Undercurrent pipe size question

[Critrgitr]

I am thinking about building an undercurrent system but I have a coupIe of questions that I need answered before I get stared.

I have noticed that most of the undercurrent systems that I see online use 3-4" drain pipe connecting all of the containers yet the return pumps are usually only 1/2" or so. Would someone please explain to me why these systems are designed with such large connecting pipe if they are only drawing small amounts of water back to the control reservoir? Why 3” over 1 1/2” (or smaller)?

Next, the systems that I have seen have a storage container that flows into the control reservoir through a float valve. I like this idea because I could keep the nutrient storage container in a different room. My question is, how do these systems chill the water in the storage container and the control res at the same time with one chiller? The only good solution that I can think of is to forget the storage res and find (or just build) a large flat control res (which could hold large volumes of chilled, nute water) and keep that unit in the other room. Am I missing something obvious?

 

[Victor6634]

They use 2 inch and 3 inch pipe and return line I believe is 3/4 inch better circulation and won’t clog as easy due to roots. I just built one a couple of weeks ago with 2 inch pipe and 3/4 inch return pipe it’s working pretty good so far if I like results I will build bigger system hope this helps a little

 

[Victor6634]

Here is my setup

 

[Sureshot2]

I initially started out using 1" connecting lines and a 1/2" feed using a reverse style system that feeds the last bucket and flows through back to the res. While I didn't experience any clogging, I had many problems with water level variation between buckets, and turning down the pump low enough to prevent somewhat defeated the purpose of RDWC. I later re-built the system using 2" PVC drains and a 3/4" feed, and have had no problems whatsoever. I am using a 400gph pump and my water levels are equal in all buckets and no clogging. I'm sure with larger runs 3" pipe would be better, but in my case of running through four buckets, 2" has suited me well.

One thing to note, if using uniseals for the PVC pipe, make sure you chamfer and debur the pipe edge well, and lube the ever loving shit out of it. Despite this you will still hate your life for trying to install pipes through uniseals in a confined tent (my pipes run through the tent walls of several tents, so I couldn't do it outside of the tent...). A rubber mallet will come in handy for tapping the pipe during installation.

For chilling multiple separate reservoirs I use coils. My chiller connects to it's own dedicated 5 gallon reservoir, which pumps water from the res to the chiller, and through various sets of stainless steel coils. Each coil is 25" of stainless 3/8" tubing wrapped roughly 8-9" in diameter and connected to each other by flexible tubing. I have coils in two main reservoirs and my cloner working flawlessly. With this system you have a lot more flexibility on controlling what you want to cool a well using bypass valves etc, and the res water never contacts the inside of the chiller.

 

[firsttimeARE]

This is my setup using 1" barbed bulkhead fittings. 3 outlets on each site that all connect together and run back to the control bucket.

Control bucket has a pump that sucks water up into the chiller which sends chilled water to the top of the sites and cascades down in a waterfall which is my source of DO.

Due to a heating element in the way I had,no choice but to have res in my room. Due to the amount of heat put off from the chiller im going to move it into the laundry room next door so its not battling against the heat it creates.

 

[thenasty1]

reducing the pipe size helps regulate water levels and flow rate.
water from your top off res will enter your system in small increments, the chiller on your control bucket can handle it.

 

[Frostythesnowman88]

I run 1/2" waterfall lines in and 1.5" pvc pipe back to res... No clogging issues yet

 

[Lordhooha]

I am thinking about building an undercurrent system but I have a coupIe of questions that I need answered before I get stared.

I have noticed that most of the undercurrent systems that I see online use 3-4" drain pipe connecting all of the containers yet the return pumps are usually only 1/2" or so. Would someone please explain to me why these systems are designed with such large connecting pipe if they are only drawing small amounts of water back to the control reservoir? Why 3” over 1 1/2” (or smaller)?

Next, the systems that I have seen have a storage container that flows into the control reservoir through a float valve. I like this idea because I could keep the nutrient storage container in a different room. My question is, how do these systems chill the water in the storage container and the control res at the same time with one chiller? The only good solution that I can think of is to forget the storage res and find (or just build) a large flat control res (which could hold large volumes of chilled, nute water) and keep that unit in the other room. Am I missing something obvious?

I have 4" returns on my under current system I went with them to avoid clogging my system and from the Rez to my plants is 1/2 on a 900gph pump. My Rez is 55 gallons with 13 gallon buckets.

 

[JSB99]

I'm using 2" sends to 3/4" returns, with my UC, and everything's working great. I use 2 hdx totes for 4 plants, and another for a controller reservoir with a waterfall.

I made my own bulkhead fittings to save some money. After doing a wet test, I noticed that it was finicky with how the totes were lined up, and would dribble a little if nudged. I ended up using aquarium-safe silicone, and it worked perfectly!

I don't know if actual bulkheads, or Uniseals, would hold better. But, I do know they're a lot more expensive.

Check out my "2017 Grow" link below for pics of my rdwc uc

 

[JSB99]

I have 4" returns on my under current system I went with them to avoid clogging my system and from the Rez to my plants is 1/2 on a 900gph pump. My Rez is 55 gallons with 13 gallon buckets.

This page shows my setup, in the early part of putting my grow room together. Hope that helps.

 

[firsttimeARE]

I feel like bigger returns just slow the flow of water down which would minimize the suction effect that pulls roots in. My issue is that I didnt wanna use uniseals and not even sure they make 4" bulkheads and if they do they prob are like $50 per

 

[Sureshot2]

I feel like bigger returns just slow the flow of water down which would minimize the suction effect that pulls roots in. My issue is that I didnt wanna use uniseals and not even sure they make 4" bulkheads and if they do they prob are like $50 per

Bigger returns speed up the water flow, you perceive it as being slower due to the decrease in pressure. Bigger returns can also handle a higher inflow, which again mixes the water better.

If you are trying to prevent the roots being sucked in you could use a large return with a slower pump. That said, I've had no issues with roots being pulled in (at least not enough to slow anything down) and i'm running 600gph on ~20 gallons.

 

[firsttimeARE]

Bigger returns speed up the water flow, you perceive it as being slower due to the decrease in pressure. Bigger returns can also handle a higher inflow, which again mixes the water better.

The rate of return is entirely dependent on the rate of removal. The pressure and FPS of the smaller pipe is greater so it flows faster.

 

[firsttimeARE]

In the HVAC world 1000CFM going thru a 4" round is going to have a greater pressure and velocity than the same airflow through a 10" round. But at the end of the day its close to the same 1000CFM exhausted provided the motor can handle the greater static pressure and doesnt bog down.

Same in the hydronic world.

Think of it this way water wants to be level and the faster you remove from the control bucket the water level drops faster and that determines how much water comes back. Theres greater restriction with smaller pipe so it flows faster. Larger pipe water passes more easier so it can flow slower.

 

[firsttimeARE]

Bigger returns speed up the water flow, you perceive it as being slower due to the decrease in pressure. Bigger returns can also handle a higher inflow, which again mixes the water better.

If you are trying to prevent the roots being sucked in you could use a large return with a slower pump. That said, I've had no issues with roots being pulled in (at least not enough to slow anything down) and i'm running 600gph on ~20 gallons.

Im using 1" returns in a 75gal system with a 1000gph pump. I can feel the water rushing in. If i used a smaller pump it would slow it down, but I already bought the pump and its not clogging yet. If it clogs ill think about a smaller pump

 

[Victor6634]

I'm using 2" sends to 3/4" returns, with my UC, and everything's working great. I use 2 hdx totes for 4 plants, and another for a controller reservoir with a waterfall.

I made my own bulkhead fittings to save some money. After doing a wet test, I noticed that it was finicky with how the totes were lined up, and would dribble a little if nudged. I ended up using aquarium-safe silicone, and it worked perfectly!

I don't know if actual bulkheads, or Uniseals, would hold better. But, I do know they're a lot more expensive.

Check out my "2017 Grow" link below for pics of my rdwc uc

I use 2 inch bulkheads I get them from marinedepot.com you will get a much better hold with bulkheads

 

[Sureshot2]

The rate of return is entirely dependent on the rate of removal. The pressure and FPS of the smaller pipe is greater so it flows faster.

In the HVAC world 1000CFM going thru a 4" round is going to have a greater pressure and velocity than the same airflow through a 10" round.

Same in the hydronic world.

First off, rate of removal isn't a thing, I believe you are referring to inflow? Second your understanding of fluid dynamics is very flawed, and comparing and HVAC system is nothing like a UC system.

What you are not accounting for is hydrostatic pressure in a UC system. The pressure behind the pipe will always be limited by the vessel, being that this is an open loop system and not a pressurized system. The exit velocity from a 1" pipe, 2" or 4" pipe will all be the same if the volume of water is the same, but mass flow will be greater in the larger pipe. The limiting factor in this case is the inflow from your pump.

If your 1" pipe can only handle 200gph for example, of course the flow will be no different on a 2" or 4" pipe. However, if you used a larger pump and ran the larger pipe at its maximum capacity the pressure would be the same as the small pipe, but the mass flow would be greatly increased.

 

[Sureshot2]

In the HVAC world 1000CFM going thru a 4" round is going to have a greater pressure and velocity than the same airflow through a 10" round. But at the end of the day its close to the same 1000CFM exhausted provided the motor can handle the greater static pressure and doesnt bog down.

Same in the hydronic world.

Think of it this way water wants to be level and the faster you remove from the control bucket the water level drops faster and that determines how much water comes back. Theres greater restriction with smaller pipe so it flows faster. Larger pipe water passes more easier so it can flow slower.

Yes, but the overall flow of the system is identical. Assuming the water remains at the same level in all buckets, the flow is the same, the 1" pipe is just more restrictive and more likely to clog and fail. The 1" pipe does not mix the water any better than a 2", 3" or 4" return assuming all variables remain the same. There is simply no reason to use 1" over a larger pipe except for cost difference which is marginal given the cost of UC anyways.

This is also from experience, having started with a UC I built using 1" pipe, and rebuilding it after a year using 2" PVC.

 

[firsttimeARE]

Yes, but the overall flow of the system is identical. Assuming the water remains at the same level in all buckets, the flow is the same, the 1" pipe is just more restrictive and more likely to clog and fail. The 1" pipe does not mix the water any better than a 2", 3" or 4" return assuming all variables remain the same. There is simply no reason to use 1" over a larger pipe except for cost difference which is marginal given the cost of UC anyways.

Right I agree the flow is the same. I never said the flow was greater. I said the speed was.

My mentor used 1" for many years without issue. I have 3 bulkheads per bucket so even if one line did get clogged it has 3 points of return to the control.

So my system uses 15 bulkheads. At $2 per for 1" vs $15 for 2". Thats $225 vs $30. I agree cost is negligible. But the way I saw it was why? A person I trust told me they use 1 inch for years.

 

[Sureshot2]

Right I agree the flow is the same. I never said the flow was greater. I said the speed was.

My mentor used 1" for many years without issue. I have 3 bulkheads per bucket so even if one line did get clogged it has 3 points of return to the control.

So my system uses 15 bulkheads. At $2 per for 1" vs $15 for 2". Thats $225 vs $30. I agree cost is negligible. But the way I saw it was why? A person I trust told me they use 1 inch for years.

I don't use bulkheads, I use uniseals, which are cheaper than even the 1" bulkheads here, so the only difference in cost is between 1" and 2" pipe which is $5 at most. I'm running close 600gph through a ~20gal system which results in fast flow through the pipe.

I built a 1" system originally based on what I read on forums and from other people, and I wished I would've started with the 2" system. I am able to pump much more water now, and recycle my entire loop roughly once every 2 minutes. If it works for you, nothing wrong with that. But I can't personally recommend it to others based on my experiences.