Calculating Sump Volume
Calculating Sump Volume
(OP)
How do you calculate the minimum sump volume in a wetwell for a duty assist system? I am able to work out the duty requirements, but not the assist....
The plan area of the wet well is 14.79m2, and the bench is under the proposed OFF levels for the pump, and therefore does not need to be considered.
The Duty pump is rated at 25 l/sec, and the assist pump is rated at 4 l/sec
The average inflow into the wetwell is 6 l/sec.
I would like to achieve 10 starts per hour.
If anyone knows how to calculate this, I would greatly appreciate it.
Thanks
Rob
The plan area of the wet well is 14.79m2, and the bench is under the proposed OFF levels for the pump, and therefore does not need to be considered.
The Duty pump is rated at 25 l/sec, and the assist pump is rated at 4 l/sec
The average inflow into the wetwell is 6 l/sec.
I would like to achieve 10 starts per hour.
If anyone knows how to calculate this, I would greatly appreciate it.
Thanks
Rob





RE: Calculating Sump Volume
T = cycle time (min)
V = L
Q = Flow out (L/min)
S = Flow in (L/min)
However, if you know T, Q and S but not V, the equation can be rearranged as follows:
V = 1/(1/(Q*T - S*T)+1/(S*T))
Factoring in your data I obtained V = 1,642 L
That will give you a cycle time of 6 minutes (10 starts/hour) under average daily flow conditions. You need to reevaluate under peak flow conditions and see if your cycling too much, which I suspect may be the case here. Generally most pump manufacturers don't like more than 8 - 10 starts/hour/pump under peak flow conditions.
I've not factored in your assist pump and feel it's not a good idea to do so anyway.
RE: Calculating Sump Volume