grinder pump - system curve

[cbski]

I have an elementary questions being new to pumps. I have 8 homes in a subdivision that need grinder pumps. No problem, went to eone website and downloaded their material. My question is when you are plotting the system curve against the pump curve, do you use the system gpm? The static head is constant no matter how many pumps are running. Do I use the TDH from 3 pumps running and then arbituarily pick another number of pumps to get my 3 points to create a system curve? But you can't plot that against the standard pump curve given by the manufacturer's because that is only one pump and you have several. How is this handled? What about I'm trying to show that the 2hp pump will be sufficient. I know it is because it is a standard application and a simple design. I just want to know how to document this properly.

Thanks for any help you can give.

 

[bimr]

You have not said so, but one must assume that you are talking about the low pressure sewer system with multiple pumps.

The E/One pump is a semi-positive displacement pump. The low pressure sewer system has a specific design pressure but the system operating prssure varies due to the randomness of the number of pumps operating. The system design pressure is 138 TDH.

If the operating pressure exceeds the 138 feet TDH, then the pump capacity will be reduced somewhat as described on the semi-positive displacement pump curve.

The answer to your question is that if you use the semi-positive displacement, you do not have to be concerned about the system pressure.

With the semi-positive displacement, your concern would be sizing the low pressure sewer system adequately based on the number of pumps installed. E/One has used statistics to determine how many pumps should be installed per section of piping.

If you are using a centrifugal pump, then the flow characteristics are complicated.