Plumbing Math/GPH question:

[WhatCouldGoWrong71]

So, I’m almost done with the closed loop plumbing on my 48x48x20 look down soon to be Acro tank. BTW, doing a look down take creates so many darn challenges that you would never think of last the “many what a great idea it would be to have a nearly 180g look down tank. Man it was a cool idea, but the headaches… anyway. For the two closed loops, I went with Reeflo Hammerheads. Mostly because I got them Each for at or below $200 BNIB. These are 1.5” in/out. Rated around 6k gph. But, let’s just shave it down to 5k gph. I’m running all 1.5” plumbing, except I had to resell one of the feed bulkhead holes to 2”. So one hammerhead is 1.5” in/out. And the other is 2” in until about 2 inches before the pump then it is reduced down to match the pump. The out is 1.5”.

For whatever reason I was curious what the max flow through 1.5” is. I could only think to ask ChatGTP since it would do the same thing I would which is ask google to find me something I could read and test my head on. But, reading ChatGTP has me all concerned that using equal to or better than the feed diameter, in my exact application, will restrict the flow. This just doesn’t make sense to me. If a pump needed a specific sized opening, wouldn’t the pumps feed size be the correct size? Maybe it’s just the devil (ChatGTP).

Anyone? Below is what I read from CGTP


Me:
How many gallons per hour can a water pump rated for 6,000 gph pull through a 1.5” bulkhead

ChatGTP:
A water pump rated for 6,000 GPH will not be able to pull the full 6,000 GPH through a 1.5” bulkhead—because the bulkhead size becomes the bottleneck, especially if the flow is gravity-fed or under suction.














Practical Limit of a 1.5” Bulkhead (Under Suction or Gravity Feed)








A 1.5-inch bulkhead, depending on setup, can generally handle:

• Gravity-fed flow: ~750 to 1,200 GPH
• Under pressure (pushed): Up to ~2,000–2,500 GPH maximum
• Under suction (pulling water through): Flow is even more restricted due to vacuum limitations and pipe friction, likely 1,000–1,800 GPH, depending on the setup.

If the pump pulls water through the 1.5” bulkhead (i.e., the bulkhead is on the suction side), then:





You are likely limited to ~1,500–1,800 GPH, well below the 6,000 GPH pump rating.














What Happens If You Try to Exceed That?

• The pump will cavitate (draw air or vapor instead of water), reducing performance and possibly causing damage.
• The water line could starve, since the pump is demanding more water than the 1.5” bulkhead can supply.

Recommendation








To supply a 6,000 GPH pump, you’d need at least:

• Two 1.5” bulkheads (each safely feeding ~2,500–3,000 GPH under pressure)
• Or ideally, a single 2.5”+ bulkhead (less common)
• Or even better, a 3-inch bulkhead (rated safely for ~6,000–7,000 GPH)

Would you like help choosing the right bulkhead or plumbing size based on your system setup (gravity vs pump-fed, etc.)?

 

[UncommonSense]

Welcome to my department!

This is the most recent one I have saved; it isn’t the easiest to read, but it gets the point across!

 

[UncommonSense]

So, I’m almost done with the closed loop plumbing on my 48x48x20 look down soon to be Acro tank. BTW, doing a look down take creates so many darn challenges that you would never think of last the “many what a great idea it would be to have a nearly 180g look down tank. Man it was a cool idea, but the headaches… anyway. For the two closed loops, I went with Reeflo Hammerheads. Mostly because I got them Each for at or below $200 BNIB. These are 1.5” in/out. Rated around 6k gph. But, let’s just shave it down to 5k gph. I’m running all 1.5” plumbing, except I had to resell one of the feed bulkhead holes to 2”. So one hammerhead is 1.5” in/out. And the other is 2” in until about 2 inches before the pump then it is reduced down to match the pump. The out is 1.5”.

For whatever reason I was curious what the max flow through 1.5” is. I could only think to ask ChatGTP since it would do the same thing I would which is ask google to find me something I could read and test my head on. But, reading ChatGTP has me all concerned that using equal to or better than the feed diameter, in my exact application, will restrict the flow. This just doesn’t make sense to me. If a pump needed a specific sized opening, wouldn’t the pumps feed size be the correct size? Maybe it’s just the devil (ChatGTP).

Anyone? Below is what I read from CGTP


Me:
How many gallons per hour can a water pump rated for 6,000 gph pull through a 1.5” bulkhead

ChatGTP:
A water pump rated for 6,000 GPH will not be able to pull the full 6,000 GPH through a 1.5” bulkhead—because the bulkhead size becomes the bottleneck, especially if the flow is gravity-fed or under suction.














Practical Limit of a 1.5” Bulkhead (Under Suction or Gravity Feed)








A 1.5-inch bulkhead, depending on setup, can generally handle:

• Gravity-fed flow: ~750 to 1,200 GPH
• Under pressure (pushed): Up to ~2,000–2,500 GPH maximum
• Under suction (pulling water through): Flow is even more restricted due to vacuum limitations and pipe friction, likely 1,000–1,800 GPH, depending on the setup.

If the pump pulls water through the 1.5” bulkhead (i.e., the bulkhead is on the suction side), then:





You are likely limited to ~1,500–1,800 GPH, well below the 6,000 GPH pump rating.














What Happens If You Try to Exceed That?

• The pump will cavitate (draw air or vapor instead of water), reducing performance and possibly causing damage.
• The water line could starve, since the pump is demanding more water than the 1.5” bulkhead can supply.

Recommendation








To supply a 6,000 GPH pump, you’d need at least:

• Two 1.5” bulkheads (each safely feeding ~2,500–3,000 GPH under pressure)
• Or ideally, a single 2.5”+ bulkhead (less common)
• Or even better, a 3-inch bulkhead (rated safely for ~6,000–7,000 GPH)

Would you like help choosing the right bulkhead or plumbing size based on your system setup (gravity vs pump-fed, etc.)?

To answer your question in more detail:

Your hammerheads have a max well height of 22ft, and 1.5” NPT female threads…

22ft x .433PSI = 9.526psi max pump outlet pressure

1.5” male NPT nipple nominal ID = 1.5” (most restrictive part)

Nipple length <=6”

70.5gpm, let’s say… so, 4,230gph is a minimum flow estimate for the most restrictive point in the plumbing!

Edit: If you want to eek a bit more flow out of your plumbing, to the tune of 5-15%, you can consider beveling sharp/squared edges on the most restrictive plumbing parts (usually the MNPT nipples), this reduces turbulence at these points, promoting laminar flow!

See below for examples of how this 3D printed manifold is filleted in such a way that it looks more like the intake manifold of an engine; not easy to manufacture using any other method, but the limiting factor becomes the pipe itself at high water velocities!

 

[BeanAnimal]

In general, the pump is oversized for the plumbing. As long as the discharge is the same size or smaller than the suction side, cavitation is unlikely. The discharge restriction will create pressure head and reduce overall flow.

 

[WhatCouldGoWrong71]

Im going to shoot a couple videos when I get home. I’ll plus you both in. It will be easier for both you and I. I have a couple more questions with what you both stated. Plus a bonus question then on my main system. I often wonder if there was a better way to plumb something on my main closed loop. I think I am negatively impacting the benefit of having an Abyzz 400 under my tank. That and I hoped to only have to clean it every couple years.

 

[WhatCouldGoWrong71]

@BeanAnimal @UncommonSense here is my pathetic attempt at videos. Thank god I have a 9-5.

 

[UncommonSense]

@BeanAnimal @UncommonSense here is my pathetic attempt at videos. Thank god I have a 9-5.

You’ve been busy!!

From what I could tell, you have three questions?

— what’s up with the different sizing to the lower flow impellers? (old vs.new)

— should you stick to the 6,000gph impellers, or switch to 4,500gph impellers, given that you’re maxing 1.5” plumbing out?

— should you replumb the closed loop pump with a tee off the outlet to, well, not tee?



1. can you get a photo of the new ~4,500gph impeller next to the old one so I can compare their differences?

2. I would just use the 4,500gph impeller on them, especially as you’re feeding RFGs! — they are restrictive by nature, and I think it would be reasonable to assume that these pumps actually have a marginally higher maximum pressure with an impeller that isn’t working the motor so hard! (think of boat propeller sizing/pitches affecting launch and top speed)

3. The tee isn’t doing too much in the way of restriction here, purely because fluid velocity would be halved, even if it was only a 1.5” tee! Because it’s a 2” tee off 1.5” pipe (or at least appears to be), fluid velocity goes down well over 2x through that fitting!

— in other words, that tee is totally fine, and not creating a significant flow loss in this low pressure, low velocity application!

 

[WhatCouldGoWrong71]

You’ve been busy!!

From what I could tell, you have three questions?

— what’s up with the different sizing to the lower flow impellers? (old vs.new)

— should you stick to the 6,000gph impellers, or switch to 4,500gph impellers, given that you’re maxing 1.5” plumbing out?

— should you replumb the closed loop pump with a tee off the outlet to, well, not tee?



1. can you get a photo of the new ~4,500gph impeller next to the old one so I can compare their differences?

2. I would just use the 4,500gph impeller on them, especially as you’re feeding RFGs! — they are restrictive by nature, and I think it would be reasonable to assume that these pumps actually have a marginally higher maximum pressure with an impeller that isn’t working the motor so hard! (think of boat propeller sizing/pitches affecting launch and top speed)

3. The tee isn’t doing too much in the way of restriction here, purely because fluid velocity would be halved, even if it was only a 1.5” tee! Because it’s a 2” tee off 1.5” pipe (or at least appears to be), fluid velocity goes down well over 2x through that fitting!

— in other words, that tee is totally fine, and not creating a significant flow loss in this low pressure, low velocity application!

I appreciate you, thank you. On 1., I’ll do that but I’ll also provide measurements. I’m going to pipe the OEM off the new one. Part of me is wondering - Not sure if you know, but you have to call Reeflo with the serial number to your pump and then they send you the other impeller for free. I’m wondering if the guy I purchased it from just had this laying around from another pump. I wonder if the 6k impeller is similar to that one or dissimilar.

2. That makes a lot of sense. Takes 10 minutes to switch the impellers. Plus my dumb butt forgetting to compensate for the glass box compressing the foam, I have to pull that pump out anyway. Sigh…

3. I am super grateful for that. Super. I’m not a fan of coming within a foot of the plumbing down there. The things I will do differently when I replace my large display. I love love this display, but, lots I would do different. It’s my first custom non-redsea like “everything you need included with purchase”

 

[UncommonSense]

On 1., I’ll do that but I’ll also provide measurements.

Fantastic! I’m also curious about the actual fin profile within each impeller, these could be changed, in addition to other more noticeable dimensions!

Plus my dumb butt forgetting to compensate for the glass box compressing the foam,

Could you just do a U shape made from NPT elbows on the pump outlet, parallel to the ground? That would let you use your existing parts, and let the NPT fittings slightly twist to compensate for tank sag!

I am super grateful for that. Super. I’m not a fan of coming within a foot of the plumbing down there.

Haha past you did future you a favor by choosing oversized plumbing! I always try to oversized whatever I can… my 30g tank has two 1” drains… my 180g tank has three 1.5” drains!

I love love this display, but, lots I would do different. It’s my first custom non-redsea like “everything you need included with purchase”

I don’t blame you! It’s a seriously impressive tank!

Keep up the good work over there, you’re moving at an impressive pace! — I look forward to seeing the build updates, and the finished products!

 

[UncommonSense]

@BeanAnimal @UncommonSense here is my pathetic attempt at videos. Thank god I have a 9-5.

I thought about that issue you had with fish spitting sand into the closed loop intake, subsequently burning up a pump..

You probably don’t have space for it, but an in-line strainer would definitely make that an issue of the past!

AquaSieve2 Pre-filter

AquaSieve2 is a Solid Separation Pre-Filter. With this high impact, implosion resistant jewel you can quit being a slave to that strainer basket on the front of your pump. No more will you have to do daily bows before that tiny strainer basket on your pump as if it were your master. Most people...

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[WhatCouldGoWrong71]

I thought about that issue you had with fish spitting sand into the closed loop intake, subsequently burning up a pump..

You probably don’t have space for it, but an in-line strainer would definitely make that an issue of the past!

AquaSieve2 Pre-filter

AquaSieve2 is a Solid Separation Pre-Filter. With this high impact, implosion resistant jewel you can quit being a slave to that strainer basket on the front of your pump. No more will you have to do daily bows before that tiny strainer basket on your pump as if it were your master. Most people...

playitkoi.com

That’s interesting. I can’t fit it on my 2 upper closed loops, by my lower with the Abyzz 400 could easily make that work. The placement of the inlet and outlet is actually perfect and it’s 2”. I once heard sand in my Abyzz and hit the emergency shut down and prayed.

On a side note: so far zero compression, lol. I’m only 2 inches from water height. I have 2.5 inches of white styrofoam and 1 layer of the same material that is under my tank. I left 1 layer out to watch over the next week to see if it compresses at all. I over did one of the joints with pipe dope and had to drain it and wipe it down with alcohol. Sigh… when I googled “how to clean glass with pipe dope on it” I now know how to clean resin off a glass pipe, lol.

 

[WhatCouldGoWrong71]

That’s interesting. I can’t fit it on my 2 upper closed loops, by my lower with the Abyzz 400 could easily make that work. The placement of the inlet and outlet is actually perfect and it’s 2”. I once heard sand in my Abyzz and hit the emergency shut down and prayed.

On a side note: so far zero compression, lol. I’m only 2 inches from water height. I have 2.5 inches of white styrofoam and 1 layer of the same material that is under my tank. I left 1 layer out to watch over the next week to see if it compresses at all. I over did one of the joints with pipe dope and had to drain it and wipe it down with alcohol. Sigh… when I googled “how to clean glass with pipe dope on it” I now know how to clean resin off a glass pipe, lol.

 

[UncommonSense]

That’s interesting. I can’t fit it on my 2 upper closed loops, by my lower with the Abyzz 400 could easily make that work. The placement of the inlet and outlet is actually perfect and it’s 2”. I once heard sand in my Abyzz and hit the emergency shut down and prayed.

On a side note: so far zero compression, lol. I’m only 2 inches from water height. I have 2.5 inches of white styrofoam and 1 layer of the same material that is under my tank. I left 1 layer out to watch over the next week to see if it compresses at all. I over did one of the joints with pipe dope and had to drain it and wipe it down with alcohol. Sigh… when I googled “how to clean glass with pipe dope on it” I now know how to clean resin off a glass pipe, lol.

There seem to be a wide variety of pond pump prefilters! The things to note would be that you need a pressure sealed one, and you’d need to be able to valve off the prefilter to clean it, or it would empty the whole tank!

Hmm… foam-wise, you could add a 1/2”-3/4” thick layer of foam flooring to take that gap up, and still support the bottom of the pump/allow for compression?

Haha I see how Google could be misled there…You don’t want to know what popped up when I searched for barrel “bung plugs” recently!