentially turn a 2gal accumulator into a 1gal accumulator with higher bladder pressure.

[drsteve]

Check the installation instructions for any bladder type tank. They all specify 2 psi under the cut-in pressure.

[RSD559]

This is really good. I'd heard 2 psi under as well, but I think that was on the interweb. Who trusts that? I would really like to do it right, so let's figure it out. FYI, I'll also be putting on an air valve extension, so it will be easier to check and adjust the pressure. I think it is 18". So it will poke through into the storage bin. I need to figure out some way to anchor it, though.

[Bobbo]

drsteve wrote:

Bobbo wrote:

Dusty R wrote:

Bobbo wrote:
I want the accumulator tank set about 2 pounds above the cut-on pressure of the pump. That way, the accumulator tank will completely empty before the pump cuts on. Since the cut on pressure can be set on at least some of the pumps, it can vary. You may have to check the documentation for your pump to find that number. (If you don't have the tank completely empty before the pump cuts on, you are effectively reducing the volume of the tank.)

I think that you mean 2 lb below cut-on/turn on, pressure, set at 2 lb above the pump will never turn on.

Dusty

No, I meant what I said. For example, if the pump cuts on when the pressure is 18 psi and cuts off at 55 psi, I would set my tank at 20 psi. As soon as the tank empties itself, it no longer exerts any effect at all on the water lines and the pressure will continue to drop, all the way to zero if the pump is turned off. Note that these are example numbers and not to be used to set anyone's tank.

A bladder tank should be set 2 psi below the pump cut in pressure.

Rationale please. I disagree with you, but am willing to be convinced. I have already given my rationale.

[SoundGuy]

SoundGuy wrote:
Shurflo does offer a 2 gal version

Planning wrote:
Shurflo also offers a 6 gal. Accumulator Tank, including side bracket and feet. It is model 14-047-10

IMO way too big, it's the size of a water heater tank :E ... 2 gal would be more than sufficient for me and of a size much easier to install. :B

[DrewE]

Lynnmor wrote:

BFL13 wrote:
There ought to be a way to use the hot water tank as the accumulator, but it would need some creative arrangements.

But it already does if the air pocket is maintained at the top.

The air pocket (at least on my RV water heater) is pretty small, and doesn't provide for a whole lot of accumulation. If, however, you use the entire tank for an accumulator--which of course precludes having hot water--it can indeed be quite effective and of a sizable capacity. I found that out, and in the process made myself rather befuddled before I figured it out, by wrongly resetting my bypass valves a year or so ago.

[Planning]

SoundGuy wrote:
Shurflo does offer a 2 gal version

Shurflo also offers a 6 gal. Accumulator Tank, including side bracket and feet. It is model 14-047-10

Here is the 6 gallon:

[drsteve]

Bobbo wrote:

Dusty R wrote:

Bobbo wrote:
I want the accumulator tank set about 2 pounds above the cut-on pressure of the pump. That way, the accumulator tank will completely empty before the pump cuts on. Since the cut on pressure can be set on at least some of the pumps, it can vary. You may have to check the documentation for your pump to find that number. (If you don't have the tank completely empty before the pump cuts on, you are effectively reducing the volume of the tank.)

I think that you mean 2 lb below cut-on/turn on, pressure, set at 2 lb above the pump will never turn on.

Dusty

No, I meant what I said. For example, if the pump cuts on when the pressure is 18 psi and cuts off at 55 psi, I would set my tank at 20 psi. As soon as the tank empties itself, it no longer exerts any effect at all on the water lines and the pressure will continue to drop, all the way to zero if the pump is turned off. Note that these are example numbers and not to be used to set anyone's tank.

A bladder tank should be set 2 psi below the pump cut in pressure.

[Lynnmor]

BFL13 wrote:
There ought to be a way to use the hot water tank as the accumulator, but it would need some creative arrangements.

But it already does if the air pocket is maintained at the top.

[BFL13]

There ought to be a way to use the hot water tank as the accumulator, but it would need some creative arrangements.

Ours is only ever heated up (and then turned off) on shower days so that would still be ok without wasting hot water. (Small hot water jobs like shaving and dishwashing get done by heating a pot of water on the stove) So most of the time the tank just sits there full of cold water.

[mbopp]

pianotuna wrote:
What working pressure is best for the tank to give the greatest benefit?

25PSI seems to be the sweet spot for me. When camping on city hookups I run it at 40PSI.