VFD
VFD
(OP)
Hi,
I am looking into installing a VFD (variable freq. drive) on an existing rotary pump (PD pump). This pump supplies several engines with fuel (3 branches). I want to figure a way to adjust the RPM of pump motor to vary the flow out of the pump all depending on what the engine really needs. Can I do this by monitoring the pressure I need at the engine? That way, as soon as the engine needs more fuel and the pressure starts dropping, the VFD would react and increase the pump speed, therefore increase the flow?
What do you think?
Any ideas?
Thanks!
I am looking into installing a VFD (variable freq. drive) on an existing rotary pump (PD pump). This pump supplies several engines with fuel (3 branches). I want to figure a way to adjust the RPM of pump motor to vary the flow out of the pump all depending on what the engine really needs. Can I do this by monitoring the pressure I need at the engine? That way, as soon as the engine needs more fuel and the pressure starts dropping, the VFD would react and increase the pump speed, therefore increase the flow?
What do you think?
Any ideas?
Thanks!





RE: VFD
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: VFD
David
RE: VFD
Regards,
SNORGY.
RE: VFD
snorgy, the piping is relatively big, between 1" and 2" pipe with aprox 15 gpm flowing at maximum conditions. the pressure will change when the engine starts consuming a little more, but i think the vfd can react quick enough, but i need to really look into it. the pressure we need at the engine is not that important and can vary, but the engine does need to be supplied in fuel.
RE: VFD
RE: VFD
David
RE: VFD
my concern is not that the VFD will not react quick enough (Why should that control circuit be slow. Maybe you mean that the fuel pressure won't build fast enough???), but that your control logic will not work. As you seem to have said, then quickly forgotten, the logic is backwards. Isn't that your real problem.
I think that flow is not the problem, your control logic is the problem. Usually a diesel engine is controlled by the fuel flow rate; user gives it more fuel by manually increasing the rpm of the fuel pump, in this case, the VFD controlled fuel pump and the diesel engine, then the machine it is driving runs faster. You seem to want to turn it around somehow, driven machine wants to go faster, or slower and has to ask the VFD to give it the proper amount of fuel necessary to do that. How does the machine know how fast it wants to go and how does it tell the VFD to set the right freq to deliver the proper amount of fuel to reach the required speed. Your control logic is not fully explained. Trying to maintain a certain fuel pressure is destained to result in trying to hold the diesel to one speed. For example, a diesel driving a bus. Bus wants go go up hill. Speed slows, diesel turns less rpm, needs less fuel, and fuel line pressure increases. You try to hold the previous fuel pressure and the diesel gets less fuel and bus stalls.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: VFD
I was answering the question asked. I am assuming that he has a constant-speed governor on the engine. When load increases the engine tries to slow down, the governor calls for more fuel, fuel system pressure goes down, the VFD gets a declining pressure signal and speeds the PD pump up. It all makes sense to me, and it doesn't have to be instantaneous. If that governor piece is missing then the control logic is truly backwards.
David
RE: VFD
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: VFD
Your response of 24 May is not exactly correct for this application
The diesel engines it self can be a fixed speed operation with
varying load such as a generator and therefore varying fuel demand.
The proposed VFD controlled PD pump is just fuel booster or transfer pump from the storage tank to the engines.
The engine has its own fuel priming pump which would be sufficient to feed the diesel to the governor controlled injection pump if the fuel tank is near by. A few PSI drop in the fuel supply header line will not affect the engine operation.
RE: VFD
David
RE: VFD
RE: VFD
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: VFD
I enjoy the occasional foray into the weeds. Usually I'm driving, but it is nice to tag along occasionally.
DLiteE30,
The fuel is delivered with a PD pump. PD pumps don't play well with pressure regulators.
David
RE: VFD
Offshore Engineering&Design
RE: VFD
RE: VFD