Maximizing Full Siphon - Herbie

FlyPenFly · 01/05/2014, 08:05 PM

I have a 20 inch high drilled at the bottom tank, overflow box goes from bottom to top. Would it be better in terms of flow rates for the main siphon to start closer to the bottom or closer to the top?

If I put in a standpipe+strainer for the main siphon, I can see how head height of where the water starts be a positive. However now you have additional friction and more distance traveled.

If I put no standpipe and just a strainer at the bottom bulkhead, there's going to be much less distance the water has to travel, less friction, and more force from the weight of the water above it.

Addon question: If the bulkhead size is 1" is there any advantage is making the standpipe and strainer 1.5 or 2 inches then reducing at the end to the native bulkhead size?

thegrun · 01/05/2014, 08:34 PM

One of the main reasons to elevate the standpipe is to keep from draining your entire overflow box when the pump is off. You get nearly the identical flow in full siphon with a raised standpipe because the weight of the extra water running down the standpipe/drain pulls water along with it nearly as well as the weight of the water above pushes.

fpv930 · 01/05/2014, 08:45 PM

Definatley have the standpipe at the top of the overflow. You will not want to drain all that water into the sump when the pump stops.
IMO there is no advantage making the standpipe strainer bigger in size. I used a durso standpipe http://www.dursostandpipes.com/in my setup. It worked much the same as you are describing. I installed a "gate valve" between the DT and the sump. That was how I created a "full' siphon.

FlyPenFly · 01/05/2014, 08:47 PM

Hmmm gated durso without an emergency drain sounds dangerous?

Good points on the box, any thoughts on larger standpipes + strainers over a matched size one?

fpv930 · 01/05/2014, 09:16 PM

I didn't say it was the smartest move I have ever made. Lol. Just that it worked for the time it was in use.

jimmyj7090 · 01/06/2014, 12:09 PM

The difference in flow from changing the height of the standpipe isn't going to matter much. If it's too close to the surface it will suck in air/bubbles.

SGT_York · 01/06/2014, 12:22 PM

There is significant advantage in terms of flow by reducing the standpipe height. The additional headloss will push far more water then lower headheight. I'll see if I can find the equation... However this is actually a downside to your backups that will cause overflows.

Downsides are drainage of the overflow during power loss, increased difficulty with adjusting the gate valve, and noise caused by water going too low in the overflow during routine variations, all cause more difficulty then benefits of removing the standpipe. 6" under the water level is perfect.

The other major downside is that if you require this much head pressure to satisfy your return pump, your open channel and/or emergency cannot handle the volume as neither of them have the required headspace, and you will have an overflow, without increasing the diameter of the open channel in which case adjusting the siphon bulkhead is an easy solution. A 1" durso cannot handle the flow required by a 3/4" pipe at full siphon with 20" of head.

If you stay with normal pumps this should never be a factor, so If you are concerned that you need more flow capacity increase the diameter of the bulkheads.

jimmyj7090 · 01/06/2014, 12:26 PM

How much friction loss would you expect from 20" of 1" pipe operating at a full siphon?

" The additional headloss will push far more water then lower headheight. I'll see if I can find the equation... "

I don't follow, how would headloss increase flow?

01/05/2014, 08:05 PM	#1
FlyPenFly SPS Killer Join Date: Dec 2012 Location: San Diego, CA Posts: 1,490	Maximizing Full Siphon - Herbie I have a 20 inch high drilled at the bottom tank, overflow box goes from bottom to top. Would it be better in terms of flow rates for the main siphon to start closer to the bottom or closer to the top? If I put in a standpipe+strainer for the main siphon, I can see how head height of where the water starts be a positive. However now you have additional friction and more distance traveled. If I put no standpipe and just a strainer at the bottom bulkhead, there's going to be much less distance the water has to travel, less friction, and more force from the weight of the water above it. Addon question: If the bulkhead size is 1" is there any advantage is making the standpipe and strainer 1.5 or 2 inches then reducing at the end to the native bulkhead size? Last edited by FlyPenFly; 01/05/2014 at 08:15 PM.

01/05/2014, 08:45 PM	#3
fpv930 Reef Addict Join Date: Jan 2011 Location: Syracuse New York Posts: 292	Definatley have the standpipe at the top of the overflow. You will not want to drain all that water into the sump when the pump stops. IMO there is no advantage making the standpipe strainer bigger in size. I used a durso standpipe http://www.dursostandpipes.com/in my setup. It worked much the same as you are describing. I installed a "gate valve" between the DT and the sump. That was how I created a "full' siphon. __________________ 36 Bow front, 10g nano and building a 90g in my basement Always dreaming of a bigger tank!!

01/05/2014, 09:16 PM	#5
fpv930 Reef Addict Join Date: Jan 2011 Location: Syracuse New York Posts: 292	I didn't say it was the smartest move I have ever made. Lol. Just that it worked for the time it was in use. __________________ 36 Bow front, 10g nano and building a 90g in my basement Always dreaming of a bigger tank!!

01/06/2014, 12:09 PM	#6
jimmyj7090 aka John K Join Date: Mar 2002 Location: Sudbury Posts: 2,367	The difference in flow from changing the height of the standpipe isn't going to matter much. If it's too close to the surface it will suck in air/bubbles. __________________ my reef ate my wallet Current Tank Info: 57G, RBTA's Zoa's and softies

01/06/2014, 12:26 PM	#8
jimmyj7090 aka John K Join Date: Mar 2002 Location: Sudbury Posts: 2,367	How much friction loss would you expect from 20" of 1" pipe operating at a full siphon? " The additional headloss will push far more water then lower headheight. I'll see if I can find the equation... " I don't follow, how would headloss increase flow? __________________ my reef ate my wallet Current Tank Info: 57G, RBTA's Zoa's and softies

01/05/2014, 08:34 PM	#2
thegrun Registered Member Join Date: Dec 2008 Location: Garden Grove, Ca Posts: 17,023	One of the main reasons to elevate the standpipe is to keep from draining your entire overflow box when the pump is off. You get nearly the identical flow in full siphon with a raised standpipe because the weight of the extra water running down the standpipe/drain pulls water along with it nearly as well as the weight of the water above pushes.

01/05/2014, 08:47 PM	#4
FlyPenFly SPS Killer Join Date: Dec 2012 Location: San Diego, CA Posts: 1,490	Hmmm gated durso without an emergency drain sounds dangerous? Good points on the box, any thoughts on larger standpipes + strainers over a matched size one?

01/06/2014, 12:22 PM	#7
SGT_York Registered Member Join Date: Sep 2012 Location: Washington State Posts: 1,746	There is significant advantage in terms of flow by reducing the standpipe height. The additional headloss will push far more water then lower headheight. I'll see if I can find the equation... However this is actually a downside to your backups that will cause overflows. Downsides are drainage of the overflow during power loss, increased difficulty with adjusting the gate valve, and noise caused by water going too low in the overflow during routine variations, all cause more difficulty then benefits of removing the standpipe. 6" under the water level is perfect. The other major downside is that if you require this much head pressure to satisfy your return pump, your open channel and/or emergency cannot handle the volume as neither of them have the required headspace, and you will have an overflow, without increasing the diameter of the open channel in which case adjusting the siphon bulkhead is an easy solution. A 1" durso cannot handle the flow required by a 3/4" pipe at full siphon with 20" of head. If you stay with normal pumps this should never be a factor, so If you are concerned that you need more flow capacity increase the diameter of the bulkheads.