45 degree cut on suction pipe

[Jacc]

Most hydraulic books I have looked in have entry loss coefficient listed for numerous configurations of cones or trumpets. However I have never seen a figure for the straight pipe with a 45 degree cut althought I have seen it being used many times. Also I've been told how important it is to do the 45 degree cut but that doesn't mean sxxt to me unless I have figures to compare with.
Ofcourse it's important to keep the suction losses low, cavitation can be a nasty thing but I want to base a design on tested and measured values rather than on rumors.

A straight pipe sticking into the tank has the highest entry loss coefficient while a trumpet mounted flush with the tank wall has the lowest entry loss coefficient.
It seems to me that the straight pipe cut at 45 degree sticking into the tank would have a pretty high entry loss coefficient as well.

Does anyone know where I can find the entry loss coefficient for straight pipes cut at 45 degrees?

 

[Unotec]

I might be wrong, but the 45º cut should not affect, since the area is still a circle (the plane cut) at the pipe past the 45º cut.

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[budt]

I was told many years back that the reason for the 45 Deg. cut because that would keep flow from being blocked if the pipe was inserted too far and happened to come close to or touch the bottom of the tank. Sounded logical to me.

Also I was told the reason for doing the same cut to pump flow return to tank lines was so the 45 Deg. cut could be aimed at the side wallof the tank to disperse the return flow against more tank area for better cooling.

Is that all true????? Sounded logial to this country boy.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[IceStationZebra]

A note of caution - on any machine with high reservoir turn-over rates be careful splashing oil around. The return should always be below the oil level to minimize aeration.

If I understand the example correctly the pipe is slash-cut at a 45° angle to the long axis of the pipe, which will result in an oval opening - not a circle.

I agree with Bud that it would prevent the pipe from getting too close to the tank wall. And even if you didn't see cavitation it would still have the benefit of not sucking as much debris from the floor of the reservoir.

As far as coefficients go, I don't have any numbers but I suspect the slash cut is much better than a straight cut since it would minimize the vena contracta and have more area open to the reservoir.

Cd's
straight pipe: ~0.5
bell mouth: ~0.98
slash cut: 0.75?? (my guess)

ISZ