Diesel Pump Exit Velocity Limitation

[stanier]

A client has specified the maximum exit velocity from a pump delivering diesel to train loading facilities. the maximum exit velocity has been defined as 7 m?s. Please advise what the rationale behind this limit may be.

 

[TD2K]

Is this in the pump discharge nozzle or the discharge piping?

For piping, 7 m/s is pretty much the upper limit I would want to design piping for. Erosion is likely not a problem as the diesel will be clean but your pressure drops will be pretty high at these velocities. At these velocities, water hammer is a potential problem if a valve was to be closed suddenly.

 

[stanier]

No its the pump nozzle exit velocity that has been defined!

Its the waterhammer that I getting ready to do.

7m/s is horrific for pipeline velocity. Any life cycle costing will shoot that design approach down.

 

[TD2K]

The only thing that jumps to mind is an erosion limit. While I have to admit I've never calculated the velocity right at the pump nozzle, I suspect I would be well over this many times given how much smaller pump nozzles are compared to your typical lines sizes.

I'll talk to a couple of people today, it's an interesting question.

 

[Montemayor]

Maybe what TD2K meant was that a design of 7 ft/sec is pretty common for liquid fluid flow. I normally employ a "design" liquid flow velocity of 5 - 7 ft/sec for clean fluids. My ceiling value is 10 - 15 ft/sec.

In a Diesel application My first concern in going beyond the maximum design criteria would be the effect on my overall pressure drop and any subsequent downstream flashing or vaporization of the parent liquid. I don't identify any safety or errosion hazards related to clean Diesel fluid in this application (although we haven't been given all the basic data - like pressure and temperature), but I normally would challenge the need to elevate or accept a velocity that high. Another item that may be important is: how long (time-wise) is this velocity maintained? If it is just "a reduced spot in the line" because of equipment characteristics, it might be OK. But the question is valid.

 

[stanier]

The velocity criteria is at the exit of the discharge nozzle of the pump. Flow is 210 m3/hr at pressure is 1600 kPag.

I am confused because I have never come across this criteria before. Unfortunately I am one removed from the client and cant get a sensible answer. Thats why I asked the Forum just in case there is something out there that I have missed in my 30 years in this business.

 

[MikeHalloran]

Well, 7 m/s is high, but the client did specify that as a maximum, right? So you are free to use a bigger nozzle and a more reasonable velocity.

I'g guess somebody put the limit in there just so that an idiot wouldn't grossly undersize the part to save weight and cost.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA