Acceptable headloss? 4

[edmeng]

What is an acceptable headloss in a pipe? I am modelling and find a proposed plan to create 17.29 m/1000m of headloss. It is obviously a high value but what standards are typically applied to determine if it is acceptable or not?

 

[bimr]

Reasonable pipe velocities depend on the application. There is no correct velocity for all applications. Here is a general guideline.

Reasonable Velocities for the Flow of Water through Pipe:

Boiler Feed.............8 to 15 ft/sec
Pump Suction ............4 to 7 ft/sec
General Service.........4 to 10 ft/sec
City.......................to 7 ft/sec
Transmission Pipelines...3 to 5 ft/sec

http://www.eng-tips.com/viewthread.cfm?qid=111206

 

[cvg]

in addition to these acceptable velocities, you need to look at service pressures supplied by your reservoir or pump station and measured at the end of your transmission main or at other points of high elevation. Will the pressures at these points be acceptable? Will additional pumping facilities be needed to keep the pressures above the minimum? If so, possibly a larger pipe is needed.

 

[enviroclean]

17.29m/1000m (1.729'/100') of headloss is not particularly high for piping sizes under 20" dia, however, you have to consider the total system head loss should it be competible to the available system head, as mentioned by CVG. Other things such as noise level (to suit the enviroment) also have to be considered. The piping will become quite noisy for velocities higher than 10 f/s.

 

[JStephen]

Ideally, you'd balance the installed cost of the pipe (cheaper for smaller size) against the pumping/ energy costs (cheaper for larger size) to come up with most economical arrangement for the long term.

Working in the water industry, I find that people don't usually seem too concerned about flow losses, though.

 

[biglil]

when i modeled the water distribution system (pressure system, of course) for a large coastal city in the metropolitan Los Angeles area (approx service area 17 sq-mi, 19300 pipes >6" dia.), we generally tried to limit the velocity to 10 fps

 

[Daiji]

This may be a dumb question, but I can't seem to find anything to help me determine an answer so I thought I'd see if maybe someone might could point me in the right direction.

In my industry, we use a column of water in a down tube(open to the atmosphere) to achieve various head pressures. In one of our down tubes, the diameter is 15" by 20' in length and is constricted to 6.75" by a nozzle at the base of the down tube. My question is, if you start out with a certain size diameter in a column of water and then nozzle it down to half that size, how do you determine how much head pressure you have coming out of the nozzle?

 

[bimr]

Go to a basic hydraulics book. Try Cranes Technical Paper 410.

Equation for flow through a nozzle:

q= CA sqrt (2gh)

C = discharge coefficient for nozzle
A = cross sectional area
g = acceleration of gravity = 32.2 feet per second
h = static head

 

[Mattysdad]

head pressure @ static conditioon same regardless of size - it's measuring height of a colum of water. the cameron head loss would be the dynamic pressure - i.e. static head less friction loss in nozzle - make sure to account for additional friction loss if there is any associated length of pipe and/or fittings....

 

[Daiji]

You are right and that's what I used to figure out the head pressure before we used the down tube with the nozzle, but there is something that I left out in my initial question. See we use head pressure to invert a liner in an existing host pipe underground. Basically its like taking your sock (if no water leaked out) and starting to turn it inside out and then filling it up with water and using the static head to complete the inversion process. With the regular down tube it seems that the normal calc. (density x gravity x height)/144 works but with the down tube with the nozzles seems to add a little more pressure and that is what I confused about because the diameter change shouldn't have an effect on the pressure right?

 

[bimr]

Daiji (Mechanical)

Go to Cranes Technical Paper 410.

Equation for flow through a nozzle:

q= CA sqrt (2gh)

C = discharge coefficient for nozzle
A = cross sectional area
g = acceleration of gravity = 32.2 feet per second
h = static head

The C is the flow coefficient for the nozzle and depends on the reynolds number. The q is the flow through the nozzle. The h in the equation is the head loss. Work backwords to find the head loss through the nozzle.

There will be a head loss through the nozzle and the amount of head loss depends on how much flow that you have.