elan,
Expecting the single 1" drainline to handle 1800 gallons of water per hour ( 30 gallons per minute ) ( 1/2 gallon per second ) .. I don't believe there is a practical way to reduce that noise.
That's a lot of water - and the drainline must vent.
Is there possible way to increase the pipe size from the drain bulkhead to the sump ?
That may help somewhat ... maybe.
RANE,
I'm not sure I follow you question exactly. Sounds like you have two independent external overflows .. right ?
Each with a 1" drain ?
A very general rule of thumb is that a 1" drain can safely handle around 700 gph. A single 1-1/4" U tube is pretty standard for these type of oveflows too.
The rate at which water will drain out of the outer box into the drainline is not always dependant on the rate at which the water flows "into" the external box.
In other words - the design of the overflow itself, and the difference in water level between the display tank and the level in the outer box dictates the flowrate up and over the U tube.
Adding two U tubes may not do squat .. but it all depends.
In my thinking .. the safe thing to try would be to keep the single U tube in each overflow .... base each on 700 gph ..... and then size either one single larger return pump, or two smaller return pumps to deliver the total 1400 gph for the entire system.
Having two smaller pumps allow for some "high" flow "lower" flow possibilities .. which can be nice at feeding time, or set on pump on a timer to make for some varying circulation/turnover.
I like having two return pumps for this reason ..... in addition to knowing that if one pump craps out .. I can still run the other one until a replacement is purchased, or the old one is repaired, etc.
I run a dual 1400 gallon overflow on my 75.
I run a Mag7 and a Mag9.5
The 9.5 runs 24/7
The 7 is set up on a timer
Works pretty well for me. Others may think differently.
Can you describe your set up in greater detail ?
Maybe start a new thread for you conditions ?
Just a thought