Tuning a Herbie Overflow

[AT_Hiker]

I'm trying to finish off the plumbing to my sump, and have been trying to get my herbie tuned properly so the water is running maybe about an inch or less over the top of the main standpipe. I have a ball valve installed in the drain line and have discovered that it's just way to difficult to get the flow right. I ordered a gate valve from BRS yesterday, and I'm going to add it after the ball valve. I'm going to leave the ball valve in place so I don't have to mess up the gate valve whenever I want to stop water flow to the sump.

Anyway, my real question is about the size of the standpipe. I have a 75gal corner flow tank, with two 1 inch bulk heads. I'm using one as the main, and the other as the emergency standpipe. I have a Ehiem Compact 2000 return pump running wide open, so it's pumping around 528 GPH. All of my plumbing is 1" PVC under the tank. I tried using a 1" standpipe, but it can barely keep up with the pump when the ball value is wide open. I switched and used a 1 1/2" standpipe reduced to 1" to connect to the bulkhead, and it keeps up with no problem with the valve half shut. The plumbing under the tank is still 1"

So what gives? It still has to go through the 1" bulkhead. Wouldn't that literally be the bottleneck? I'm just curious as to what principle causes the 1 1/2" standpipe to work better.

Thanks,
Steve

[Gregs138]

Not sure on the exact equation, but volume of water through a pipe is something like

Volume = Pi * radius of PipeSquared * length of Pipe.

The volume that can flow through a pipe is determined by the length as well as the radius.

Your first scenario:
Volume = Pi * .5in Squared * 24 inches

Your second scenario:

Volume = (Pi * .5in squared * 6inches) + (Pi * .75 Inches squared * 18 Inches).


It gets a little wordy, but the flow rate of the water/sec in the first scenario was > than the maximum flow rate the pipe could allow-based on its volume. Gravity and acceleration also come into play but I'm not that good, lol.

[MrClam]

I use an Eheim 1262 that runs a little over 700gph after head loss. I use two 1'' PVC drain pipes for a herbie return. The 1'' adjusted with a ball valve is easily able to take all the flow from the pump if wide open. My ball valve only open about 3/4 of full flow and I have a stronger pump than yours.

So something must be wrong in your setup. How long are the drain pipes and how many elbows do you have in the plumbing?

Remember that to establish a full syphon water must be about 1-2'' over the top of the standpipe so no air can get into the pipe. Otherwise the herbie will not work. I would guess that you are not establishing a full syphon, which will greatly reduce the flow that a 1'' pipe can take.

[mginani]

that is very suprising to me. I would think that a 1" standpipe opened wide would drain much faster than 528 gph when a full siphon is created. I have 1" standpipe on my 90 gallon with a herbie and it drains much faster than that.

[sleepydoc]

Total resistance is additive so the resistance for your bulkhead pipe would be Top + bulkhead + bottom. Also, resistance is proportional to r^4, so a small increase in diameter means a relatively large drop in resistance. The 1" bulkhead may be the bottleneck, but is is not the only source of resistance. Increasing the pipe to 1.25" will increase the flow somewhat. Depending, the ball valve may be limiting flow a bit as well, even if it's wide open. You should be getting more than 550 gph, though.

The flow from your return pump will depend on the head pressure (see the calculator on the Reef Central home page) which is dependent on vertical rise, total length of pipe, turns/elbows, and diameter. If your return flow is that close to the maximum standpipe flow, you may want to put in a valve to throttle back your return pump.

Also, it will be a lot easier to make fine adjustments if you use a gate valve rather than a ball valve on your overflow pipe.

[AT_Hiker]

I use an Eheim 1262 that runs a little over 700gph after head loss. I use two 1'' PVC drain pipes for a herbie return. The 1'' adjusted with a ball valve is easily able to take all the flow from the pump if wide open. My ball valve only open about 3/4 of full flow and I have a stronger pump than yours.

So something must be wrong in your setup. How long are the drain pipes and how many elbows do you have in the plumbing?

Remember that to establish a full syphon water must be about 1-2'' over the top of the standpipe so no air can get into the pipe. Otherwise the herbie will not work. I would guess that you are not establishing a full syphon, which will greatly reduce the flow that a 1'' pipe can take.

At one time I was trying to run an Eheim 1262, but it was just too much volume for my overflow, plus the 1262 was a little noisy. I don't have the exact measurements at the moment, but my standpipe is ~ 18". It then goes thru a 1" bulkhead straight into a 1" PVC ball valve, and and coupling. It immediately takes a 90 degree turn for about 8" then another 90 down into the water for maybe another 8". The exit of the pipe is ~ 3" under water. I've considered using a Tee that's opened on the top instead of a 90 for the last turn. But to be honest, even though I've seen it done I don't know exactly why people do that. I am a noobie after all.

I've spent more time standing in Lowe's Hardware looking a PVC parts than I care to think about. :)

Maybe I've been trying to keep the water too low over my standpipe. I didn't realize you needed 1-2"

[MrClam]

Yes that sounds similar to the setup for my drain piping. Yes you need the drain completely submerged to establish a full siphon.

I drilled five 1/2'' holes in my drain standpipe about 1.5'' lower than the top. Helps to lower the amount of water you need over the top and prevent blockages.

I was just playing with my overflow and found that apprx 1.25'' of water was needed over mine to prevent air from entering. HTH

[sleepydoc]

You don't need to have the outlet under water to establish a siphon, but it reduces splashing, salt spray and bubbles

[MrClam]

No, but the standpipe must be completely submerged. I think thats where he was having a problem.

[AT_Hiker]

My standpipe is completely submerged, but I've been trying to keep the water level about 1/2" - 1" over the top of the pipe. I was trying to limit the amount of water going into the sump during a power outage. It sounds like I need to increase it to at least 2". I saw some website that recommended 6". That seem excessive to me.

[mginani]

Mine works well with a little over an inch over the standpipe. You should know when it is working well because it will be silent. You will not hear any crashing water thru the pipe.

[MrClam]

Like I said try drilling some holes in the pipe to allow flow in at a lower level. That should help you reduce the amount of height necessary to create a siphon.

6'' is way more than is necessary on my system. Mayb it depends on your setup but I cant imagine that much water would be required for a 1'' pipe.

[sleepydoc]

The amount of water going into the sump during a power outage will be determined by two things:

the height/depth of your overflow weir
your return nozzle configuration. If you have a functioning check valve and /or siphon break hole in the return, then #1 will be be the deciding factor. Because of reliability issues with check valves and anti-siphon holes, I simply designed my sump to have enough excess capacity to hold the water that siphons down until the return nozzles themselves break the siphon.


The height/depth of the standpipe in your overflow has very little to do with how much water will drain down - as water drains it simply gets replaced by water coming over the overflow until the tank level drops below it.

MrClam has a good suggestion; either way, you need to have enough water above the standpipe so it doesn't entrain air. 1-2" should be sufficient, but it really doesn't matter a whole lot. If you're doing a true Herbie (i.e. the backup standpipe is completely dry), having a larger difference between your siphon and your backup/emergency standpipe will make it easier to tune.

[AT_Hiker]

The issue is fixed.
I switched back to 1" PVC, lowered the main standpipe so that it's 2" lower than the emergency standpipe. The emergency standpipe is 1/4" lower than the teeth from the overflow. I adjusted the ball valve on the main pipe so the water is just barely level with the emergency pipe, and it now works great.

Thanks everyone for the great advice!

Steve