drbitboy
Lifetime Supporting Member
The pump manufacturer is my customer. I am building a PLC Controlled VFD package for their Pump with sensors and Tank Level automation. The customer is adamant on keeping the pump within the curves.
The pump will always somewhere on its curves, so I find this statement very odd.
But, if the Pressure and Flow are correct at a certain point, should I go for a lower Pump Speed if the Pump can still maintain that Pressure and Flow?
@rzuhair there have been three us now, me, then Peter, then Ron, saying the same things: if the flow is set by the process*, then throttling flow to set a discharge pressure to operate pump as max efficiency loses money; power is flow times pressure rise; etc.
* If the pump flow into or out of the tank is the control element to maintain tank level, then there is a corresponding flow out of or into the tank, which sets what the pump needs to match to maintain steady-state level. If that corresponding flow it outside the customer's target range on the pump curves, then do they expect the control system maintain target flow and let the tank either overflow or drain until empty?
Thermodynamics do not lie, and something is amiss in this thread, which is not at all uncommon.
You say the customer adamantly wants this, and also that the customer is a pump manufacturer. That seems odd, that a pump manufacturer does not understand how pump curves and system curves work. Is this customer the pump manufacturer engineering staff, or sales staff, or someone else?
#1 Why would there be a control valve in a system with a VFD pump? Certainly there needs to be a block valve for maintenance, but it would be left wide open during operations.
Wait a minute, you have mentioned controlling flow, and controlling pressure, but not tank level. what's up with that?
Is the pump feeding the tank, and the pressure is a proxy for tank level? It doesn't seem that would be the case as you say the pressure measurement is between the pump discharge and the control valve.
What don't we know?
From what we do know, it seems you may have two choices: convince the customer they are asking for the wrong thing; or, give them what they want, get paid, and move on.