Reverse Head Pressure

ca1ore · 10/20/2017, 02:37 PM

RC head pressure calculator has been quite useful to me (though more directional than absolute), but I'm trying to work out how to estimate flow for a drain. For example, if a 1 1/2" straight pipe with a 10' drop will flow 3,000 gph (a guess) how much is lost with the addition of a few elbows? Probably the answer is - still way more than needed. Still curious though.

billdogg · 10/20/2017, 02:57 PM

I've got a chart at home that lists maximum flow rates with gravity drains. I'll post it this evening for you. It has everything from 1/2" up to 2 or 3" I think

hth

hkgar · 10/20/2017, 03:02 PM

Durso or Herbie? Here is some info on Durso
https://www.dursostandpipes.com/freq...urso-standpipe

ca1ore · 10/20/2017, 03:12 PM

Thanks chaps. It's the 1 1/2" open channel on my pending tank build. I'm trying to work out what the max flow would be when operating as a siphon. I'm using ultra flex as the drain pipe but may still have to add a couple of elbows. Drop is significant at 10 feet so my guess is that even a couple of elbows won't make much difference. The perils of assumptions though .....

mcgyvr · 10/20/2017, 03:19 PM

everything you need should be here..
https://flexpvc.com/Reference/WaterF...PipeSize.shtml

hkgar · 10/20/2017, 03:25 PM

Quote:

Originally Posted by mcgyvr

everything you need should be here..
https://flexpvc.com/Reference/WaterF...PipeSize.shtml

Interesting that when using flex the flow rate is reduced.

mcgyvr · 10/20/2017, 03:33 PM

Quote:

Originally Posted by hkgar

Interesting that when using flex the flow rate is reduced.

Just a bit as the interior is not as smooth as rigid..

hkgar · 10/20/2017, 04:21 PM

Quote:

Originally Posted by mcgyvr

Just a bit as the interior is not as smooth as rigid..

So does the lack of elbows make up for the difference?

Imagine what we could do if friction was eliminated!

ca1ore · 10/20/2017, 05:58 PM

Quote:

Originally Posted by hkgar

Interesting that when using flex the flow rate is reduced.

There are actually two types, regular and EZ flow. Latter used to be called ultra flex, which was apparently misleading because it would kink if you tried to bend it too much. I don't know which kind is referenced in the flow charts, but the EZ flow has thinner walls and a larger ID.

ca1ore · 10/20/2017, 06:00 PM

Quote:

Originally Posted by mcgyvr

everything you need should be here..
https://flexpvc.com/Reference/WaterF...PipeSize.shtml

I'm familiar with that chart - having bought all my flex PVC from them. Not clear to me that it really answers my question, but perhaps it's the best I'll get. Thanks for 'reminding' me.

jewlz · 10/20/2017, 10:41 PM

you can do it, but it's not a closed form single analytical equation that you need to solve. You need to solve a system of equations iteratively and converge on a flow rate.

http://www.engineeringtoolbox.com/da...ion-d_646.html

The problem is that you need to know what the roughness of the inside of your pipe is, and what the "minor loss coefficient" K-value of the elbows is.

Bottom line, it's a pain in the butt, and there are numerical tools that engineers use when it's a critical application. When it's not, just make sure that your pipe is 2X as big as it needs to be

ca1ore · 10/20/2017, 10:44 PM

probably the best answer ......

jewlz · 10/20/2017, 10:44 PM

I should say too, that it gets more complicated with drains, because they typically have air entrained in the flow, which tends to slow it down.

10/20/2017, 02:37 PM	#1
ca1ore Grizzled & Cynical Join Date: Apr 2006 Location: Stamford, CT Posts: 17,319	Reverse Head Pressure RC head pressure calculator has been quite useful to me (though more directional than absolute), but I'm trying to work out how to estimate flow for a drain. For example, if a 1 1/2" straight pipe with a 10' drop will flow 3,000 gph (a guess) how much is lost with the addition of a few elbows? Probably the answer is - still way more than needed. Still curious though. __________________ Simon Got back into the hobby ..... planned to keep it simple ..... yeah, right ..... clearly I need a new plan! Pet peeve: anemones host clowns; clowns do not host anemones! Current Tank Info: 450 Reef; 120 refugium; 60 Frag Tank, 30 Introduction tank; multiple QTs

10/20/2017, 02:57 PM	#2
billdogg Registered Member Join Date: Apr 2008 Location: Grove City, Ohio Posts: 10,806	I've got a chart at home that lists maximum flow rates with gravity drains. I'll post it this evening for you. It has everything from 1/2" up to 2 or 3" I think hth __________________ I'll try to be nice if you try to be smarter! I can't help that I grow older, but you can't make me grow up! Current Tank Info: 120 mixed reef with 40b sump, RO 150 skimmer, AI Sol Blue x 2, and a 60g Frag Tank with 100g rubbermaid sump. 2 x Kessil A360w lights, BM curve 5 skimmer

10/20/2017, 03:02 PM	#3
hkgar Registered Member Join Date: Oct 2002 Location: Dewitt MI Posts: 5,051	Durso or Herbie? Here is some info on Durso https://www.dursostandpipes.com/freq...urso-standpipe __________________ Gary 180 gallon, 40 gallon sump, 3 250 W MH + 4 80W ATI T5's, MTC MVX 36 Skimmer, Apex controller Aquamaxx T-3 CaRx Current Tank Info: A 2 Barred Rabbitfish, Red Head Salon, Yellow/Purple, McMaster Fairy, Possum, 2 Leopard Wrasses, Kole, & Atlantic Blue Tangs, 2 Percula Clown, 3 PJ and 1 Banggai Cardinalfish , Swallowtail, Bellus and Coral Beauty Angels

10/20/2017, 03:12 PM	#4
ca1ore Grizzled & Cynical Join Date: Apr 2006 Location: Stamford, CT Posts: 17,319	Thanks chaps. It's the 1 1/2" open channel on my pending tank build. I'm trying to work out what the max flow would be when operating as a siphon. I'm using ultra flex as the drain pipe but may still have to add a couple of elbows. Drop is significant at 10 feet so my guess is that even a couple of elbows won't make much difference. The perils of assumptions though ..... __________________ Simon Got back into the hobby ..... planned to keep it simple ..... yeah, right ..... clearly I need a new plan! Pet peeve: anemones host clowns; clowns do not host anemones! Current Tank Info: 450 Reef; 120 refugium; 60 Frag Tank, 30 Introduction tank; multiple QTs

10/20/2017, 03:19 PM	#5
mcgyvr Registered Member Join Date: Sep 2003 Location: North Carolina Posts: 20,050	everything you need should be here.. https://flexpvc.com/Reference/WaterF...PipeSize.shtml __________________ Who me?

10/20/2017, 10:41 PM	#11
jewlz Registered Member Join Date: Apr 2011 Location: North America Posts: 116	you can do it, but it's not a closed form single analytical equation that you need to solve. You need to solve a system of equations iteratively and converge on a flow rate. http://www.engineeringtoolbox.com/da...ion-d_646.html The problem is that you need to know what the roughness of the inside of your pipe is, and what the "minor loss coefficient" K-value of the elbows is. Bottom line, it's a pain in the butt, and there are numerical tools that engineers use when it's a critical application. When it's not, just make sure that your pipe is 2X as big as it needs to be

10/20/2017, 10:44 PM	#12
ca1ore Grizzled & Cynical Join Date: Apr 2006 Location: Stamford, CT Posts: 17,319	probably the best answer ...... __________________ Simon Got back into the hobby ..... planned to keep it simple ..... yeah, right ..... clearly I need a new plan! Pet peeve: anemones host clowns; clowns do not host anemones! Current Tank Info: 450 Reef; 120 refugium; 60 Frag Tank, 30 Introduction tank; multiple QTs