logic behind larger drains, and smaller returns?

[shamrock]

hey

just came across this video on youtube by tidal gardens. i understand what's being said, but is there a need? the reason i'm asking is that i was considering a 1" pvc for all my drains/returns. having seen this, would it be more logical to have a slightly larger drainage diameter and still keep the return at 1"

reference:
thanks for your knowledge as always

sk

 

[Jaebster]

The amount of forced water that the return pushes in a piece of tubing/piping can much more than the passive flow (drain) in the same piece of tubing/plumbing. Of course if you have you pump on a low flow, the drain will probably handle it. Look at all of the pre-manufactured tanks with sumps. Return pipe is ALWAYS narrower than drain pipe.

 

[shamrock]

awesome. thanks for the response. i might change my setup a bit accordingly. ;Pompus

 

[rushbattle]

I have a small tank with a Varios-8 pump. With a 1” return at full power on the pump, I can’t overwhelm a 1” siphon drain.

 

[Twitchy]

There is nothing wrong with it, as long as you size your drain(s) for the intended flow rate, and you have your return pump dialed in properly. You can actually get slightly more flow out of a smaller pump this way due to the small decrease in head pressure. The reason it is typically done is it is much harder to overwhelm the drain when the return is sized smaller, which is extra useful if you are a manufacturer, and don't know what kind of setup a customer is going to install. It is also cheaper when it comes to buying fittings, checkvalves, drilling holes, etc.

 

[Thub]

Flow through a tube is a function of head(among other things). The head pressure for the drain is just the vertical distance from the DT's surface to the sump level ~4 feet first example. If your return pump has more head pressure than double that number, you'll overflow the DT with equally sized plumbing.

 

[thediscobandit]

The way i always thought of it was the smaller the diameter return gets, the less pressure the pump needs to make to push the water up, making it easier on your pump. Of course you don't want the return too small for your pump either though.

 

[RocketEngineer]

The way i always thought of it was the smaller the diameter return gets, the less pressure the pump needs to make to push the water up, making it easier on your pump. Of course you don't want the return too small for your pump either though.

Not quite. The column of water at a given height has pretty much the same static pressure no matter the pipe diameter. Fittings and pipe all add friction that resists water movement. To simplify things, some smart folks a long time ago worked out the pressure drop from fitting XYZ and related that to vertical “head”. Same for a given length of pipe of diameter abc. If you add up actual vertical distance you need to move the water, plus the head contributions from the fittings and pipe length, you end up with the “head” that pump would be subjected to in that situation. You can then compare that to a pump chart showing flow rate vs head which should tell you about how much water that pump can move in that setup.

A little technical but hopefully informative.

 

[ca1ore]

Larger return pipe presents less friction pressure than does smaller pipe. Depends a bit on your applications, but when dealing with higher head pressure applications a larger diameter return can be significant. For example, on my system moving from a 1" return to 1 1/2" gave me an additional 200 gph with the same pump.

Whether you need ti upsize the drain also depends a lot on the application. A siphon drain will move more water than will an open channel. A drain with a lot of drop (think head pressure in reverse) will move more water than one with less drop.

 

[shamrock]

great input. thank you