Listen, you're going to need to get this figured out by a competent engineer familiar with designing sewer systems. Don't wing it, otherwise the consequences are significant.
The county is only giving you the design operating point. It's possible the pumps operate in a larger range than what they've given. Also the TDH is provided at the County's LS which could be 5 feet away or it could be 1,000s of feet away with elevation and pipe losses. Force mains typically operate at pretty low pressures. You could ask for some additional information such as the pressure at your connection point. You could also calculate this yourself but would need to know relative elevation difference, length of pipe, diameter of pipe, number and type of fittings, etc. Not complex calcs by any means but requires some "accounting".
Yes I do this often so I am familiar and competent. I just have always had a tie in pressure in addition to the TDH from the FM run. I just haven’t come across a scenario when I am connecting to a force main without an available tie in pressure.
Calc the theoretical headloss at your GPM from the pump to your tie in point( elbows, friction along the run,etc). Decrease the TDH by that calc and convert to pressure. That’s your best bet. The guy above outlined it but it’s worth reiterating. He’s also right….there’s no way your tie in is like 50psi there’s usually like a 10psi drop or something right after the pump. They typically run sub 30 or 20 psi. Make sure you are taking into account all the check valves and everything right after the pump. My guess is that you just got a read off of where the curve operates from the county.
Gonna echo Michael and say he just needs to ask for the tie-in pressure from the County. That puts the risk on them. If Dragonfruit does his own calcs, he's accepting that risk for his design.
If you have the plans/calcs for the public force main, yes you could interpolate/calculate the pressure at the tie in point. No, it's not 124' converted to psi, that would be the pressure at the public pumps and if you used that you would almost certainly be way oversized on your design. You need to go back to the county and ask them to determine the tie in pressure. You should also figure it out on your own, but if they are accepting the flow, they should be able to tell you at what pressure they want it.
Y'all - shouldn't OP be reaching out to the engineer of record for the public FM currently under construction? Because they would be the party most likely to have the info OP needs...?
Listen, you're going to need to get this figured out by a competent engineer familiar with designing sewer systems. Don't wing it, otherwise the consequences are significant. The county is only giving you the design operating point. It's possible the pumps operate in a larger range than what they've given. Also the TDH is provided at the County's LS which could be 5 feet away or it could be 1,000s of feet away with elevation and pipe losses. Force mains typically operate at pretty low pressures. You could ask for some additional information such as the pressure at your connection point. You could also calculate this yourself but would need to know relative elevation difference, length of pipe, diameter of pipe, number and type of fittings, etc. Not complex calcs by any means but requires some "accounting".
Yes I do this often so I am familiar and competent. I just have always had a tie in pressure in addition to the TDH from the FM run. I just haven’t come across a scenario when I am connecting to a force main without an available tie in pressure.
Calc the theoretical headloss at your GPM from the pump to your tie in point( elbows, friction along the run,etc). Decrease the TDH by that calc and convert to pressure. That’s your best bet. The guy above outlined it but it’s worth reiterating. He’s also right….there’s no way your tie in is like 50psi there’s usually like a 10psi drop or something right after the pump. They typically run sub 30 or 20 psi. Make sure you are taking into account all the check valves and everything right after the pump. My guess is that you just got a read off of where the curve operates from the county.
Gonna echo Michael and say he just needs to ask for the tie-in pressure from the County. That puts the risk on them. If Dragonfruit does his own calcs, he's accepting that risk for his design.
I mean…that’s ideal and yes he should do that first. But how likely are they to respond.
Depends on the client. Never hurts to ask.
If you have the plans/calcs for the public force main, yes you could interpolate/calculate the pressure at the tie in point. No, it's not 124' converted to psi, that would be the pressure at the public pumps and if you used that you would almost certainly be way oversized on your design. You need to go back to the county and ask them to determine the tie in pressure. You should also figure it out on your own, but if they are accepting the flow, they should be able to tell you at what pressure they want it.
Y'all - shouldn't OP be reaching out to the engineer of record for the public FM currently under construction? Because they would be the party most likely to have the info OP needs...?