Pump Efficiencies and Power.

Foximus

Foximus

CFL Cheapass.
Location
Oviedo, Fl
Ok so the its pretty much undisputed, you have a Mag pump, the Pump is more efficient yada yada, but more of less you need much more power to push it.

However thats not what I want to talk about here.


What is the difference between Setback and Non-setback? I'm not talking the actual physical differences. I know it allows more water to be stored in the intlet tract and allows the water to be processed somewhat faster.

But I'm talking the actual running hydralic characteristics.

Does having more water in the inlet tract create higher pump pressures and therefore increase engine load even more? Just wondering because no one seems to talk about the engine requirements for setback pumps... just mag pumps in general.
 
kevbo

kevbo

Location
dfw
Mag pumps typically go no faster on smooth water, if they did then that would be their main selling point. They tend to lose less speed/thrust in rough water compared to a stock pump. The load may be different for a given prop but that is easy to change. The big engine guys boil enough water with the high pitched props they use to mandate a Mag pump.
 
ATS_Aaron

ATS_Aaron

X-
Location
Shady Shores, TX
Kevbo is right. From my weak understanding the setback pump gives you more volume in front of the pump. This doesn't matter when the pump is on smooth water and is fully loaded, but in rough water when the pump can come out, the extra water in front is like a reserve and allows the pump to stay thrusting.

Aaron
 
Foximus

Foximus

CFL Cheapass.
Location
Oviedo, Fl
ATS_Aaron said:
Kevbo is right. From my weak understanding the setback pump gives you more volume in front of the pump. This doesn't matter when the pump is on smooth water and is fully loaded, but in rough water when the pump can come out, the extra water in front is like a reserve and allows the pump to stay thrusting.

Aaron
Click to expand...

Right, I understand that much. But just wondering if that changes the load of the motor any? I know when working with 550s, we had to be very careful of which intake grate and pump shoe curve we were working with or it would completely overload the motor, or cause it to cavitate baddly. Since the TBM/Mag hub turns a pump into a mixed flow setup, I was just wondering if I have to start paying attention to the smaller details again...
 
kevbo

kevbo

Location
dfw
You are going to need a tach when playing with pumps. There is little correlation between brands and styles of props and how they are marked. The current crop of small hub swirl types have been around a long time so we know exactly what to expect. Some guys are having trouble with their new large hubs being too much for a given pitch. I dont know how well TBMs work in foamy water but do know they don't on smooth stuff.
 
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