Maximum backwash hose length at 1/2"

[Brain2000]

Greetings all. I have a question about the maximum length of the drain hose used for backwashing. I've read that if you go over 20' that you should use a 3/4" inch hose instead of 1/2". If I needed, say, a 30 foot hose, would increasing the size of the DLFC to add a little extra pressure in a 1/2" hose be equivalent to changing out to a 3/4" hose?

I need to drill a hole in the outside wall to run the drain hose down from the second floor and would like to keep the hose as small as possible.

 

[Reach4]

If you wanted to reduce pressure drop while keeping the hole through the wall down, you could use 3/4 tubing and convert to 1/2 inch copper pipe for the penetration. 1/2 inch copper pipe is 5/8 OD. The cheapest, type M, has an ID of 0.569 and type L has an ID of 0.545 inches.

However you probably wouldn't have a problem with 1/2 inch all of the way, even if it violates the printed word:

The pipe size for residential drain line
should be a minimum of 1/2 inch (13 mm). Backwash
flow rates in excess of 7 gpm (26.5 Lpm) or length in
excess of 20 feet (6 m) require 3/4 inch (19 mm) drain line.​

I am not a pro, but I think that is a simplification. If your incoming water pressure stays higher, say 40 PSI or above, and if your backwash flow rate is is 2.4 GPM, I would expect your flow would be quite fine for your 30 ft. If you played with a pipe calculator and compared the pressure drop for different diameters and different flow rates, you will find the pressure drop is lower for lower flow rates for a given diameter.

 

[Sponsor]

 

[Brain2000]

If you wanted to reduce pressure drop while keeping the hole through the wall down, you could use 3/4 tubing and convert to 1/2 inch copper pipe for the penetration. 1/2 inch copper pipe is 5/8 OD. The cheapest, type M, has an ID of 0.569 and type L has an ID of 0.545 inches.

However you probably wouldn't have a problem with 1/2 inch all of the way, even if it violates the printed word:

The pipe size for residential drain line
should be a minimum of 1/2 inch (13 mm). Backwash
flow rates in excess of 7 gpm (26.5 Lpm) or length in
excess of 20 feet (6 m) require 3/4 inch (19 mm) drain line.​

I am not a pro, but I think that is a simplification. If your incoming water pressure stays higher, say 40 PSI or above, and if your backwash flow rate is is 2.4 GPM, I would expect your flow would be quite fine for your 30 ft. If you played with a pipe calculator and compared the pressure drop for different diameters and different flow rates, you will find the pressure drop is lower for lower flow rates for a given diameter.

I did look at the PSI at the tank and it was hanging at a little over 45 psi during the backwash stage. The rate is 4 gpm. Thanks, that all makes sense!

 

[Reach4]

I did look at the PSI at the tank and it was hanging at a little over 45 psi during the backwash stage. The rate is 4 gpm. Thanks, that all makes sense!

4 GPM would be for a really big softener (12 inches?) or a really small backwashing filter. Which is it?

 

[Bannerman]

As you are planning a substantial amount of vertical drain drop, you might want to consider installing a vacuum breaker on the drain line directly after the KL filter, regardless of the drain diameter. The v breaker will permit the entry of air into the drain line to allow the line to freely drain without placing negative pressure on the filter tank, particularly if the pump should ever quit during backwash.

Filter tanks are built to withstand positive pressure but can be easily crushed if exposed to even slight negative pressure.

The recommended increase in drain diameter is to ensure the appropriate backwash rate without frictional line restriction impairing that flow rate. Always recommended to follow the manufacturer's direction.

 

[ditttohead]

Velocity is key. How fast water flows through pipe usually calculated in feet per second. Excessive flow rates (typically anything above 8 FPS) will can cause noise, vibration etc. Higher velocities can be done with PEX and specially engineered systems, but it simpler to just run the drain in a larger pipe size. It is not like it costs any more. 3/4" PVC over a 30' run might add $5 in material cost.

 

[Reach4]

As you are planning a substantial amount of vertical drain drop, you might want to consider installing a vacuum breaker on the drain line directly after the KL filter, regardless of the drain diameter. The v breaker will permit the entry of air into the drain line to allow the line to freely drain without placing negative pressure on the filter tank, particularly if the pump should ever quit during backwash.

Emptying that pipe after a backwash will be nice to help prevent freezing of the discharge pipe outside into an Ohio January.

 

[Brain2000]

As you are planning a substantial amount of vertical drain drop, you might want to consider installing a vacuum breaker on the drain line directly after the KL filter, regardless of the drain diameter. The v breaker will permit the entry of air into the drain line to allow the line to freely drain without placing negative pressure on the filter tank, particularly if the pump should ever quit during backwash.

Filter tanks are built to withstand positive pressure but can be easily crushed if exposed to even slight negative pressure.

The recommended increase in drain diameter is to ensure the appropriate backwash rate without frictional line restriction impairing that flow rate. Always recommended to follow the manufacturer's direction.

I didn't know that about Filter tanks! Very useful information that might save me someday. I had no idea they didn't like negative pressure. And the vacuum breaker, I didn't even know those existed, but that makes sense. Thank you for the info.

The vertical drop is about 17 feet. The manufacturer recommends to use 3/4" if going over 7 gpm or 20 feet. That makes me believe there is an equation to back that up which figures the back pressure based on flow rate, distance, elbows, pipe type, etc... So if I can go can 7 gpm at 20 feet, I was wondering how one would go about finding how far a particular drain could go at 4 gpm. I would imagine, find the backpressure and then make sure it is at least n psi higher than the sustained well pressure during the backwash period?

 

[Brain2000]

Emptying that pipe after a backwash will be nice to help prevent freezing of the discharge pipe outside into an Ohio January.

No doubt, I'm installing a vacuum breaker for sure!

 

[Bannerman]

Why not simply drain to the regular septic/sewer system? A local drain would no doubt be reasonably close by, no unsightly exterior pipe run would be needed and, would less prone to freezing.

 

[Reach4]

Here are some pipe calculators. There is probably a rule of thumb about how much to add to the measured length to compensate for fittings.

http://www.pipeflowcalculations.net/pipediameter.xhtml
http://www.engineeringtoolbox.com/hazen-williams-water-d_797.html
http://www.pressure-drop.com/Online-Calculator/

 

[Brain2000]

Why not simply drain to the regular septic/sewer system? A local drain would no doubt be reasonably close by, no unsightly exterior pipe run would be needed and, would less prone to freezing.

Wait, can you do that? There is a drain behind the wall (I'm not afraid to rip the wall out to get to it). I didn't think it was good to pipe down all the iron and manganese backwash to a septic, because that would contribute to solids that need to be pumped out. No?

 

[Brain2000]

Here are some pipe calculators. There is probably a rule of thumb about how much to add to the measured length to compensate for fittings.

http://www.pipeflowcalculations.net/pipediameter.xhtml
http://www.engineeringtoolbox.com/hazen-williams-water-d_797.html
http://www.pressure-drop.com/Online-Calculator/

The engineeringtoolbox.com seemed to work without crashing. The other ones want other settings (like viscosity) that I'm not sure what to put in. Plus the Javascript crashes.

I ran through numbers :
I'm currently at -> 4gpm @ 20 feet = 3.7 psi loss.

The manufacturer recommends -> 7gpm @ 20 feet = 10.4 psi loss. The equivalent psi loss at 4gpm = 56.5 feet.

If that equation is correct and that's all I need to take into account, 4gpm @ 30 feet = 5.5 psi loss, which is well under 10.4 psi.

Since my pressure meter shows over 40 psi constantly during the backwash, this might work. Regardless I may get something to measure flow so I can be sure that I'm still pushing 4gpm through the hose. I will also visually inspect the amount of lift on the media during backwash with a strong backlight on the tank to make sure it achieves the same height with either hose length.

 

[Bannerman]

because that would contribute to solids that need to be pumped out. No?

The same iron and manganese removed by the filter, would otherwise be within virtually all of the the water entering the septic tank if no filter was utilized.
Solids sent to a septic tank are broken down and digested by bacteria within the tank otherwise, you would likely need to pump-out the tank every few months.

 

[Brain2000]

..

The same iron and manganese removed by the filter, would otherwise be within virtually all of the the water entering the septic tank if no filter was utilized.
Solids sent to a septic tank are broken down and digested by bacteria within the tank otherwise, you would likely need to pump-out the tank every few months.

In some states I was reading that they prohibit backwash with iron and manganese from going to the septic due to occasional failures*. I figured I was doing my septic a favor by installing the filtration system. I imagine there also lies the possibility that iron and manganese could actually improve a septic system, due to some reason that I am unaware. I'll do more research.

What's the saying? You don't know what you don't know. At the same time, I don't always trust government to make competent decisions.

* http://www.ct.gov/deep/lib/deep/pub...9lowflowwatertreatmentwastewaterfactsheet.pdf

 

[Brain2000]

4 GPM would be for a really big softener (12 inches?) or a really small backwashing filter. Which is it?

It's a 9" backwash filter. I was told it was 4gpm, but I wanted to be sure so I pulled the drain valve to visually inspect the flow restrictor. It's actually a 5 gpm button.

That combined with the effective distance of the drain being closer to 40 feet, I clearly had to use 3/4" for the drain.
I also picked up a vacuum protection valve for the drain line.

Thanks everyone for the input! I learned a lot about the available options and pros/cons while installing the backwash drain.