Chizer & Bunoi 67 gallon

[sphelps]

Originally Posted by midgetwaiter

Actually lowering or removing the primary drain standpipe will make life a lot easier in this configuration and it has everything to do with "head". Everybody remembers their first go at trying to adjust a herbie style overflow, even if you did shell out the bucks for a gate valve it can be a complete PITA to try and maintain with the primary standpipe that high.

However if you were to remove the primary drain standpipe and close the valve controlling that drain until the water level in the overflow stays within and inch or so of the top it so it's quiet as well it becomes much easier to do minute adjustments. The reason for this is the pressure built up in the box remains constant when it is at at given level, with a high drain pipe you get much less drain pressure and it fluctuates somewhat making it difficult to adjust. The force of the water is "static head", not to be confused the the "head pressure" we try and work out when sizing a return pump.

Some things to consider in this configuration; When the pump shuts down you will drain the entire overflow box, make sure you have room to catch the water. Also you are at a slightly increased risk of clogging the drain, make sure you open it up once in a while to flush built up gunk. You should be doing that in either configuration though.

Completely false in regards to how pressure works, basic fluid mechanics here guys it's very simple.

Look at these two cases, the static head pressure at the valve (X) is identical for both cases. It's science don't argue with it cause you'll loose

Shortening the pipe will do nothing for pressure and unless you're getting a vertex it will make no difference for adjustment and only result in issues relating to the entire overflow box draining during shut down.

[sphelps]

Originally Posted by ChizerBunoi

Steve - Your method worked very well. It sure is time consuming and cutting a 1/4" of PVC off on the mitre off is scarry. The rebound and kick back sure is dangerous.

Ha, I know all about that. Keep the saw down until the blade stops moving. You usually get a kick back by lifting it back up with the blade still going full tilt.

Glad you got everything working.

[kien]

Originally Posted by sphelps

Completely false in regards to how pressure works

so what you're trying to say is that size doesn't matter??

[midgetwaiter]

Originally Posted by sphelps

Completely false in regards to how pressure works, basic fluid mechanics here guys it's very simple.

Look at these two cases, the static head pressure at the valve (X) is identical for both cases. It's science don't argue with it cause you'll loose

You assume that the volume of water coming over the weir is constant but it's not. Having a larger volume of water over the drain makes adjustment easier because it evens it out.

[sphelps]

Originally Posted by midgetwaiter

You assume that the volume of water coming over the weir is constant but it's not. Having a larger volume of water over the drain makes adjustment easier because it evens it out.

First it is constant unless your pump is fluctuating which it shouldn't be and second volume has nothing to do with static head pressure.

[midgetwaiter]

Originally Posted by sphelps

First it is constant unless your pump is fluctuating which it shouldn't be and second volume has nothing to do with static head pressure.

Possibly I am using the term "Static Head " incorrectly, I'm more a wrench bender than an engineer. However I can show that the height of the water above the drain determines the velocity of the water draining by applying Bernoulli's Principle. There's all sorts of handy calculators on the web that help figure this out, like this:

http://www.efunda.com/formulae/fluids/draining_tank.cfm

It has been my experience that this increase in velocity makes adjusting a gate or ball valve on the drain MUCH easier. Determining the reason for this goes well beyond my math skills but it's very easy to demonstrate. I think it's because you end up with a full pipe before the drain valve which ends up giving you a more even flow rate. Regardless it translates into easy, repeatable and reliable adjustments.

[sphelps]

Originally Posted by midgetwaiter

Possibly I am using the term "Static Head " incorrectly, I'm more a wrench bender than an engineer. However I can show that the height of the water above the drain determines the velocity of the water draining by applying Bernoulli's Principle. There's all sorts of handy calculators on the web that help figure this out, like this:

http://www.efunda.com/formulae/fluids/draining_tank.cfm

It has been my experience that this increase in velocity makes adjusting a gate or ball valve on the drain MUCH easier. Determining the reason for this goes well beyond my math skills but it's very easy to demonstrate. I think it's because you end up with a full pipe before the drain valve which ends up giving you a more even flow rate. Regardless it translates into easy, repeatable and reliable adjustments.

You're still way off, the velocity at the valve and in the pipe will be the same regardless (delta z is equal for both cases), the formula you linked doesn't take an internal pipe into account, reason being is that it doesn't matter. Yes with the pipe extended the input velocity is shifted from the bulkhead to the top of the extended pipe but this won't effect flow and the velocity will be constant throughout the pipe until after the valve. Even if you want to break out Bernoulli's equation all you'll end up proving is the pipe friction from the extra 6" of straight pipe makes no difference, and even if it did it would still give constant flow and not result in anything constantly changing.

The issues you've experience are likely from the pipe being too close to the surface creating a partial or occasional vortex like I've mentioned a few times now. You need enough space from top of the pipe to the water surface to eliminate any vortex effects but you certainly don't need to remove it all together.

I assure you the typical Herbie has an extended pipe to prevent the overflow from draining and it doesn't cause issues. This you should have noticed with the problem already being corrected with an extended pipe.

If you wish to continue learning about fluid mechanics PM me, I'll happily discuss it with you but don't post incorrect information in this guys build thread.

[Skimmin]

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[gregzz4]

Originally Posted by sphelps

but don't post incorrect information in this guys build thread.

I'll take some of the blame for this as I'm the one who first posted increased head on his main drain

When I lowered my main from 10" to 4" I thought I saw improved drainage, even though I had no vortex issues, hence my assumption

Thanks for the great info Steve

[kien]

Originally Posted by Skimmin

.........

In other words, nevermind?