drain sump sizing

[sbradt]

We are planning to drain all of the floor/trench drains in the brewery into a central sump pit, then pump out of the pit into a treatment tank to adjust pH and make some other minor adjustments prior to sending our effluent out to the municipal sewer. The treatment tanks have a capacity of about 700 gallons total. My mechanical engineer has it stuck in his head that we need a 4' dia sump pit that's 12' deep (1,200 gallons), combined with a 1 HP pump! I'm more inclined towards something in the range of 50-75 gallon capacity and a .5 HP pump. Anybody care to comment from their experience?

[bunnyfeet]

It depends mainly on the pattern of flow into the sump rather than the capacity of any downstream processes. 1,200 gallons may seem high at first blush for a system that only has a capacity of 700 gallons, and it may be. On the other hand, it may not be. Depends on a lot of things.

Your engineer should be able to look at flow patterns into the sump and the capacity of the downstream processes and arrive at a compromise between sump size and pump size. If your flow rates have lots of intermittent peaks, you need enough buffer capacity to allow the pump to keep up. He should be able to show you how he arrived at his sump and pump sizing, so definitely ask for that. You don't want to have to put in a 12' deep sump if you don't have to, and depending on the size of your operations, that does sound as if it may be a bit oversized.

I'd be happy to give a 2nd opinion if you have any info you can give on flows - total daily flow, avg gpm, peak flows and durations.

Brandon
Alaskan Brewing

[Moonlight]

Unless it is sealed really well, a sump that large is going to smell. It is ideal to have enough volume so it won't flood if you put an unexpectedly large amount of liquid down. Also, if your pump fails, you have some cushion to realize there is a problem before your boots are submerged. I had a 10 gallon one for my old 7 bbl brewhouse that worked pretty well, except for the previously mentioned problems. It helped when I finally made a sump out of a small stainless drum, as plastic ones failed due to the heat.

[jtomelia]

I'm an environmental engineer and I've designed a bunch of drains and sumps and that seems a curious solution. I suspect your engineer knows what he's doing (I'm required to think that) but it seems you don't know what he's doing. I'd ask for a more complete explanation. We engineers pretty much always get our calculations right, and our solutions often work, but sometimes we solve problems our clients don't have.