I am involved in the design of a sewage lifting station. Could any one help me with the level setting?
We have considered four levels (as per existing lifting stations) to be sensed by a level transmitter.
The following are the levels - highest to lowest.
1. high level alarm (set below the invert level of lowest inlet pipe to the lifting station)
2. pump start (how much below the high level alarm should I set this?)
3. pump stop (I have used the prevalent formula: t=4V/Q, this seems to be fine)
4. pump trip (minimum submergence. how much below the pump stop level should I set this?)
Is there any international standard or guide to be used as reference?
For item 2, will it be logical to consider a volume equivalent to 5 mins of inflow and select the height accordingly?
Likewise, for item 4, will it be fine to consider a volume equivalent to 5 min outflow (pump flow) and select height accordingly?
One more question..we don't have redundancy for level transmitter. What could be the worst case scenario if the level transmitter malfunctions and pump starts operating below minimum submergence level?.. Probably before the impeller and seal jams due to over heat, will the motor breaker trip? I doubt this bcz the client specifications calls for an over sized motor. Apart from selecting the mtor 10-15 percent more than the end of performance curve power input, the motor is supposed to be derated to 52 Degree celcius.
Note: It is a one duty/one stand by configuration (without duty - assist operation)
Thanks in advance.